2015 Group 5 Project

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Laminin.png


Introduction

Laminin (LM) is a glycoprotein, found within the extracellular matrix [1], of many embryonic and adult tissues [2]. LMs have a cross – shaped structure, formed by three short arms (alpha, beta, and gamma chains) and one long arm which is a globular domain that binds to cellular receptors[3]. LMs are the building blocks for cellular networks bridging the intracellular and extracellular compartments of the basement membranes (BM) [4]. They regulate the development and function of numerous tissues and organs [5], playing an important role in tissue homeostasis and maintenance[6]. LMs are also believed to play a role in cancer progression [6], by contributing to tumour dissemination and metastasis in advanced breast carcinomas as well as other tumor types [7]. Furthermore, LMs are believed to influence adipose tissue structure [3], have a role in the blood – brain barrier [8] and also regulate cellular processes, such as cell migration, differentiation and proliferation[9].


Defects in laminin chains can result in:

  • Ocular diseases, such as in the development of the eye [10]
  • Epidermolysis Bullosa, a disorder resulting in structural weakening of the skin and mucous layer [11]
  • Muscular dystrophy, which is a group of disorders characterised by the weakening of the skeletal muscle [12]


Current and potential investigations into laminin include:

  • The regenerative ability of human adipose tissue derived from stromal cells, which is currently being investigated in the field of regenerative medicine [13]
  • The effects on individual truncated LM chains in the absence of their normal partner [9]
  • And possible therapeutic solutions for advanced cancer patients [7].

In this page, we will discuss the structure of LM. We will look at the overall function of LM and five out of 15 of its different isoforms. We will discuss the effect of LM abnormalities, specifically in cancer, epidermolysis bullosa, muscular dystrophy, and development. We also included the current research surrounding LMs.


History

This graph represents the number of publications on Laminin, per year, from 1975 to 2014. A rapid increase in publications can be seen from 1979 onwards, when Laminin was first discovered.

First Laminin Isoform Discovered

In 1979, a large, non-collagenous glycoprotein was isolated from both an Engelbreth-Holm-Swarm (EHS) sarcoma and basement membrane producing cells[4].

Experimental Process

( In a transplantable mouse tumor, the EHS sarcoma, which produces an ECM of BM, was found to be a convenient source for the isolation of the collagenous component, excluding the capsule because tumor proteins are made up of approximately 5-10% of type IV collagen. Using neutral buffers little amounts of this collagen can be extracted. However, with dilute acetic acids can be extracted from the tumours found in lathyritic mice. Neutral buffers though, are still able to extract large amounts of non-collagenous proteins. Following, it was purified in quantities sufficient for biochemical, structural and immunological characterisation, and given the name laminin. Laminin was concluded as a major component of the tumour matrix and was localised to the basement membrane in normal tissues by immunological techniques[14].

Of the extracts, a large component was found to be a high molecular weight non-collagenous glycoprotein, which they named ‘laminin’[14].


Findings

Biochemical analysis revealed that the LM structure consisted of three linked polypeptides, which were given the names A, B1 and B2.

Electron microscopy observations revealed that these three chains formed an asymmetrical cross-shaped structure. This cross-shaped structure consisted of a long arm and three short arms.

Further discoveries of various cells and tissues, cloning and automated sequencing techniques, genetically different LM subunits in humans and other species were identified.

This highlighted that the LM molecule from the EHS sarcoma was not unique, but part of a new protein family. Hence, in order to distinguish between the diverse members, the LMs were named and numbered in order of their discovery[4].


Unifying Nomenclature Introduced

In 1994 (as reviewed in [15]), the consecutive A, B1 and B2 chains were re – named with the Greek letters, α, β, and γ, respectively.

Because it was noticed that the sequencing of the subunits provided evidence for distinct polypeptide sequences at the amino acid level, they were named by the addition of numbers to the Greek letters[4].


Laminins Today

Today, LM isoforms are known by their chain compositions. The α1, β1, and γ1 chain is known as laminin 111. This chain is the prototype of the laminin family and is the best characterized laminin isoform[4].


Structure

Laminin is the major component of the basal lamina, the extracellular matrix (ECM) which surrounds all epithelia, muscle, peripheral nerve and fat cells. Then it is related with cell adhesion, migration, growth, differentiation, neurite outgrowth and tumor metastases and its structural level is now well characterized[16].

Fig. 1 The laminin structure is composed of three polypeptides chains named A, B1 and B2 (nowadays α, β and γ chains, respectively) which are held together in cruciform-like structure by disulphide bonds (three disulfide-linked polypeptides).Red is collagen binding, blue is entactin binding and black is proteoglycan binding.

Laminin is a mosaic glycoprotein of the ECM of metazoans composed of different domains with different structures and functions [17]. According to H.K. Kleinman et al. laminin has multiple structures in different tissues due to variations in the number and type of chains. The LM structure is composed of three polypeptides chains named A, B1 and B2 (nowadays α, β and γ chains, respectively) which are held together in cruciform-like structure by disulphide bonds (three disulfide-linked polypeptides). H.K. Kleinman et al. explains the A chain has three globular domains at the amino terminus separated by three epidermal growth factor (EGF)-like repeats. The B1 (or β) and B2 (or γ) chains are structurally similar but contain only two amino terminal globules and EGF-like repeats and lack the globule at the carboxyl end [18]. Furthermore, observations indicated that the chains form an asymmetrical cross-shaped structure, with a long arm of about 77 nm carrying a large globule at its end, and three short arms, two of 34 nm and one of 48 nm, each being terminated by a globular domain [19].The human genome encodes 11 genetically distinct LM chains differing at the level of the amino acid sequences. However, the polypeptide chains in a cross-shaped pattern is conserved among laminin isoforms. [4] Fig.1 is an example of a basic laminin structure.


Structure and ECM Interactions

The laminin structure has an important role in the extracellular matrix interactions. The heterotrimeric structure is one of the major components of basement membrane (BM) and it is critical to assemble the cell network. The three arms of the laminin form the network nodes and all the arms are required (α, β and γ arm) for it. The globular domain of the long arm binds to cellular receptors, such as integrins, heparan sulfates, α-dystroglycan, sulfated glycolipids. The proteoglycans (perlecan and agrin) provide the collateral anchorage of the laminin network and the type IV collagen interacts with the laminin network through the heparan sulfate chains (perlecan and agrin) and entactin (nidogen), forming a second network (see again the Fig. 1). Furthermore, it is interesting to mention that the difficulty of imaging BM in situ prevents a direct understanding of BM architecture, because the process of imaging involves a harmful extraction from tissues. Therefore, the current model is more based on indirect observation that involves multitude clues than direct observation. From these observations, some questions are raised: the dimension of thickness of a BM is of the same order as a single laminin molecule, which makes unlikely that laminins are erected on the surface of cells. Finally, the researchers are not sure if they know all of the important interactions between laminin and the BM assembly and maturation. One reason for this is because some of current understanding about the interactions is based on early experiments with crude protein preparations. Then, the modern recombinant and proteomic techniques might be useful for the future researches in additional laminin interactions.[3].Figure 2 is an example of laminin interactions.

(A) Schematic drawing of the laminin-111 heterotrimer. The three short arms of the cross-shaped molecule have a common domain structure and consist of laminin N-terminal (LN) domains, laminin-type epidermal growth factor-like (LE) domains, and L4 domains, as indicated for the α1 chain. The α1 chain uniquely contains five laminin G-like (LG) domains. LG1-3 likely interact with the C-terminal residues of the γ1 chain. (B) The three-arm interaction model of laminin self-assembly. The ternary nodes in the network are formed by the N-terminal regions of one α, one β and one γ chain. The long arm of the laminin heterotrimer is not involved in network formation[3].


The recent researches found relations between LM structure and its influence in phenotypes. The research "Laminin α4 deficient mice exhibit decreased capacity for adipose tissue expansion and weight gain” shows an understanding of the mechanisms related to extracellular matrix (ECM) and regulation of adipose tissue expansion. The research describes the role of laminin α4 (ECM protein that surrounds adipocytes) on weight gain and adipose tissue function. Two mice were examined in adipose tissue accumulation, lipogenesis, and structure. The mice with a null mutation of the laminin α4 gene (Lama4-/-) exhibited reduced weight gain in response to both age and high fat diet when compared wild-type (Lama4+/+) control animals. These results suggest that laminin α4 influences adipose tissue structure and function. Furthermore, it could be applied in therapies that reduce obesity morbidity and mortality[5].

Function

Laminins play a role in BM assembly, adhesion [20], cell proliferation, migration, and differentiation[21][1]. They control cellular behaviour by interacting with cell surface receptors (e.g. integrins, syndecans, and a-dystroglycans) [22]. The interaction between integrins and LMs causes cells to be anchored to the BM and initiate intracellular signals [23]. As reviewed in [4], LM has 2 terminal ends, the C-terminal end and the N-terminal end. The N-terminal end is responsible for interacting with the different ECM proteins and is therefore important for the assembly of the BM. The C-terminal end is involved with the interaction with cell surface receptors. Therefore, this terminal end is responsible for cellular adhesion, migration, signalling, and survival.

The different combinations of the three chains of LM form different LM heterotrimers, or better known as isoforms. Each LM isoform has different functions in the body. Furthermore, the function of each isoform can vary depending on the environment they are in, i.e. the type of cell or tissue where they are located [22]. For example, laminin-111 in muscle promote the regeneration of muscle cells [21] whereas in human mesenchymal stem cells, they promote the outgrowth of neurites [24]. In this section, the function of 5 laminin isoforms, (laminin-111, laminin-211, laminin-332, laminin-411, and laminin-511) in the body will be discussed in detail. Below is a table containing a brief description of the function of all the different laminin isoforms.


Laminin Heterotrimer Function
Laminin-111
involved in regulating muscular morphogenesis by promoting regeneration in muscle cells[21][25]; promotes neurite outgrowth in human mesenchymal cells via activation of FAK and MAPK cascades[24]
Laminin-211
essential for the contractility of airway smooth muscle cells[26][27]
Laminin-121
has a strong affinity for a7B1 integrin, which promotes neurite outgrowth [28]
Laminin-221
Laminin-332
involved in the synthesis of tyrosine, which increase the level of melanin produced by melanocytes[29]
Laminin-311
involved in the maintenance of the alveolar tissue architecture [30]
Laminin-321
Laminin-411
has a vascular role; increases the migration and adhesion of human dermal microvascular endothelial cells (HDMECs), which promote the tubule formation of endothelial cells[31]
Laminin-421
Laminin-511
a potent substrate for up regulating a3b1, which is a promoter for hair growth[32][33]
Laminin-521
essential for the formation of the glomerular filtration barrier (as reviewed in [34]; also involved in preventing Schwann cells from invading the synaptic cleft in a neuromuscular junction [35]
Laminin-213
Laminin-423
Laminin-522
Laminin-523
Laminin 111

Laminin 111 (LM-111) is the one of the first, and predominant, ECM proteins expressed during embryonic development[21][20]. LM-111 provides structural support to the BM[20]. More importantly, this LM isoform’s main role is to regulate muscular regeneration[21][25]. LM-111 is known to prevent the effects of muscular dystrophy, such as skeletal muscle weakness due to damages in cells and tissues[21][25]. It does this by playing a role in myoblast fusion[21], the formation of new and larger myofibres, and acting as a substitute to LM-α2 deficiency[25]. The injection of LM-111 helps re-establish the sarcolemma in muscle cells that are laminin-a2 deficient[25]. This LM isoform also increases muscle integrity by interacting with a7B1 integrin and a-dystroglycan[25], which improves the number of satellite cells by improving satellite cell proliferation[21][25]. LM-111 provides a link between the ECM and the sarcolemma, which prevents muscle degeneration and apoptosis, and promotes muscular adhesion to the basal lamina[25]. There is evidence showing that LM-111 prevents muscle damage. In postexercise mice, those that were treated with the laminin isoform had fewer muscle fibres with centrally located nuclei, which is commonly a sign for muscle damage[21]. LM-111 also plays a role in the epithelial-to-mesenchymal transition (EMT) in cells. A fragment of the LM molecule interacts with matrix metalloproteinases (MMPs), specifically MMP2. The LM-111 fragment down-regulates MMP2, which in turn lowers the amount of BM undergoing degradation[20].

Laminin 211

Laminin 211 (LM-211) plays a role in the contractility of airway smooth muscle (ASM) cells, which relates to the pathology of asthmatic attacks. The expression of this LM isoform in ASM cells is essential for its contractility as well as reducing the levels of proapoptotic proteins in ASM cells [26][27], which results in the hypertrophy of these cells[26]. This relates to asthma because asthmatic airways are characterised to have ASM cells with increased contractility[27]. LM-211 also has a role in the control in the interactions between thymocytes and thymic epithelial cells (TECs). The deposit of LM-211 creates a microenvironment for thymocytes to proliferate, maturate, differentiate, and migrate. Furthermore, the thymocyte-TEC interaction was blocked when antibodies specific for LM-211 were introduced[36].

Laminin 332

Melanocytes are cells that synthesise melanin, a component of the pigmentary system of the skin. The melanin, produced by melanocytes, migrate to keratinocytes for protection. Laminin 332 (LM-332) is derived from keratinocytes and plays a role in the migration and adhesion of melanocytes[29][37]. LM-332 is also promotes the synthesis of melanin in melanocytes by controlling the levels of tyrosine[29]. Tyrosine is essential for the synthesis of melanin and it's level is proportional to the level of melanin i.e. an increase in the level of tyrosine will also increase the level of melanin made[37]. This links to LM-332 because this LM isoform increases the intracellular tyrosine levels and also increases the uptake of extracellular tyrosine[37]. However, the mechanism behind the control of tyrosine levels by LM-322 is still unknown.

Laminin 411

Laminin 411 (LM-411) is expressed in the endothelial BM and plays a significant role in the maintenance of the vascular endothelial BM[31]. Although, Laminin-511 maybe expressed in vascular endothelial BMs as well, LM-411 is expressed in all BMs of all blood vessels, whereas Laminin-511 is only expressed in capillaries and some veins and venules[38]. This LM heterotrimer is involved in the survival of endothelial cells, particularly in their migration and adhesion[31]. The presence of LM-411 increases the migration and adhesion of human dermal microvascular endothelial cells (HDMECs). In turn, the migration of HDMECs promotes tubule formation of endothelial cells[31]. Therefore, it can be deduced that this laminin heterotrimer is involved in vascular formation. Therefore, a lack in LM-411 expression leads to disrupted vascular endothelial BMs. In a study, the lack of LM-411 expression resulted in a bleeding phenotype in newborn mice[38]. LM-411 is related to type IV collage, in that the overexpression of LM-411 increases the number of type IV collagen in capillary BM. The absence of LM-411 leads to no formation of type IV collagen, which affects the assembly of the BM[31].

Laminin 511

Laminin 511 (LM-511) is one of the first ECM proteins expressed during embryogenesis[21]. LM-511 is another LM heterotrimer, release by keratinocytes[39], associated with hair downgrowth[40][39]. Lm-511 is found in the BMZ and interfollicular epithelia but it is most numerous in the BMZ, specifically around the hair follicles[40]. Unlike LMm-332, LM-511 is the primary LM [33] for the stimulation of hair growth and elongation[32]. LM-511 is associated with α3 integrin, in terms of regulating hair growth[40]. α3 integrin acts as a promoter of hair growth[40]. This links back to LM-511, which is a potent substrate for the upregulation the expression of the α3β1 integrin[32][33][39]. Therefore, the presence of LM-511 promotes hair growth via α3β1 integrins[32][33]. Another process as to how LM-511 affects hair follicle involves dermal blood vessels. α3 integrin is also involved in the migration of endothelial cells. Therefore, it is plausible that LM-511 is associated with the recruitment of dermal blood vessels essential for the formation of hair follicles[33]. LM-511 is also involved in the formation of the BMZ. The lack of LM-511 results in a discontinuous lamina densa, which hinders the downgrowth of the hair follicles[39].

Together with LM-411, LM-511 also plays a role in the maintenance of the vascular endothelial BM[38]. Unlike LM-411, LM-511 is expressed only in capillaries and some venules and veins. However, the failure to express LM-411 leads to compensation by LM-511. Due to this event, angiogenesis is increased, which conseuquently enhances the growth of tumours and finally metastasis. Therefore, this LM heterotrimer, even if not directly, is also involed in angiogenesis, tumour formation and metastasis[38].

Abnormalities

Cancer

Laminin 332 expression in breast carcinoma[41]

Laminin 332 or LN332 is a basally expressed extracellular matrix protein that is part of a group of laminin isoforms that demonstrates tumor-promoting properties. In normal tissue Laminin 332’s main role is to maintain epithelial-mesenchyme cohesion when the tissue is exposed to external disruptive forces. It also stimulates cells including carcinoma cells to migrate allowing for metastasis and has thus been associated with the progression of a tumor. Past research has found a direct correlation between LN331 and both Tumor invasiveness and a poor patient prognosis. The role of Laminin 332 in breast carcinomas is however unclear. This study aims to examine the relationship between Laminin 332 and breast carcinomas. The researchers tested the expression of LN332 in surgically excised breast carcinomas using immunohistochemistry (IHC) and western blot. The primary objective of the study was to examine patterns of expression in varying molecular classes of breast carcinomas. The basal-like phenotypic subgroup has a worse prognosis observed, and thus was of particular interest. The genetic profiling method that defines the basal phenotype was not widely available, so a surrogate was used, namely Triple negative (TN) breast cancer. Triple negative is a sub group of breast carcinomas that lack progesterone receptors, estrogen receptors and HER2 positivity. Results revealed 70% of TN carcinomas stained for LN332 and 14.7% of non-TN carcinomas indicating its expression with a basal phenotype. The combination of LN332 and CK 5/6 or EGFR identified 92% of triple negative breast carcinoma. Expression of the basal marker LN332 and CK 5/6 or EGFR may help in the identification of breast carcinomas with the basal phenotype. Furthermore the expression of LN332 a pro-invasive protein in TN breast carcinomas suggests another mechanism by which the TN phenotype could be aggressive. Further study will need to be performed in order to determine weather LN332 has an effect on the invasive or migratory phenotype.


Epidermolysis Bullosa

Molecular identification of collagen 17a1 as a major genetic modifier of laminin gamma 2 mutation-induced junctional epidermolysis bullosa in mice[11]


Epidermolysis bullosa (EB) is a disorder resulting in structural weakening of the skin and mucous layer. Junctional EB is caused by a mutation that results in the cleavage of the dermal-epidermal junction. An unexplained phenotypic variability that is present in these mutations promotes the idea of genetic modifier effects. The study in question aims to analyze the effect of genetic modifiers on the strength of dermal-epidermal adhesion and clinical severity of Junctional EB. The results indicated that Col17a1 is a strong genetic modifier of Junctional EB that develops by mutation of Lamc2.jeb Allelic variants in Col17a1 alters the strength of dermal-epidermal adhesion therefore impacting the severity of Junctional EB. Overall the results indicated that normally innocuous allelic variants could cause mutations to have an impact on the strength of dermal-epidermal adhesion and severity of Junctional EB. This may help the genetic prognosis and diagnosis of Epidermolysis bullosa.

Variation in the onset and severity of JEB-nH[11]

Muscular Dystrophy

Laminin alpha2 deficiency and muscular dystrophy; genotype-phenotype correlation in mutant mice [12]

Muscular dystrophy is a group of disorders characterized by the weakening of the skeletal muscle. The muscular disorders that can be caused by over 30 mutated genes, many of which encode for molecules involved in maintain structural integrity and cell adhesion. One of the most sever forms of muscular dystrophy involve the mutation of laminin α2 or LAMA2. Mutations on LAMA2 have been reported to range from absence of laminin α2 to the partial deficiency. It is however not clear as to how a laminin α2 mutation may effect protein expression and how these effected proteins cause affect disease. The aim of this study to analyze the genotype and phenotype, determine the mechanism of disease and determine the function of laminin. The study uses animal models to do this. An allelic series of mutations in the mice were used to facilitate genotype-phenotype correlation. The allelic series included mice with absence of laminin α2, reduced levels of laminin α2, truncated protein and reduced levels of truncated protein. Three lines of LAMA2 mutated mice with a complete deficiency in laminin α2 and two lines of transgenic mice with overexpressed laminin α2 were used to analyze protein expression. All the mutated mice lacked laminin α2 in peripheral nerve. The results indicate the muscular dystrophy in truncate protein mice was mild but more severe than that of the laminin α2 absent mice. The mechanisms for expression of laminin α2 in muscle and nerve also appeared different. The results provided evidence that the amount of laminin α2 is critical in the prevention of muscular dystrophy and could thus act as a possible treatment.


Development

Biologically-active laminin-111 fragment that modulates the epithelial-to-mesenchymal transition in embryonic stem cells [20]

Epithelial-to-mesenchymal transition (EMT) is a process allowing an epithelial cell to assume a mesenchymal phenotype through biochemical changes via its basement membrane and is essential for cell migration and early embryonic development. This process is regulated by signalling pathways and cellular changes involving the expression of E-cadherin, matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9). Laminin-111, a trimeric basement membrane glycoprotein is one of the first extracellular matrix (ECM) proteins expressed during the two-cell stage in early embryogenesis and its importance together with other proteins, collagen IV, nidogen and perlecan in the assembly of the basement membrane is known. This study proposes a previously unidentified role of Laminin-111, namely its ability to influence the regulation of EMT. They report the generation of a biologically active Laminin-111 fragment by MMP2 processing and demonstrate that the fragment acts through the α3β1-integrin/extracellular matrix metalloproteinase inducer complex to trigger the down-regulation of MMP2 in human and mouse ECM. Recognizing ECM and MMP2 interactions will increase our understanding of the pluripotent stage of early embryonic development to develop new applications and disease-modeling platforms.

Current Research

The Heterotrimeric Laminin Coiled – Coil Domain Exerts Anti – Adhesive Effects and Induces a Pro – Invasive Phenotype [9]

Study: To determine what would happen to individual truncated LM chains in the absence of their normal partners.

Method: A transfectable cell line with low endogenous LM chain expression was selected, by first encoding the truncated LM α1, β1 and γ1 chains which encode the entire laminin coiled - coil domain (LCC).

Results: Truncated α1 chains were found to be efficiently secreted as a monomer when expressed alone, as opposed to the β1 and γ1, which were poorly secreted. But, when all three were expressed together, they formed a trimer that was secreted into the medium. This confirmed, consistent with previous findings, that a chain subunit expression is necessary for the secretion of the β1 and γ1 chain partners and that the truncated chains can also assemble into the trimetric coiled - coil structure independent of the rest of the molecule. It was also revealed and demonstrated that the LCC domain inhibits cell adhesion and spreading, however anti-adhesive properties of ECM proteins were not commonly observed.

Background Information & Explanation
Laminins have multiple binding partners and also exert multiple biological functions by interacting with other ECM molecules and cell surface receptors. However, majority of the cell-binding sites map to regions distinct from the LCC domain. This domain is believed to play a key role in chain assembly yet it is considered a functionally silent domain, with a few exceptions.

Cell adhesion modulation is often related to cell migration. The actin cytoskeleton plays an important role in the processes of cell movement, with filopodia and lamellipodia formation being crucial. Because decreased actin stress fibre formation and increased membrane ruffle formation are consistent with the promotion of cell migration, it is a tempting speculation that the adhesive property of the LCC domain is linked to the modulation of cell migration in tissues where the LCC domain became accessible.

[9]


The Laminin Response in Inflammatory Bowel Disease: Protection or Malignancy? [6]

Study: When there is inflammation in Inflammatory Bowel Disease (IBD), mucosal ulceration and subsequent tissue repairs occur, promoting the constant remodelling of the BM, hence it is believed that laminin may play an unknown role in the inflammation response, impacting the bodies response to inflammation. Furthermore, it has also been described that altered immunoreactivity of the BM constituents in the IBD, have shown an increase in alpha laminin, meaning it is likely that LM participates in the regeneration of the intestine.

Method: The above was highlighted when an increase in LMα1 and LMα5 expression was present in the colon tissues of IBD patients and in DSS-driven colitis in mice. The inflammation in these cases was accompanied by the nuclear accumulation of p53 as well as changes in the properties of the cell, caused in particular by the presence of the ulcer-associated cell lineage glands (UACL) in IBD. It was also revealed that the LMα1 and LMα5 chains were over-expressed, when inflamed, in human IBD and murine colitis specimens.

Results: The forced expression of LMα1 and LMα5 protected against DDS-induced inflammation, yet in carcinogenic conditions, accelerated colitis-associated tumorigenesis. Furthermore, results suggested that LMs could play a role in tissue restitution, as LMs promoted wound closure in tissue rebuilding when there were disrupted epithelial cell monolayers.

Background Information & Explanation

Laminins are major components of the epithelial BM. They are also found present in intestinal BMs, functioning alongside collagen IV, perlecans and nidogens, as specialised ECM networks that separate epithelial cells from underlying connective tissue. Overall they play a crucial role in tissue homeostasis and also have an important role in tissue maintenance and cancer progression, which represents an inherent risk of Irritable Bowel Disease (IBD).

Because the BM functions as a physical and chemical barrier, defects in the BM assembly or composition can cause several human disorders. Repetitive tissue destruction, repair and oxidative damage can together trigger mutagenesis and potentially initiate cancer causing events. In wound healing and tissue repair, it's made prevalent that inflammatory responses are commonly associated with the remodelling of the extracellular matrix (ECM). Altered ECM expression and ECM binding integrin adhesion receptors have been located in several inflamed tissues.

Keratinocyte – Targeted Expression of Human Laminin y2 Rescues Skin Blistering and Early Lethality of Laminin γ2 Deficient Mice [2]

Study: To test whether or not the expression of the human laminin γ2 in mice helped prevent early lethality.

Method: A dox – controllable human laminin γ2 transgene was expressed, under a keratinocyte-specific promoter on the laminin γ2 knockout background.

Results: Newborn offspring that lacked the transgene had blistered skin, resulting in a separted epidermal layer, smaller milk pouches and died a few days after birth. However, the mice that were carrying the human gene, as a result appeared similar to their wild-type littermates at birth, with similar weights and lengths, didn’t develop skin blisters, showing a more attached structure, were fertile and survived for more than 1.5 years.

Background Information & Explanation

Laminin-332 (LM-332) is heterotrimetric BM component comprised of α3, β3 and γ2 laminin chains, responsible for epithelial cell processes, including adhesion, migration and differentiation. It is present in the basement membranes of many embryonic and adult tissues, including the brain, gastrointestinal tract, heart, kidney, liver, lung, trachea, skin, spleen, thymus, salivary gland, mammary gland, ovary, prostate and testis.

Skin is a protective barrier, composed of two primary layers, known as the epidermis and dermis. These two layers are separated a sheet of specialised ECM known at the BMZ. The BMZ functions as a border, for structural support, influences cell attachment, proliferation, differentiation and migration. Should a defect occur in the structure or in one of the components of the BMZ, tissue separation and blister formation may result.

Keratinocytes are responsible for the secretion of LM-332 in the skin, which is identified as a key component of hemidesmosomes that connect the keratinocytes to the underlying dermis, functioning as an adhesion molecule between the epidermis and dermis. In mice, when any of the three LM-332 chains are not expressed, impaired anchorage and detachment of the epidermis occurs. This is similarly seen in human Junctional Epidermolysis Bullosa (JEB).

JEB is a genetic skin blistering disease, which results in, in the most severe cases, the death of infants within their first year of life. JEB is mostly caused by the absence of LM-332, due to mutations arising within the chains. Generally, those who experience skin blistering also experience blistering of the mucous membranes of the mouth and gastrointestinal tract, in turn affecting nutrition. This was confirmed on detection of laminin γ2 in the mouth of the mice, when examining the effects of the human gene expression on them.

Laminin – 511 A multi – functional adhesion protein regulating cell migration, tumor invasion and metastasis [7]

Study: To reinforce recent studies that indicate that Laminin-511 (LM-511) contributes to tumour dissemination and metastasis in advanced breast carcinomas as well as other tumour types. Furthermore, to look into experimental evidence that suggests that there is prognostic significance with higher expressions of LM-511 and that by targeting tumour-LM-511 interactions, there may be a therapeutic potential in advanced cancer patients.

Method: Specifically observing that metastatic breast tumour lines adhere and migrate more efficiently on LM-511, as opposed to on metastatic lines seen in the laboratory results are consistent with theories that metastatic breast tumours are mediated through attachments to LM-511. If observations are found correct then metastatic potential can be impacted by blocking the production of LM-511 and or the function and expression of its receptors.

Results: Increasing experimental evidence is supporting the link of LM-511 to cancer progression and reinforcing the belief that LM-511 has a broad role in tumour invasion and metastasis. However, questions in regards to its prognostic significance, precise mechanism of action and potential as a therapeutic target still need to be addressed and answered. As metastasis is responsible for majority of cancer – related deaths and is a clinical challenge, the continuation of research of LMs has the potential to present several information and solutions to overcoming this disease, as well as assist in the development of alternative strategies to prevent and/ or delay metastatic progression.

Background Information & Explanation

Laminins are abundant extracellular matrix proteins, present predominately in BMs. There are approximately 15 isoforms, named according to their specific combination of the α, β and γ chains. A combination of technological advances and experiments has contributed to the belief that LM-511 and its receptors regulate cancer progression.

The LM – 511 expression patterns vary between different tumour types whether it be basement membrane localisation to diffuse stromal or tumour cell expression. It’s level in tumour cells or surrounding vasculature varies based on the stage of tumour progression. Many studies show that LM-511 expressions in advanced tumours is maintained or even increased. It’s also observed that in advanced human breast cancers and bone metastases, there is high tumour cell expression of LM-511. Discussions are about whether future studies should look at LM-511 expression in tumours and whether it has a particular clinical relevance with a propensity to metastasise to bone. Whether or not LM-511 expression has any contribution to breast tumours, has not yet been fully confirmed.

As has been found from previous studies, many tumour lines synthesise, secrete and adhere to LM-511, potentially indicating that LM-511 is able to produce it’s effect on tumours via autocrine stimulation in part. Receptor studies are the reason for the many believed functions of LMs in breast cancer progression and metastasis and it's possibly inferred, from several observations that LM-binding integrins in metastatic breast tumours are mediated through attachment to LM-511.

Because there are no definitive answers in regards to the prognostic significance of LM-511, exact mechanism and potential therapeutically, the following should be looked into:

For staining archival material, the generation of more robust antibodies. Clarification of the precise contribution of LM-511 to the metastatic process. Contribution (if any) of stromal/ vascular LM-511 to metastasis (tumour-derived LM-511 in metastasis is already supported). Studies in vivo, to provide proof of the therapeutic benefits that targeting LM receptors could have.

Remodeling of ECM by normal and tumour-associated fibroblasts promotes cervical cancer progression [42]

Study: The experiment was conducted to study the communication between tumour cells and fibroblasts.

Method: Light was shown through in - vitro models of tumour-stroma interaction. Some of the fibroblasts from the normal cervix and cervical cancers were grown separately, while others were in co-culture with CSCC7 cervical cancer cell-line. Changes in the glycoproteins, integrins and matrix metallo-proteases were examined.

Results: It was concluded that the tumour microenvironment played an influential role in the behaviour of cancer, with changes seen in the upregulation and redistribution of LM-111 in those cells which had undergone cancerous transformation, depositing into the BM and fibrillar connective tissue. It was also seen that there was a presence of activated myofibroblasts, which produce ECM, in the stroma. LM-5 was also found to reside in the cytoplasm of cancer cells, consistent with earlier findings. As a result, it was concluded that the tumour microenvironment played a pivotal role in the behaviour of cancer.

Background Information & Explanation

Tumour microenvironments have become the focus of intensive research for cancer therapy. Parenchymal cells and their stromal components are separated by a BM in normal epithelium. When a local host stroma is activated, the normal epithelium transitions into an invasive carcinoma. This malignant progression then prevents the normal functioning of the BM, causing the reorientation of its structure. As a result, the invasive tumour cells acquire a more metastatic phenotype, losing their epithelial characteristics. During this process, stromal cells release numerous microenvironment-influencing macromolecules, causing changes to the ECM.

Fibroblasts, which play a prominent role in the pathology of solid tumours, are characteristic cell types in the microenvironment. The cancer – associated fibroblasts exhibit large quantities of ECM protein, proteases, within the reactive stroma. Matrix metalloproteinases (MMP’s) degrade the BM and stromal ECM, influencing the production of malignant tumours. As a result, newly synthesised ECM proteins assist in the movement of motile tumour cells and the development of new vessels.

In order to display an invasive phenotype, cervical carcinomas use the stromal MMP’s. MMP-7 and MMP-9 are induced into the cancer cells, made larger by tumour-stromal interactions. The stromal cells generate growth signals to the cancer cells by integrins, which are essential for the communication between cancer cells and tumorous stroma. It is this integrin communication that plays a big role in the cells survival, proliferation, migration and tumour invasion.

The cytokine, TGF-β1, produced by fibroblasts is an important regulator of the ECM assembling and remodelling the ECM during cancer progression. Its known to exert a growth inhibitory action on epithelial cells, however this is lost in malignant transformation. This causes the growth factor of the ECM to convert from inhibitor to tumour promotor. This cytokine is activated through EC mechanisms such as proteases, thrombospodin – 1 and integrins. This exchange between tumour cells and fibroblasts is what influences growth factors, modifying the role they play on the tumour tissue.


Antibodies

Laminin antibodies are most predominantly used to highlight basement membranes and blood vessels.

Antibody Species Working Concentration Secondary Antibody Publication
Laminin Antibody 0.1 ml Basement Membrane Marker (NB300 - 144) Rabbit, polyclonal to Laminin 1 ug at 1.0 mg/ ml Anti - Rabbit IgG (H&L) (Goat) Antibody Peroxidase Conjugated <pubmed> 22511849 </pubmed>
Anti-Laminin 5 antibody Rabbit, polyclonal to Laminin 5 50 µg at 1 mg/ml F(ab')2 fragment goat anti-rabbit Alexa Fluor 594 <pubmed>25133673</pubmed>
Laminin α-1 Antibody (M-20) Goat polyclonal IgG 200 µg/ml Donkey anti-goat IgG-HRP <pubmed>17364662</pubmed>
Anti-Laminin antibody (ab11575) Rabbit polyclonal to Laminin 250 µl at 0.54 - 0.72 mg/ml Biotin-conjugated goat anti-rabbit IgG polyclonal (1/1000) <pubmed>24334445</pubmed>

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