Blocking L-type calcium channels reduced the threshold of cAMP-induced steroidogenic acute regulatory gene expression in MA-10 mouse Leydig cells.
Previous studies have reported the roles of Ca(2+) in steroidogenesis. The present study has investigated an inhibitory effect of Ca(2+) influx through L-type Ca(2+) channels on gene expression of steroidogenic acute regulatory (STAR) protein that regulates the transfer of substrate cholesterol to the inner mitochondrial membrane for steroidogenesis. Blocking Ca(2+) influx through L-type Ca(2+) channels using the selective Ca(2+) channel blocker, nifedipine, markedly enhanced cAMP-induced STAR protein expression and progesterone production in MA-10 mouse Leydig cells. This was confirmed by utilization of different L-type Ca(2+) channel blockers. Reverse transcription-PCR analyses of Star mRNA and luciferase assays of Star promoter activity indicated that blocking Ca(2+) influx through L-type Ca(2+) channels acted at the level of Star gene transcription. Further studies showed that blocking the Ca(2+) channel enhanced Star gene transcription by depressing the expression of DAX-1 (NR0B1 as listed in the MGI Database) protein, a transcriptional repressor of Star gene expression. It was also observed that there is a synergistic interaction between nifedipine and cAMP. Normally, sub-threshold levels of cAMP are unable to induce steroidogenesis, but in the presence of the L-type Ca(2+) channel blocker, they increased STAR protein and steroid hormone to the maximal levels. However, in the absence of minimal levels of cAMP, none of the L-type Ca(2+) channel blockers are able to induce Star gene expression. These observations indicate that Ca(2+) influx through L-type Ca(2+) channels is involved in an inhibitory effect on Star gene expression. Blocking L-type Ca(2+) channel attenuated the inhibition and reduced the threshold of cAMP-induced Star gene expression in Leydig cells.
Pandey
Akhilesh K
AK
Garrison Institute on Aging, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
Li
Wei
W
Yin
Xiangling
X
Stocco
Douglas M
DM
Grammas
Paula
P
Wang
Xingjia
X
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D057137:DAX-1 Orphan Nuclear Receptor / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D015870:Gene Expression / Q000187:drug effects*; D007985:Leydig Cells; D008297:Male; D051379:Mice; D009543:Nifedipine / Q000008:administration & dosage / Q000494:pharmacology*; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011374:Progesterone / Q000096:biosynthesis; D013256:Steroids / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology; D000098682:Steroidogenic Acute Regulatory Protein
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D057137:DAX-1 Orphan Nuclear Receptor; C539966:Nr0b1 protein, mouse; D010750:Phosphoproteins; D013256:Steroids; D000098682:Steroidogenic Acute Regulatory Protein; D011374:Progesterone; D003994:Bucladesine; D014700:Verapamil; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D009543:Nifedipine