In mammals, the suprachiasmatic nuclei (SCN) of the hypothalamus control endogenous circadian rhythms and entrainment to the environment. Light stimuli transiently increase the gene expression of Period 1 (Per1) that is important in resetting of the mammalian central clock in the SCN. Pervious studies demonstrated that glutamate and N-Methyl-D-Aspartate (NMDA) mediate the effect of light stimuli on the central clock in vivo. However, molecular mechanism underlying the acute induction of Per1 by the extra stimuli remains unclear. The present study is designed to set up an in vitro model and to examine the effect of calcium ion on Per1 gene expression in the SK-N-SH human neuroblastoma cells using ribonuclease protection assay. Calcium ionophore A23187 (A23187) dramatically increased Per1 mRNA levels in a time- and dose-dependent manner although glutamate and NMDA were unable to alter Per1 gene expression in the SK-N-SH human neuroblastoma cells. In addition, the activity of human Per1 promoter (-3829 to +123) was significantly promoted by treatment with A23187. The transcriptional inhibitor actinomycin D completely blocked A23187-induced increases in Per1 mRNA levels, whereas cycloheximide, a potent translational inhibitor, did not. These results suggest that calcium ion may play an important role in the activation of Per1 gene expression at the transcriptional level probably through the calcium responsive cis-elements located in 4.0 kb promoter region of Per1 gene.

Keywords: Period 1(Per1), clock gene, calcium ion, A23187, circadian clock, SK-N-SH human neuroblastoma cells