ABSTRACT
The circadian system regulates rhythmically most of the mammalian physiology in synchrony with the environmental light/dark cycle. Alteration of circadian clock gene expression has been associated with tumour progression but the molecular links between the two mechanisms remain poorly defined. Here we show that Stra13 and Dec2, two circadian transcriptional regulators which play a crucial role in cell proliferation and apoptosis are overexpressed and no longer rhythmic in serum shocked fibroblasts treated with CoCl(2,) a substitute of hypoxia. This effect is associated with a loss of circadian expression of the clock genes Rev-erbalpha and Bmal1, and the clock-controlled gene Dbp. Consistently, cotransfection assays demonstrate that STRA13 and DEC2 both antagonize CLOCK:BMAL1 dependent transactivation of the Rev-erbalpha and Dbp promoters. Using a transplantable osteosarcoma tumour model, we show that hypoxia is associated with altered circadian expression of Stra13, Dec2, Rev-erbalpha, Bmal1 and Dbp in vivo. These observations collectively support the notion that overexpression of Stra13 and Dec2 links hypoxia signalling to altered circadian clock gene expression.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/genetics , Bone Neoplasms/genetics , Circadian Rhythm/genetics , Gene Expression Regulation, Neoplastic , Homeodomain Proteins/genetics , Osteosarcoma/genetics , Transcription Factors/genetics , ARNTL Transcription Factors , Animals , Basic Helix-Loop-Helix Transcription Factors/metabolism , CLOCK Proteins , Cell Hypoxia/genetics , Circadian Rhythm/drug effects , Cobalt/toxicity , DNA-Binding Proteins/genetics , Fibroblasts/drug effects , Fibroblasts/metabolism , Gene Expression/drug effects , Homeodomain Proteins/metabolism , Hypoxia-Inducible Factor 1/genetics , Hypoxia-Inducible Factor 1/metabolism , Male , Mice , Mice, Inbred Strains , Nuclear Receptor Subfamily 1, Group D, Member 1 , Promoter Regions, Genetic , Receptors, Cytoplasmic and Nuclear/genetics , Trans-Activators/antagonists & inhibitors , Trans-Activators/genetics , Transcription Factors/metabolism , Transcriptional ActivationABSTRACT
Central and peripheral mammalian circadian clocks regulate a variety of behavioral and physiological processes through the rhythmic transcription of hundreds of clock-controlled genes. The circadian expression of many transcriptional regulators suggests that a major part of this circadian gene network is indirectly regulated by clock genes. Here we show that the basic helix-loop-helix transcriptional repressor Stra13 is rhythmically expressed in mouse peripheral organs. The circadian transcription of Stra13 is mediated by a response element recognized by the CLOCK-BMAL1 heterodimer and located in the proximal promoter region. CLOCK-BMAL1-dependent activation of Stra13 is strongly repressed by CRY1 and also by STRA13 itself. To determine putative Stra13 output genes, we performed microarray analyses of differential gene expression in the liver between wild type and Stra13-/- mice and identified 42 target genes including a subset of 20 previously known as clock-controlled genes. Importantly, we demonstrate that circadian gene expression of the serum protein insulin-like growth factor-binding protein 1 and of the NKG2D receptor ligand retinoic acid early transcript was suppressed in Stra13-/- mice. These biochemical and genetic data establish a role for the basic helix-loop-helix repressor STRA13 as a circadian output regulator in the periphery.