Reduced cholecystokinin: Receptor phosphorylation and restored signalling in protein kinase C down-regulated rat pancreatic acinar cells

Rolf L.L. Smeets, Rammohan V. Rao, Sjenet E. Van Emst-de Vries, Jan Joep H.H.M. De Pont, Laurence J. Miller, Peter H.G.M. Willems

Research output: Contribution to journalArticle

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Abstract

Receptor phosphorylation in response to agonist stimulation is a key regulatory principle in signal transduction. Previous work has suggested the concerted action of protein kinase C (PKC) and a staurosporine-insensitive receptor kinase in homologous phosphorylation of the cholecystokinin (CCK) receptor in freshly isolated rat pancreatic acinar cells [Gates, Ulrich, Miller (1993) Am J Physiol 264:G840-G847]. The present study shows that down-regulation of PKC by prolonged (2 h) treatment with 0.1 μM 12-O-tetradecanoylphorbol-13-acetate (TPA) markedly reduced basal CCK receptor phosphorylation as well as that induced by TPA (0.1 μM) and cholecystokinin-(26-33)-peptide amide (CCK8, 0.1 μM). The phosphorylation level reached was the same with both stimulants and equalled basal phosphorylation in untreated control cells. The absence of any CCK8-stimulated phosphorylation reflecting the activity of a putative staurosporine-insensitive receptor kinase raises the intriguing possibility that a basal level of PKC-mediated receptor phosphorylation is required for the action of such a receptor kinase. Immunoblot analysis revealed that the decrease in receptor phosphorylation coincided with a marked reduction of PKC-α and, to a lesser extent, PKC-ε. In addition, TPA-induced inhibition of the increase in cytosolic free Ca2+ concentration ([Ca2+](i) evoked by the high-affinity CCK receptor agonist JMV-180 was completely reversed. The time-course of recovery closely matched that of the reduction of PKC-α. Finally, digital imaging microscopy of individual PKC down-regulated cells revealed a marked increase in the duration of JMV-180-evoked oscillatory changes in [Ca2+](i). Taken together, the present findings are in agreement with the idea that PKC-α-mediated receptor phosphorylation leads to a shortening of the duration of the [Ca2+](i) oscillations and eventually to inhibition of high-affinity Ca2+ signalling through the native CCK receptor in pancreatic acinar cells.

Original languageEnglish (US)
Pages (from-to)422-428
Number of pages7
JournalPflugers Archiv European Journal of Physiology
Volume435
Issue number3
DOIs
StatePublished - Feb 18 1998

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Keywords

  • Cholecystokinin
  • Cholecystokinin-A receptor
  • Cytosolic free calcium concentration
  • Down-regulation
  • JMV-180
  • Pancreatic acinar cells
  • Phorbol ester
  • Protein kinase C
  • Staurosporine

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Physiology (medical)

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