Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of immunosuppressant blockers of calcineurin (protein phosphatase 2B) on cAMP formation and hormone release were investigated in mouse pituitary tumor (AtT20) cells. Immunosuppressants enhanced corticotropin-releasing factor- and isoproterenol-evoked cAMP production in proportion with their potency to block calcineurin. Further analysis of cAMP production revealed that intracellular Ca2+ derived through voltage-regulated calcium channels reduces cAMP formation induced by corticotropin releasing-factor or beta 2-adrenergic stimulation and that this effect of Ca2+ is inhibited by blockers of calcineurin. AtT20 cells were found to express at least three species of adenylyl cyclase mRNA-encoding types 1 and 6 as well as a novel isotype, which appeared to be the predominant species. In two cell lines expressing very low or undetectable levels of the novel cyclase mRNA (NCB20 and HEK293 cells respectively), corticotropin-releasing factor-induced cAMP formation was not altered upon blockage of calcineurin activity. These data identify calcineurin as a Ca2+ sensor that mediates the negative feedback effect of intracellular Ca2+ on receptor-stimulated cAMP production. Furthermore, the effect of calcineurin on cAMP synthesis appears to be associated with the expression of a novel adenylyl cyclase isotype, which is highly abundant in AtT20 cells.
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PMID:Calcineurin feedback inhibition of agonist-evoked cAMP formation. 749 91

Dephosphorylation of Ca2+ channels by the Ca(2+)-activated phosphatase 2B (calcineurin) has been previously suggested as a mechanism of Ca(2+)-dependent inactivation of Ca2+ current in rat pituitary tumor (GH3) cells. Although recent evidence favors an inactivation mechanism involving direct binding of Ca2+ to the channel protein, the alternative "calcineurin hypothesis" has not been critically tested using the specific calcineurin inhibitors cyclosporine A (CsA) or FK506 in GH3 cells. To determine if calcineurin plays a part in the voltage- and/or Ca(2+)-dependent components of dihydropyridine-sensitive Ca2+ current decay, we rapidly altered the intracellular Ca2+ buffering capacity of GH3 cells by flash photolysis of DM-nitrophen, a high affinity Ca2+ chelator. Flash photolysis induced a highly reproducible increase in the extent of Ca2+ current inactivation in a two-pulse voltage protocol with Ca2+ as the charge carrier, but had no effect when Ba2+ was substituted for Ca2+. Despite confirmation of the abundance of calcineurin in the GH3 cells by biochemical assays, acute application of CsA or FK506 after photolysis had no effect on Ca(2+)-dependent inactivation of Ca2+ current, even when excess cyclophilin or FK binding protein were included in the internal solution. Prolonged preincubation of the cells with FK506 or CsA did not inhibit Ca(2+)-dependent inactivation. Similarly, blocking calmodulin activation with calmidazolium or blocking calcineurin with fenvalerate did not influence the extent of Ca(2+)-dependent inactivation after photolysis. The results provide strong evidence against Ca(2+)-dependent dephosphorylation as the mechanism of Ca2+ current inactivation in GH3 cells, but support the alternative idea that Ca(2+)-dependent inactivation reflects a direct effect of intracellular Ca2+ on channel gating.
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PMID:Mechanism of Ca(2+)-dependent inactivation of L-type Ca2+ channels in GH3 cells: direct evidence against dephosphorylation by calcineurin. 907 Apr 64

Dephosphorylation by the Ca2+/calmodulin-dependent phosphatase calcineurin has been suggested as an important mechanism of Ca2+-dependent inactivation of voltage-gated Ca2+ channels. We have tested whether calcineurin plays a role in the inactivation process of two types of high-voltage-activated Ca2+ channels (L and N type) widely expressed in the central nervous system, using the immunosuppressive drug FK506 (tacrolimus), which inhibits calcineurin after binding to intracellular FK506 binding proteins. Inactivation of L- and N-type Ca2+ channels was studied in a rat pituitary tumor cell line (GH3) and chicken dorsal root ganglion neurons, respectively. With the use of antisera directed against the calcineurin subunit B and the 12,000 mol. wt binding protein, we show that both proteins are present in the cytoplasm of GH3 cells and chicken dorsal root ganglion neurons. Ionic currents through voltage-gated Ca2+ channels were investigated in the perforated-patch and whole-cell configurations of the patch-clamp technique. The inactivation of L- as well as N-type Ca2+ currents could be well fitted with a bi-exponential function. Inactivation was largely reduced when Ba2+ substituted for extracellular Ca2+ or when the Ca2+ chelator EGTA was present intracellularly, indicating that both types of Ca2+ currents exhibited Ca2+-dependent inactivation. Extracellular (perforated-patch configuration) or intracellular (whole-cell configuration) application of FK506 to inactivate calcineurin had no effect on the amplitude and time-course of Ca2+ channel current inactivation of either L- or N-type Ca2+ channels. In addition, we found that recovery from inactivation and rundown of N-type Ca2+ channel currents were not affected by FK506. Our results provide direct evidence that the calcium-dependent enzyme calcineurin is not involved in the inactivation process of the two Ca2+ channel types which are important for neuronal functioning, such as gene expression and transmitter release.
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PMID:Calcium-dependent inactivation of neuronal calcium channel currents is independent of calcineurin. 1061 80