MYB AND ETS RELATED TRANSCRIPTION FACTORS ARE REQUIRED FOR ACTIVITY OF THE HUMAN LCK TYPE-I PROMOTER

The lck gene, which encodes a lymphoid-specific Src family tyrosine ki nase, is transcribed from two promoters that are differentially utiliz ed during T cell development. We have shown previously that the human lck type I promoter, which is preferentially expressed in immature thy mocytes, requires a binding site (-97 to -90) for the Ets family of tr anscription factors for its activity in Jurkat T leukemia cells. Three putative Myb binding sites (-86 to -82, -77 to -72 and -59 to -54) we re analysed for their ability to activate the lck type I promoter. In vitro assays demonstrated specific binding of purified, bacterially ex pressed c-Myb DNA binding domain to the Myb (-59 to -54) site. Transie nt transfection assays using the site-directed mutants of the lck type I promoter in Jurkat cells revealed that mutation of the Myb (-59 to -54) site abolished transcriptional activity. In transiently transfect ed HeLa cells, the lck type I promoter was activated by cotransfection with a vector that expresses c-Myb. This c-Myb dependent activation r equired the presence of intact Myb and Ets binding sites, indicating t hat the expressed c-Myb functions with endogenous Ets related transcri ption factors to activate the lck type I promoter. This effect was fur ther enhanced by co-transfection with vectors that express either Ets1 or Ets2. These results demonstrate that Myb and Ets related transcrip tion factors synergistically activate the human lck type I promoter.