title: Induced ATF-2 represses CDK4 transcription through dimerization with JunD inhibiting intestinal epithelial cell growth after polyamine depletion.
abstract: Intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is tightly regulated by numerous factors including polyamines. Decreased levels of cellular polyamines increase activating transcription factor (ATF)-2, but the exact role and mechanism of induced ATF-2 in the regulation of intestinal epithelial cell (IEC) growth remain elusive. Cyclin-dependent kinase (CDK) 4 is necessary for the G1-to-S phase transition during the cell cycle, and its expression is predominantly controlled at the transcription level. Here, we reported that induced ATF-2 following polyamine depletion repressed CDK4 gene transcription in IECs by increasing formation of the ATF-2/JunD heterodimers. ATF-2 formed complexes with JunD as measured by immunoprecipitation using the ATF-2 and JunD antibodies and by glutathione S-transferase (GST) pull-down assays using GST-ATF-2 fusion proteins. Studies using various mutants of GST-ATF-2 revealed that formation of the ATF-2/JunD dimers depended on the COOH-terminal basic region-leucine zipper domain of ATF-2. Polyamine depletion increased ATF-2/JunD complex and inhibited CDK4 transcription as indicated by a decrease in the levels of CDK4-promoter activity and its mRNA. ATF-2 silencing not only prevented inhibition of CDK4 transcription in polyamine-deficient cells but also abolished repression of CDK4 expression induced by ectopic JunD overexpression. ATF-2 silencing also promoted IEC growth in polyamine-depleted cells. These results indicate that induced ATF-2/JunD association following polyamine depletion represses CDK4 transcription, thus contributing to the inhibition of IEC growth.
authors.affiliation: Department of Surgery, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Lan
authors.initials: L
authors.lastname: Xiao
authors.forename: Jaladanki N
authors.initials: JN
authors.lastname: Rao
authors.forename: Tongtong
authors.initials: T
authors.lastname: Zou
authors.forename: Lan
authors.initials: L
authors.lastname: Liu
authors.forename: Ting-Xi
authors.initials: TX
authors.lastname: Yu
authors.forename: Xiao-Yu
authors.initials: XY
authors.lastname: Zhu
authors.forename: James M
authors.initials: JM
authors.lastname: Donahue
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Wang
mesh_terms: D051698:Activating Transcription Factor 2 / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018938:Caco-2 Cells; D002460:Cell Line; D051358:Cyclin-Dependent Kinase 4 / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology; D008969:Molecular Sequence Data; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016755:Proto-Oncogene Proteins c-jun; D034622:RNA Interference; D051381:Rats; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D051698:Activating Transcription Factor 2; C497107:Atf2 protein, rat; C549531:JunD protein, rat; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D016755:Proto-Oncogene Proteins c-jun; D014157:Transcription Factors; C495903:Cdk4 protein, rat; D051358:Cyclin-Dependent Kinase 4