title: Differentiation of cultured human epidermal keratinocytes at high cell densities is mediated by endogenous activation of the protein kinase C signaling pathway.
abstract: Normal human epidermal keratinocytes (NHEK) grown in serum-free medium on a plastic substrate spontaneously differentiate at high cell densities in vitro. Because protein kinase C (PKC) regulates murine keratinocyte differentiation triggered by a variety of stimuli, we examined the role of this signaling pathway in density-dependent activation of NHEK differentiation. Relative to subconfluent cultures, confluent NHEK expressed markedly higher levels of multiple differentiation markers assayed by immunoblotting, including keratin 1, loricrin, filaggrin, involucrin, TGK, and SPR-1. Expression of several of these markers continued to increase for several days after cells reached confluency. The total level of several PKC isoforms was not substantially altered in NHEK harvested at different cell densities, based on immunoblotting; however, subcellular fractionation revealed that PKCalpha underwent a redistribution to the particulate fraction in confluent and postconfluent NHEK cultures, suggesting that this isozyme was activated under these conditions and may be involved in triggering the terminal differentiation program. Supporting this concept, inhibition of PKC function using bryostatin 1 or GF 109203X blocked the induction of keratinocyte differentiation markers at high cell densities. These data suggest that endogenous activation of PKC is responsible for cell density-mediated stimulation of NHEK differentiation, establishing a critical role for this pathway in regulating human as well as murine keratinocyte differentiation.
authors.affiliation: Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
authors.forename: Y S
authors.initials: YS
authors.lastname: Lee
authors.forename: S H
authors.initials: SH
authors.lastname: Yuspa
authors.forename: A A
authors.initials: AA
authors.lastname: Dlugosz
mesh_terms: D000943:Antigens, Differentiation / Q000502:physiology; D002452:Cell Count / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D004789:Enzyme Activation / Q000502:physiology; D000091344:Filaggrin Proteins; D006801:Humans; D007527:Isoenzymes / Q000235:genetics; D015603:Keratinocytes / Q000166:cytology* / Q000276:immunology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D015398:Signal Transduction; D014178:Translocation, Genetic; D015854:Up-Regulation
chemical_list: D000943:Antigens, Differentiation; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D007527:Isoenzymes; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha