Role of a STAT binding site in the regulation of the human perforin promoter

The pore-forming protein perforin is preferentially expressed in NK and cyt otoxic T cells. To investigate the molecular regulation of human perforin g ene transcription, the activity of the human perforin promoter was analyzed in human NK and T cell lines using various promoter fragments linked to a luciferase reporter gene. A core promoter was identified within 55 bp upstr eam of the transcription start site. This promoter region contains a guanin e/cytosine box and has basal activity in YT, Kit225-k6, and Jurkat cells. A strong enhancer activity was identified between positions -1136 and -1076, a region that includes a STAT-like element. This enhancer region was activ e in YT cells, which have constitutive perforin expression and activated ST AT3 protein, but not in Kit225-k6 or Jurkat cells, which do not have consti tutive perforin expression. Mutation of the STAT binding site resulted in a dramatic down-regulation of promoter activity. Electrophoretic mobility sh ift assays, using a probe containing the STAT element of the perforin promo ter, indicated that this element can bind STAT3 from YT cells. Moreover, th e STAT element was shown to bind STAT5a/b induced by IL-2 as well as STAT1 alpha induced by IL-6 in human NK cells. Together, these results suggest th at STAT proteins play a key role in perforin gene transcription and provide a model by which cytokines can regulate perforin gene expression.