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)

Whereas it has been established that the phosphorylation of 20 kD regulatory myosin light chain (MLC20) is a key regulator of contraction in smooth muscle, troponin complex has been thought to be that of myofibrillar Ca2+ sensitivity in cardiac muscle. To elucidate the role of the phosphorylation of cardiac regulatory myosin light chain (MLC2) in the regulation of cardiac muscle contraction, we observed effects of calmodulin and okadaic acid, a protein phosphatase inhibitor, on myofibrillar Ca2+ sensitivity as estimated by pCa50 values obtained from pCa-tension relationships using beta-escin-skinned cardiomyocytes from Wistar rat hearts, in relation to changes in the phosphorylation of myofibrillar regulatory proteins. Whereas myofibrillar Ca2+ sensitivity tended to be progressively decreased by repeated Ca2+-activation in the absence of calmodulin (pCa50; from 5.91 to 5.86, n = 5), calmodulin (2.5 microM) significantly increased myofibrillar Ca2+ sensitivity (pCa50; from 5.92 to 6.03, n = 5, p < 0.05). Okadaic acid over 3 microM enhanced Ca2+-activated force, which was inhibited by 50 microM trifluoperazine, a calmodulin antagonist. Okadaic acid (3 microM) significantly increased myofibrillar Ca2+ sensitivity (pCa50; from 5.96 to 6.11, n = 6, p < 0.05). Whereas the phosphorylation level of troponin I was not changed by 3 microM okadaic acid, that of MLC2 was significantly increased by the same dose of okadaic acid (from 12 to 31%, n = 4, p < 0.05). These results suggest that MLC2 phosphorylation plays a partial role in the regulation of myofibrillar Ca2+ sensitivity in cardiac muscle.
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PMID:Effects of calmodulin and okadaic acid on myofibrillar Ca2+ sensitivity in cardiac myocytes. 1200 61

In striated muscles myosin light chain (MLC)2 phosphorylation regulates calcium sensitivity and mediates sarcomere organization. Little is known about the changes in MLC2 phosphorylation in relation to skeletal muscle plasticity. We studied changes in MLC2 phosphorylation in rats receiving three treatment conditions causing slow-to-fast transitions: 1) atrophy induced by 14 days of hindlimb suspension (HS), 2) hypertrophy induced by 14 days of clenbuterol administration (CB), and 3) 14 days of combined treatment (CB-HS). Three variants of the slow (MLC2s) and two variants of the fast MLC2 (MLC2f) isoform were separated with two-dimensional electrophoresis and identified with monoclonal and polyclonal antibodies specific for MLC2; their relative proportions were densitometrically quantified. In control soleus muscle MLC2s predominated over MLC2f (91.4 +/- 3.9% vs. 8.5 +/- 3.9%) and was separated into two spots, the less acidic spot being 73.5 +/- 4.3% of the total. All treatments caused a decrease of the less acidic unphosphorylated spot of MLC2s (CB: 64.1 +/- 5.6%, HS: 62.4 +/- 6.8%, CB-HS: 56.4 +/- 4.4%), the appearance of a third more acidic variant of MLC2s (representing 3.9-5.9% of total MLC2s), an increase of MLC2f (CB: 30.9 +/- 3.1%, HS: 23.9 +/- 3.3%, CB-HS: 25.3 +/- 3.9%), and the phosphorylation of a large fraction of MLC2f (CB: 30.4 +/- 6.7%, HS: 28.7 +/- 6.5%, CB-HS: 21.8 +/- 2.1%). Treatment with alkaline phosphatase or with protein phosphatase 1 (PP1) removed the most acidic spots of both MLC2f and MLC2s. We conclude that in rat skeletal muscles an increase of MLC2 phosphorylation is associated with the slow-to-fast transition regardless of whether hypertrophy or atrophy develops.
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PMID:Increased phosphorylation of myosin light chain associated with slow-to-fast transition in rat soleus. 1274 68

Neural stimulation controls the contractile properties of skeletal muscle fibres through transcriptional regulation of a number of proteins, including myosin isoforms. To study whether neural stimulation is also involved in the control of post-translational modifications of myosin, we analysed the phosphorylation of alkali myosin light chains (MLC1) and regulatory myosin light chains (MLC2) in rat slow (soleus) and fast (extensor digitorum longus EDL) muscles using 2D-gel electrophoresis and mass spectrometry. In control rats, soleus and EDL muscles differed in the proportion of the fast and slow isoforms of MLC1 and MLC2 that they contained, and also in the distribution of the variants with distinct isoelectric points identified on 2D gels. Denervation induced a slow-to-fast transition in myosin isoforms and increased MLC2 phosphorylation in soleus, whereas the opposite changes in myosin isoform expression and MLC2 phosphorylation were observed in EDL. Chronic low-frequency stimulation of EDL, with a pattern mimicking that of soleus, induced a fast-to-slow transition in myosin isoforms, accompanied by a decreased MLC2 phosphorylation. Chronic administration (10 mg x kg(-1) x d(-1) intraperitoneally) of cyclosporin A, a known inhibitor of calcineurin, did not change significantly the distribution of fast and slow MLC2 isoforms or the phosphorylation of MLC2. All changes in MLC2 phosphorylation were paralleled by changes in MLC kinase expression without any variation of the phosphatase subunit, PP1. No variation in MLC1 phosphorylation was detectable after denervation or cyclosporin A administration. These results suggest that the low-frequency neural discharge, typical of soleus, determines low levels of MLC2 phosphorylation together with expression of slow myosin, and that MLC2 phosphorylation is regulated by controlling MLC kinase expression through calcineurin-independent pathways.
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PMID:Nerve influence on myosin light chain phosphorylation in slow and fast skeletal muscles. 1627 42

Protein dephosphorylation by protein phosphatase 1 (PP1), acting in concert with protein kinase C (PKC) and protein kinase A (PKA), is a pivotal regulatory mechanism of protein phosphorylation. Isolated rat cardiac myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 were used in determining dephosphorylation specificities, Ca(2+)-stimulated Mg(2+)ATPase activities, and Ca(2+) sensitivities. In reconstituted troponin (Tn) complex, PP1 displayed distinct substrate specificity in dephosphorylation of TnT preferentially to TnI, in vitro. In situ phosphorylation of cardiomyocytes with calyculin A, a protein phosphatase inhibitor, resulted in an increase in the phosphorylation stiochiometry of TnT (0.3 to 0.5 (67%)), TnI (2.6 to 3.6 (38%)), and MLC2 (0.4 to 1.7 (325%)). These results further confirmed that though MLC2 is the preferred target substrate for protein phosphatase in the thick filament, the Tn complex (TnI and TnT) from thin filament and C-protein in the thick filament are also protein phosphatase substrates. Our in vitro dephosphorylation experiments revealed that while PP1 differentially dephosphorylated within TnT at multiple sites, TnI was uniformly dephosphorylated. Phosphopeptide maps from the in vitro experiments show that TnT phosphopeptides at spots 4A and 4B are much more resistant to PP1 dephosphorylation than other TnT phosphopeptides. Mg(2+)ATPase assays of myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 delineated that while PKC and PKA phosphorylation decreased the Ca(2+)-stimulated Mg(2+)ATPase activities, dephosphorylation antagonistically restored it. PKC and PKA phosphorylation decreased Ca(2+) sensitivity to 3.6 microM and 5.0 microM respectively. However, dephosphorylation restored the Mg(2+)ATPase activity of PKC (99%) and PKA (95%), along with the Ca(2+) sensitivities (3.3 microM and 3.0 microM, respectively).
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PMID:Dephosphorylation specificities of protein phosphatase for cardiac troponin I, troponin T, and sites within troponin T. 1658 47