Transcription factor Sp1 regulates basal transcription of the human DRG2 gene

Developmentally regulated GTP-binding protein 2 (DRG2) is an evolutionarily conserved GTP-binding protein. DRG2 mRNA expression has been confirmed in many animal and human tissues. DRG2 is thought to play an essential role in the control of cell growth and differentiation. However, transcriptional regulation of DRG2 is largely unknown. To investigate the mechanisms controlling DRG2 expression, we cloned 1509 bp of the 5′-flanking sequence of this gene. Deletion analysis showed that the region between −113 and −70 is essential for the basal level expression of the DRG2 gene in K562 human erythroleukemic cells. Mutation of a putative stimulating protein 1 (Sp1) regulatory site located at position −108 resulted in a significant decline in DRG2 promoter activity. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis revealed that Sp1 binds to this site. Knockdown of Sp1 expression using siRNA inhibited the promoter activation as well as the endogenous DRG2 transcriptional level. Taken together, these results demonstrate that basal expression level of DRG2 is regulated by the Sp1 transcription factor.

Research highlights
► In K562 cells, transcription factor Sp1 binds to GC-rich region of DRG2 promoter.
► Downregulation of Sp1 decreases the expression of DRG2.
► Point mutation of the Sp1 binding motif blocks the DRG2 promoter activity.
► Thus, the Sp1 is responsible for the basal expression of DRG2.