Carbachol stimulates binding of a photoreactive calmodulin derivative to calmodulin-binding proteins in intact SK-N-SH human neuroblastoma cells.
Calmodulin (CaM) mediates the Ca(2+)-dependent activation of many enzyme systems in accordance with its cellular localization. We have described previously a muscarinic receptor-mediated translocation of CaM from membranes into the cytosol of SK-N-SH human neuroblastoma cells. To explore the potential targets (CaM-binding proteins, CaMBP) for CaM upon translocation, a photoreactive CaM derivative was introduced into living SK-N-SH cells using a scrape-loading technique. Scrape-loading incorporated rhodamine isothiocyanate-labeled CaM with an efficiency of 38%. CaM-diazopyruvamide (CaM-DAP), a Ca(2+)-dependent and CaM-specific probe, was also introduced into the cells. The muscarinic agonist carbachol stimulated a translocation of CaM from membranes into cytosol in CaM-DAP-loaded SK-N-SH cells. Upon photochemical cross-linking, cross-linked adducts of CaM-CaMBP were detected by immunoblotting with anti-CaM antibody. Carbachol stimulated increased photoaffinity labeling of three proteins with relative adduct molecular masses of 70, 120, and 180 kDa. The time course of labeling for the 70- and 120-kDa adducts showed maximal increased by 15-30 min. The 180-kDa adduct displayed a slower time course of maximal labeling, with increases maintained for 2-4 h. Subtracting the molecular mass of CaM, carbachol stimulated binding to CaMBPs of 55, 105, and 163 kDa. Predominant cellular CaMBP were identified using a biotinylated CaM overlay procedure. Western blot analysis indicated the expression of specific CaM-dependent enzymes such as calcineurin, phosphodiesterase, the beta-isoform (rat brain) of CaM kinase II, and Ca(2+)-ATPase. Numerous cytoskeletal CaMBP were expressed such as microtubule-associated protein-2, spectrin, tubulin, caldesmon, adducin, and neuromodulin. Of the CaMBP expressed, phosphodiesterase, calcineurin, caldesmon, and adducin cross-linked with CaM-DAP in the loaded SK-N-SH cells. Carbachol stimulated the time-dependent CaM-DAP labeling of calcineurin and adducin. This study demonstrates the novel incorporation of a photoreactive CaM derivative into living cells, as well as muscarinic receptor-activated CaM-DAP interaction with several cellular CaMBP. We postulate that carbachol-stimulated CaM translocation in SK-N-SH cells may affect the activity of CaM-dependent enzymes and may alter aspects of cytoskeletal function.
Mangels
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Department of Pharmacology, University of Michigan Medical School, Ann Arbor 49109-0626.
Gnegy
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D000345:Affinity Labels / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008970:Molecular Weight; D009447:Neuroblastoma; D010782:Photolysis; D011773:Pyruvates / Q000378:metabolism*
D000345:Affinity Labels; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D011773:Pyruvates; C073879:calmodulin-diazopyruvamide; D002217:Carbachol