Specific protein kinases modulated during T cell mitogenesis. Activity of a 55-kDa serine kinase is associated with growth arrest in human T cells.
The intracellular events which are involved in controlling the G1 to S phase transition during the eucaryotic cell cycle are important to define in order to understand the mechanisms by which mitogenic and growth arrest-inducing agents control cell growth. Because a change in protein kinase activity is associated with the initial response of cells to mitogenic stimulants and growth factors, we used a kinase renaturation assay to identify specific protein kinases which are modulated as human T cells make the G1 to S phase transition after mitogenic stimulation with lectin. We identified four protein serine/threonine kinases of 180, 97, 85, and 38 kilodaltons which are increased in activity as these cells enter S phase. A-55 kDa serine/threonine kinase (PK55) was shown to have maximal activity during G0 and its activity was reduced by 95% upon movement into S phase. PK55 is inducible in human T cells by removal of interleukin 2 and low serum incubation which arrests cells in G1 phase, indicating that it is closely associated with G1 phase growth arrest. Furthermore, a similar PK55 activity was induced upon growth arrest in HL-60 cells treated with dimethyl sulfoxide and in Daudi cells treated with interferon alpha. Because the cAMP-dependent protein kinase (PK-A) family has been shown to be antiproliferative to lectin stimulated T cells, we were interested in determining whether PK55 was in fact an isozyme of PK-A. Comparative analysis using a specific peptide inhibitor of PK-A activity revealed that PK55 is catalytically distinct from PK-A. This data suggest that increases in PK55 may be associated with the growth-arrested state and further that PK55 is distinct from PK-A.
Evans
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GA
Biological Carcinogenesis and Development Program, Program Resources Inc./DynCorp, Frederick, Maryland 21702-1201.
Linnekin
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D
Grove
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S
Farrar
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WL
D002460:Cell Line; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D016193:G1 Phase; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology; D008934:Mitogens; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D016196:S Phase; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology
D016898:Interferon-alpha; D008934:Mitogens; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases