ERBB-2 NUCLEAR VARIANTS DRIVE TUMOR GROWTH AND PREDICT CLINICAL OUTCOME IN TNBC

MARÍA FLORENCIA CHERVO; NICOLAS BELLORA; PATRICIA VIRGINIA ELIZALDE

Buenos Aires

Congreso; Joint Meeting of Bioscience Societies 2017; 2017

Argentine Society of Clinical Investigation (SAIC)

Triple negative breast cancer (TNBC) refers to the group of tumorswith poor prognosis without clinically significant levels of estrogenand progesterone receptors, and which lack ErbB-2 overexpressionor gene amplification. Our hypothesis is that BCs defined as TN indeedexpress ErbB-2 which instead of being localized at the membraneis present in the nucleus where it modulates tumor growth. Wedetected ErbB-2 variants of different molecular weight (MW) in thenucleus of TNBC cell lines by western blot: MDA-MB-453 expressedfull-length ErbB-2 (185 kDa, p185ErbB-2); MDA-MB-468 expresseda variant of lower MW (165 kDa, p165ErbB-2); HCC-70 and MDAMB-231 expressed p185 and p165ErbB-2. Different ErbB-2 transcriptvariants were reported, among them an alternative splicedisoform lacking exon 16 (ErbB-2D16) is associated with high oncogenicand metastatic potential in BC. Here, we studied ErbB-2 transcriptvariants expression by conventional PCR using splice-specificprimers. All TNBC cells expressed high levels of the ErbB-2 variantC (NM_001289936) which is predicted to be localized in the nucleussince it lacks the N-terminal signal peptide. We also showed thatErbB-2D16 was expressed in TNBC cells. We further discover astrong NErbB-2 presence in TNBC cells by immunofluorescenceand confocal microscopy. These results were confirmed in a cohortof 57 TNBCs in which 26 patients showed NErbB-2 positivity. We revealedNErbB-2 as a significant predictor of worse overall survival inTNBC. Finally, we explored the biological relevance of NErbB-2 bytransfection with the hErbB-2DNLS mutant which is unable to translocateto the nucleus and also acts as dominant negative inhibitor ofendogenous NErbB-2 translocation. Blockade of NErbB-2 presenceinhibited TNBC cell proliferation and tumor growth in TNBC xenografts.In conclusion, our results identified NErbB-2 variants as keyplayers in TNBC and highlighted NErbB-2 as potential biomarkerand therapeutic target in these tumors.