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Multiple protein kinases from human lymphocytes. Identification enzymes phosphorylating exogenous histon and casein.

ABSTRACT: 1. Cell-free lysates of human peripheral blood lymphocytes contained two casein kinase activities and two histone kinase activities, which could be separated by chromatography on DEAE-Sephadex. 2. Neither of the casein kinase activities were stimulated by cyclic AMP. The major activity was eluted from DEAE-Sephadex between 0.4 and 0.45M-KCl, had a molecular weight of approx. 130,000 (sucrose density gradients) and was stimulated by KCl (maximum 150mM). It also formed higher-molecular-weight aggregates when centrifuged in sucrose gradients containing 150mM-KCl. The minor activity was not retained by DEAE-Sephadex, had a molecular weight of approx. 50,000 and was not stimulated by KCl. 3. The major histone kinase activity was stimulated by cyclic AMP and was eluted from the DEAE-Sephadex column between 0.05 and 0.2M-KCl. The other activity was not stimulated by cyclic AMP and was insensitive to the rabbit muscle protein kinase inhibitor. 4. Evidence was obtained suggesting that the lymphocyte casein kinases were located primarily in the nuclei.

SUBMITTER: Kemp BE

PROVIDER: S-EPMC1165213 | biostudies-other | 1975 Feb

REPOSITORIES: biostudies-other

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Project description:BackgroundThe oncogenic PIM kinases and the tumor-suppressive LKB1 kinase have both been implicated in the regulation of cell growth and metabolism, albeit in opposite directions. Here we investigated whether these kinases interact with each other to influence AMPK activation and tumorigenic growth of prostate and breast cancer cells.MethodsWe first determined how PIM and LKB1 kinases affect AMPK phosphorylation levels. We then used in vitro kinase assays to demonstrate that LKB1 is phosphorylated by PIM kinases, and site-directed mutagenesis to identify the PIM target sites in LKB1. The cellular functions of PIM and LKB1 kinases were evaluated using either pan-PIM inhibitors or CRISPR/Cas9 genomic editing, with which all three PIM family members and/or LKB1 were knocked out from PC3 prostate and MCF7 breast cancer cell lines. In addition to cell proliferation assays, we examined the effects of PIM and/or LKB1 loss on tumor growth using the chick embryo chorioallantoic membrane (CAM) xenograft model.ResultsWe provide both genetic and pharmacological evidence to demonstrate that inhibition of PIM expression or activity increases phosphorylation of AMPK at Thr172 in both PC3 and MCF7 cells, but not in their derivatives lacking LKB1. This is explained by our observation that all three PIM family kinases can phosphorylate LKB1 at Ser334. Wild-type LKB1, but not its phosphodeficient derivative, can restore PIM inhibitor-induced AMPK phosphorylation in LKB1 knock-out cells. In the CAM model, loss of LKB1 enhances tumorigenicity of PC3 xenografts, while cells lacking both LKB1 and PIMs exhibit slower proliferation rates and form smaller tumors.ConclusionPIM kinases are novel negative regulators of LKB1 that affect AMPK activity in an LKB1-dependent fashion. The impairment of cell proliferation and tumor growth in cells lacking both LKB1 and PIMs indicates that these kinases possess a shared signaling role in the context of cancer. These data also suggest that PIM inhibitors may be a rational therapeutic option for LKB1-deficient tumors. Video Abstract.

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Multiple protein kinases from human lymphocytes. Identification enzymes phosphorylating exogenous histon and casein.

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