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

Contraction of intraocular fibrous membranes is an important feature in the pathogenesis of retinal detachment in proliferative vitreoretinopathy (PVR). Collagen gel contraction is a useful in vitro model of membrane contraction in PVR. We studied the role of protein kinase C (PKC) in collagen gel contraction induced by bovine choroidal fibroblasts and retinal pigment epithelial (RPE) cells. Collagen gels embedded with the cells were formed in culture dishes and gel contraction was evaluated. The PKC stimulator, phorbol 12-myristate 13-acetate (PMA), and the protein phosphatase 1 and 2A inhibitor, okadaic acid (OA), were used to evaluate the role of the PKC-mediated phosphorylation system in this gel contraction. Fifteen min incubation with PMA stimulated gel contraction, but 180 min incubation had no effect. Choroidal fibroblast- but not RPE cell-induced gel contraction was stimulated by OA. These effects were inhibited by the broad spectrum protein kinase inhibitor staurosporine and the specific PKC antagonist calphostin C. Transforming growth factor-beta (TGF-beta)1 and TGF-beta 2, which are known to be present in eyes with PVR, were evaluated to determine their effect on gel contraction. Both TGF-beta 1 and 2 had a stimulatory effect on contraction of gels seeded with choroidal fibroblasts and RPE cells, but staurosporine and calphostin C inhibited this TGF-beta-induced gel contraction. These results indicate that activation of PKC/protein phosphorylation is an important factor in gel contraction caused by choroidal fibroblasts and RPE cells, and that TGF-beta-induced gel contraction is mediated at least in part via the PKC pathway.
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PMID:Collagen gel contraction induced by retinal pigment epithelial cells and choroidal fibroblasts involves the protein kinase C pathway. 792 9

Okadaic acid, a specific inhibitor of phosphoserine/threonine protein phosphatases 1 and 2A, was used to determine whether these protein phosphatases play a role in collagen-induced platelet aggregation and release reaction as measured by ATP release. Collagen-induced platelet aggregation and ATP release were inhibited by the addition of okadaic acid to platelet-rich plasma in a dose-dependent manner. The inhibitory effect of okadaic acid on collagen-induced platelet aggregation correlated with phosphorylation of proteins with M(r) 14.4, 25, 32, 36, 50, 60, and 80 kDa. The 14.4-kDa protein was purified to apparent homogeneity by electroelution from gel slices. This protein reacted with antibodies to phospholipase A2 (PLA2). Since okadaic acid inhibited PLA2 activity in platelet-rich plasma but not in the PLA2 assay mixture, the effect appears to be indirect. Furthermore, using a combination of immunoprecipitation and measurement of enzyme activity, PLA2 activity was inhibited in the presence of okadaic acid. The inhibited activity could not be restored by the addition of collagen. These results suggest that the phosphorylated form of PLA2 is inactive. Using [32P]glycogen phosphorylase a as substrate, protein phosphatase activity was inhibited by okadaic acid in a concentration-dependent manner. An immunoblot of platelet homogenates with anti-protein phosphatase 1 showed a band with M(r) 50 kDa reacting with the antibodies, suggesting that the 50-kDa protein is protein phosphatase 1. These data clearly show that okadaic acid increases the phosphorylation and indirectly decreases the activity of PLA2, but whether inhibition of PLA2 activity is related to collagen-induced platelet aggregation and release reaction remains to be determined.
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PMID:The role of protein phosphatases 1 and 2A in collagen-platelet interaction. 838 5

Collagen and the cross-linked collagen-related peptide (CRP-XL) each induced platelet p38 mitogen-activated protein kinase (p38) phosphorylation after 2 min. Subsequent dephosphorylation occurred in platelets activated with collagen, but not with CRP-XL, demonstrating glycoprotein VI-independent regulation of p38. Okadaic acid and fostriecin, inhibitors specific for protein phosphatase 2A (PP2A), blocked p38 dephosphorylation, and PP2A co-immunoprecipitated with phospho-p38. In addition, use of phenylarsine oxide suggested that tyrosine phosphatases and PP2A may act in concert to dephosphorylate p38. Finally, regulation of p38 in collagen-stimulated Glanzmann's platelets was indistinguishable from that in normal platelets, showing that p38 regulation is independent of integrin alphaIIbbeta3.
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PMID:P38 mitogen-activated protein kinase dephosphorylation is regulated by protein phosphatase 2A in human platelets activated by collagen. 1229 94