title: Apoptosis in keratinocytes is not dependent on induction of differentiation.
abstract: During embryological development and throughout life, regulation of the thickness of skin is likely to involve modulation of keratinocyte proliferation, differentiation, and cell death. One major mechanism of cell death is apoptosis; but the precise relationship between apoptosis and differentiation has not been well-defined. In this report, we demonstrate that when cultured undifferentiated keratinocytes have their adhesive interactions interrupted by either enzymatic treatment (ie, trypsin) and suspension in a semi-solid methyl cellulose medium, or exposure to antibodies against beta 1 integrins and E-cadherin, induction of differentiation occurs (expression of involucrin), as well as apoptosis (positive terminal deoxynucleotidyl transferase (Tdt)-mediated dUTP-biotin nick end labeling (TUNEL) assay and DNA fragmentation). However, these events are not directly interdependent processes, as determined by two-color immunofluorescence staining. Thus, apoptosis can occur without evidence of differentiation and vice versa. The process o apoptosis in keratinocytes was dissected at the molecular level and found to be correlated with increased expression of Bax and decreased levels of Bcl-XL, with no role for either Bcl-2 or Bcl-XS. We conclude that keratinocytes do not need to undergo differentiation before undergoing apoptosis.
authors.affiliation: Department of Pathology, University of Michigan, Ann Arbor, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Mitra
authors.forename: T
authors.initials: T
authors.lastname: Wrone-Smith
authors.forename: P
authors.initials: P
authors.lastname: Simonian
authors.forename: K E
authors.initials: KE
authors.lastname: Foreman
authors.forename: G
authors.initials: G
authors.lastname: Nunez
authors.forename: B J
authors.initials: BJ
authors.lastname: Nickoloff
mesh_terms: D000328:Adult; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis; D015415:Biomarkers; D015820:Cadherins / Q000276:immunology / Q000502:physiology; D002448:Cell Adhesion / Q000187:drug effects; D002454:Cell Differentiation; D002478:Cells, Cultured; D004249:DNA Damage; D004253:DNA Nucleotidylexotransferase / Q000032:analysis / Q000096:biosynthesis; D005434:Flow Cytometry; D006801:Humans; D019012:Integrin beta1 / Q000276:immunology / Q000502:physiology; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D008747:Methylcellulose / Q000494:pharmacology; D011498:Protein Precursors / Q000096:biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2; D012867:Skin / Q000166:cytology; D014357:Trypsin / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000906:Antibodies; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D015415:Biomarkers; D015820:Cadherins; D019012:Integrin beta1; D011498:Protein Precursors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C032253:involucrin; D008747:Methylcellulose; D004253:DNA Nucleotidylexotransferase; D014357:Trypsin