Nuclear function of ErbB-2/ErbB-3 heterodimers in breast cancer cells resistant to trastuzumab and lapatinib

SANTIAGO MADERA; MARIA FLORENCIA CHERVO; VIOLETA CHIAUZZI; DIEGO MONTERO; FRANCO IZZO; LEANDRO VENTURUTTI; MARIA ALICIA CORTÉS; CECILIA PROIETTI; ROXANA SCHILLACI; EDUARDO CHARREAU; ROSALIA INES CORDO-RUSSO; PATRICIA V. ELIZALDE

Mar del Plata

Congreso; Congreso LXII Reunión de la sociedad Argentina de Investigación en Clínica. (SAIC); 2017

Sociedad Argentina de Investigación en Clinica

ErbB-2 overexpression or amplification is associated with poor prognosis in breast cancer (BC) and is therapeutically targeted by monoclonal antibodies (trastuzumab, TZ) or by kinase-inhibitors (lapatinib, L). Despite clinical efficiency, resistance to said drugs is a major issue. ErbB-2 translocates to the nucleus (NErbB-2), where it acts as transcription factor (TF, e.g. to modulate ERK5 expression) or as coactivator of TF Stat3 (e.g., to regulate cyclin D1 -CCND1- or p21CIP1 expression). We showed that NErbB-2 function is vital for proliferation of ErbB2+ BC cells sensitive (BT474) and resistant (JIMT1) to TZ and L. Here we explored the molecular mechanisms within NErbB-2 function. We demonstrated that heregulin (HRG), ligand of ErbBs, stimulates ErbB-2 and ErbB-3 nuclear (NErbB-3) translocation and colocalization with Stat3 in BT474 and JIMT1 cells. Basal levels of NErbB-2/NErbB-3 were higher in JIMT1 than in BT474 and were not modulated by TZ or L. To block NErbB-2 presence we used ErbB-2ΔNLS mutant unable to translocate to the nucleus. It also acts as a dominant negative inhibitor of endogenous NErbB-2. We found that ErbB-2ΔNLS colocalized with ErbB-3 at the cytoplasm and abrogated NErbB-2 and NErbB-3 migration in JIMT1 cells. We also found that HRG induces CCND1, p21CIP1 and ERK5 expression and that ErbbB-2ΔNLS inhibited their levels in JIMT1 cells. In silico analysis of microarray datasets of BT474 cells sensitive vs resistant to L (GSE16179) showed that levels of NErbB-2 target genes (CCND1, p21CIP1) were increased in resistant cells. We developed a preclinical model in JIMT1 cells and demonstrated that transfection with ErbB-2∆NLS significantly inhibits in vivo tumor growth. Ex vivo culture of JIMT1 xenografts showed that blockade of NErbB-2 function induced release of LDH (lactate dehydrogenase) necrosis marker to the supernatant. These findings highlight the relevance of targeting NErbB-2 function as a novel therapeutic strategy in TZ and L-resistant BC.