Thapsigargin induces phosphorylation of the 27-kDa heat shock protein in human keratinocytes

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In the human keratinocyte line HaCaT, the non-phosphorylated 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°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.

Original languageEnglish (US)
Pages (from-to)749-754
Number of pages6
JournalJournal of Investigative Dermatology
Issue number5
StatePublished - 1996


  • HaCaT keratinocytes
  • HSP27 isoforms
  • Intracellular calcium
  • Stress protein

ASJC Scopus subject areas

  • Dermatology


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