Haploinsufficiency and acquired loss of Bcl11b and H2AX induces blast crisis of chronic myelogenous leukemia in a transgenic mouse model

Chronic myelogenous leukemia (CML) is a hematological malignancy that begins as indolent chronic phase (CP) but inevitably progresses to fatal blast crisis (BC). p210BCR/ABL, a chimeric protein with enhanced kinase activity, initiates CML CP, and additional genetic alterations account for progression to BC, but the precise mechanisms underlying disease evolution are not fully understood. In the present study, we investigated the possible contribution of dysfunction of Bcl11b, a zinc-finger protein required for thymocyte differentiation, and of H2AX, a histone protein involved in DNA repair, to the transition from CML CP to BC. For this purpose, we crossed CML CP-exhibiting p210BCR/ABL transgenic (BA(tg/-)) mice with Bcl11b heterozygous (Bcl11b(+/-)) mice and H2AX heterozygous (H2AX(+/-)) mice. Interestingly, p210BCR/ABL transgenic, Bcl11b heterozygous (BA(tg/-)Bcl11b(+/-)) mice and p210BCR/ABL transgenic, H2AX heterozygous (BA(tg/-)H2AX(+/-)) mice frequently developed CML BC with T-cell phenotype and died in a short period. In addition, whereas p210BCR/ABL was expressed in all of the leukemic tissues, the expression of Bcl11b and H2AX was undetectable in several tumors, which was attributed to the loss of the residual normal allele or the lack of mRNA expression. These results indicate that Bcl11b and H2AX function as tumor suppressor and that haploinsufficiency and acquired loss of these gene products cooperate with p210BCR/ABL to develop CML BC. (Cancer Sci 2009; 100: 1219-1226)