Abstract
The pro-apoptotic P2X(7) receptor regulates growth of epithelial cells. The objectives of the study were to understand P2X(7) gene transcription; to identify the active promoter and the transcription initiation site (TpIS); and to begin understanding regulation of P2X(7) gene transcription. Experiments in vitro utilized normal and cancerous cultured human uterine cervical epithelial cells, and HEK293 cells overexpressing P2X(7)-luciferase reporters. Experiments in vivo used surgical specimen of normal and cancerous uterine cervix. Assays involved DNA, RNA, and protein techniques. (a) The P2X(7) TpIS was localized to adenine (+1) at nt 1683 of the human P2X(7) gene [GenBank Y12851]), with a TTAAA sequence at nt -32/-28 and an active promoter region within nt -158/+32. (b) P2X(7) transcription was found to be regulated by two enhancers located at nt + 222/+232 and +401/+573 regions downstream of the active P2X(7) promoter. (c) The putative enhancer regions formed four DNA-protein complexes. (d) P2X(7) transcription was found to be controlled by hypermethylated cytosines at cytosine-phosphodiester-guanosines (CpG) that cluster or co-localize with the enhancers' sites. (e) We identified nine CpGs as inhibitory cis elements, and three CpG sites that are hypermethylated in cultured cervical epithelial cells and in cervix epithelia in vivo. (f) In cancer cervical cells, the degree of hypermethylation of the CpG sites was greater than in the normal cervical cells. Expression of the P2X(7) receptor is controlled by hypermethylated CpGs that flank transcription enhancers located within a 547-nt region downstream of the promoter.