Interaction of pituitary hormones and expression of clock genes modulated by bone morphogenetic protein-4 and melatonin

Mar 3, 2015Biochemical and biophysical research communications

How pituitary hormones and body clock genes interact under the influence of bone growth signals and melatonin

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Abstract

A significant correlation between the mRNA expression of proopiomelanocortin (POMC) and Per2 was revealed in corticotrope AtT20 cells.

Knockdown of Per2 in AtT20 cells led to a notable reduction in POMC mRNA levels, regardless of corticotropin-releasing hormone (CRH) stimulation.
Treatment with BMP-4 and melatonin reduced both Per2 mRNA and protein levels in AtT20 cells, indicating their suppressive effect on POMC expression.
In GH3 lactosomatotrope cells, a correlation was observed between prolactin (PRL) and Clock mRNA levels, which diminished with forskolin treatment.
SiRNA knockdown of Clock significantly decreased PRL mRNA levels in GH3 cells, while Bmal1 knockdown did not produce a similar effect.
Clock mRNA and protein levels remained stable during treatments with melatonin, BMP-4, or forskolin, although Bmal1 expression increased with forskolin.

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Functional interaction of clock genes and pituitary hormones was investigated by focusing on bone morphogenetic protein (BMP)-4 and melatonin actions in anterior pituitary cells. A significant correlation between the mRNA expression of proopiomelanocortin (POMC) and Per2 was revealed in serial cultures of corticotrope AtT20 cells. Knockdown of Per2 expression by siRNA in AtT20 cells resulted in a significant reduction of POMC mRNA level with or without corticotropin-releasing hormone (CRH) stimulation. Treatments with BMP-4 and melatonin, both of which suppress POMC expression, reduced Per2 mRNA as well as protein levels in AtT20 cells. On the other hand, in lactosomatotrope GH3 cells, an expressional correlation was found between prolactin (PRL) and Clock mRNA levels, which was attenuated in the presence of forskolin treatment. The siRNA-mediated knockdown of Clock expression, but not that of Bmal1, significantly reduced PRL mRNA levels in GH3 cells. Interestingly, Clock mRNA and protein levels did not fluctuate with melatonin, BMP-4 or forskolin treatment, although Bmal1 expression was significantly increased by forskolin treatment. Collectively, a significant correlation between the expression of POMC and Per2 and that between PRL and Clock were uncovered in corticotrope and lactosomatotrope cells, respectively. Per2 expression was inhibited by POMC modulators including melatonin and BMP-4, while Clock expression was steadily maintained. Thus, the effects of melatonin and BMP-4 on clock gene expression may imply differential stability of circadian rhythms of adrenocorticotropin (ACTH) and PRL secreted from the anterior pituitary.

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Interaction of pituitary hormones and expression of clock genes modulated by bone morphogenetic protein-4 and melatonin

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