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)

The identification of three highly conserved phosphorylation sites in the cytoplasmic domain of each of the monomeric subunits of the macrophage scavenger receptor suggests that protein phosphorylation may regulate this receptor pathway. To investigate this, mouse peritoneal macrophages were pretreated with either the protein phosphatase inhibitor okadaic acid or the protein kinase inhibitor staurosporine to modulate cellular protein phosphorylation and their effects on the metabolism of acetyl-LDL were measured. Both okadaic acid and staurosporine inhibited the degradation of acetyl-low density lipoprotein (LDL) without affecting cellular lactic dehydrogenase (LDH) levels. The inhibition by okadaic acid was due to a 70% decrease in acetyl-LDL binding whereas post-receptor processing was minimally affected. Calyculin A, another serine/threonine phosphatase inhibitor, also reduced acetyl-LDL binding, whereas lithium chloride, an inositol phosphatase inhibitor, did not. Okadaic acid did not decrease steady state receptor mRNA levels nor decrease the number of total cellular receptors, consistent with a posttranslational mechanism of action. Interestingly, protease sensitivity studies showed that the receptors were still located on the cell surface. These studies suggest that okadaic acid inhibits acetyl-LDL binding by causing the redistribution of surface receptors into a sequestered compartment or inactivating the receptors. In contrast, staurosporine produced a paradoxical increase in receptor expression (30%) but slowed post-receptor processing (2.3-fold decrease). The latter was due to an inhibition of ligand internalization (2.9-fold decrease) via a protein kinase C-independent mechanism. Macrophage pinocytosis was also slowed by staurosporine (38% decrease); however, this does not appear to account for the inhibition of scavenger receptor internalization. Direct receptor phosphorylation was also slowed by staurosporine (38% decrease); however, this does not appear to account for the inhibition of scavenger receptor internalization. Direct receptor phosphorylation was also investigated and it was established that the receptor can be phosphorylated; however, changes in receptor function did not correlate with changes in the degree of receptor phosphorylation. Together these studies demonstrate that changes in cellular protein phosphorylation affect the expression, surface transport, and internalization of the macrophage scavenger receptor and suggest that the regulated phosphorylation/dephosphorylation of cellular proteins may be an important biochemical mechanism that controls normal processing of ligands by this receptor pathway.
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PMID:Modulation of macrophage scavenger receptor transport by protein phosphorylation. 872 20

Many agents that activate hematopoietic cells use phos pha tidyl ino si tol 3,4,5-trisphosphate (PtdIns 3,4,5-P(3)) to initiate signaling cascades. The SH2 domain-containing inositol 5' phosphatase, SHIP1, regulates hematopoietic cell function by opposing the action of phos pha tidyl ino si tol 3-kinase and reducing the levels of PtdIns 3,4,5-P(3). Activation of the cyclic AMP-de pend ent protein kinase (PKA) also opposes many of the pro-inflammatory responses of hematopoietic cells. We tested to see whether the activity of SHIP1 was regulated via phos pho ryl a tion with PKA. We prepared pure recombinant SHIP1 from HEK-293 cells and found it can be rapidly phos pho ryl a ted by PKA to a stoichiometry of 0.6 mol of PO(4)/mol of SHIP1. In (32)P-labeled HEK-293 cells transfected with SHIP1, stimulation with Sp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Sp-cAMPS) or activation of the beta-adrenergic receptor increased the phos pho ryl a tion state of SHIP1. Inhibition of protein phosphatase activity with okadaic acid also increased the phos pho ryl a tion of SHIP1. Phosphorylation of SHIP1 in vitro or in cells by PKA increased the 5' phosphatase activity of SHIP1 by 2-3-fold. Elevation of Ca(2+) in DT40 cells in response to B cell receptor cross-linking, an indicator of PtdIns 3,4,5-P(3) levels, was markedly blunted by pretreatment with Sp-cAMPS. This effect was absent in SHIP(-/-) DT40 cells showing that the effect of Sp-cAMPS in DT40 cells is SHIP1-de pend ent. Sp-cAMPS also blunted the ability of the B cell receptor to increase the phos pho ryl a tion of Akt in DT40 and A20 cells. Overall, activation of G protein-coupled receptors that raise cyclic AMP cause SHIP1 to be phosphorylated and stimulate its inositol phosphatase activity. These results outline a novel mechanism of SHIP1 regulation.
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PMID:Regulation of the Src homology 2 domain-containing inositol 5'-phosphatase (SHIP1) by the cyclic AMP-dependent protein kinase. 1949 9