Abstract B20: The molecular function of ASPSCR1-TFE3 in alveolar soft part sarcoma

Abstract

Abstract Alveolar soft part sarcoma (ASPS) is a soft-tissue sarcoma that affects predominantly adolescents and young adults with lower legs and buttocks as frequent primary sites. ASPS is characterized by alveolar structure of tumor cells, abundant vascularization, and high frequency of hematogenous metastasis. As for gene abnormality, ASPSCR1-TFE3 fusion gene is observed in all ASPS cases. To understand the exact mechanisms of ASPSCR1-TFE3 and tumorigenesis of ASPS, we have developed an ex vivo mouse model for human ASPS (Tanaka et al., Cancer Res 2017;77(4). In mouse ASPS, the tumor cells frequently showed tumor intravasation, with the intravascular tumor cells presenting as organoid structures covered with hemangiopericytes, which is also observed in human ASPS. Moreover, culture supernatant of mouse ASPS cells strongly induced hemangiopericyte migration in vitro. The search for hemangiopericyte-inducing factors which are released from ASPS cells is in progress. We identified Gpnmb that plays an important role in intravasation of ASPS tumor cells as a direct target of the ASPSCR1-TFE3 fusion transcription factor. The ChIP-seq analysis detected an ASPSCR1-TFE3 binding peak at the Gpnmb promoter, and Gpnmb expression was significantly upregulated in ASPS tumors. Enhanced localization of GPNMB at the front of tumor invasion and intravasation in both mouse and human ASPS. Knockdown of Gpnmb suppressed transendothelial migration of ASPS tumor cells, indicating that Gpnmb is required for intravasation. TFE3 is a member of the TFE/MITF family, which has been found involved in human cancer such as renal cell carcinoma and malignant melanoma. The present model enabled us to evaluate tumorigenic activity of TFE/MITF family proteins. To examine the oncogenic activity of ASPSCR1 fusion genes, artificial chimeric genes were generated consisting of the 5 ASPSCR1 and 3 TFE/MITF sequences. The ASPSCR1-TFE3 and ASPSCR1-TFEB but not ASPSCR1-TFEC and ASPSCR1-MITF induced sarcoma. The results suggest the presence of TFE3/TFEB-specific cofactors and mechanisms for tumorigenesis. In order to identify such novel cofactors and functional motifs, human ASPS cell-nuclear extract was incubated with TFE3 or MITF proteins and TFE3- or MITF-bound fractions were analyzed by mass spectrometry. The TFE3-specific interaction partners were identified and their roles in tumorigenesis, angiogenesis, and/or metastasis are subjected to the subsequent analysis. These studies will provide valuable information for our understanding of the biology of ASPS and functions of TFE/MITF family transcription factors. Citation Format: Miwa Tanaka, Takuro Nakamura. The molecular function of ASPSCR1-TFE3 in alveolar soft part sarcoma [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr B20.