Targeting soluble CD146 with a neutralizing antibody inhibits vascularization, growth and survival of CD146-positive tumors.

CD146 (MUC-18, MCAM) expression on cancer cells correlates with cancer progression and a bad prognosis in several tumors, including melanoma and pancreatic tumors. Deciphering the mechanism mediating the CD146 role in cancer is essential for generating new therapeutic strategies. We found that CD146 expression in cancer cells is associated with a secretion of soluble CD146 (sCD146) that constitutes an active player in tumor development. Indeed, sCD146 induces the overexpression of its binding protein, angiomotin, on both endothelial and cancer cells and promotes both paracrine effects on angiogenesis and autocrine effects on cancer cells proliferation and survival. These last effects are mediated in part through the induction and phosphorylation of c-myc in cancer cells. In mice models xenografted with human CD146-positive melanoma or pancreatic cancer cells, administration of a novel monoclonal antibody specifically targeting sCD146, but not its membrane form, successfully suppresses tumor vascularization and growth. Our findings demonstrate that sCD146 secreted by CD146-positive tumors mediates important pro-angiogenic and pro-tumoral effects. Targeting sCD146 with a novel neutralizing antibody could thus constitute an innovative therapeutic strategy for the treatment of CD146-positive tumors.

Transcriptome analysis reveals an osteoblast-like phenotype for human osteotropic breast cancer cells.

Metastatic breast cancer cells exhibit the selective ability to seed and grow in the skeleton. We and others have previously reported that human breast tumors which metastasize to the skeleton overexpress bone matrix extracellular proteins. In an attempt to reveal the osteoblast-like phenotype of osteotropic breast cancer cells, we performed a microarray study on a model of breast cancer bone metastasis consisting of the MDA-MB-231 human cell line and its variant B02 selected for its high capacity to form bone metastases in vivo. Analysis of B02 cells transcriptional profile revealed that 11 and 9 out of the 50 most up- and down-regulated mRNAs, respectively, corresponded to genes which expression has been previously associated with osteoblastic differentiation process. Thus, osteoblast specific cadherin 11 which mediates the differentiation of mesenchymal cells into osteoblastic cells is up-regulated in B02. While S100A4, recently described as a key negative regulator of osteoblast differentiation, is the most down-regulated gene in B02 cells. RT-PCR and western blotting experiments allowed the validation of the modulation of several genes of interest. Using immunohistochemistry, performed on human breast primary tumors and their matched liver and bone metastases, we were able to confirm that the osteoblast-like pattern of gene expression observed in our model holds true in vivo. This is the first report demonstrating a gene-expression pattern corresponding to the acquisition of an osteomimetic phenotype by bone metastatic breast cancer cells.

Differential expression and subcellular localization of murine BRCA1 and BRCA1-delta 11 isoforms in murine and human cell lines.

BRCA1 mutations are involved in breast and ovarian cancer predisposition in humans. The biological functions of the murine BRCA1 gene have been extensively studied but little is known about murine BRCA1 proteins. To better characterize these proteins, we have cloned the full-length murine BRCA1 cDNA and a splice variant deleted of exon 11, BRCA1-delta 11, by RT-PCR method. Three polyclonal antibodies raised against various parts of murine BRCA1 were used in our study: D16, M20 and 5MO, which were generated in our laboratory. This allowed us to analyze the expression and subcellular localization of both isoforms in murine and human cell lines by immunoblotting, immunoprecipitation, cell fractionation and immunofluorescence. Endogenous BRCA1 was detected in murine cell lines but not splice variant BRCA1-delta 11, whereas both ectopically expressed murine isoforms were detected in transfected human Bosc 23 cells. Subcellular fractionation and immunofluorescence results showed that the BRCA1 protein was mainly located in the nucleus, whereas BRCA1-delta 11 was preferentially cytoplasmic. The conservation of exon 11 splicing and the differential subcellular localization of BRCA1 and BRCA1-delta 11 in human and mouse suggest that these proteins could play distinct roles and that they could differentially act in the pathological mechanisms leading to the development of breast and ovarian cancer. The characterization of the murine BRCA1 proteins and antibodies will be useful to further study BRCA1 functions in murine models.