Transcriptional Protein Sp1 Regulates LEDGF Transcription by Directly Interacting with Its Cis-Elements in GC-Rich Region of TATA-Less Gene Promoter

Abstract

LEDGF/p75 interacts with DNA/protein to regulate gene expression and function. Despite the recognized diversity of function of LEDGF/p75, knowledge of its transregulation is in its infancy. Here we report that LEDGF/p75 gene is TATA-less, contains GC-rich cis elements and is transcriptionally regulated by Sp1 involving small ubiquitin-like modifier (Sumo1). Using different cell lines, we showed that Sp1 overexpression increased the level of LEDGF/p75 protein and mRNA expression in a concentration-dependent fashion. In contrast, RNA interference depletion of intrinsic Sp1 or treatment with artemisinin, a Sp1 inhibitor, reduced expression of LEDGF/p75, suggesting Sp1-mediated regulation of LEDGF/p75. In silico analysis disclosed three evolutionarily conserved, putative Sp1 sites within LEDGF/p75 proximal promoter (−170/+1 nt). DNA-binding and transactivation assays using deletion and point mutation constructs of LEDGF/p75 promoter-CAT revealed that all Sp1 sites (−50/−43, −109/−102 and −146/−139) differentially regulate LEDGF/p75. Cotransfection studies with Sp1 in Drosophila cells that were Sp1-deficient, showed increased LEDGF/p75 transcription, while in lens epithelial cells (LECs) promoter activity was inhibited by artemisinin. These events were correlated with levels of endogenous Sp1-dependent LEDGF/p75 expression, and higher resistance to UVB-induced cell death. ChIP and transactivation assays showed that Sumoylation of Sp1 repressed its transcriptional activity as evidenced through its reduced binding to GC-box and reduced ability to activate LEDGF/p75 transcription. As whole, results revealed the importance of Sp1 in regulating expression of LEDGF/p75 gene and add to our knowledge of the factors that control LEDGF/p75 within cellular microenvironments, potentially providing a foundation for LEDGF/p75 expression-based transcription therapy.