Abstract P4-06-14: CD146-suppresses breast tumor invasion via a novel transcription target TIMPv

Abstract

Abstract The function of the cell adhesion receptor CD146, a recently discovered marker of endothelial cells and a tumor promoter of melanoma and other cancers, is controversial in breast cancer (BC). However several lines of evidence supports its role as a tumor suppressor in BC. Further, the molecular mechanisms underpinning this suppression are unknown, neither has the ligand for CD146 been identified. Using a novel validated Enhanced Green Fluorescent Protein (EGFP)-inducible systems of CD146 expression both in vitro and in vivo, we provide here molecular and functional evidence of CD146 and its novel transcriptional target TIMPv (a variant of tissue inhibitor of metallo-proteinases) in underpinning the suppression of BC invasion. Tetracycline (tet-on) CD146 system was developed in both MCF-7 and MDA-231 BC founder cell lines, and validated using time course RT-PCR and western blot analyses, and fluorescent microscopy. In functional experiments, induction of CD146 inhibited BC cell migration and invasion. TIMPv, the only endogenous protein inhibitor known for metallocarboxypeptidases, was identified by expression profiling as a novel transcriptional target of CD146-signaling, an association validated by quantitative PCR and immunoblotting experiments in a range of breast and melanoma cancer cells. However, siRNA inhibition of CD146 in the SKMel-28 melanoma cell line increased TIMPv expression, suggesting that while TIMPv is a positive transcriptional target of CD146 in BC cells, it is negatively regulated in melanoma cells. Furthermore, using invasion assay, the functional relevance of TIMPv to CD146-suppressed metastasis was demonstrated by selective suppression of TIMPv in CD146-expressing BC inducible cells using RNAi. More interestingly, induction of CD146 expression in vivo, using the tet-on CD146 expression system in BC Xenograft model resulted in suppression of breast tumor growth. Further, Clinical analysis of breast tissue samples by Immunohistochemistry showed that TIMPv expression patterns paralleled those of CD44s during breast tumor progression. Pharmacological and molecular approaches revealed that the activation of NFκB via Akt pathway couples CD146 to the transcription of TIMPv in BC cells. Our study is the first report to provide a functional molecular link of a novel transcriptional target of CD146, TIMPv, to cancer via a unique axis that underpin CD146-suppressed BC progression; TIMPv is a potential target for guiding the development of novel therapeutic strategies for BC. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-06-14.