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

VENTURUTTI L; CORTES MA; SCHILLACI R; ELIZALDE PV.; CHERVO MF; CHIAUZZI VA; PROIETTI CJ; CORDO RUSSO RI; MADERA S; IZZO F; AMASINO MF; CHARREAU EH

Congreso; 99th Annual Meeting of the Endocrine Society; 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.