Lack of Bcl11b tumor suppressor results in vulnerability to DNA replication stress and damages

Bcl11b/Rit1 is involved in T-cell development and undergoes chromosomal rearrangements in human T-cell leukemias. Thymocytes of Bcl11b(-/-) newborn mice exhibit apoptosis at a certain developmental stage when thymocytes re-enter into the cell-cycle. Here, we show that Bcl11b-knockdown T-cell lines, when exposed to growth stimuli, exhibited apoptosis at the S phase with concomitant decreases in a cell-cycle inhibitor, p27 and an antiapoptotic protein, Bcl-xL, owing to transcriptional repression. This repression was a likely consequence of the impairment of Sirt1, a nicotinamide adenine dinucleotide-dependent deacetylase associating with Bcl11b. Activation of the apoptotic process cleaved the mediator protein, Claspin, and inhibited phosphorylation of cell-cycle checkpoint kinase 1 (Chk1) that plays a central role in sensing and responding to incomplete replication. Bcl11b(-/-) thymocytes also failed to phosphorylate Chk1 when UV irradiated. These results implicate Bcl11b in the remedy for DNA replication stress and maintenance of genomic integrity.