Promotion Of Metastatic Processes By Laminin And Laminin

Dental &Craniofacial Research

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Abstract

Studies are conducted to define the mechanisms involved in tumor growth and metastasis and to develop new animal models of human cancers. We have found that a basement membrane extract (Matrigel) when premixed with human breast and prostate tumor cells (which do not grow well in mice) promotes tumor incidence and growth. We have been able to culture new highly differentiated human tumor cell lines from the tumors grown in mice, including certain colon and prostate cell lines. Laminin, a major basement membrane component, has been found to promote the malignant phenotype of tumor cells. Laminin-adherent melanoma and colon cancer cells are more malignant than either the non-adherent cells or the parental cells. Various biologically active laminin-derived synthetic peptides have been identified. One peptide A5G27 from the alpha 5 chain blocks breast cancer growth and angiogenesis in vivo by binding in a dominant-negative manner to its receptor. We have now begun to further develop this peptide as a therapeutic (working with a peptide chemist) and to define its signaling pathways. Another peptide, LQVQLSIR, increases metastases in various tumor cell types (breast cancer, melanoma, and ovarian cancer) and binds to the receptor CD44. This is the only site on laminin found to date that promotes tumor metastasis. The receptor for this peptide has already been shown by others to be important in metastasis in a broad range of tumor cell types. We also find that CD44 is higher in melanoma cells that are adhesion-selected to this peptide, and when these peptide-adhesion-selected cells are injected into mice, more metastases are observed in the absence of added peptide. Using antibody array technology, we have identified genes regulated by this peptide. One of these genes, fibronectin, is upregulated by this peptide in all tumor cell types tested to date. We now have a better understanding of how this peptide promotes tumor metastasis. Our goal is to define the molecular mechanisms involved in tumor growth and metastases. Our approach is to (1) select for and isolate highly malignant cells, (2) define their cellular laminin receptors, (3) identify additional sequences on laminin which promote or reduce the malignant phenotype, (4) identify genes involved in malignancy, and (5) define molecules in bone responsible for prostate and breast cancer organ-specific metastases. We work with several models, including B16F10 melanoma cells, breast, prostate, and salivary gland tumor cells. We were the first to show that estrogen promotes angiogenesis. We now have begun to define the mechanisms by which estrogen promotes angiogenesis and malignancy. Using gene analysis, we have identified several genes important in the function of estrogen. We find that estrogen upregulates the enzyme heparanase which degrades the extracellular matrix. This enzyme thus increases growth factor activity by release of many growth factors from the matrix. Estrogen also down decreases the expression of a certain soluble growth factor receptor, VEGFR-1, that acts as a "decoy". Decreased expression of soluble VEGFR-1 increases the amount of VEGF (vascular endothelial cell growth factor)available. The growth factor, VEGF, promotes both angiogenesis and tumor growth by directly acting on the tumor cells. Thus, estrogen actively regulates the "angiogenic switch" in malignancy by multiple mechanisms.