PU.1 activates transcription of SHP-1 gene in hematopoietic cells.

Protein-tyrosine phosphatase SHP-1 is the key negative regulator of numerous signaling pathways. SHP-1 is expressed in the hematopietic and epithelial cells as two structurally similar mRNA transcripts controlled by two different promoters designated P2 and P1, respectively. Whereas the transcriptional regulation of the SHP-1 gene P1 promoter has been partially elucidated, the structure and functional control of the P2 promoter remain unknown despite the critical role played by SHP-1 in the normal and malignant lymphoid and other hematopoetic cells. Using luciferase reporter assays with the set of constructs that contained a gradually truncated intron 1 of the SHP-1 gene, we identified the minimal (<120 bp) fragment that is able to fully activate expression of the reporter gene. Furthermore, we found that PU.1 (a member of the Ets transcription factor family that plays a crucial role in differentiation and function of the lymphoid and myeloid cells) binds to the identified P2 promoter both in vitro and in vivo. PU.1 also activates the promoter in the sequence specific manner and is critical for its expression as evidenced by the profound supression of the SHP-1 gene transcription upon the siRNA-mediated depletion of PU.1. These findings provide an insight into the structure of the hematopoietic cell-specific P2 promoter of the SHP-1 gene and identify PU.1 as the transcriptional activator of the P2 promoter.