Tbx3 impinges on the p53 pathway to suppress apoptosis, facilitate cell transformation and block myogenic differentiation.

Tbx3 is a member of the T-box family of transcription factors. Mutations in Tbx3 cause ulnar-mammary syndrome, an autosomal dominant disorder characterized by upper limb defects, apocrine-gland defects including mammary hypoplasia, and tooth, hair and genital defects. In cell culture, Tbx3 and its close relative Tbx2 are capable of immortalizing mouse embryo fibroblasts. We show that expression of Tbx3 together with Myc or oncogenic Ras (H-Ras(Val17)) leads to efficient transformation of mouse embryo fibroblasts. Oncogene cooperation by Tbx3 correlates with an ability of Tbx3 to suppress the induction of p19ARF and p53 that is typically caused by overexpression Myc and Ras, and to protect against Myc-induced apoptosis. Whereas Tbx3 is capable of interfering with apoptosis caused by excessive Myc levels, a Tbx3 mutant lacking its C-terminal repression domain shows no anti-apoptotic activity and fails to repress levels of p19ARF or p53. Consistent with an ability to suppress p53 pathway function, we find that Tbx3, but not a Tbx3 C-terminal mutant, efficiently blocks myogenic differentiation of C2C12 myoblasts. Our results support the idea that deregulation and/or excessive levels of Tbx3 may have oncogenic potential in vivo.