Molecular mechanisms of insulin-like growth factor-I mediated regulation of the steroidogenic acute regulatory protein in mouse leydig cells.
Growth factors are known to play diverse roles in steroidogenesis, a process regulated by the mitochondrial steroidogenic acute regulatory (StAR) protein. The mechanism of action of one such growth factor, IGF-I, was investigated in mouse Leydig tumor (mLTC-1) cells to determine its potential role in the regulation of StAR expression. mLTC-1 cells treated with IGF-I demonstrated temporal and concentration-dependent increases in StAR expression and steroid synthesis. However, IGF-I had no effect on cytochrome P450 side-chain cleavage or 3beta-hydroxysteroid dehydrogenase protein levels. IGF-I was capable of augmenting N,O'-dibutyrl-cAMP-stimulated steroidogenic responsiveness in these cells. The steroidogenic potential of IGF-I was also confirmed in primary cultures of isolated mouse Leydig cells. IGF-I increased phosphorylation of ERK1/2, an event inhibited by the MAPK/ERK inhibitors, PD98059 and U0126. Interestingly, inhibition of ERK activity enhanced IGF-I-mediated StAR protein expression, but phosphorylation of StAR was undetectable, an observation in contrast to that seen with N,O'-dibutyrl-cAMP signaling. Further studies demonstrated that these events were tightly correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 and scavenger receptor class B type 1. Whereas both protein kinase A and protein kinase C signaling were involved in the IGF-I-mediated steroidogenic response, the majority of the effects of IGF-I were found to be mediated by the protein kinase C pathway. Transcriptional activation of the StAR gene by IGF-I was influenced by several transcription factors, its up-regulation being dependent on phosphorylation of the cAMP response element-binding protein (CREB) and the activator protein 1 family member, c-Jun. Conversely, StAR gene transcription was markedly inhibited by expression of nonphosphorylatable CREB (Ser(133)Ala), dominant negative A-CREB, and dominant negative c-Jun (TAM-67) mutants. Collectively, the present studies identify molecular events in IGF-I signaling that may influence testicular growth, development, and the Leydig cell steroidogenic machinery through autocrine/paracrine regulation.
Manna
Pulak R
PR
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
Chandrala
Syam P
SP
King
Steven R
SR
Jo
Youngah
Y
Counis
Raymond
R
Huhtaniemi
Ilpo T
IT
Stocco
Douglas M
DM
D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology; D005786:Gene Expression Regulation; D007328:Insulin / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D007985:Leydig Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000502:physiology; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000494:pharmacology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000098682:Steroidogenic Acute Regulatory Protein
D017362:Cyclic AMP Response Element-Binding Protein; D007328:Insulin; D010750:Phosphoproteins; D016755:Proto-Oncogene Proteins c-jun; D013256:Steroids; D000098682:Steroidogenic Acute Regulatory Protein; D003994:Bucladesine; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D015096:3-Hydroxysteroid Dehydrogenases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3