Novel roles of PKG isoforms in cyclin D1 transcription

초록

Although protein kinase G (PKG) plays important role in the inhibition of cell proliferation and cell cycle progression, the isoform-specific role of PKG in mediating these functions is still obscure. To elucidate the role of PKG isoforms in transcriptional control of cyclin D1, we employed a series of expression vectors of PKG 1α and PKG 1β which encode hemagglutinin-tagged wild type (WT) and constitutively active (SD and ΔN) mutants. Our present study demonstrates that both the constitutively active mutants of PKG1β downregulate the transcription of cyclin D1 when transiently transfected in NIH3T3 cells, whereas PKG 1α mutants show weak inhibition. We further studied the transcriptional regulators of cyclin D1, such as, c-fos, NF-κB, and CRE by using the luciferase reporter assay. Constitutively active mutants of PKG 1β showed marked transcriptional downregulation of c-fos in NIH3T3 cells, whereas PKG 1α downregulated c-fos to a lesser extent. We also found that the constitutively active mutants of PKG negatively regulate the activation of NF-κB and CRE, suggesting their involvement in the regulation of cyclin D1. Thus we can conclude that the activation of PKG in NIH3T3 cells is responsible for the downregulation of cyclin D1.