Role of Proteoglycans in Tumor Progression

Involvement of stromal proteoglycans in tumour progression

Glycosaminoglycans (GAGs) and proteoglycans (PGs) belong to a class of extracellular macromolecules necessary for the growth of any multicellular structures, including tumours. Transformed cells induce stromal reaction either per se or by activation of the mesenchymal cells. Tumour stroma contains several chondroitin sulphate and heparan sulphate proteoglycans. These proteoglycans and their glycosaminoglycan chains modify cell behaviour by interacting with different molecules such as growth factors, cytokines, chemokines, proteinases and their inhibitors. This review describes the main proteoglycans of tumour stoma and discusses their implication in the regulation of the activity of extracellular proteins and peptides.

Proteoglycans and tumor progression: Janus-faced molecules with contradictory functions in cancer

Understanding the details of the molecular mechanism of tumor dissemination revealed that several proteoglycan species are involved in the process but their role can be described as Janus-faced. One level of proteoglycan alterations is at the expression of their genes coding for the core protein. Characteristically, in progressing tumors two patterns emerged: loss or neoexpression of surface proteoglycans (PG) depending on the initial expression pattern of the cell type of origin. The situation is similarly complex concerning the changes of glycosaminoglycan (GAG) of the PG during tumor progression. This is due to the fact that the majority of PGs involved is hybrid molecule meaning that their core protein can be glycanated both with chondroitin and heparan sulfate. However, such an alteration in glycanation of PG may fundamentally change the function of the molecule, especially the one operating at the cell surface. Among the extracellular PGs, decorin emerged as inhibitor of progression while perlecan as a promoter of the process. Analysis of the available data indicate that during metastatization tumor cells must express at least one cell surface HSPG species from the syndecan-glypican-CD44v3 group. Furthermore, the HS-chain of these proteoglycan(s) carry important molecular signatures (suphution or epimerization patterns). Experimental data suggest that tumor cell surface heparan sulfate (PG) may provide a target for specific anti-metastatic interventions.

Expression of a decorin-like moleculein human melanoma

Decorin, a member of the family of small leucin-rich proteoglycans, has originally been described as a secreted proteoglycan component of the connective tissues, and has been implicated in the negative regulation of cell proliferation directly or via interactions with TGF-beta. It was reported to be generally absent from tumor cells. Here we show that human melanoma cell lines express a decorin-like molecule. We detected decorin mRNA by RT-PCR in 7 out 7 human melanoma lines characterized by various metastatic potential. Using polyclonal antiserum against the core protein of decorin, the typical 80-120 kD glycanated form as well as a high molecular weight aberrant version (200-210 kD) of decorin were demonstrated by Western blot technique in the culture supernatants as well as in lysates of human melanoma cells. Finally, decorin epitope was also demonstrated immunohistochemically in human melanoma xenografts, as well as in tumor cells of surgically resected melanomas but not in melanocytes of nevi. The expression of this aberrant decorin did not inhibit the in vitroor in vivogrowth of human melanoma cells, and it was independent of their metastatic potential. Human melanoma cell lines expressing aberrant decorin retained sensitivity to the antiproliferative and gelatinase-stimulatory effects of exogenous TGF-beta.

Liver metastatic ability of human melanoma cell line is associated with losses of chromosomes 4, 9p21-pter and 10p

Genetic changes underlying the aggressive progression of human cutaneous melanoma are not completely understood. In order to characterise genetic alterations associated with the metastatic behaviour of this neoplasm we used comparative genomic hybridisation (CGH) in combination with fluorescence in situ hybridisation (FISH) on an experimental metastatic model of three related human melanoma cell lines. Tumour lines were selected based on their various metastatic capacity to liver in immunosuppressed mice. The parental cell line (A2058) was a human amelanotic melanoma cell line, adaptation of this line to in vivo growth as xenograft the HT168 tumour and its cell line was established. After intrasplenic transplantation of HT168 cells into immunosuppressed mice, a highly metastatic variant (HT168-M1) was selected. Several chromosomal aberrations common to all three lines indicating common clonal origin, as well as additional non-shared chromosomal changes were found. The original cell line (A2058) exhibited the highest number of genetic changes. Chromosomal alterations present only in the highly metastatic line (HT168-M1) involved losses on chromosome 4, 9p21.3-pter and 10p. Chromosome copy number patterns and the nature of chromosome 4 loss were further investigated by FISH using different centromeric probes and a chromosome 4 painting probe. According to our CGH and FISH results we assume that alterations present only in the aggressive metastatic subline are associated with the increased - metastatic potential. Our observations further support the hypothesis, based on some recently published data, that certain (so far unidentified) suppressor genes having an important role in tumour progression are located on these chromosomes.