C-type natriuretic peptide (CNP) has recently been implicated as a key meiotic arrest factor in oocytes, and mechanistic studies suggest that the transcriptional regulation of the CNP gene (Nppc) and of its receptor, GC-B (Npr2) is sensitive to gonadotrophin-dependent cAMP accumulation. We have shown CNP to be a major regulator of gonadotrophs in the pituitary, but have yet to establish how either Nppc or Npr2 are transcriptionally controlled locally. In the current study, the Nppc promoter, spanning -1209 to +56 relative to the transcriptional start site was cloned into pGL3LUC from a BAC containing mouse Ch1. αT3-1 and GH3 cells were transiently transfected with Nppc-LUC plasmid, treated with the adenylyl cyclase activator, Forskolin (FSK, 10−910−5 M) for 24 h, after which whole cell lysates were collected and luciferase reporter assays performed. A dose dependent increase in Nppc promoter activity was observed with increasing concentrations of FSK in αT3-1 cells (1.5±0.58.0±3.5-fold increase compared with baseline), with a similar pattern observed in GH3 cells (1.4±0.13.4±1.6-fold increase), although maximal activity was seen at 10−6 M (3.9±0.7-fold increase). To establish whether cAMP signalling could also affect the expression of the CNP receptor, GC-B, similar experiments were performed using a reporter construct containing the human NPR2 promoter, spanning −2129 from the transcriptional start site (NPR2-LUC). Interestingly, FSK failed to stimulate the NPR2-LUC promoter in αT3-1 and GH3 cells, and surprisingly caused an apparent inhibition at lower concentrations (33.9±10.026.7±7.5%, 18.4±3.823.2±4.6% respectively). In summary, these data suggest that cAMP signalling can differentially alter transcriptional regulation of Nppc and Npr2 in pituitary cell lines, providing some parallels with the regulation of these genes in ovarian tissues. However, the specific mechanisms involved in these transcriptional effects remain to be established.
Declaration of funding: Wellcome Trust Project Grant (WT093257MA).