Revealing nuclear ErbB-2 function in trastuzumab and lapatinib resistant breast cancer cells

SANTIAGO MADERA, M. FLORENCIA CHERVO, LEANDRO VENTURUTTI, FRANCO IZZO, VIOLETA CHIAUZZI, M. ALICIA CORTES, MATIAS AMASINO, CECILIA J. PROIETTI, ROXANA SCHILLACI, EDUARDO H. CHARREAU, ROSALÍA I. CORDO RUSSO AND PATRICIA V. ELIZALDE

Orlando, FL

Congreso; Endocrine Society's 99th Annual Meeting (ENDO 2017); 2017

Membrane overexpression of ErbB-2, a member of the ErbB family of receptor tyrosine kinases, or its gene amplification occurs in 15-20% of breast cancer (BC) patients. ErbB2 is therapeutically targeted with monoclonal antibodies such as trastuzumab (T), and tyrosine kinase inhibitors, i.e. lapatinib (L). Despite their clinical efficiency, 25% of patients treated with T+L relapse because of intrinsic or acquired resistance to such therapies. The dogma of ErbB-2 mechanism of action has been challenged by the demonstration that ErbB-2 migrates to the nucleus (NErbB-2) of BC cells where it acts as a transcription factor (TF) or as coactivator of TF. Recently, we identified NErbB-2 as the major proliferation driver in T-resistant BC. Here, we explored the role of NErbB-2 in L resistance. For this purpose, we transfected BC cells with the ErbB-2∆NLS mutant which is unable to translocate to the nucleus and also acts as a dominant negative inhibitor of endogenous ErbB-2 nuclear translocation, and compare ErbB-2∆NLS, T and L effects on ErbB-2-overexpressing human BC cells sensitive (BT-474) or resistant (JIMT-1) to T and L. As previously found, analysis of ErbB-2 subcellular distribution showed that ErbB-2 was mainly located at the plasma membrane in BT-474 cells and that heregulin (HRG), a ligand of ErbBs, induced NErbB-2 localization. In JIMT-1 cells, NErbB-2 was constitutively detected and further enhanced by HRG. Nor T neither L blocked NErbB-2 presence in BT-474 and JIMT-1, or revoked HRG effects, allowing us to correlate high levels of NErbB-2 with resistance to said therapies. Subcellular fractionation assays confirmed the presence of full-length ErbB-2 protein in the nucleus of both cell lines. Despite basal proliferation in BT-474 was inhibited by ErbB-2∆NLS, T and L, only ErbB2∆NLS was able to block HRG-induced proliferation. Notably, ErbB-2∆NLS was the only strategy able to inhibit JIMT-1 proliferation, even so in HRG-induced conditions. We previously demonstrated that NErbB-2 modulates BC growth acting as a coactivator of the TF Stat3 and regulating Cyclin D1 (CCND1) expression. We revealed that HRG induces CCND1 expression and that while ErbB-2ΔNLS inhibits its expression in JIMT-1 cells, both T and L failed to do so. These findings identify full-length NErbB-2 role in resistance to T and L and highlight NErbB-2 blockade as a novel therapeutic strategy, aiming the ErbB-2 oncogenic pathway unreached by current therapies.