Targeting nuclear ErbB-2 function in trastuzumab-resistant breast cancer cells

CORDO RUSSO, R; BEGUELIN, WENDY; MARIA C.DIAZ FLAQUE; GALIGNIANA, N; CJ PROIETTI; VENTURUTTI, L; CHARREAU, EDUARDO; R SCHILLACI; ELIZALDE, PATRICIA

San Francisco

Congreso; Endocrine Society Annual Meeting; 2013

Steroid hormone receptors for estrogen (ER) and progesterone as well as ErbB-2, a member of the ErbB family of membrane receptor tyrosine kinases, are all major players in the breast cancer (BC) scenario, ER and ErbB-2 being the only markers with associated targeted therapy. ErbB-2 overexpression is associated with poor prognosis and is therapeutically targeted by Trastuzumab (TZ). Although much is known about resistance to anti-ER therapy, the mechanisms underlying TZ resistance remain poorly understood. Notably, 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 or as a transcriptional coactivator. Here, we explored the role of NErbB-2 in BC growth and in TZ resistance. For this purpose, we transfected BC cells with the ErbB-2 NLS mutant, which is unable to translocate to the nucleus and acts as a dominant negative inhibitor of endogenous ErbB-2 nuclear translocation, and compared ErbB-2 NLS and TZ effects on ErbB-2-overexpressing cells sensitive (BT-474, SKBR-3) or resistant (JIMT-1) to TZ. Analysis of ErbB-2 intracellular distribution showed that ErbB-2 was mainly located at the plasma membrane in BT-474 and SKBR-3 cells, and that heregulin (HRG), a ligand of ErbBs, induced NErbB-2 localization. Surprisingly, NErbB-2 constitutive presence was detected in JIMT-1 cells and was further enhanced by HRG. ErbB-2 NLS, but not TZ, significantly blocked HRG-induced ErbB-2 nuclear localization in both TZ-sensitive and -resistant cells. Although basal proliferation of BT-474 and SKBR-3 was inhibited by TZ and ErbB-2 NLS, only ErbB-2 NLS blocked HRG-induced proliferation. In addition, ErbB-2 NLS, but not TZ, inhibited basal and HRG-induced proliferation in JIMT-1 cells. Similar results were observed in other TZ-resistant cells like HCC-1569, HCC-1419, and MDA-MB-453, thus supporting the involvement of NErbB-2 in proliferation of TZ-resistant cells. We then developed a preclinical trial in JIMT-1 cells and demonstrated that ErbB-2 NLS significantly inhibits in vivo tumor growth. We previously revealed that progestin regulates cyclin D1 expression via the assembly of a transcriptional complex in which ErbB-2 acts as coactivator of signal transducer and activator of transcription 3 (Stat3). This nuclear Stat3/ErbB-2 transcriptional complex drives progestin-induced BC growth. Here, we found that HRG also induces the assembly of a Stat3/ErbB-2 complex at cyclin D1 promoter in JIMT-1 cells and that ErbB-2 NLS, but not TZ, abolishes HRG-induced recruitment of ErbB-2 and activation of cyclin D1 promoter. Our present findings highlight that the assembly of the nuclear Stat3/ErbB-2 complex plays a key role in HRG-induced BC growth. Most importantly, we demonstrate that abrogation of NErbB-2 localization constitutes a novel therapeutic strategy in TZ-resistant BC.