Abstract 2102: TBX2 promotes rhabdomyosarcoma (RMS) tumorigenesis by repression of PTEN expression

Abstract

Abstract RMS is most common soft tissue sarcoma in children. We previously identified TBX2 as an oncogene and showed that TBX2 is required for tumor formation. Here, we identified the tumor suppressor PTEN as a novel target of TBX2 in RMS and normal muscle. PTEN, which regulates the PI3K-AKT pathway, is repressed in RMS. Our work shows that TBX2 functions to regulate PTEN expression and thus, PI3K-AKT signaling, to enhance the malignancy of RMS tumors. Both quantitative real time PCR and western blot assays were used to assay PTEN expression at the level of mRNA and protein respectively. Immunofluorescence staining was performed to assay the protein expression in human RMS tumor samples. Muscle tissue slides of proliferating myoblasts were assayed by co-immunofluorescence staining, and the proliferating myoblasts were induced by activating satellite cells with cardiotoxin induced muscle damage. Reporter constructs for luciferase assay were based on PTEN promoter. Chromatin immunoprecipitation (ChIP) assays were used to detect protein binding on gene promoters. Xenograft assays were conducted to assay TBX2 function in tumor malignancy. We have found that PTEN was up-regulated upon muscle differentiation, but little expression of PTEN was observed in RMS cells. Although TBX2 was expressed in proliferating myoblasts, it was highly down-regulated upon myogenic differentiation. Human RMS tumor samples showed a down-regulation of PTEN and an up-regulation of TBX2 compared with normal tissues. Over-expression of TBX2 repressed PTEN expression in both C2C12 myoblasts and 10T1/2 fibroblasts. Either depletion of TBX2 or a dominant negative TBX2 increased PTEN expression in RMS cells. Luciferase assays confirmed the regulation of PTEN by TBX2 and ChIP assays demonstrated that TBX2 recruited HDAC1 to the PTEN promoter for repression. The role of HDAC1 in repression of PTEN was confirmed by treatment with HDAC inhibitors, which abrogated the repression of PTEN by TBX2. This work demonstrates that the high expression of TBX2 in RMS is involved in the activation of PI3K-AKT signaling pathway by repressing PTEN, underlying the oncogenic function of TBX2 in tumor cells. Citation Format: Bo K. Zhu, Judith K. Davie. TBX2 promotes rhabdomyosarcoma (RMS) tumorigenesis by repression of PTEN expression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2102. doi:10.1158/1538-7445.AM2015-2102