for eosinophil differentiation of human cord blood derived CD34+ cells Signal transducer and activator of transcription 5a (STAT5a) is required

Abstract Signal transducers and activators of transcription (STATs) have been reported to play a critical role in differentiation of several myeloid cell lines, although the importance of STATs in differentiation of primary human hematopoietic cells remains to be established. Terminal eosinophil differentiation is induced by IL-5, which has also been demonstrated to activate STAT5. We have investigated whether STAT5 plays a critical role during eosinophil differentiation, using umbilical cord blood (UCB) derived CD34 + cells. In this ex-vivo system, both STAT5 expression and activation are high early during differentiation, and STAT5 protein expression is down-regulated during the final stages of eosinophil differentiation. Retroviral transductions were performed to ectopically express both wild-type and dominant-negative STAT5a (STAT5a 750) in CD34 + cells. Transduction of cells with STAT5a resulted in enhanced proliferation compared to cells transduced with empty vector alone. Interestingly, ectopic expression of STAT5a also resulted in an accelerated differentiation. In contrast, ectopic expression of STAT5a 750 resulted in a block in differentiation while proliferation was also severely inhibited. Similar results were obtained with dominant-negative STAT5b. Forced expression of STAT5a enhanced expression of the STAT5 target genes Bcl-2 and p21