Circadian and photic regulation of MAP kinase by Ras- and protein phosphatase-dependent pathways in the chick pineal gland

Chick pineal mitogen-activated protein kinase (MAPK) exhibits circadian act ivation and tight-dependent deactivation at nighttime, Here we report that, in the chick pineal gland, levels of active forms of MAPK, MEK, Raf-l and Ras exhibited synchronous circadian rhythms with peaks during the subjectiv e night, suggesting a sequential activation of components in the classical Ras-MAPK pathway in a circadian manner. In contrast, the light-dependent de activation of MAPK was not accompanied by any change of MEK activity, but i t was attributed to the light-dependent activation of protein phosphatase d ephosphorylating MAPK. These results indicate that the photic and clock sig nals regulate MAPK activity via independent pathways, and suggest a pivotal role of MAPK in photic entrainment and maintenance of the circadian oscill ation. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B,V, All rights reserved.