Erk5 regulated by ErbB-2 Drives Proliferation of Triple Negative Breast Cancer Cells

M.F. CHERVO, W. BÉGUELIN, S. MADERA, F. IZZO, M. DE MARTINO, L. VENTURUTTI, H.R. QUINTÁ, V.A. CHIAUZZI, C. J. PROIETTI, E.H CHARREAU, R. SCHILLACI, R.I. CORDO RUSSO AND P.V. ELIZALDE.

Congreso; LXI Reunión Anual de SAIC, 2016; 2016

Triple negativebreast cancer (TNBC) refers to the group of tumors with poor prognosis withoutclinically significant levels of estrogen and progesterone receptors, and whichlack membrane ErbB-2 (MErbB-2) overexpression or gene amplification. Our hypothesis is that BC defined asTN indeed expresses ErbB-2 which instead of being localized at the membrane ispresent in the nucleus where it modulates tumor growth. We explored NErbB-2 presence in TNBC usingimmunofluorescence (IF) and confocal microscopy. We found a strong NErbB-2 expressionin a panel of TNBC cell lines (MDA-MB-468, HCC-70, MDA-MB-231 and MDA-MB453). Toexplore the biological function of NErbB-2, cells were transfected withErbB-2DNLS mutant which is unable to translocate to the nucleus and acts asdominant negative inhibitor of endogenous NErbB-2 translocation. ErbB-2DNLSabolished NErbB-2 presence and proliferation in TNBC cell lines. Interestingly,we also demonstrated that in vivoblockade of NErbB-2 expression suppresses tumor growth in two pre-clinicalmodels of TNBC. We previously perform a ChIP-Seq study to identify ErbB-2 binding sites in T47D cells treatedwith HRG, a ligand of ErbBs family. These cells express moderate amounts ofMErbB-2 and HRG treatment induces its nuclear migration. In this ChIP-Seq weidentified Erk5 as a downstream target of NErbB-2. Here we explored Erk5 expression and function inTNBC. We found that protein and mRNA levels of Erk5 were increased in TNBC cells.Through ChIP assays usingprimers spanning the ErbB-2 binding site described in our ChIP-Seq, we observeda specific binding of NErbB-2 to the Erk5 promoter in TNBC. Moreover wedemonstrated that blockade of Erk5 expression inhibits cell proliferation. Thisindicates that NErbB-2 may modulate Erk-5 expression, thus leading toproliferation of TNBC. Our results identify NErbB-2 as a key player in TNBC andhighlight both NErbB-2 and Erk5 as potential therapeutic targets in thesetumors.