Phosphorylation at a tyrosine residue of lipomodulin in mitogen-stimulated murine thymocytes.

Abstract

When murine thymocytes were stimulated by mitogens such as concanavalin A, the Ca2+ ionophore A23187, or 4j-phorbol 12-myristate 13-acetate, there was a marked increase of 32p incorporation into immunoprecipitable lipomodulin, a phospholipase inhibitory protein. These compounds enhanced 45Ca21 influx into thymocytes, which, in turn, increased protein phosphorylation, probably by Ca2+-and phospholipid-dependent protein kinase (protein kinase C). Cyclic 8-bromo-AMP, an inhibitor of lymphocyte mitogenesis, blocked the mitogen-stimulated phosphorylation of lipomodulin, although it stimulated the protein phosphorylation via cyclic AMP-dependent kinase (protein kinase A). On electrophoresis, the hydrolysates of 35P-labeled lipomodulin showed a single radioactive spot, which comigrated with authentic phosphotyrosine. The partially purified middle-sized tumor antigen was able to phosphorylate lipomodulin after being phosphorylated by protein kinase C but not by the catalytic subunit of protein kinase A. Our findings suggest that the activity of a tyrosine-specific kinase, which phosphorylates lipomodulin in vivo as well as in vitro, is stimulated by protein kinase C and inhibited by protein kinase A.

Inhibitors of arachidonic acid metabolism eliminate the increase in cytosolic free calcium induced by the mitogen concanavalin A in rat thymocytes

“…Indomethacin also inhibits the Ca response to Con A; however, its effect is pronounced only at concentrations of about 10/1M which cannot only block the cyclooxygenase but also the lipoxygenase pathway. At a concentration of l-2 pM, at which indomethacin selectively blocks cyclooxygenase [8, 12,14], its inhibitory effect on the Ca response is rather weak (fig.1).…”

“…An increase in [Ca*+]i and pHi is observed during the first minutes of stimulation of rat thymocytes with the mitogenic lectin Con A [3,4]. The mechanism of generation of these ionic signals and their relation to another crucial event in lymphocyte activation, the stimulation of phospholipid metabolism, remains unclear [3-61. AA and its metabolites formed by the lipoxygenase or cyclooxygenase pathways play an important role in regulation of various physiological processes [7,8] [11,12]. However, the role of AA and its metabolites in the generation of ionic signals under the action of mitogens has not been investigated.…”

Role of arachidonic acid metabolism in thymocyte apoptosis after irradiation

“…The thymocytes (1.5× 107 cells/ml) were labelled in 3 ml RPMI 1640 medium supplemented with 1% bovine serum and 1 ~tCi/ml [3H]arachidonic acid (150 Ci/mM; 6.7 nM) for 1 h at 37°C as described previously [21,22]. After the incubation, the supernatant was removed, and the cells were washed three times with RPMI 1640 supplemented with 0.5% albumin and once with Hanks' solution.…”

Some aspects of rat platelet and serum phospholipase A2 activities

“…Inhibitor proteins for phospholipase A, have been described by Flower and coworkers in guinea pig lungs [15], and rat peritoneal leukocytes [16], by Hirata et al in rabbit neutrophils [17,18], and murine thymocytes [19], and by Rothut et al [20] in rat renomedullary interstitial cells. The formation of these inhibitor proteins appears to be induced by glucocorticoids.…”