Bimodal regulation of mPeriod promoters by CREB-dependent signaling and CLOCK/BMAL1 activity.

Circadian rhythmicity in mammals is under the control of a molecular pacemaker constituted of clock gene products organized in transcriptional autoregulatory loops. Phase resetting of the clock in response to light involves dynamic changes in the expression of several clock genes. The molecular pathways used by light to influence pacemaker-driven oscillation of clock genes remain poorly understood. We explored the functional integration of both light- and clock-responsive transcriptional regulation at the promoter level of the Period (Per) genes. Three Per genes exist in the mouse. Whereas mPer1 and mPer2 are light-inducible in clock neurons of the hypothalamic suprachiasmatic nucleus, mPer3 is not. We have studied the promoter structure of the three mPer genes and compared their regulation. All three mPer promoters contain E-boxes and respond to the CLOCK/brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein 1 (BMAL1) heterodimer. On the other hand, only mPer1 and mPer2 promoters contain bona fide cAMP-responsive elements (CREs) that bind CRE-binding protein (CREB) from suprachiasmatic nucleus protein extracts. The mPer1 promoter is responsive to synergistic activation of the cAMP and mitogen-activated protein kinase pathways, a physiological response that requires integrity of the CRE. In contrast, activation of mPer promoters by CLOCK/BMAL1 occurs regardless of an intact CRE. Altogether, these results constitute strong evidence that CREB acts as a pivotal endpoint of signaling pathways for the regulation of mPer genes. Our results reveal that signaling-dependent activation of mPer genes is distinct from the CLOCK/BMAL1-driven transcription required within the clock feedback loop.