title: Mcl-1 functions as major epidermal survival protein required for proper keratinocyte differentiation.
abstract: Rapid downregulation of the antiapoptotic Bcl-2 family protein myeloid cell leukemia 1 (Mcl-1) is required for UV-induced apoptosis, underlining an important role for Mcl-1 in epidermal pathology. To determine if Mcl-1 has a specific role in normal keratinocyte (KC) biology, Mcl-1 was downregulated in human KCs by RNAi and these KCs were induced to differentiate in organotypic raft cultures. Mcl-1 shRNA organotypic cultures showed increased levels of spontaneous premature apoptosis, implicating Mcl-1 as an essential KC survival protein. Mcl-1-downregulated cultures also had reduced granular and cornified layers, and produced lower levels of cross-linked protein and cornified envelopes. Cornification could only partially be rescued with the general caspase inhibitor z-VAD, suggesting that reduced cornification was not entirely because of premature apoptosis. Differentiation markers (K1, K10, filaggrin, loricrin, cleaved caspase-14) were normally expressed in control organotypic cultures, but were expressed at reduced levels in organotypic cultures with downregulated Mcl-1. The defect in differentiation marker expression was independent of apoptosis as it could not be rescued by z-VAD. Thus, Mcl-1 serves two important, independent functions in epidermal KCs: acting as a major survival protein by inhibiting premature apoptosis in the spinous and granular layers to promote conification, and promoting the robust induction of KC differentiation markers.
authors.affiliation: Department of Pathology, Loyola University Medical Center, Maywood, Illinois 60153, USA.
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Sitailo
authors.forename: Anita
authors.initials: A
authors.lastname: Jerome-Morais
authors.forename: Mitchell F
authors.initials: MF
authors.lastname: Denning
mesh_terms: D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002470:Cell Survival; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004817:Epidermis / Q000378:metabolism*; D000091344:Filaggrin Proteins; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D012867:Skin / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D053148:Caspase 3