Identification of Sp1 targets involved in proliferation and cancer

Sp1 is a transcription factor able to regulate many genes through its DNA binding domain, containing three zinc fingers. We were interested in identifying target genes regulated by Sp1, with a special emphasis to those involved in proliferation and cancer. Our approach was to treat HeLa cells with a siRNA directed against Sp1 mRNA (siSp1) to decrease the expression of Sp1 and, in turn, the genes activated by this transcription factor. Sp1 siRNA treatment led to a great number of differentially expressed genes as determined by whole genome cDNA microarray analysis. Underexpressed genes were selected since they represent putative genes activated by Sp1. These underexpressed genes were classified in six Gene Onthology categories, namely proliferation and cancer, mRNA processing, lipidic metabolism, glucidic metabolism, transcription and translation. Putative Sp1 binding sites were found in the promoters of the selected genes using the MatchTM software. After literature mining, 11 genes were selected for further validation of their expression levels using RT-real time PCR. Underexpression was confirmed for the 11 genes plus Sp1 in HeLa cells after siSp1 treatment. Additionally, EMSA and chromatin immunoprecipitation assays were performed to test for binding between Sp1 and the promoters of these genes. We observed binding of Sp1 to the promoters of RAB20, FGF21, IHPK2, ARHGAP18, NPM3, SRSF7, CALM3, PGD and Sp1 itself. Finally, the mRNA levels of RAB20, FGF21 and IHPK2, three genes related with proliferation and cancer, were determined after overexpression of Sp1 in HeLa cells, to confirm their relationship with Sp1. The aim of our study was to evaluate, by using whole genome microarrays, the effects of a siRNA against the transcription factor of Sp1 in HeLa cells. Using this methodology genes activated by Sp1 could be downregulated. The obtective was to determine new genes regulated at the cellular level. Triplicate samples were hybridized for each experimental condition (6 samples in total). The samples provided were analyzed using the specific software GeneSpring GX.