Expression of human beta-defensin 1 is regulated via c-Myc and the biological clock.
Human beta-defensin 1 (hBD-1) is an important antibacterial polypeptide whose expression is not induced by infection or inflammation. Our objective was to study the regulation of hBD-1 expression. Recently, we found that albumin up-regulated hBD-1 as well as c-Myc expression, suggesting that c-Myc may regulate hBD-1 expression via a non-inflammatory pathway. Direct evidence for the involvement of c-Myc was achieved by the inhibition of hBD-1 expression in the presence of a specific c-Myc inhibitor. Since both c-Myc and CLOCK:BMAL1 heterodimer, the complex of the core clock mechanism, bind to E-box (5'-CACGTG-3') and E-box-like sequences to activate transcription, we studied whether hBD-1 expression was also regulated by the biological clock. Synchronization of HCT-116 cells by dexamethasone showed oscillation of hBD-1 and c-myc mRNA indicating that both are clock-controlled output genes. Using transfections and luciferase reporter assays in human embryonic kidney (HEK-293) cells, we found that hBD-1 promoter was induced by CLOCK:BMAL1 co-expression. hBD-1 promoter truncation and mutagenesis analyses revealed that the distal E-box-like binding sequence was the target of both CLOCK:BMAL1 and c-Myc for hBD-1 expression. This activation was abolished when CRY1 was co-expressed in these cells. Thus, hBD-1 expression is mediated by c-Myc and the CLOCK:BMAL1 heterodimer, whereas CRY1 expression represses this complex. These changes in hBD-1 levels lead to its circadian oscillation.
Sherman
Hadas
H
Institute of Biochemistry, Food Science and Nutrition, Faculty of Agricultural, Food and Environmental Quality, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.
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D056930:ARNTL Transcription Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D001683:Biological Clocks / Q000235:genetics*; D056926:CLOCK Proteins; D002417:Cattle; D002940:Circadian Rhythm / Q000187:drug effects; D056931:Cryptochromes; D019281:Dimerization; D005420:Flavoproteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D008957:Models, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics; D023083:beta-Defensins / Q000235:genetics* / Q000378:metabolism
D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D056931:Cryptochromes; D005420:Flavoproteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012710:Serum Albumin, Bovine; D015534:Trans-Activators; D023083:beta-Defensins; C538960:BMAL1 protein, human; C538963:CRY1 protein, human; C406407:DEFB1 protein, human; C538943:CLOCK protein, human