Abstract 268: Regulation and function of ERBB3 signaling pathway in clear cell sarcoma

Abstract

Abstract Clear Cell Sarcoma (CCS), a soft tissue malignancy of tendons and aponeuroses in children and young adults, is notoriously resistant to radiation and chemotherapy, and new approaches to treatment are needed. We recently demonstrated the involvement of the MET receptor tyrosine kinase (RTK) in regulation of the growth, migration, and invasion of CCS cells. However, pharmacologic agents targeting the HGF:MET axis could neither completely inhibit cell growth nor significantly induce apoptosis. To determine whether other RTKs might cooperate with MET in control of survival and proliferation of CCS cells, we used phospho-RTK arrays to assess the activation status of RTKs in three CCS cell lines (CCS292, DTC1, SU-CCS-1). We found that in addition to MET, ERBB3 was strongly activated in CCS. Western blot analysis confirmed constitutive activation of ERBB3 in CCS292 and DTC-1 cell lines and expression in all three lines. Since ERBB3 lacks intrinsic kinase activity, we searched for potential heterodimerization partners. Interestingly, we found that the activation of ERBB3 in different CCS cell lines relied on different partners: ERBB2 as a pivotal partner in CCS292, and MET as a pivotal partner in DTC-1. Moreover, we explored the possibility of a linkage between the CCS pathognomonic EWS-ATF1 fusion product and ERBB3 activation. We found that EWS-ATF1 knockdown resulted in both decreased expression of the ERBB3 ligand Neuregulin 1 and less ERBB3 phosphorylation in CCS292 cells, but had no effects on ERBB3 phosphorylation in DTC-1 cells. To explore the biological function of ERBB3, we applied siRNA or small molecule inhibitors of RTKs to CCS cell lines and determined the biological consequences by cell viability, cell cycle and apoptosis assays; these studies show that ERBB3 in conjunction with MET played an important regulatory role in the proliferation and survival of CCS cells. These data suggest that combined inhibition of the MET and EGFR signaling pathways may be a rationally designed strategy for treatment of patients with advanced CCS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 268.