Regulation of Tryptophan Hydroxylase by Cyclic AMP, Calcium, Norepinephrine, and Light in Cultured Chick Pineal Cells (original) (raw)

2002, Journal of Neurochemistry

The level of 35S incorporation into tryptophan hydroxylase (TPH) shows a circadian rhythm in cultured chick pineal cells. The TPH oscillation peaks in the early subjective night, persists in constant darkness, and can be phase shifted by light, in parallel to the effect of these treatments on melatonin synthesis. Using quantitative two-dimensional polyacrylamide gel electrophoresis, we have examined the regulation of TPH by agents known to affect melatonin synthesis in the chick pineal. We report here that 35S incorporation into TPH is induced by cyclic AMP and calcium, and partially inhibited by acute exposure to light. Cyclic AMP also causes a proportional increase in the radiolabeling of one of the TPH isoforms and a concomitant decrease in another isoform, possibly reflecting a change in the phosphorylation state of TPH. This effect is reversed by treatments known to reduce intracellular cyclic AMP levels in the chick pineal. Cyclic AMP thus appears to be involved in both translational and posttranslational processes regulating the expression of TPH in chick pineal cells. Key Words: Tryptophan hydroxylase-Melatonin-Pineal-Circadian rhythm -Cyclic AMP-Two-dimensional polyacrylamide gel electrophoresis. AMP-dependent protein kinase; TCA, trichloroacetic acid; TPH, tryptophan hydroxylase; ZT, Zeitgeber time or time in a 24-h light/dark cycle, with ZT 0 defined as lights-on and ZT 12 defined as lights-off.

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