Identification of RACK1 and protein kinase Calpha as integral components of the mammalian circadian clock.
At the core of the mammalian circadian clock is a negative feedback loop in which the dimeric transcription factor CLOCK-BMAL1 drives processes that in turn suppress its transcriptional activity. To gain insight into the mechanisms of circadian feedback, we analyzed mouse protein complexes containing BMAL1. Receptor for activated C kinase-1 (RACK1) and protein kinase C-alpha (PKCalpha) were recruited in a circadian manner into a nuclear BMAL1 complex during the negative feedback phase of the cycle. Overexpression of RACK1 and PKCalpha suppressed CLOCK-BMAL1 transcriptional activity, and RACK1 stimulated phosphorylation of BMAL1 by PKCalpha in vitro. Depletion of endogenous RACK1 or PKCalpha from fibroblasts shortened the circadian period, demonstrating that both molecules function in the clock oscillatory mechanism. Thus, the classical PKC signaling pathway is not limited to relaying external stimuli but is rhythmically activated by internal processes, forming an integral part of the circadian feedback loop.
Robles
Maria S
MS
Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
Boyault
Cyril
C
Knutti
Darko
D
Padmanabhan
Kiran
K
Weitz
Charles J
CJ
D056930:ARNTL Transcription Factors / Q000378:metabolism; D000818:Animals; D056926:CLOCK Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D025461:Feedback, Physiological; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D051571:Protein Kinase C-alpha / Q000378:metabolism*; D034622:RNA Interference; D000075370:Receptors for Activated C Kinase; D015398:Signal Transduction; D014158:Transcription, Genetic
D056930:ARNTL Transcription Factors; C538961:Bmal1 protein, mouse; D009479:Neuropeptides; C090294:RACK1 protein, mouse; D000075370:Receptors for Activated C Kinase; D056926:CLOCK Proteins; C538944:Clock protein, mouse; D051571:Protein Kinase C-alpha