NUCLEAR FUNCTION OF ERBB-2/ERBB-3 HETERODIMERS IN BREAST CANCER CELLS RESISTANT TO TRASTUZUMAB AND LAPATINIB

VIOLETA A. CHIAUZZI; LEANDRO VENTURUTTI; GONZALO SEQUEIRA; EDUARDO H. CHARREAU; M. FLORENCIA CHERVO; FRANCO IZZO; PAOLA ROJAS; ROXANA SCHILLACI; PATRICIA V. ELIZALDE; SANTIAGO MADERA; DIEGO MONTERO; M. ALICIA CORTÉS; CECILIA J. PROIETTI; ROSALÍA I. CORDO RUSSO

Buenos Aires

Simposio; Reunión Conjunta de Sociedades de Biociencias; 2017

ErbB-2 overexpression or amplification is associated with poorprognosis in breast cancer (BC) and is therapeutically targeted bymonoclonal antibodies (trastuzumab, TZ) or by kinase-inhibitors(lapatinib, L). Despite clinical efficiency, resistance to said drugs is amajor issue. ErbB-2 translocates to the nucleus (NErbB-2), where itacts as transcription factor (TF, e.g. to modulate ERK5 expression)or as coactivator of TF Stat3 (e.g., to regulate cyclin D1 -CCND1- orp21CIP1 expression). We showed that NErbB-2 function is vital forproliferation of ErbB2+ BC cells sensitive (BT474) and resistant(JIMT1) to TZ and L. Here we explored the molecular mechanismswithin 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 JIMT1cells. Basal levels of NErbB-2/NErbB-3 were higher in JIMT1 thanin BT474 and were not modulated by TZ or L. To block NErbB-2presence we used ErbB-2ΔNLS mutant unable to translocate to thenucleus. It also acts as a dominant negative inhibitor of endogenousNErbB-2. We found that ErbB-2ΔNLS colocalized with ErbB-3 at thecytoplasm and abrogated NErbB-2 and NErbB-3 migration in JIMT1cells. We also found that HRG induces CCND1, p21CIP1 and ERK5expression and that ErbbB-2ΔNLS inhibited their levels in JIMT1cells. In silico analysis of microarray datasets of BT474 cells sensitivevs resistant to L (GSE16179) showed that levels of NErbB-2target genes (CCND1, p21CIP1) were increased in resistant cells.We developed a preclinical model in JIMT1 cells and demonstratedthat transfection with ErbB-2ΔNLS significantly inhibits in vivo tumorgrowth. Ex vivo culture of JIMT1 xenografts showed that blockade ofNErbB-2 function induced release of LDH (lactate dehydrogenase)necrosis marker to the supernatant. These findings highlight the relevanceof targeting NErbB-2 function as a novel therapeutic strategyin TZ and L-resistant BC.