Is collagen XV a tumor suppressor?

Origin and evolution of animal multicellularity in the light of phylogenomics and cancer genetics

The rise of animals represents a major but enigmatic event in the evolutionary history of life. In recent years, numerous studies have aimed at understanding the genetic basis of this transition. However, genome comparisons of diverse animal and protist lineages suggest that the appearance of gene families that were previously considered animal specific indeed preceded animals. Animals' unicellular relatives, such as choanoflagellates, ichthyosporeans, and filastereans, demonstrate complex life cycles including transient multicellularity as well as genetic toolkits for temporal cell differentiation, cell-to-cell communication, apoptosis, and cell adhesion. This has warranted further exploration of the genetic basis underlying transitions in cellular organization. An alternative model for the study of transitions in cellular organization is tumors, which exploit physiological programs that characterize both unicellularity and multicellularity. Tumor cells, for example, switch adhesion on and off, up- or downregulate specific cell differentiation states, downregulate apoptosis, and allow cell migration within tissues. Here, we use insights from both the fields of phylogenomics and tumor biology to review the evolutionary history of the regulatory systems of multicellularity and discuss their overlap. We claim that while evolutionary biology has contributed to an increased understanding of cancer, broad investigations into tissue-normal and transformed-can also contribute the framework for exploring animal evolution.

Clusterin suppresses invasion and metastasis of testicular seminoma by upregulating COL15a1

Seminoma is the most common subtype of testicular germ cell tumor, with an increasing incidence worldwide. Clusterin (CLU) expression was found to be downregulated in testicular seminoma in our previous study. We now expanded the sample size, and further indicated that CLU expression correlates with tumor stage. Tcam-2 cell line was used to investigate the CLU function in testicular seminoma, and CLU was found to inhibit the proliferation and metastasis abilities. Besides, extracellular matrix protein COL15a1 was demonstrated as the downstream of CLU to affect the epithelial-mesenchymal transition (EMT) process via competitively binding to DDR1 with COL1A1 and inhibiting the phosphorylation of PYK2. MEF2A was found to interact with CLU and bind to the promoter of COL15a1 and so upregulate its expression. This is the first study using testicular xenografts in situ to simulate testicular seminoma metastatic and proliferative capacities. In conclusion, CLU acts as a tumor suppressor to inhibit the metastasis of testicular seminoma by interacting with MEF2A to upregulate COL15a1 and blocking the EMT process.

Deletion of Col15a1 Modulates the Tumour Extracellular Matrix and Leads to Increased Tumour Growth in the MMTV-PyMT Mouse Mammary Carcinoma Model

Basement membrane (BM) zone-associated collagen XV (ColXV) has been shown to suppress the malignancy of tumour cells, and its restin domain can inhibit angiogenesis. In human breast cancer, as well as in many other human carcinomas, ColXV is lost from the epithelial BM zone prior to tumour invasion. Here, we addressed the roles of ColXV in breast carcinogenesis using the transgenic MMTV-PyMT mouse mammary carcinoma model. We show here for the first time that the inactivation of Col15a1 in mice leads to changes in the fibrillar tumour matrix and to increased mammary tumour growth. ColXV is expressed by myoepithelial and endothelial cells in mammary tumours and is lost from the ductal BM along with the loss of the myoepithelial layer during cancer progression while persisting in blood vessels and capillaries, even in invasive tumours. However, despite the absence of anti-angiogenic restin domain, neovascularisation was reduced rather than increased in the ColXV-deficient mammary tumours compared to controls. We also show that, in robust tumour cell transplantation models or in a chemical-induced fibrosarcoma model, the inactivation of Col15a1 does not affect tumour growth or angiogenesis. In conclusion, our results support the proposed tumour suppressor function of ColXV in mammary carcinogenesis and reveal diverse roles of this collagen in different cancer types.

Exploring the roles of MACIT and multiplexin collagens in stem cells and cancer

The extracellular matrix (ECM) is ubiquitously involved in neoplastic transformation, tumour growth and metastatic dissemination, and the interplay between tumour and stromal cells and the ECM is now considered crucial for the formation of a tumour-supporting microenvironment. The 28 different collagens (Col) form a major ECM protein family and display extraordinary functional diversity in tissue homeostasis as well as in pathological conditions, with functions ranging from structural support for tissues to regulatory binding activities and storage of biologically active cryptic domains releasable through ECM proteolysis. Two subfamilies of collagens, namely the plasma membrane-associated collagens with interrupted triple-helices (MACITs, including ColXIII, ColXXIII and ColXXV) and the basement membrane-associated collagens with multiple triple-helix domains with interruptions (multiplexins, including ColXV and ColXVIII), have highly interesting regulatory functions in tissue and organ development, as well as in various diseases, including cancer. An increasing, albeit yet sparse, data suggest that these collagens play crucial roles in conveying regulatory signals from the extracellular space to cells. We summarize here the current knowledge about MACITs and multiplexins as regulators of stemness and oncogenic processes, as well as their roles in influencing cell fate decisions in healthy and cancerous tissues. In addition, we present a bioinformatic analysis of the impacts of MACITs and multiplexins transcript levels on the prognosis of patients representing a wide array of malignant diseases, to aid future diagnostic and therapeutic efforts.

Collagens XV and XVIII show different expression and localisation in cutaneous squamous cell carcinoma: type XV appears in tumor stroma, while XVIII becomes upregulated in tumor cells and lost from microvessels

As the second most common skin malignancy, cutaneous squamous cell carcinoma (cSCC) is an increasing health concern, while its pathogenesis at molecular level remains largely unknown. We studied the expression and localisation of two homologous basement membrane (BM) collagens, types XV and XVIII, at different stages of cSCC. These collagens are involved in angiogenesis and tumorigenesis, but their role in cancer development is incompletely understood. Quantitative RT-PCR analysis revealed upregulation of collagen XVIII, but not collagen XV, in primary cSCC cells in comparison with normal human epidermal keratinocytes. In addition, the Ha-ras-transformed invasive cell line II-4 expressed high levels of collagen XVIII mRNA, indicating upregulation in the course of malignant transformation. Immunohistochemical analyses of a large human tissue microarray material showed that collagen XVIII is expressed by tumor cells from grade 1 onwards, while keratinocytes in normal skin and in premalignant lesions showed negative staining for it. Collagen XV appeared instead as deposits in the tumor stroma. Our findings in human cSCCs and in mouse cSCCs from the DMBA-TPA skin carcinogenesis model showed that collagen XVIII, but not collagen XV or the BM markers collagen IV or laminin, was selectively reduced in the tumor vasculature, and this decrease associated significantly with cancer progression. Our results demonstrate that collagens XV and XVIII are expressed in different sites of cSCC and may contribute in a distinct manner to processes related to cSCC tumorigenesis, identifying these collagens as potential biomarkers in the disease.

Collagen XV: exploring its structure and role within the tumor microenvironment

The extracellular matrix (ECM) is a critical component of stroma-to-cell interactions that subsequently activate intracellular signaling cascades, many of which are associated with tumor invasion and metastasis. The ECM contains a wide range of proteins with multiple functions, including cytokines, cleaved cell-surface receptors, secreted epithelial cell proteins, and structural scaffolding. Fibrillar collagens, abundant in the normal ECM, surround cellular structures and provide structural integrity. However during the initial stages of invasive cancers, the ECM is among the first compartments to be compromised. Also present in the normal ECM is the nonfibrillar collagen XV, which is seen in the basement membrane zone but is lost prior to tumor metastasis in several organs. In contrast, the tumor microenvironment often exhibits increased synthesis of fibrillar collagen I and collagen IV, which are associated with fibrosis. The unique localization of collagen XV and its disappearance prior to tumor invasion suggests a fundamental role in maintaining basement membrane integrity and preventing the migration of tumor cells across this barrier. This review examines the structure of collagen XV, its functional domains, and its involvement in cell-surface receptor-mediated signaling pathways, thus providing further insight into its critical role in the suppression of malignancy.

Collagen XV inhibits epithelial to mesenchymal transition in pancreatic adenocarcinoma cells

Collagen XV (COLXV) is a secreted non-fibrillar collagen found within basement membrane (BM) zones of the extracellular matrix (ECM). Its ability to alter cellular growth in vitro and to reduce tumor burden and increase survival in vivo support a role as a tumor suppressor. Loss of COLXV during the progression of several aggressive cancers precedes basement membrane invasion and metastasis. The resultant lack of COLXV subjacent to the basement membrane and subsequent loss of its interactions with other proteins in this zone may directly impact tumor progression. Here we show that COLXV significantly reduces invasion of pancreatic adenocarcinoma cells through a collagen I (COLI) matrix. Moreover, we demonstrate that epithelial to mesenchymal transition (EMT) in these cells, which is recapitulated in vitro by cell scattering on a COLI substrate, is inhibited by over-expression of COLXV. We identify critical collagen-binding surface receptors on the tumor cells, including the discoidin domain receptor 1 (DDR1) and E-Cadherin (E-Cad), which interact with COLXV and appear to mediate its function. In the presence of COLXV, the intracellular redistribution of E-Cad from the cell periphery, which is associated with COLI-activated EMT, is inhibited and concurrently, DDR1 signaling is suppressed. Furthermore, continuous exposure of the pancreatic adenocarcinoma cells to high levels of COLXV suppresses endogenous levels of N-Cadherin (N-Cad). These data reveal a novel mechanism whereby COLXV can function as a tumor suppressor in the basement membrane zone.

Tumor suppression by collagen XV is independent of the restin domain

Non-fibrillar collagen XV is a chondroitin sulfate modified glycoprotein that is associated with the basement membrane zone in many tissues. Its precise functions remain to be fully elucidated though it clearly plays a critical role in the structural integrity of the extracellular matrix. Loss of collagen XV from the basement membrane zone precedes invasion of a number of tumor types and we previously showed that collagen XV functions as a dose-dependent suppressor of tumorigenicity in cervical carcinoma cells. The carboxyl terminus of another non-fibrillar collagen (XVIII) is cleaved to produce endostatin, which has anti-angiogenic effects and thus may act as a tumor suppressor in vivo. Since collagen XV has structural similarity with collagen XVIII, its C-terminal restin domain could confer tumor suppressive functions on the molecule, though our previous data did not support this. We now show that expression of collagen XV enhances the adhesion of cervical carcinoma cells to collagen I in vitro as does the N-terminus and collagenous regions of collagen XV, but not the restin domain. Destruction of a cysteine residue in the collagenous region that is critical for intermolecular interactions of collagen XV abolished the enhanced adhesion to collagen I. Finally, we demonstrate that unlike full length collagen XV, expression of the restin domain alone does not suppress tumorigenicity of cervical carcinoma cells in vivo; hence, this process is dependent on functions and interactions of other parts of the protein.

Cancer models, genomic instability and somatic cellular Darwinian evolution

The biology of cancer is critically reviewed and evidence adduced that its development can be modelled as a somatic cellular Darwinian evolutionary process. The evidence for involvement of genomic instability (GI) is also reviewed. A variety of quasi-mechanistic models of carcinogenesis are reviewed, all based on this somatic Darwinian evolutionary hypothesis; in particular, the multi-stage model of Armitage and Doll (Br. J. Cancer 1954:8;1-12), the two-mutation model of Moolgavkar, Venzon, and Knudson (MVK) (Math. Biosci. 1979:47;55-77), the generalized MVK model of Little (Biometrics 1995:51;1278-1291) and various generalizations of these incorporating effects of GI (Little and Wright Math. Biosci. 2003:183;111-134; Little et al. J. Theoret. Biol. 2008:254;229-238).

Complete suppression of tumor formation by high levels of basement membrane collagen

Suppression of tumorigenicity was first shown in hybrids produced by the fusion of a range of different highly malignant tumor cells with diploid fibroblasts. Cytogenetic analysis of these hybrids revealed that suppression involved a genetic region located in one specific chromosome donated to the hybrid cell by the fibroblast parent. The identity of the gene responsible for this dramatic effect has remained obscure. We now present strong evidence that the primary determinant is the gene specifying collagen XV, a proteoglycan closely associated with the basement membrane. We transfected a line of highly tumorigenic human cervical carcinoma cells with an expression vector carrying the full-length cDNA of the human collagen XV gene. We selected clones making various amounts of collagen XV, examined their growth in vitro, and tested their tumorigenicity in nude mice. High levels of collagen XV altered the growth properties of the cells in three-dimensional cultures. Moreover, we found that, in a dose-dependent manner, the production of collagen XV completely suppressed tumorigenicity in clones that synthesized this molecule at high levels. Immunohistologic studies suggest that suppression is associated with extracellular deposition of the proteoglycan at the cell periphery.

Microenvironment of the involuting mammary gland mediates mammary cancer progression

Breast cancer diagnosed after a completed pregnancy has higher metastatic potential and therefore a much poorer prognosis. We hypothesize that following pregnancy the process of mammary gland involution, which returns the gland to its pre-pregnant state, co-opts some of the programs of wound healing. The pro-inflammatory milieu that results, while physiologically normal, promotes tumor progression. In this review, the similarities between mammary gland involution after cessation of milk-production and pathological tissue remodeling are discussed in light of emerging data demonstrating a role for pathological tissue remodeling in cancer.

Endogenous stimulators and inhibitors of angiogenesis in gastrointestinal cancers: basic science to clinical application

Progression of cancer is dependent on acquisition of vascular networks within the tumor. Tumor angiogenesis is dependent on up-regulation of angiogenesis stimulators to overcome the endogenous anti-angiogenic barrier. Such disruption of angiogenesis balance to favor neovascularization is a key step for progression of tumor growth and metastasis. In this regard, the vascular basement membrane and the extracellular matrix have been found to be rich sources of angiogenesis stimulators and inhibitors that become bioavailable on proteolysis of the matrix by tumor microenvironment-related enzymes. In this review the subgroup of endogenous angiogenesis stimulators and inhibitors is discussed, and their mechanism of action during tumor angiogenesis is evaluated. The role in regulating tumor growth and the possibility of using them as prognostic markers for human gastrointestinal cancers is discussed. Furthermore, we specifically address the role of vascular endothelial growth factor in human gastrointestinal cancers and discuss the development and use of bevacizumab (Avastin; anti-vascular endothelial growth factor antibody [Genentech, CA]) in the treatment of colorectal and other gastrointestinal cancers.

The collagen superfamily: from the extracellular matrix to the cell membrane

The collagen superfamily is highly complex and shows a remarkable diversity in molecular and supramolecular organization, tissue distribution and function. However, all its members share a common structural feature, the presence of at least one triple-helical domain, which corresponds to a number of (Gly-X-Y)n repeats (X being frequently proline and Y hydroxyproline) in the amino acid sequence. Several sub-families have been determined according to sequence homologies and to similarities in the structural organization and supramolecular assembly. In the present review, we focus on the newly described fibrillar collagens, fibrillar-associated collagens with interrupted triple helix, membrane collagens and multiplexins. Recent advances in the characterization of proteins containing triple-helical domains but not referred to as collagens are also discussed.

The contribution of vascular basement membranes and extracellular matrix to the mechanics of tumor angiogenesis

The goal of this review is to highlight the contribution of extracellular matrix and vascular basement membranes to the regulation of angiogenesis and tumor progression. Here we present a new concept that vascular basement membrane influences endothelial cells and possibly other cell types in a solid state assembled form, and also in a degraded solution state form. Depending on the structural integrity, composition and exposure of cryptic sites, the vascular basement membrane proteome exerts functional influences on proliferating and resting endothelial cells. This review provides the reader with an appreciation of this newly evolved concept in the area of vascular biology.