P53 DEFICIENCY AND MISEXPRESSION OF PROTEIN-KINASE CK2-ALPHA COLLABORATE IN THE DEVELOPMENT OF THYMIC LYMPHOMAS IN MICE

Protein kinase CK2 (casein kinase II) is a serine-threonine protein ki nase with many substrates, some of which are involved in cell cycle re gulation. CK2 activity is elevated in human solid tumors and leukemia, and dysregulated expression of CK2 induces lymphoma in transgenic mic e. Mice that are deficient in p53 also develop lymphomas, and p53 acti vity may be regulated by CK2 phosphorylation, Here we demonstrate that CK2 alpha transgenic mice partially or completely deficient in p53 de velop thymic lymphomas at a markedly accelerated rate when compared to p53-deficient mice lacking the transgene, Lymphomas originating from CK2 alpha transgenic mice that are heterozygous for p53 generally Lose the wild type p53 allele, indicating that loss of p53 is an important step in tumor progression. Moreover, though lymphomas occur as early as 3 weeks of age in the transgenic mice that are nullizygous for p53, they are still monoclonal, indicating that additional stochastic muta tions are required for their development. These lymphomas express high levels of myc mRNA and frequently ectopically express Lmo-2, a transc ription factor involved in human T cell acute lymphocytic leukemia. Th e p53-null CK2 alpha transgenic lymphomas grow rapidly but are highly prone to apoptosis, suggesting that transformation occurs through syne rgistic dysregulation of cell cycle control induced by misexpression o f CK2 and loss of function of p53.