CDK9 modulates circadian clock by attenuating REV-ERBα activity.

Circadian clock and cell cycle are vital cellular programs acting in a timely-regulated, cyclic manner. The two cellular oscillators are coupled in various ways to facilitate biological processes. Here we report CDK9, a kinase belongs to the CDK family in regulating cell cycle and RNA Pol II activity, can serve as a modulator for circadian clock. We identified CDK inhibitor LY2857785 potently blocked PER2:LUC expression in MEFs from a screen of 17 commonly-used CDK inhibitors. We further analyzed the possible targets of LY2857785 by siRNA approach, and confirmed CDK9 as the main effector. LY2857785 treatment, as well as Cdk9 knock-down, led to lowered expression of Bmal1 in accordance with elevated expression of Rev-Erbα. CDK9 associated with REV-ERBα thus attenuated REV-ERBα binding to the RORE for Bmal1 suppression. To conform the circadian-modulating activity of CDK9 in vivo, we knocked down CDK9 in mice at the anterior hypothalamus covering the central oscillator SCN, and found the respiratory exchange ratio, daily activity and circadian period were altered in the Cdk9-knockdown mice. Together, our finding designated CDK9 as a novel modulator in circadian clock. CDK9 may serve as a vital basis to understand circadian- and cell cycle-misregulated ailments such as cancer.