title: Alteration of keratinocyte differentiation and senescence by the tumor promoter dioxin.
abstract: Exposure to the environmental contaminant dioxin, elicits a variety of responses, which includes tumor promotion, embryotoxicity/teratogenesis, and carcinogenesis in both animals and humans. Many of the effects of dioxin are mediated by the aryl hydrocarbon receptor (AHR), a ligand-activated bHLH (basic helix-loop-helix)/PAS transcription factor. We initiated this study to determine whether dioxin's tumor-promoting activities may lie in its ability to alter proliferation, differentiation, and/or senescence using normal human epidermal keratinocytes (HEKs). Here, we report that dioxin appears to accelerate differentiation as measured by flow cytometry and by increased expression of the differentiation markers involucrin and filaggrin. In addition, dioxin appears to increase proliferation as indicated by an increase in NADH/NADPH production and changes in cell cycle. Finally, dioxin decreases SA (senescence associated) beta-galactosidase staining, an indicator of senescence, in the differentiating keratinocytes. These changes were accompanied by decreases in the expression levels of key cell cycle regulatory proteins p53, p16INK4a, and p14ARF. Our findings support the idea that dioxin may exert its tumor-promoting actions, in part, by downregulating the expression levels of key tumor suppressor proteins, which may impair the cell's ability to maintain its appropriate cellular status.
authors.affiliation: Department of Molecular and Biomedical Pharmacology, University of Kentucky Medical Center, 800 Rose Street, MS 305, Lexington, KY 40536, USA.
authors.forename: Soma S
authors.initials: SS
authors.lastname: Ray
authors.forename: Hollie I
authors.initials: HI
authors.lastname: Swanson
mesh_terms: D002273:Carcinogens / Q000633:toxicity*; D018797:Cell Cycle Proteins / Q000096:biosynthesis*; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000187:drug effects*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis; D004147:Dioxins / Q000633:toxicity*; D000091344:Filaggrin Proteins; D005434:Flow Cytometry; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000032:analysis; D025803:Tumor Suppressor Protein p14ARF / Q000096:biosynthesis; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis
chemical_list: D002273:Carcinogens; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004147:Dioxins; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D012333:RNA, Messenger; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53