Interleukio 2 stimulates serine phosphorylation of CD45 in CTLL-2.4 cells

Autor: Jeffrey A. Ledbetter, Edward A. Clark, Mary A. Valentine, Michael B. Widmer, David L. Brautigan, Fran M. Pinault, Robert F. Voice, Byron M. Gallis
Rok vydání: 1991
Předmět:
Zdroj: European Journal of Immunology. 21:913-919
ISSN: 1521-4141
0014-2980
Popis: Ligation of interleukin 2 (IL2) is known to regulate both protein tyrosine and serine/threonine phosphorylation. A family of leukocyte transmembrane proteins whose cytoplasmic domain exhibits intrinsic protein tyrosine phosphatase activity is collectively called CD45 and is identified by a set of common cell surface epitopes. Although CD45 is known to be a phosphoprotein, it is not known how phosphorylation specifically regulates its function. We therefore identified a cell line, the IL 4-dependent line CTLL-2.4, in which CD45 could be phosphorylated in response to addition of IL 2. These cells are a variant of an IL 2-dependent murine cell line which were selected for long-term growth on IL 4 but which retain the ability to proliferate on exposure to IL 2. Incubation of CTLL-2.4 in low serum concentrations followed by stimulation with IL 2 caused a three- to fivefold increase in the phosphorylation of CD45 in a time- and concentration-dependent manner. CD45 in non-stimulated cells contained one major tryptic phosphopeptide, whereas, after exposure of the cells to IL 2, two new phosphopeptides were present in CD45. The pattern of IL 2-induced phosphorylation was different from that found following addition of phorbol 12-myristate 13-acetate (PMA) to the cells. Although IL 2 induced rapid and potent tyrosine phosphorylation in CTLL-2.4 cells, all of the basal and cytokine-activated phosphorylation of CD45 occurred on serine residues. The IL 2-stimulated phosphorylation caused no change in the amount of cell surface CD45 and no alteration of its catalytic activity using an artificial tyrosine phosphorylated substrate-RCM-lysozyme. We speculate that the increase in phosphorylation of CD45 may modify its association with potential substrates. The differences in the phosphorylation patterns induced by IL 2 and PMA further suggest that more than one kinase can use CD45 as substrate and that IL2 activates a protein serine/threonine kinase different from protein kinase C.
Databáze: OpenAIRE
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