title: Keratinocyte differentiation induced by calcium, phorbol ester or interferon-gamma elicits distinct changes in the retinoid signalling pathways.
abstract: BACKGROUND
  Retinoids influence keratinocyte proliferation and differentiation via binding to nuclear retinoic acid receptors (RARalpha, -gamma) and retinoid X receptor alpha (RXRalpha). The effect of keratinocyte differentiation on expression of nuclear retinoid receptors and on the conversion of retinol into retinoic acid has not been examined earlier in depth.
  
  
  OBJECTIVE
  Our aim was to examine the expression of retinoid receptors and a retinoid-regulated gene CRABPII, as well as the metabolism of exogenous [(3)H]retinol in cultured human keratinocytes induced to differentiate by exposure to either calcium, phorbol 12-myristate 13-acetate (PMA), or interferon-gamma (IFNgamma).
  
  
  METHODS
  Normal human keratinocytes were cultured and exposed to differentiation-inducing agents. The mRNA and protein expression of retinoid receptors were examined using real-time PCR and Western blot. [(3)H]Retinol uptake and metabolism was monitored by HPLC with on-line radioactivity detection.
  
  
  RESULTS
  In calcium-exposed cells, increased expression of RARgamma and RXRalpha, enhanced metabolism of [(3)H]retinol to 3,4-didehydro-RA (ddRA), and an induction of CRABPII mRNA and protein was noted. In contrast, treatment with PMA and IFNgamma reduced the RARgamma and RXRalpha protein expression (preventable by the proteasome inhibitor MG132), increased the accumulation of [(3)H]RA and/or [(3)H]ddRA in the cells, and changed the CRABPII transcription.
  
  
  CONCLUSIONS
  Retinoid signalling is profoundly altered upon differentiation of keratinocytes and the effects depend on how cellular differentiation is initiated.
authors.affiliation: Department of Medical Sciences, Section of Dermatology and Venereology, Uppsala University, Sweden.
authors.forename: Teresa
authors.initials: T
authors.lastname: Karlsson
authors.forename: Anders
authors.initials: A
authors.lastname: Vahlquist
authors.forename: Hans
authors.initials: H
authors.lastname: Törmä
mesh_terms: D002118:Calcium; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D007371:Interferon-gamma; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D061988:Proteasome Inhibitors; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors; D015533:Transcriptional Activation; D011503:Transglutaminases / Q000378:metabolism; D014801:Vitamin A / Q000378:metabolism*
chemical_list: D061988:Proteasome Inhibitors; D018168:Receptors, Retinoic Acid; D018808:Transcription Factor AP-1; C082928:retinoic acid binding protein II, cellular; D014801:Vitamin A; D007371:Interferon-gamma; D011503:Transglutaminases; C105804:transglutaminase 1; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium