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MN/CA IX is a cell surface protein, strongly associated with several types of human carcinomas. It exerts activity of carbonic anhydrase and capacity of binding to cell surface receptors. In the present work, we used affinity purified MN/CA IX protein to demonstrate that the cells adhere to immobilized MN/CA IX and that the monoclonal antibody M75 abrogates cell attachment to MN/CA IX. Using synthetic oligopeptides, we identified M75 epitope and located it in the proteoglycan domain, which contains a sixfold tandem repeat of six amino acids GEEDLP. From phage display library of random heptapeptides we identified and chemically synthesized those which compete for the epitope with M75 and inhibit adhesion of cells to MN/CA IX. These heptapeptides might serve as lead compounds for drug design. © 2000 Cancer Research Campaign

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CAIX is strongly expressed by ccRCC. Although CAIX is associated with outcome in patients with ccRCC, it is not an independent prognostic marker. Furthermore, CAIX expression is apparent in extrarenal organs. As such, exploitation of CAIX as a prognostic marker and therapeutic target merits additional consideration.

MaTu is a novel agent which may be of relevance in human oncogenesis, and has 2 components. One of them, the exogenous MX (coding for protein p58X), is transmissible to human fibroblasts, to HeLa and to HeLa x fibroblast (H/F) hybrids. The other component, MN, is a cellular gene. Its product, the protein p54/58N, is inducible by infecting HeLa cells with MX or by growing them in dense cultures. This p54/58N appears to be a tumor-associated antigen: it is expressed in HeLa and in tumorigenic cells (H/F-T), but not in fibroblasts or in nontumorigenic hybrid cells (H/F-N). Proteins related to p54/58N were also found on immunoblots prepared from human carcinomas of ovary, endometrium and uterine cervix, but not from normal tissues from corresponding organs or from placenta. Using genetically engineered MN protein, we developed a radioimmunoassay for MN-specific antibodies, and for quantitative determination of MN proteins in cell extracts. In HeLa cells infected with MX we observed conspicuous ultrastructural alterations: formation of abundant filaments on the cell surface and amplification of mitochondria. Using immunogold-staining, we visualized the p54/58N on the surface microvilli and in the nucleus, particularly in nucleoli.