The STING (stimulator of interferon genes) signaling pathway plays a pivotal role in the immune defense against viral infections in a wide range of vertebrates and invertebrates. However, the regulatory picture of this pathway is still incomplete. Herein, we investigate the involvement of Roq (Roquin), a typical RNA-binding protein, in modulating the Drosophila melanogaster (fruit fly) STING antiviral innate immunity. We show that Roq harbors a negative impact on the STING signaling pathway in a manner depending on its ROQ and CBM (CAF40-binding motif) domains. Importantly, viral infection induces the STING/NF-kB signaling-dependent expression of Roq, which forms a functional ribonuclease complex with CCR4/NOT for the deadenylation and degradation of Sting mRNA. Silencing of the Roq/CCR4/NOT axis leads to an excessive STING signaling upon viral infection. Collectively, our study sheds light on a feedback regulatory loop involving Roq-CCR4-NOT-Sting in the contribution to the fly antiviral immune defense.

The Drosophila melanogaster (fruit fly) misexpression suppressor of Ras 4 (MESR4) gene encodes a potential transcription factor and plays critical roles in various biological processes, including embryonic development, lipid metabolism, eye-antennal development, and germline stem cell differentiation. However, whether it is involved in modulating intestinal homeostasis remains elusive. In this study, we provide compelling evidence demonstrating that MESR4 is a bona fide regulator in preventing age-onset intestinal leakage and dysbiosis in adult flies. Mechanistically, MESR4 is predominantly located at the nucleus of intestinal cells and controls the expression of bag-of-marbles (bam), thereby restricting the excessive activation of immune deficiency signaling during aging. The silencing of Relish (Rel), which encodes a key transcription factor of the immune deficiency signaling pathway, reverses the beneficial effects of MESR4 in mediating intestinal barrier function and fly lifespan. Collectively, our studies uncover an undescribed function of Drosophila MESR4 in the maintenance of intestinal homeostasis and overall organismal fitness.

ABSTRACT:Ca2+/calmodulin-dependent protein kinase II γ (CAMKIIγ) has been identified as a potential target for treating cancer. Based on our previous study of berbamine (BBM) as a CAMKIIγ inhibitor, we have synthesized a new BBM derivative termed PA4. Compared with BBM, PA4 showed improved potency and specificity and was more cytotoxic against lymphoma and leukemia than against other types of cancer. In addition to indirectly targeting c-Myc protein stability, we demonstrated that its cytotoxic effects were also mediated via increased reactive oxygen species production in lymphoma cells. PA4 significantly impeded tumor growth in vivo in a xenograft T-cell lymphoma mouse model. Pharmacokinetics studies demonstrated quick absorption into plasma after oral administration, with a maximum concentration of 1680 ± 479 ng/mL at 5.33 ± 2.31 hours. The calculated oral absolute bioavailability was 34.1%. Toxicity assessment of PA4 showed that the therapeutic window used in our experiments was safe for future development. Given its efficacy, safety, and favorable pharmacokinetic profile, PA4 is a potential lead candidate for treating lymphoma.

Abstract Background Uncontrolled neuroinflammation contributes to a range of neurodegenerative diseases, as such targeting neuroinflammation may be a promising therapeutic strategy. Germacrone (GE) is the primary ingredient of Curcumae Wenyujin Y.H. Chenet C Ling, one of the most commonly used traditional Chinese medicine boasting anti-inflammatory pharmacology effects. However, there are no reports related to the protective effects of GE on LPS-induced neuroinflammation in mice. In the present study, the therapeutic effects of GE on the LPS-induced neuroinflammation in mice were assessed and the molecular mechanisms regarding neuroinflammation and neuronal apoptotic pathways was investigated. Methods C57 mice were treated with LPS for 7 days, followed by treatment with GE for 14 days. Behavioral testing was carried out to examine cognitive functions using the Morris water maze. Nissl Staining was applied to assess pathological changes. Immunohistochemistry was used to analyze the expression levels of inflammatory cytokines TNF-α and Iba-1 in the hippocampus. Immunofluorescence staining was used to detect the inhibitory effect of GE on microglia activation. RNA-seq technique was used to analyze the differential gene regulation of neuroinflammation in brain tissue of LPS-stimulated mice to investigate the anti-inflammation effect of GE. Results In C57 mice, GE counteracted cognitive decline, effectively alleviating the neuronal injury induced by LPS, and attenuated the activation of microglia and astrocytes in the cortex and hippocampus. GE significantly reduced the concentration of inflammation factor TNF-α and Iba-1 in both the hippocampus and cerebral cortex, particularly in the former. The gene expression variances post LPS treatment and GE treatment revealed that GE has the potential to diminish neuroinflammation by suppressing the production of inflammatory factors induced by LPS stimulation. Conclusions GE effectively counteracted cognitive decline by regulating neuroinflammation through reducing the concentration of inflammation factor TNF-α and Iba-1 in both hippocampus and cerebral cortex in LPS-induced neuroinflammation in C57 mice, providing preliminary experimental evidence that GE is a promising therapeutic agent in neurodegenerative diseases treatment.

The circadian clock drives rhythmic oscillations of metabolic processes to orchestrate metabolic homeostasis, and disruption of this mechanism predisposes to obesity and insulin resistance. Preserving or augmenting clock function could be a potential therapeutic target for metabolic diseases, particularly with the wide-spread of circadian misalignment in a modern lifestyle. To date, targeting the clock for metabolic disease prevention or treatment remains to be explored. Adipocyte possesses cell-autonomous clocks that exert transcriptional control of the Wnt pathway to inhibit adipocyte development. Using a high through-put screening pipeline, we recently identified Chlorhexidine as a novel clock-activating molecule that targets the key driver of the circadian clock transcriptional feedback loop, the CLOCK protein. Based on clock function in suppressing adipogenesis, we hypothesize that Chlorhexidine and related compounds may possess adipogenic-inhibitory properties suitable for anti-obesity drug development. In distinct adipogenic progenitor models, we demonstrate the activity of Chlorhexidine in inhibiting adipogenic lineage commitment and terminal differentiation. Furthermore, we report the structural optimization of Chlorhexidine chemical scaffold that led to the discovery of new analogs with improved anti-adipogenic effcacy. Consistent with its activity for clock activation, in adipogenic progenitors containing a Period2::dLuc luciferase reporter, Chlorhexidine induced significant shortening of clock period length with induction of core clock components. Chlorhexidine treatment of adipogenic mesenchymal precursors robustly suppressed their adipogenic maturation, with a comparable effect observed on inhibiting terminal differentiation of primary preadipocytes in a clock-dependent manner. Mechanistically, Chlorhexidine stimulates clock-controlled Wnt signaling that mediates its anti-adipogenic effect. Through medicinal chemistry modification of its chemical scaffold, we generated a panel of Chlorhexidine analogs with validation for their clock-modulatory activities. Structure activity relationship analysis of these analogs led to the identification of CM002 as a new clock activator with improved clock-dependent anti-adipogenic activity. Collectively, our findings uncovered a new class of clock-modulatory compounds that inhibit adipocyte development for potential anti-obesity drug discovery and provide clock-targeting chemical probes for dissecting clock function in metabolic physiology. This project was supported by grants from National Institute of Aging R56AG080294 and Arthur Riggs-Diabetes & Metabolism Research Institute T2D and T1D Innovative Awards to KM. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The host antimicrobial immune response relies on a complex interplay of molecular mechanisms to effectively combat microbial infections. Herein, we investigate the functional role of Cullin-3 (Cul3), one critical constituent of cullin-RING ubiquitin ligases, in the Drosophila melanogaster (fruit fly) antimicrobial immune defense. We show that silencing of Cul3 leads to a decreased induction of antimicrobial peptides and high mortality in adult flies after bacterial infection. Through biochemical approaches, we demonstrate that Cul3 predominantly relies on its BTB-binding domain and neddylation domain to physically associate with death-associated inhibitor of apoptosis 2 (Diap2). Importantly, Cul3 ameliorates the Diap2-mediated ubiquitination of death-related ced-3/Nedd2-like caspase (Dredd), a process essential for robust immune deficiency signaling upon bacterial infection. Taken together, our findings highlight a previously unrecognized regulatory axis of Cul3/Diap2/Dredd in the fly antimicrobial immune defense, providing potential insights into therapeutic strategies for combating bacterial infections in humans.

An iron-catalyzed efficient C-H amination for the construction of imidazole-fused-ring systems was developed under aerobic conditions. Compared to previous studies, this work exhibited green features. The reaction was conducted in the green solvent anisole, with water as the only byproduct. Four C(sp3)-H bonds were cleaved and three C-N bonds were formed in this transformation. Imidazo[1,5-a]pyridine-, imidazo[5,1-b]oxazole-, imidazo[5,1-b]thiazole-, imidazo[1,5-a]pyrazine-, and imidazo[1,5-a]imidazole-related N-heterocycles were obtained in acceptable-to-excellent yield.

The circadian clock is driven by a transcriptional-translational feedback loop that elicits ~24 hour rhythms in behavior and physiology. The cell-autonomous clock exerts temporal regulation in adipocyte development and clock disruption leads to the development of obesity. There is current intense effort to identify clock-targeting interventions for metabolic disease therapy. Cryptochrome 2 (Cry2) is a circadian clock repressor, and it binds with Period proteins as a heterodimer complex to inhibit CLOCK/Bmal1-activated clock transcription that constitutes the negative feedback arm of the clock circuit. Our previous studies demonstrated that clock activator Bmal1 inhibits adipogenesis via the Wnt signaling pathway. To date, the role of Cry2 in adipogenic regulation remains unknown. Here we show that Cry2 inhibits adipogenesis and identify a critical residue that mediates interaction with Per2 required for this regulation. Cry2 transcript and protein are markedly induced during adipogenic differentiation. Via site-directed mutagenesis, we identified that Cysteine 432 within the lid domain of Cry2 protein is required for interaction with Per2, and a C432A mutant abolished this interaction. As a result, Cry2 repression activity of CLOCK/Bmal1-mediated transcription was abolished by the C432A mutant, as shown by Per2-luc reporter luciferase assay. Cry2 C432 mutation also led to elevated ubiquitination that accelerated protein degradation, an additional mechanism contributing to its loss of function. In 3T3L1 preadipocyte, we found that ectopic expression of Cry2 enhanced adipogenesis, whereas its loss-of-function suppressed adipocyte differentiation. In line with these findings, a Cry-stabilizing compound KL001 markedly augmented adipogenic differentiation. As compared to wild-type Cry2 effect on promoting adipogenesis, Cry2 C432A mutant largely abolished differentiation consistent with loss of repressive function in clock modulation. Mechanistically, we show that Cry2 induces adipogenesis via negative regulation of Wnt signaling pathway leading to inhibition of CCAAT/enhancer binding protein α (C/EBPα) expression. Together, our findings reveal a novel function of Cry2 in promoting adipocyte development via a critical residue involved in interaction with Per2. Our study thus provides a mechanistic basis for clock-targeting interventions to inhibit Cry2 activity for the treatment of obesity and its associated complications This work is supported by NIDDK grants 1R01DK112794, 1R01DK130499 and AR-DMRI 2023 T2D Innovation Grant. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Background The circadian clock is an evolutionarily conserved mechanism that exerts pervasive temporal control in stem cell behavior. This time-keeping machinery is required for orchestrating myogenic progenitor properties in regenerative myogenesis that ameliorates muscular dystrophy. Here we report a screening platform to discover circadian clock modulators that promote myogenesis and identify chlorhexidine (CHX) as a clock-activating molecule with pro-myogenic activities. Methods A high-throughput molecular docking pipeline was applied to identify compounds with a structural fit for a hydrophobic pocket within the key circadian transcription factor protein, Circadian Locomotor Output Cycles Kaput (CLOCK). These identified molecules were further screened for clock-modulatory activities and functional validations for pro-myogenic properties. Results CHX was identified as a clock activator that promotes distinct aspects of myogenesis. CHX activated circadian clock that reduced cycling period length and augmented amplitude. This action was mediated by the targeted CLOCK structure via augmented interaction with heterodimer partner Bmal1, leading to enhanced CLOCK/Bmal1-controlled transcription with upregulation of core clock genes. Consistent with its clock-activating function, CHX displayed robust effects on stimulating myogenic differentiation in a clock-dependent manner. In addition, CHX augmented the proliferative and migratory activities of myoblasts. Conclusion Our findings demonstrate the feasibility of a screening platform to discover clock modulators with myogenic regulatory activities. Discovery of CHX as a pro-myogenic molecule could be applicable to promote regenerative capacities in ameliorating dystrophic or degenerative muscle diseases.

Background The circadian clock exerts temporal control of metabolic pathways to maintain homeostasis, and its disruption leads to the development of obesity and insulin resistance. In adipose tissue, key regulators of clock machinery orchestrate adipogenic processes via the Wnt signaling pathway to impact mature adipocyte development. Methods Based on the recent finding of chlorhexidine as a new clock activator, we determined its potential anti-adipogenic activities in distinct adipogenic progenitor models. Furthermore, we report the structural optimization of chlorhexidine leading to the discovery of analogs with improved efficacy in inhibiting adipogenesis. Results In adipogenic progenitors with Per2::dLuc luciferase reporter, Chlorhexidine shortened clock period length with induction of core clock components. Consistent with its clock-activating function, Chlorhexidine robustly suppressed the lineage commitment and maturation of adipogenic mesenchymal precursors, with comparable effect on inhibiting preadipocyte terminal differentiation. Mechanistically, we show that Chlorhexidine induces signaling components of the Wnt pathway resulting in activation of Wnt activity. Via modification of its chemical scaffold, we generated analogs of chlorhexidine that led to the identification of CM002 as a new clock- activating molecule with improved anti-adipogenic activity. Conclusions Collectively, our findings uncovered the anti-adipogenic functions of a new class of small molecule clock activators. These compounds provide novel chemical probes to dissect clock function in maintaining metabolic homeostasis and may have therapeutic implications in obesity and associated metabolic disorders.

The circadian clock is driven by a transcriptional-translational feedback loop, and Cryptochrome 2 (Cry2) represses CLOCK/Bmal1-induced transcription activation. Despite the established role of clock in adipogenic regulation, whether the Cry2 repressor activity functions in adipocyte biology remains unclear. Here we identify a critical cysteine residue of Cry2 that mediates interaction with Per2, and demonstrate that this mechanism is required for clock transcriptional repression that inhibits Wnt signaling to promote adipogenesis. Cry2 protein is enriched in white adipose depots and was robustly induced by adipocyte differentiation. Via site-directed mutagenesis, we identified that a conserved Cry2 Cysteine at 432 within the loop interfacing with Per2 mediates heterodimer complex formation that confers transcription repression. C432 mutation disrupted Per2 association without affecting Bmal1 binding, leading to loss of repression of clock transcription activation. In preadipocytes, whereas Cry2 enhanced adipogenic differentiation, the repression-defective C432 mutant suppressed this process. Furthermore, silencing of Cry2 attenuated, while stabilization of Cry2 by KL001 markedly augmented adipocyte maturation. Mechanistically, we show that transcriptional repression of Wnt pathway components underlies Cry2 modulation of adipogenesis. Collectively, our findings elucidate a Cry2-mediated repression mechanism that promotes adipocyte development, and implicate its potential as a clock intervention target for obesity.

The circadian clock exerts temporal control in metabolic processes to maintain homeostasis, with its disruption leading to the development of obesity and insulin resistance. Adipose fibrosis in obese subjects exacerbates insulin resistance by restricting healthy tissue expansion and remodeling. Rev-erbα is a key circadian clock repressor that displays circadian rhythmic expression in adipose tissue, although its role in adipose tissue fibrosis is not known. Here we show that Rev-ebα inhibits the fibrogenic fate of adipocyte progenitors while promoting beige adipogenic potential via transcription repression of the MRTF/SRF-actin cytoskeleton axis. ChIP-seq analysis of Rev-erbα cistrome in adipogenic precursors identified its transcriptional control of pathways involved in cytoskeleton modulation, including established myofibroblast gene markers small muscle α-actin and Tropomysin. Gain-of-function of Rev-erbα in beige adipogenic precursors markedly suppressed MRTF/SRF activity with enhanced beige differentiation, while Rev-erbα silencing suppressed beige adipogenesis. Prrx1-Cre-mediated subcutaneous beige fat-selective Rev-erbα knock-in induced browning with augmented mitochondrial metabolism, resulting in increased energy expenditure, resistance to obesity and insulin sensitivity. Furthermore, single cell RNA-seq of beige progenitors with Rev-erbα overexpression revealed striking loss of preadipcyte-like (PAL) subpopulations with myofibroblastic characteristics that arise from pericyte lineage. PAL beige progenitors displayed enrichment of epithelial mesenchymal transition-related gene signature and contractile program as compared to preadipocytes. Preadipocyte population with Rev-erbα overexpression exhibited activated oxidative phosphorylation pathway with inhibition of myofibrolast characteristics. Taken together, our findings identify a novel regulatory function of Rev-erbα in modulating adipogenic progenitor fate choice that may promote adipose tissue beigeing while suppressing fibrotic complications. NIDDK grant 1R01DK112794, 1R01DK130499 and AR-DMRI 2023 T2D Innovation Grant This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Drosophila ovary has been one of the most mature and excellent systems for studying the in vivo regulatory mechanisms of stem cell fate determination. It has been well-known that the bone morphogenetic protein (BMP) signaling released by the niche cells promotes the maintenance of germline stem cells (GSCs) through inhibiting the transcription of the bag-of-marbles (bam) gene, which encodes a key factor for GSC differentiation. However, whether Bam is regulated at the post-translational level remains largely unknown. Here we show that the E3 ligase Cullin-2 (Cul2) is involved in modulating Bam ubiquitination, which occurs probably at multiple lysine residues of Bam's C-terminal region. Genetic evidence further supports the notion that Cul2-mediated Bam ubiquitination and turnover are essential for GSC maintenance and proper germline development. Collectively, our data not only uncovers a novel regulatory mechanism by which Bam is controlled at the post-translational level, but also provides new insights into how Cullin family protein determines the differentiation fate of early germ cells.

The circadian clock machinery exerts transcriptional control to modulate adipogenesis and its disruption leads to the development of obesity. Here, we report that Nobiletin, a circadian clock amplitude-enhancing molecule, displays antiadipogenic properties via activation of Wnt signaling pathway that is dependent on its clock modulation. Nobiletin augmented clock oscillatory amplitude with period lengthening in the adipogenic mesenchymal precursor cells and preadipocytes, accompanied by an induction of Bmal1 and clock components within the negative feedback arm. Consistent with its clock-modulatory activity, Nobiletin strongly inhibited the lineage commitment and terminal differentiation of adipogenic progenitors. Mechanistically, we show that Nobiletin induced the reactivation of Wnt signaling during adipogenesis via transcriptional up-regulation of key components within this pathway. Furthermore, Nobiletin administration in mice markedly reduced adipocyte hypertrophy, leading to a significant loss of fat mass and reduction of body weight. Last, Nobiletin inhibited the differentiation of primary preadipocytes, and this effect was dependent on a functional clock regulation. Collectively, our findings uncover a novel activity of Nobiletin in suppressing adipocyte development in a clock-dependent manner, implicating its potential application in countering obesity and associated metabolic consequences.

The circadian clock is entrained to daily environmental cues. Integrin-linked intracellular signaling via actin cytoskeleton dynamics transduces extracellular matrix interactions to Myocardin-related Transcription Factor (MRTF)/Serum Response Factor (SRF)-mediated transcription. Actin cytoskeleton organization in liver displays diurnal oscillations and SRF-MRTF activity exert transcriptional control to entrain clock. By interrogating disparate upstream events involved in actin cytoskeleton-MRTF-A/SRF signaling cascade, here we show that this signaling cascade transduce cellular niche cues to modulate circadian clock function. Pharmacological inhibitions of MRTF-A/SRF, by disrupting actin polymerization or blocking ROCK kinase, induced period lengthening with augmented clock amplitude, and genetic loss-of-functions of Srf or Mrtf-a mimic that of actin-depolymerizing agents. In contrast, actin-polymerization induced by Jasplakinolide shortened period with attenuated amplitude. In addition, interfering with cell-matrix interaction through blockade of integrin, inhibition of focal adhesion kinase or attenuating matrix rigidity led to reduced period length while enhancing amplitude. Mechanistically, we identify that core clock repressors, Per2, Nr1d1, and Nfil3, are direct transcriptional targets of MRTF-A/SRF in mediating actin dynamic-induced clock response. Collectively, our findings defined an integrin-actin cytoskeleton-MRTF/SRF pathway in linking clock entrainment with extracellular microenvironment that may facilitate cellular adaptation to its physical niche. Summary statement Our study revealed the role of actin cytoskeleton-MRTF/SRF signaling in entraining circadian clock to its extracellular physical niche environment.

The morphological transformation of adipogenic progenitors into mature adipocytes requires dissolution of actin cytoskeleton with loss of myocardin-related transcription factor (MRTF)/serum response factor (SRF) activity. Circadian clock confers temporal control in adipogenic differentiation, while the actin cytoskeleton-MRTF/SRF signaling transduces extracellular physical niche cues. Here, we define a novel circadian transcriptional control involved in actin cytoskeleton-MRTF/SRF signaling cascade that modulates beige fat thermogenic function. Key components of actin dynamic-MRTF/SRF pathway display circadian regulation in beige fat depot. The core clock regulator, brain and muscle arnt-like 1 (Bmal1), exerts direct transcriptional control of genes within the actin dynamic-MRTF/SRF cascade that impacts actin cytoskeleton organization and SRF activity. Employing beige fat-selective gene-targeting models together with pharmacological rescues, we further demonstrate that Bmal1 inhibits beige adipogenesis and thermogenic capacity in vivo via the MRTF/SRF pathway. Selective ablation of Bmal1 induces beigeing with improved glucose homeostasis, whereas its targeted overexpression attenuates thermogenic induction resulting in obesity. Collectively, our findings identify the clock-MRTF/SRF regulatory axis as an inhibitory mechanism of beige fat thermogenic recruitment with significant contribution to systemic metabolic homeostasis.

The circadian clock confers temporal regulation in metabolism, and its disruption leads to obesity and insulin resistance. In the current study, we identify that the opposing circadian clock regulators, transcription activator Bmal1 and its repressor Rev-erbα, exert concerted control of the actin cytoskeleton-MRTF/SRF pathway to drive beige adipocyte development, and that this clock regulatory axis is required for beige fat thermogenic capacity. Key components of the MRTF/SRF signaling display circadian oscillations in beige fat, and cistromic analyses revealed Bmal1 and Rev-erbα chromatin occupancy of genes involved in MRTF/SRF regulation. Genetic loss- or gain-of-functions of Bmal1 and Rev-erbα in adipogenic precursors markedly altered actin cytoskeleton organization. Bmal1 silencing inhibits F-actin formation and MRTF/SRF activity whereas its forced expression augments actin cytoskeleton. Notably, Bmal1 and Rev-erbα transcriptional control of the MRTF/SRF signaling modulates beige fat thermogenic capacity in vivo. Prrx1-Cre-mediated subcutaneous beige fat-selective Bmal1 ablation induced browning with augmented mitochondrial metabolism, resulting in resistance to obesity that improved insulin sensitivity. Conversely, overexpression of Bmal1 in beige depot suppressed the thermogenic program with adipose expansion and impaired glucose tolerance. In contrast, Rev-erbα gain-of-function phenocopied that of Bmal1 ablation, leading to browning of beige fat, resistance to obesity and insulin sensitivity. Mechanistically, we show that genetic loss of Bmal1 enhanced beige precursor differentiation and thermogenic induction, whereas Rev-erbα overexpression similarly promoted beige adipogenesis. Collectively, these findings uncover a novel concerted circadian clock control in beige adipocyte development that determines thermogenic capacity via the cytoskeleton-MRTF/SRF signaling cascade. Disclosure X.Xiong: None. W.Li: None. R.Liu: None. V.Yechoor: n/a. K.Ma: None. Funding NIH 1R01DK112794 to KM and DK097160 to VY

The circadian clock is entrained to daily environmental cues. Integrin-linked signaling via actin cytoskeleton dynamics transduces physical niche cues from the extracellular matrix to myocardin-related transcription factor (MRTF)/serum response factor (SRF)-mediated transcription. The actin cytoskeleton organization and SRF-MRTF activity display diurnal oscillations. By interrogating disparate upstream events in the actin cytoskeleton-MRTF-A/SRF signaling cascade, we show that this pathway transduces extracellular niche cues to modulate circadian clock function. Pharmacological inhibition of MRTF-A/SRF by disrupting actin polymerization or blocking the ROCK kinase induced period lengthening with augmented clock amplitude, and genetic loss of function of Srf or Mrtfa mimicked the effects of treatment with actin-depolymerizing agents. In contrast, actin polymerization shortened circadian clock period and attenuated clock amplitude. Moreover, interfering with the cell-matrix interaction through blockade of integrin, inhibition of focal adhesion kinase (FAK, encoded by Ptk2) or attenuating matrix rigidity reduced the period length while enhancing amplitude. Mechanistically, we identified that the core clock repressors Per2, Nr1d1 and Nfil3 are direct transcriptional targets of MRTF-A/SRF in mediating actin dynamics-induced clock response. Collectively, our findings defined an integrin-actin cytoskeleton-MRTF/SRF pathway in linking clock entrainment with extracellular cues that might facilitate cellular adaptation to the physical niche environment.

AbstractThe circadian clock is entrained to daily environmental cues. Integrin-linked intracellular signalingviaactin 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 ofSrforMrtfmimics 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, Per2andNr1d1, 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 transductionviaactin cytoskeleton remodeling, and that this mechanism may facilitate circadian clock adaptation to cellular physical niche.