Functional Regulation of TEL through MOZ-Induced Acetylation.

TEL, a member of ETS transcription factors, acts as a transcriptional repressor and a tumor suppressor. TEL is inactivated by genomic alterations such as deletion and chromosomal translocation in a variety of human leukemia. TEL also has important roles in the maintenance of hematopoietic stem cells and differentiation of erythroid progenitors. Regulation of its function through phosphorylation and sumoylation has been described in the past literatures. We here demonstrated that TEL is also regulated by acetylation, another mode of post-translational modification. First, immunoprecipitation assay using anti-acetylated lysine (Ack) antibody showed that TEL proteins overexpressed in 293T cells were acetylated in vivo. To determine the acetylated lysine residue(s), we used a set of TEL mutants in which one of 16 lysine residues in the molecule was left with all the others substituted with arginine. We found that TEL was acetylated only at Lys99. To confirm that TEL is acetylated in hematopoietic cells, we established mouse erythroleukemia (MEL) cell clones expressing wild-type-TEL or K99R mutant in which Lys99 was substituted with arginine, and demonstrated acetylation of TEL at the same lysine residue in MEL cells by in vivo acetylation assay using [1–14C] acetic acid. Next, to identify histone acetyltransferase that is responsible for acetylation of TEL, we co-expressed each one of several known histone acetyltransferases such as p300, CBP, P/CAF and MOZ with TEL. The immunoprecipitation assay using anti-Ack antibody showed that only MOZ induced acetylation of TEL proteins among them. Physical interaction between TEL and MOZ was detected in immunoprecipitation assay. In order to get insights into functional modification of TEL through MOZ-induced acetylation, we examined whether the acetylation alters trans-repressional abilities of TEL. We employed pGL2-754TR reporter that has a natural promoter derived from stromelysin-1, one of TEL’s target genes, in luciferase assays. A two-fold decrease in luciferase activities was observed when TEL was expressed. Importantly, co-expression of MOZ attenuated the transcriptional suppression by TEL. Furthermore, to analyze alterations of TEL’s biological functions through acetylation, we employed MEL cells whose erythroid differentiation is accelerated by TEL, and compared the effect of overexpression between wild-type-TEL and its K99R mutant. Interestingly, K99R mutant stimulated erythroid differentiation with a more extent than wild-type-TEL. All these data suggest that molecular and biological functions of TEL might be controlled negatively through MOZ-induced acetylation at Lys99. Being a tumor suppressor, functional inactivation of TEL through protein modification mechanisms could be critical in the development and progression of human leukemia.