Integrin signaling via actin cytoskeleton activates MRTF/SRF to entrain circadian clock

The circadian clock is entrained to daily environmental cues. Integrin-linked intracellular signaling via actin cytoskeleton dynamics transduces cellular niche signals to induce Myocardin-related Transcription Factor (MRTF)/Serum Response Factor (SRF)-mediated transcription. So far, how the integrin-associated signaling cascade may transmit cellular physical cues to entrain circadian clock remains to be defined. Using combined pharmacological and genetic approaches, here we show that the transcription factors mediating integrin to actin cytoskeleton signaling, MRTF-A and SRF, exert direct transcriptional control of core clock components, and that this signaling cascade modulates key properties of clock circadian activity. Pharmacological inhibition of MRTF/SRF activity by disrupting actin polymerization significantly augmented clock amplitude with period shortening, whereas an actin polymerizing compound attenuated oscillation amplitude with period lengthening. Genetic loss-of-function of Srf or Mrtf mimics that of actin-depolymerizing agents, validating the role of actin dynamics in driving clock function. Furthermore, integrin-mediated focal adhesion with extracellular matrix and its downstream signaling modulates the circadian clock, as blockade of integrin, focal adhesion kinase or Rho-associated kinase (ROCK) increased clock amplitude and shortened period length. Mechanistically, we identify specific core clock transcription regulators, Per1, Per2 and Nr1d1, as direct target genes of MRTF-A/SRF. Collectively, our findings uncovered an integrin-actin cytoskeleton-MRTF/SRF signaling cascade in linking clock entrainment to its extracellular microenvironment, which may mediate cellular adaptation to its physical niche. Author SummaryThe circadian clock anticipates and adapts to environmental changes. Interestingly, serum, as a universal clock synchronizing signal, drives intracellular actin cytoskeleton reorganization through modulation of MRTF/SRF activity. However, mechanisms that may transduce extracellular niche signals to circadian clock remains to be defined. We hypothesize that integrin-mediated intracellular signaling to actin cytoskeleton links extracellular microenvironment with MRTF/SRF transcriptional regulation to control clock function. Using small molecules and genetic approaches targeting distinct steps of integrin-actin cytoskeleton-MRTF/SRF signaling cascade, we uncover the effects of this pathway in controlling circadian clock oscillation. We also identify specific core clock regulators as direct gene target genes of MRTF and SRF-mediated transcriptional control. Our study revealed how integrin-mediated cellular interaction with its physical environment influences its intrinsic clock properties through signaling transduction via actin cytoskeleton remodeling, and that this mechanism may facilitate circadian clock adaptation to cellular physical niche.