title: The hsp27kD heat shock protein and p38-MAPK signaling are required for regular epidermal differentiation.
abstract: BACKGROUND
  In human epidermal keratinocytes the expression of hsp27 is closely related to differentiation in vitro and in situ.
  
  
  OBJECTIVE
  We aimed to gain further insight into the role of hsp27 in epidermal differentiation by specific inhibition through siRNA and inhibition of p38-MAPK, the key enzyme of hsp27 phosphorylation.
  
  
  METHODS
  Normal human keratinocytes (KC) and organotypic skin cultures (SE-skin equivalents) were used. Expression and phosphorylation of hsp27 was inhibited in these models by siRNA and SB203580, a specific inhibitor of p38-MAPK, respectively. Modification of morphology and expression of hsp27 and other differentiation associated proteins was investigated by immunofluorescence, western blot, and RT-PCR.
  
  
  RESULTS
  Inhibition of p38-MAPK resulted in a downregulation of hsp27 in KC and SE. Additionally, in the presence of SB203580 Ca(2+) induced expression of pro-filaggrin and loricrin was inhibited at the protein level and expression of filaggrin, keratin 10, and transglutaminase 1 at the mRNA level. Addition of SB203580 to SE, as well as hsp27 knockdown in this model resulted in identical patterns of irregular differentiation, disturbance of epidermal layers, and delayed expression of K10.
  
  
  CONCLUSIONS
  These results provide evidence that the expression of hsp27 and its phosphorylation by p38-MAPK are required for keratinocyte differentiation and for the formation of a regularly stratified epidermis.
authors.affiliation: Department of Dermatology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. constanze.jonak@meduniwien.ac.at
authors.forename: Constanze
authors.initials: C
authors.lastname: Jonak
authors.forename: Michael
authors.initials: M
authors.lastname: Mildner
authors.forename: Gabriele
authors.initials: G
authors.lastname: Klosner
authors.forename: Verena
authors.initials: V
authors.lastname: Paulitschke
authors.forename: Rainer
authors.initials: R
authors.lastname: Kunstfeld
authors.forename: Hubert
authors.initials: H
authors.lastname: Pehamberger
authors.forename: Erwin
authors.initials: E
authors.lastname: Tschachler
authors.forename: Franz
authors.initials: F
authors.lastname: Trautinger
mesh_terms: D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D015536:Down-Regulation; D000091344:Filaggrin Proteins; D015870:Gene Expression; D055551:HSP27 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism; D053550:Keratin-10 / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D010766:Phosphorylation; D034741:RNA, Small Interfering; D012867:Skin / Q000254:growth & development* / Q000378:metabolism; D012879:Skin Physiological Phenomena / Q000235:genetics; D011503:Transglutaminases / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*
chemical_list: C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D055551:HSP27 Heat-Shock Proteins; D007381:Intermediate Filament Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; C064554:loricrin; D053550:Keratin-10; D011503:Transglutaminases; C105804:transglutaminase 1; D048051:p38 Mitogen-Activated Protein Kinases