title: Involvement of a p53-independent and post-transcriptional up-regulation for p21WAF/CIP1 following destabilization of the actin cytoskeleton.
abstract: The tumor suppressor p21WAF/CIP1 mediates the proliferation arrest via p53-dependent or -independent gene transactivation following distinct environmental stresses. In this study, we show that direct destabilization of the actin cytoskeleton by actin-targeting reagents leads to a p53-independent up-regulation of p21WAF/CIP1. The actin-targeting agent cytochalasin B (10 microM) quickly disrupted the actin cytoskeleton of p53 wild-type and p53-null cells accompanied by up-regulation of p21WAF/CIP1. Nevertheless, both total p53 and ser-15 phosphorylated p53 were not accumulated concomitantly, compared to the effect caused by ionizing irradiation. P53-independent up-regulation of p21WAF/CIP1 was also observed by two other actin-targeting agents cytochalasin D and latrunculin B, but not by the microtubule inhibitor colcemid. Furthermore, we showed that p21WAF/CIP1 mRNA level was not increased, whereas the protein degradation was delayed. A reduction of ubiquitination for p21WAF/CIP1 protein was detected using immunoprecipitation/immunoblot analysis. Up-regulation of p21WAF/CIP1 was not associated with cytotoxicity induced by cytochalasin B that influenced DNA integrity and plating efficiency only after 24 h of treatment. In addition, up-regulated p21WAF/CIP1 was accompanied by reduction of phosphorylation on retinoblastoma (Rb) protein in p53-null cells, implying that p21WAF/CIP1 might in part account for the molecular regulation of cytochalasin B induced G1 phase arrest. Together, current results suggest that p21WAF/CIP1 level can be mediated by actin organization in the absence of p53 via a post-transcriptional machinery, and it may contribute to the growth ablation by agents targeting the actin cytoskeleton.
authors.affiliation: Department of Biomedical Imaging and Radiological Sciences, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan, ROC. yjlee2@ym.edu.tw
authors.forename: Yi-Jang
authors.initials: YJ
authors.lastname: Lee
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Tsai
authors.forename: Jeng-Jong
authors.initials: JJ
authors.lastname: Hwang
authors.forename: Shu-Jun
authors.initials: SJ
authors.lastname: Chiu
authors.forename: Tzong-Jen
authors.initials: TJ
authors.lastname: Sheu
authors.forename: Peter C
authors.initials: PC
authors.lastname: Keng
mesh_terms: D000199:Actins / Q000378:metabolism; D000230:Adenocarcinoma / Q000235:genetics; D001859:Bone Neoplasms / Q000235:genetics; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics; D002453:Cell Cycle; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics*; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000235:genetics; D016158:Genes, p53 / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics; D012516:Osteosarcoma / Q000235:genetics; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D053778:Thiazolidines / Q000494:pharmacology; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004273:DNA, Neoplasm; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D053778:Thiazolidines; D025801:Ubiquitin; D015638:Cytochalasin D; C037068:latrunculin B