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; 99th Annual Meeting of the Endocrine Society; 2017

Membrane overexpression of ErbB-2, a member of theErbB family of receptor tyrosine kinases, or its gene amplification occurs in15-20% of breast cancer (BC) patients. ErbB2 is therapeutically targeted withmonoclonal antibodies such as trastuzumab (T), and tyrosine kinase inhibitors, i.e.lapatinib (L). Despite their clinical efficiency, 25% of patients treated withT+L relapse because of intrinsic or acquired resistance to such therapies. Thedogma of ErbB-2 mechanism of action has been challenged by the demonstrationthat ErbB-2 migrates to the nucleus (NErbB-2) of BC cells where it acts as atranscription factor (TF) or as coactivator of TF. Recently, weidentified NErbB-2 as the major proliferation driver in T-resistant BC. Here, we explored the role of NErbB-2 in Lresistance. For this purpose, we transfected BCcells with the ErbB-2∆NLS mutant which is unable to translocate to the nucleusand also acts as a dominant negative inhibitor of endogenous ErbB-2 nucleartranslocation, and compare ErbB-2∆NLS, T and L effects on ErbB-2-overexpressinghuman BC cells sensitive (BT-474) or resistant (JIMT-1) to T and L. As previously found, analysis of ErbB-2 subcellulardistribution showed that ErbB-2 was mainly located at the plasma membrane in BT-474cells and that heregulin (HRG), a ligand of ErbBs, induced NErbB-2localization. In JIMT-1 cells, NErbB-2 was constitutively detected and furtherenhanced 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 withresistance to said therapies. Subcellular fractionation assays confirmed thepresence of full-length ErbB-2 protein in the nucleus of both cell lines. Despite basalproliferation in BT-474 was inhibited by ErbB-2∆NLS, T and L, only ErbB2∆NLSwas able to block HRG-induced proliferation. Notably, ErbB-2∆NLS was the onlystrategy able to inhibit JIMT-1 proliferation, even so in HRG-inducedconditions. We previously demonstrated that NErbB-2 modulates BCgrowth 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 expressionin JIMT-1 cells, both T and L failed to do so. These findings identify full-length NErbB-2 rolein resistance to T and L and highlight NErbB-2 blockade as a novel therapeuticstrategy, aiming the ErbB-2 oncogenic pathway unreached by current therapies