Transcriptional control of cyclin D1 promoter by protein kinase G

초록

Protein kinase G (PKG) plays various roles in the inhibition of cell proliferation and cell cycle progression in many types of cells. To examine the roles of PKG isoforms in transcriptional control of cyclin D1, we employed a series of expression vectors of PKG1alpha and PKG1beta which encode wild type and constitutively active mutants. In our present study we found that both the constitutively active mutants of PKG1beta downregulate the transcription of cyclin D1 when transiently transfected in NIH3T3 cells, whereas PKG1alpha mutants show weak inhibition. We further examined the transcriptional regulators of cyclin D1, such as, c-fos, NF-κB, and CRE by using the luciferase reporter assay. Constitutively active mutants of PKG1beta showed stronger transcriptional downregulation of c-fos in NIH3T3 cells, whereas PKG 1 alpha downregulated c-fos to a weaker extent. We also found that the constitutively active mutants of PKG negatively regulate the activation of NF-kB and CRE, suggesting their involvement in the regulation of cyclin D1. These results indicate that PKG downregulates transcription of cyclin D1 and plays a role in the inhibition of cell proliferation in NIH3T3 cells.