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Effect of phorbol ester on the regulation of LH/hCG receptors
K Nakamura1, T Minegishi, M Tano
1Department of Obstetrics and Gynecology, Gunma University School of Medicine, Maebashi, Japan.
Abstract:
Granulosa cells have been used to study the regulation of LH/hCG receptor protein and mRNA expression. Phorbol 12-myristate 13-acetate (PMA) dose-dependently attenuates the increases in LH/hCG receptor mRNA and protein induced by FSH and forskolin (FSK). The presence of PMA caused a decrease in cAMP production stimulated by FSH and FSK. These results suggest that PMA-mediated decreases in cAMP are a major factor in PMA-mediated decreases in LH/hCG receptor mRNA. On the other hand, in the presence of 8-Br-cAMP, PMA significantly increased LH/hCG receptor mRNA and protein, with maximal stimulation between PMA concentrations of 3 to 30 nM (1.5 fold) with 8-Br-cAMP. These findings suggest that activation of protein kinase C by PMA attenuates the increase in cAMP accumulation induced by FSH but enhances the effect of cAMP on LH/hCG receptor expression, and that the inhibitory and stimulatory effects of PMA on LH/hCG receptor content are correlated with regulation of LH/hCG receptor mRNA levels. Since the half-life study revealed no change in the stability of the LH/hCG receptor mRNA following PMA treatment, a change in the rate of LH/hCG receptor gene transcription must be responsible for the change in the LH/hCG receptor mRNA levels.
Insights
Phorbol 12-myristate 13-acetate (PMA) affects luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor expression in granulosa cells. PMA decreases cyclic AMP (cAMP) levels, reducing LH/hCG receptor mRNA and protein, but enhances expression when cAMP is supplemented.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Biology
Background:
- Granulosa cells are key models for studying luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor regulation.
- Follicle-stimulating hormone (FSH) and forskolin (FSK) increase LH/hCG receptor mRNA and protein expression.
Purpose of the Study:
- To investigate the effects of Phorbol 12-myristate 13-acetate (PMA) on LH/hCG receptor expression in granulosa cells.
- To elucidate the role of cyclic adenosine monophosphate (cAMP) and protein kinase C (PKC) in PMA's regulation of LH/hCG receptor mRNA and protein levels.
Main Methods:
- Granulosa cells were treated with PMA, FSH, FSK, and 8-Br-cAMP.
- LH/hCG receptor mRNA and protein levels were quantified.
- cAMP production was measured.
- mRNA stability was assessed.
Main Results:
- PMA dose-dependently attenuated FSH- and FSK-induced increases in LH/hCG receptor mRNA and protein.
- PMA decreased FSH- and FSK-stimulated cAMP production.
- In the presence of 8-Br-cAMP, PMA significantly increased LH/hCG receptor mRNA and protein.
- PMA's effects were correlated with changes in LH/hCG receptor mRNA levels, independent of mRNA stability.
Conclusions:
- PMA activation of PKC attenuates FSH-induced cAMP accumulation but enhances cAMP's effect on LH/hCG receptor expression.
- PMA's inhibitory and stimulatory effects on LH/hCG receptor are linked to cAMP regulation and gene transcription rates.
- Changes in LH/hCG receptor mRNA levels are primarily due to altered gene transcription rates.