Erk5 regulated by nuclear ErbB-2 drives proliferation of triple negative breast cancer.

CHERVO, MARÍA FLORENCIA; IZZO, FRANCO; DE MARTINO, MARA; VENTURUTTI, LEANDRO; MADERA, SANTIAGO; CENCIARINI, MAURO EZEQUIEL; CHIAUZZI, VIOLETA ALICIA; AMASINO, MATÍAS; PROIETTI, CECILIA JAZMÍN; GUZMÁN, PABLO; ROA, JUAN CARLOS; CHARREAU, EDUARDO HERNÁN; SCHILLACI, ROXANA; CORDO RUSSO, ROSALÍA INÉS; ELIZALDE, PATRICIA VIRGINIA

Florida

Congreso; The Endocrine Society's 99th Annual Meeting and Expo; 2017

Endocrine Society

Triple negative breast cancer (TNBC) refers to the group of tumors with poor prognosis without clinically significant levels of estrogen and progesterone receptors, and lack membrane ErbB-2 (MErbB-2) overexpression or gene amplification. ErbB-2 is a tyrosine kinase receptor that plays a major role in breast cancer (BC). This protein typically acts as a membrane receptor, but its classical mechanism of action has been challenged by the demonstration that MErbB-2 migrates to the nucleus of BC cells where it acts as a transcription factor (1) or as a transcriptional co-activator modulating breast cancer growth (2,3). Our hypothesis is that breast cancers defined as TNBC indeed express ErbB-2 which instead of being localized at the membrane is present in the nucleus where it modulates tumor growth. We evaluated NErbB-2 presence in TNBC using immunofluorescence (IF) and confocal microscopy. We found a strong NErbB-2 expression in a panel of TNBC cell lines: MDA-MB-468, HCC-70, MDA-MB-231 and MDA-MB-453. To explore the biological relevance of NErbB-2, cells were transfected with hErbB-2ΔNLS mutant, which is unable to translocate to the nucleus and also acts as dominant negative inhibitor of endogenous NErbB-2 translocation (2,3). As expected, hErbB-2ΔNLS abolished NErbB-2 localization and strikingly inhibited proliferation of TNBC cell lines. Furthermore, in vivo blockade of NErbB-2 translocation with hErbB-2ΔNLS inhibited tumor growth in MDA-MB-468 and MDA-MB-231 xenografts. On the other hand Erk5, a member of the mitogen-activated protein kinase (MAPK) family, is highly involved in proliferation of tumor cells (4). As well, Erk5 has recently been postulated as a potential therapeutic target in TNBC (5,6). In fact, we revealed that both protein and mRNA expression levels of Erk5 were increased in TNBC cell lines. Interestingly, the transfection with hErbB-2ΔNLS significantly reduced Erk5 protein and mRNA levels as compared to those found in wild-type cells. To explore the nuclear function of ErbB-2, we performed a qChIP assays where we found a specific recruitment of NErbB-2 to the Erk5 promoter in TNBC. Moreover, we demonstrated that blockade of Erk5 expression using siRNAs inhibits TNBC cell proliferation. This findings indicates that NErbB-2 may modulate Erk5 expression, thus leading to proliferation of TNBC. Finally, we assessed the clinical significance of NErbB-2 in tissue microarrays from a cohort of 226 primary invasive breast carcinomas by IF. Of the total cohort, 51 (23%) patients were classified as TNBC. Our results revealed NErbB-2 as a significant predictor of worse overall survival in TNBC patients. In conclusion, we identified NErbB-2 as a key player in TNBC and highlighted both NErbB-2 and Erk5 as potential therapeutic targets in these tumors.