Cloning and characterization of the human USP22 gene promoter

Ubiquitin-specific processing enzyme 22 (USP22) plays a direct role in regulating cell cycle, and its overexpression has been reported to be involved in tumor progression. However, little is known about the regulation of USP22 transcription. In this study, we cloned and characterized the human USP22 promoter. Using 5' RACE (rapid amplification of cDNA ends) analysis, the transcriptional initiation site was identified. Promoter deletion analysis showed that the sequence between -210 and -7 contains the basal promoter for USP22 in human fibroblast and tumor cells. Surprisingly, mutations in a putative Sp1 binding site immediately upstream of the USP22 transcriptional start site (-13 to -7) resulted in a significant induction of promoter activity. Further study revealed that Sp1 binds to this site in human normal fibroblast cells, and treatment with the Sp1 inhibitor mithramycin A led to a marked increase in USP22 transcript levels. Forced expression of exogenous Sp1 repressed the USP22 promoter activity in HeLa cells. In contrast, knockdown of Sp1 enhanced USP22 promoter activity and mRNA levels. These data suggest that Sp1 is a crucial regulator of USP22 transcription.