TY - JOUR
T1 - Molecular mechanisms of insulin-like growth factor-I mediated regulation of the steroidogenic acute regulatory protein in mouse leydig cells
AU - Manna, Pulak R.
AU - Chandrala, Syam P.
AU - King, Steven R.
AU - Jo, Youngah
AU - Counis, Raymond
AU - Huhtaniemi, Ilpo T.
AU - Stocco, Douglas M.
PY - 2006/2
Y1 - 2006/2
N2 - 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 sidechain cleavage or 3β-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 ERKactivity 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 upregulation 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 133Ala), 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.
AB - 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 sidechain cleavage or 3β-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 ERKactivity 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 upregulation 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 133Ala), 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.
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U2 - 10.1210/me.2004-0526
DO - 10.1210/me.2004-0526
M3 - Article
C2 - 16166197
AN - SCOPUS:31444442754
SN - 0888-8809
VL - 20
SP - 362
EP - 378
JO - Molecular Endocrinology
JF - Molecular Endocrinology
IS - 2
ER -