ABSTRACT
The expression of β-catenin, a potent oncogene, is causally linked to tumorigenesis. Therefore, it was surprising that the transgenic expression of oncogenic β-catenin in thymocytes resulted in thymic involution instead of lymphomagenesis. In this report, we demonstrate that this is because the expression of oncogenic β-catenin induces DNA damage, growth arrest, oncogene-induced senescence (OIS), and apoptosis of immature thymocytes. In p53-deficient mice, the expression of oncogenic β-catenin still results in DNA damage and OIS, but the thymocytes survive and eventually progress to thymic lymphoma. β-Catenin-induced thymic lymphomas are distinct from lymphomas that arise in p53−/− mice. They are CD4− CD8−, while p53-dependent lymphomas are largely CD4+ CD8+, and they develop at an earlier age and in the absence of c-Myc expression or Notch1 signaling. Thus, we report that oncogenic β-catenin-induced, p53-independent growth arrest and OIS and p53-dependent apoptosis protect developing thymocytes from transformation by oncogenic β-catenin.
Transgenic Expression of the p16INK4aCyclin-Dependent Kinase Inhibitor Leads to Enhanced Apoptosis and Differentiation Arrest of CD4−CD8−Immature Thymocytes