Characterization of protein serine/threonine phosphatase activities in human lung mast cells and basophils

Peirce, M.J., Munday, M. and Peachell, P.T. (1998) Characterization of protein serine/threonine phosphatase activities in human lung mast cells and basophils. British Journal of Pharmacology, 125 (5). pp. 1095-1101. 10.1038/sj.bjp.0702169.

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DOI: 10.1038/sj.bjp.0702169

Abstract

1. The serine/threonine protein phosphatase (PP) inhibitors, okadaic acid and calyculin, attenuated the IgE-mediated release of histamine from human lung mast cells (HLMC) and basophils in a dose-dependent manner whereas an alternative PP inhibitor, microcystin, was ineffective. Calyculin was more potent than okadaic acid in both cell types. The concentration required to inhibit by 50% (IC50) the release of histamine was 15 (HLMC) and 50 nM (basophils) for calyculin and 200 (HLMC) and 300 nM (basophils) for okadaic acid. 2. Lysates of purified HLMC and basophils dephosphorylated radiolabelled glycogen phosphorylase, a substrate for both PP1 and PP2A. The PP activity in lysates of both cell types was inhibited in a dose-dependent fashion by the PP inhibitors with the following rank order of activity, calyculin (approximate IC50; 0.02-0.1 nM) ≥ microcystin (0.1 nM) > okadaic acid (70 nM). 3. The PP1-selective inhibitor, inhibitor-2 (I-2), attenuated the dephosphorylation of glycogen phosphorylase in lysates of both HLMC and basophils. I-2 (20 nM) inhibited the glycogen phosphorylase PP activity by 71 ± 3% and 49 ± 13% in HLMC and basophil extracts, respectively. There were, approximately, 6 fold greater levels of I-2-sensitive activity in HLMC than in basophils. Qualitatively similar results were obtained with an alternative PP1-selective inhibitor, inhibitor-1 (I-1). 4. Lysates derived from HLMC and basophils dephosphorylated radiolabelled casein which is a PP2A-restricted substrate. HLMC lysates contained, approximately, 2.5 fold higher levels of casein PP activity than basophil lysates. 5. These data indicate that HLMC and basophils both contain PP1 and PP2A. The data suggest that, on a per cell basis, HLMC have higher levels of both PP1 and PP2A. Moreover, the ratio of PP1 to PP2A is higher in HLMC than in basophils.

Item Type:Article
Uncontrolled Keywords:Basophils; Dephosphorylation; Mast cells; Okadaic acid; Phosphatases
Departments, units and centres:Department of Pharmaceutical and Biological Chemistry > Department of Pharmaceutical and Biological Chemistry
ID Code:3008
Journal or Publication Title:British Journal of Pharmacology
Deposited By:Library Staff
Deposited On:22 Mar 2012 10:47
Last Modified:22 Mar 2012 10:47

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