CRHSP-24 phosphorylation is regulated by multiple signaling pathways in pancreatic acinar cells.
Ca2+-regulated heat-stable protein of 24 kDa (CRHSP-24) is a serine phosphoprotein originally identified as a physiological substrate for the Ca2+-calmodulin regulated protein phosphatase calcineurin (PP2B). CRHSP-24 is a paralog of the brain-specific mRNA-binding protein PIPPin and was recently shown to interact with the STYX/dead phosphatase protein in developing spermatids (Wishart MJ and Dixon JE. Proc Natl Acad Sci USA 99: 2112-2117, 2002). Investigation of the effects of phorbol ester (12-o-tetradecanoylphorbol-13-acetate; TPA) and cAMP analogs in 32P-labeled pancreatic acini revealed that these agents acutely dephosphorylated CRHSP-24 by a Ca2+-independent mechanism. Indeed, cAMP- and TPA-mediated dephosphorylation of CRHSP-24 was fully inhibited by the PP1/PP2A inhibitor calyculin A, indicating that the protein is regulated by an additional phosphatase other than PP2B. Supporting this, CRHSP-24 dephosphorylation in response to the Ca2+-mobilizing hormone cholecystokinin was differentially inhibited by calyculin A and the PP2B-selective inhibitor cyclosporin A. Stimulation of acini with secretin, a secretagogue that signals through the cAMP pathway in acini, induced CRHSP-24 dephosphorylation in a concentration-dependent manner. Isoelectric focusing and immunoblotting indicated that elevated cellular Ca2+ dephosphorylated CRHSP-24 on at least three serine sites, whereas cAMP and TPA partially dephosphorylated the protein on at least two sites. The cAMP-mediated dephosphorylation of CRHSP-24 was inhibited by low concentrations of okadaic acid (10 nM) and fostriecin (1 microM), suggesting that CRHSP-24 is regulated by PP2A or PP4. Collectively, these data indicate that CRHSP-24 is regulated by diverse and physiologically relevant signaling pathways in acinar cells, including Ca2+, cAMP, and diacylglycerol.
Schäfer
Claus
C
Department of Internal Medicine II, Klinikum Grosshadern, Ludwig-Maximilians-University of Munich, Germany.
Steffen
Hanna
H
Krzykowski
Karen J
KJ
Göke
Burkhard
B
Groblewski
Guy E
GE
D000475:Alkenes / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics; D008387:Marine Toxins; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011090:Polyenes; D011753:Pyrones; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors
D000475:Alkenes; D065095:Calcineurin Inhibitors; C513278:Carhsp1 protein, rat; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D010750:Phosphoproteins; D011090:Polyenes; D011753:Pyrones; D014157:Transcription Factors; D019319:Okadaic Acid; C059041:calyculin A; D016572:Cyclosporine; D002766:Cholecystokinin; D000242:Cyclic AMP; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; C040313:fostriecin