Bim is a suppressor of Myc-induced mouse B cell leukemia

Top Cited Papers
Publisher Website
Google Scholar
Abstract
Impaired apoptosis is now recognized to be central to tumor development. Bcl2, activated by chromosomal translocation in human follicular lymphoma, promotes oncogenesis by inhibiting apoptosis. Bim, a distant proapoptotic relative, is emerging as a major physiologic antagonist of Bcl2. Here, we show that loss of Bim is oncogenic. Bim protein levels were elevated in the apoptosis-prone B lymphoid cells of Emicro-Myc-transgenic mice, and Bim-mutant Emicro-Myc mice had increased numbers of IgM-bearing B cells. Emicro-Myc-expressing B lymphoid cells deficient in Bim were refractory to apoptosis induced in vitro by cytokine deprivation or antigen receptor cross-linking. Thus, Bim is induced by Myc in B cells and mediates apoptosis. Remarkably, inactivation of even a single allele of Bim accelerated Myc-induced development of tumors, particularly acute B cell leukemia. None of the primary tumors from Bim(+/-) Emicro-Myc mice displayed loss of the second allele of Bim. These findings indicate that Bim is a tumor suppressor, at least in B lymphocytes, and is haploinsufficient. Whereas the p19Arf/p53 pathway is frequently mutated in tumors arising in Bim(+/+) Emicro-Myc mice, it was unaffected in most Bim-deficient tumors, indicating that Bim reduction is an effective alternative to loss of p53 function.