CD146 expression is associated with a poor prognosis in human breast tumors and with enhanced motility in breast cancer cell lines.

INTRODUCTION: Metastasis is a complex process involving loss of adhesion, migration, invasion and proliferation of cancer cells. Cell adhesion molecules play a pivotal role in this phenomenon by regulating cell-cell and cell-matrix interactions. CD146 (MCAM) is associated with an advanced tumor stage in melanoma, prostate cancer and ovarian cancer. Studies of CD146 expression and function in breast cancer remain scarce except for a report concluding that CD146 could act as a tumor suppressor in breast carcinogenesis. METHODS: To resolve these apparent discrepancies in the role of CD146 in tumor cells, we looked at the association of CD146 expression with histoclinical features in human primary breast cancers using DNA and tissue microarrays. By flow cytometry, we characterized CD146 expression on different breast cancer cell lines. Using siRNA or shRNA technology, we studied functional consequences of CD146 downmodulation of MDA-MB-231 cells in migration assays. Wild-type, mock-transfected and downmodulated transfected cells were profiled using whole-genome DNA microarrays to identify genes whose expression was modified by CD146 downregulation. RESULTS: Microarray studies revealed the association of higher levels of CD146 with histoclinical features that belong to the basal cluster of human tumors. Expression of CD146 protein on epithelial cells was detected in a small subset of cancers with histoclinical features of basal tumors. CD146+ cell lines displayed a mesenchymal phenotype. Downmodulation of CD146 expression in the MDA-MB-231 cell line resulted in downmodulation of vimentin, as well as of a set of genes that include both genes associated with a poor prognosis in a variety of cancers and genes known to promote cell motility. In vitro functional assays revealed decreased migration abilities associated with decreased CD146 expression. CONCLUSIONS: In addition to its expression in the vascular compartment, CD146 is expressed on a subset of epithelial cells in malignant breast. CD146 may directly or indirectly contribute to tumor aggressiveness by promoting malignant cell motility. Changes in molecular signatures following downmodulation of CD146 expression suggest that CD146 downmodulation is associated with the reversal of several biological characteristics associated with epithelial to mesenchymal transition, and the phenomenon associated with the metastatic process.

High urokinase expression contributes to the angiogenic properties of endothelial cells derived from circulating progenitors.

Endothelial progenitor cells (EPC) display a unique ability to repair vascular injury and promote neovascularization although the underlying molecular mechanisms remain poorly understood. Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) play a critical role in cell migration and angiogenesis by facilitating proteolysis of extracellular matrix. The aim of the present study was to characterize the uPA/uPAR-dependent proteolytic potential of EPC outgrown from human umbilical cord blood and to analyze its contribution to their angiogenic properties in vitro. Cells derived from EPC (EPDC), presenting typical features of late outgrowth endothelial cells, were compared to mature endothelial cells, represented by human umbilical vein endothelial cells (HUVEC). Using quantitative flow cytometry, enzyme-linked immunosorbent assays and zymography, we demonstrated that EPDC displayed higher levels of uPA and uPAR. In conditioned culture media, uPA-dependent proteolytic activity was also found to be significantly increased in EPDC. This activity was paralleled by a higher secretion of pro-metalloproteinase-2 (pro-MMP-2). Inhibition of EPDC-associated uPA by monoclonal antibodies that block either uPA activity or receptor binding, significantly reduced proliferation, migration and capillary like tube formation. Moreover, tumor necrosis factor-alpha and vascular endothelial growth factor, known to be locally secreted in ischemic areas, further increased the proteolytic potential of EPDC by up-regulating uPA and uPAR expression respectively. The EPDC response to these factors was found to be more pronounced than that of HUVEC. In conclusion, these findings indicated that EPDC are characterized by high intrinsic uPA/uPAR-dependent proteolytic potential that could contribute to their invasive and angiogenic behaviour.