title: Thapsigargin induces phosphorylation of the 27-kDa heat shock protein in human keratinocytes.
abstract: In the human keratinocyte line HaCaT, the nonphosphorylated 27-kDa heat shock protein (HSP27) isoform A (pI 6.5) is constitutively expressed. Application of thapsigargin, which inhibits Ca2+-ATPase in the endoplasmic reticulum, results in the rapid formation of the phosphorylated HSP27 isoform B (pI 6.0) and reduction of HSP27 A without affecting the synthesis of HSP27. The thapsigargin-dependent HSP27 isoform change is similar to that induced by 43 degrees C heat shock, but different from that induced by arsenite, where the biphosphorylated isoform HSP27 C (pI 5.7) is observed. The receptor agonist bradykinin, which increases intracellular Ca2+ (Ca(i)) level, shows no effect on the distribution of HSP27 isoforms. The responses of HSP27 isoforms to thapsigargin are independent of Ca(i) concentration in HaCaT cells. These observations suggest that the thapsigargin-induced change in HSP27 isoforms is dependent on the depletion of internal Ca2+ stores rather than on the increase in Ca(i) concentration. The thapsigargin-induced change in HSP27 isoforms is reduced by the tyrosine kinase inhibitor, genistein, but not the protein kinase C inhibitor, H-7. We propose that the modulation of HSP27 phosphorylation status by Ca(i) homeostasis may be mechanistically linked to control of keratinocyte growth and differentiation and responses of keratinocytes to extracellular stresses.
authors.affiliation: Department of Dermatology, University of California Davis School of Medicine, USA.
authors.forename: B
authors.initials: B
authors.lastname: Shi
authors.forename: R R
authors.initials: RR
authors.lastname: Isseroff
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D018053:Arsenites / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019833:Genistein; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation; D019284:Thapsigargin / Q000494:pharmacology*
chemical_list: D018053:Arsenites; D004791:Enzyme Inhibitors; D006360:Heat-Shock Proteins; D007529:Isoflavones; D019284:Thapsigargin; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D019833:Genistein; D000252:Calcium-Transporting ATPases; C015001:arsenite; D002118:Calcium