title: Mechanisms of protein kinase C signaling in the modulation of 3',5'-cyclic adenosine monophosphate-mediated steroidogenesis in mouse gonadal cells.
abstract: The protein kinase C (PKC) signaling pathway plays integral roles in the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. PKC can modulate the activity of cAMP/protein kinase A signaling involved in steroidogenesis; however, its mechanism remains obscure. In the present study, we demonstrate that activation of the PKC pathway, by phorbol 12-myristate 13-acetate (PMA), was capable of potentiating dibutyryl cAMP [(Bu)(2)cAMP]-stimulated StAR expression, StAR phosphorylation, and progesterone synthesis in both mouse Leydig (MA-10) and granulosa (KK-1) tumor cells. The steroidogenic potential of PMA and (Bu)(2)cAMP was linked with phosphorylation of ERK 1/2; however, inhibition of the latter demonstrated varying effects on steroidogenesis. Transcriptional activation of the StAR gene by PMA and (Bu)(2)cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of the cAMP response element binding protein (CREB). An oligonucleotide probe containing a CREB/activating transcription factor binding region in the StAR promoter was found to bind nuclear proteins in PMA and (Bu)(2)cAMP-treated MA-10 and KK-1 cells. Chromatin immunoprecipitation studies revealed that the induction of phosphorylated CREB was tightly correlated with in vivo protein-DNA interactions and recruitment of CREB binding protein to the StAR promoter. Ectopic expression of CREB binding protein enhanced CREB-mediated transcription of the StAR gene, an event that was markedly repressed by the adenovirus E1A oncoprotein. Further studies demonstrated that the activation of StAR expression and steroid synthesis by PMA and (Bu)(2)cAMP was associated with expression of the nuclear receptor Nur77, indicating its essential role in hormone-regulated steroidogenesis. Collectively, these findings provide insight into the mechanisms by which PKC modulates cAMP/protein kinase A responsiveness involved in regulating the steroidogenic response in mouse gonadal cells.
authors.affiliation: Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
authors.forename: Pulak R
authors.initials: PR
authors.lastname: Manna
authors.forename: Ilpo T
authors.initials: IT
authors.lastname: Huhtaniemi
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Stocco
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D050882:CREB-Binding Protein / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D005260:Female; D006106:Granulosa Cell Tumor; D007984:Leydig Cell Tumor; D008297:Male; D051379:Mice; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D010750:Phosphoproteins / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology*; D011987:Receptors, Steroid / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic / Q000502:physiology; D000098682:Steroidogenic Acute Regulatory Protein
chemical_list: C492004:Creb1 protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; C539818:Nr4a1 protein, mouse; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D010750:Phosphoproteins; D011987:Receptors, Steroid; D000098682:Steroidogenic Acute Regulatory Protein; D003994:Bucladesine; D000242:Cyclic AMP; D050882:CREB-Binding Protein; C494364:Crebbp protein, mouse; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D013755:Tetradecanoylphorbol Acetate