Nuclear Function of ErbB-2/ErbB-3 Heterodimers in Trastuzumab-Resistant Breast Cancer Cells

CORDO RUSSO RI; BÉGUELIN W; DÍAZ FLAQUÉ, MC; CHIAUZZI VA; VENTURUTTI L; GALIGNIANA NM; PROIETTI CJ; CHARREAU EH; SCHILLACI R; ELIZALDE PV

Chicago, IL

Congreso; 16th International Congress of Endocrinology & Endocrine Society 96th Annual Meeting (ICE-ENDO 2014),; 2014

ErbB-2, a member of the ErbB family of membrane receptor tyrosine kinases, is a major player in the breast cancer (BC) scenario. ErbB-2 overexpression is associated with poor prognosis and is therapeutically targeted by trastuzumab (TZ). The dogma of ErbB-2 mechanism of action has been challenged by the demonstration that membrane ErbB-2 (MErbB-2) migrates to the nucleus (NErbB-2) of BC cells where it acts as a transcription factor or, according to our previous findings, as a transcriptional coactivator. We have recently demonstrated that NErbB-2 function is absolutely necessary for in vitro and in vivo growth of MErbB-2-positive BC cells both sensitive (BT-474) and resistant (JIMT-1) to TZ (1). Besides, we revealed that blockade of NErbB-2 localization constitutes a novel therapeutic strategy in TZ-resistant BC (1). Here, we explored the molecular mechanisms underlying NErbB-2 promotion of growth. Our findings demonstrated that heregulin (HRGß1), a ligand of ErbB-3 and ErbB-4 which recognizes ErbB-2 as co-receptor, stimulates ErbB-2 and ErbB-3 nuclear (NErbB-3) translocation and their colocalization with signal transducer and activator of transcription 3 (Stat3) in human T47D BC cells devoid of basal NErbB-2 and NErbB-3. HRGß1 also enhanced formation of nuclear ErbB-2/ErbB-3 heterodimers in BT-474 and JIMT-1 cells, which express basal levels of NErbB-2 and NErbB-3. To block NErbB-2 presence, we used a human ErbB-2 nuclear localization domain mutant (hErbB-2-deltaNLS), unable to translocate to the nucleus, and which we have previously showed acts as a dominant negative inhibitor of endogenous NErbB-2 migration (2). Interestingly, we found that hErbB-2-deltaNLS colocalized with ErbB-3 at the cytoplasm and abrogated basal and HRGß1-induced ErbB-3 nuclear migration in BT-474 and JIMT-1 cells. Our recent findings revealed that progestin regulates cyclin D1 expression, a cancer-related gene that contains Stat3 binding sites (GAS sites) but lacks ErbB-2 response elements (HAS sites) in its proximal promoter, via the assembly of a transcriptional complex in which ErbB-2 acts as coactivator of Stat3 (2). Here, we found that HRGß1 induces in vivo binding of Stat3, ErbB-2, and ErbB-3 to the GAS sites of the cyclin D1 promoter in T47D, BT-474, and JIMT-1 cells. Transfection of JIMT-1 cells with hErbB-2-deltaNLS abolished both basal and HRGß1-induced recruitment of ErbB-2 and ErbB-3 to the cyclin D1 promoter as well as HRGß1-induced up-regulation of cyclin D1 protein and mRNA levels, indicating that the hErbB-2-deltaNLS growth inhibitory effects on TZ-resistant cells lies in the disruption of the Stat3/ErbB-2/ErbB-3 nuclear complex driving cyclin D1 expression. These findings for the first time reveal the nuclear interaction and function of ErbB-2/ErbB-3 heterodimers and highlight the importance of targeting NErbB-2 function as a novel therapeutic strategy in TZ-resistant BC. (1) Cordo Russo RI et al., Endoc Rev 2013; SAT-313. (2) Béguelin W et al., Mol Cell Biol 2010; 30 (23): 5456-72.