Specific isoforms of protein kinase G downregulate the transcription of cyclin D1 in NIH3T3

초록

Although protein kinase G (PKG) plays important role in apoptosis induction and cell migration, the isoform specific role of PKG in mediating these functions is still obscure. To elucidate the role of PKG isoforms in transcription control we constructed a series of expression vectors of PKG1α and PKG1β that encode hemagglutinin tagged wild type (WT), constitutively active (S80D and ΔN) and dominant negative (K405R) mutants. Our present study demonstrates that both the constitutively active mutants of PKG 1β downregulate the transcription of cyclin D1 when transiently transfected in NIH3T3 cells, whereas PKG1α mutants show insignificant regulation. We further studied the transcriptional regulators of cyclin D1, such as, c-fos, c-jun, SRE and TRE by using the luciferase reporter assay. Constitutively active mutants of PKG1β showed marked transcriptional downregulation of c-fos in NIH3T3 cells, whereas PKG 1α showed lesser extent. We also found that the constitutively active mutants of PKG1β negatively regulate the activation of SRE and TRE, suggesting their involvement in the regulation of cyclin D1. Interestingly we did not observe any kind of relationship of SRE and TRE with PKG1α mutants. Thus we can conclude that the activation of PKG1β in NIH3T3 cells is responsible for the downregulation of cyclin D1.