Localization of protein phosphokinase activities in the nucleolus distinct from extra-nucleolar regions in rat ventral prostate nuclei

Protein kinase CK2 – diverse roles in cancer cell biology and therapeutic promise

The association of protein kinase CK2 (formerly casein kinase II or 2) with cell growth and proliferation in cells was apparent at early stages of its investigation. A cancer-specific role for CK2 remained unclear until it was determined that CK2 was also a potent suppressor of cell death (apoptosis); the latter characteristic differentiated its function in normal versus malignant cells because dysregulation of both cell growth and cell death is a universal feature of cancer cells. Over time, it became evident that CK2 exerts its influence on a diverse range of cell functions in normal as well as in transformed cells. As such, CK2 and its substrates are localized in various compartments of the cell. The dysregulation of CK2 is documented in a wide range of malignancies; notably, by increased CK2 protein and activity levels with relatively moderate change in its RNA abundance. High levels of CK2 are associated with poor prognosis in multiple cancer types, and CK2 is a target for active research and testing for cancer therapy. Aspects of CK2 cellular roles and targeting in cancer are discussed in the present review, with focus on nuclear and mitochondrial functions and prostate, breast and head and neck malignancies.

Characterization of low-molecular-weight acid phosphoprotein phosphatase associated with rat splenic cell nucleoli

Evidence is presented on the existence of an acid phosphoprotein phosphatase (APPase) associated with rat splenic cell nucleoli. The enzyme is purified 1250-fold from 0.3 M NaCl nucleolar extract by means of chromatography on P cellulose and Sephacryl S-200. The nucleolar acid phosphoprotein phosphatase is a very basic protein (pI 8.3) and shows maximal activity at pH 5.8. It dephosphorylates acidic phosphoproteins (casein and phosvitin), ATP, and p-nitrophenyl phosphate, but not basic phosphoproteins (histones and protamine phosphate). The enzyme activity is very dependent on reducing agents, especially on ascorbic acid. Divalent and monovalent cations did not affect phosphatase activity, but heavier divalent metals, Co2+ and Zn2+, strongly inhibit the enzyme activity. The activity was also inhibited by N-ethylmaleimide, indicating a requirement for free sulfhydryl groups. The estimated molecular weight of the purified enzyme is approximately 38,000 by gel filtration and sedimentation in sucrose gradient concentration.

Presence and characterization of two protein kinase activities in human seminal fluid

The presence of two protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) activities has been demonstrated in human seminal fluid, utilizing partially dephosphorylated phosvitin and lysine-rich histones as model acceptor substrates. Both kinase activities were maximal in the presence of MgCl2 and a sulfhydryl-protecting agent such as dithiothreitol; however, the histone kinase was stimulated to a greater extent by the latter. The histone kinase displayed a broad shoulder of activity at pH values of 7.1 to 7.6 with optimal activity at pH 8.0, and was inhibited by increased ionic strength (53% at 160 mM NaCl) and by the cyclic AMP-dependent protein inhibitor from rabbit muscle. The kinase activity towards phosvitin exhibited a broad pH profile with maximal activity at pH 7.2, was slightly stimulated by NaCl (20% at 160 mM), and was unaffected by the cyclic AMP-dependent protein kinase inhibitor. Kinetic studies revealed more than one apparent Km for the protein substrates and ATP. These differences in enzymic properties of kinase activities towards phosvitin and lysine-rich histones strongly indicate the presence of multiple enzymes. It appears that the histone kinase activity is attributable to the free catalytic subunit of a cyclic AMP-dependent enzyme. The protein kinase activities of seminal fluids from vasectomized men were 12-20% of those found for seminal fluids of normal men. This suggests that sperm may be a major source of protein kinase activities in seminal fluid.

Polyamine-activated protein kinase reaction from nuclei and nucleoli of Physarum polycephalum which phosphorylates a unique Mr 70 000 nonhistone protein

Methods are described for the detection and purification of a protein kinase from nuclei and nucleoli of Physarum polycephalum which catalyzed transfer of phosphate from [gamma-32P]ATP to a unique nonhistone protein of Mr 70 000 in a reaction that was polyamine dependent. Enzymatic phosphorylation of the nonhistone protein by the purified protein kinase was stimulated greatly, at times more than 60-fold, by the polyamines spermidine and spermine. This unique polyamine-dependent reaction was localized on the rDNA minichromosome of the nucleolus. The polyamine-dependent protein kinase, which was first partially purified with the acidic nonhistone protein fraction from isolated nucleoli, was resolved from at least six other protein kinases by phosphocellulose chromatography into a catalytic component of Mr 26 000 and a complex comprised of the catalytic component associated with a phosphate acceptor protein of Mr 70 000. The complex also catalyzed polyamine-dependent phosphorylation of the endogenous Mr 70 000 component. The resolved catalytic component catalyzed polyamine-dependent phosphorylation of a dephosphorylated Mr 70 000 nonhistone protein that had been independently isolated from nucleoli and previously demonstrated to have properties concordant with a specific regulatory role in rRNA gene transcription [Keuhn, G. D., Affolter, H. U., Atmar, V. J., Seebeck, T., Gubler, U., & Braun, R. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 2541-2545]. These studies indicate one way that the polyamines may regulate rRNA gene transcription through the mediation of a highly specific nonhistone protein kinase.

Effects of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions

Studies are presented on the influence of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions involving both exogenous and endogenous substrates. The activities toward the model acidic protein substrate, dephosphophosvitin, were maximal at 160--200mM-NaCl (or -KCl or -NH4Cl). Under these conditions, spermidine and spermine added in concentrations up to 2mM were essentially without effect. However, without addition of NaCl to the medium, marked stimulation of these reactions was elicited by these polyamines at 1--2mM concentrations. The stimulatory effects were not due to non-specific changes in the ionic strength or to substitution of spermine for Mg2+, as maximal stimulation by 1 mM-spermine was observed only at optimal (2--4mM) Mg2+ concentrations. Qualitatively similar effects of polyamines were observed with enzyme preparations from the prostates of castrated rats, and with chromatin and non-histone-protein preparations from other tissues besides ventral prostate. When phosphorylation of endogenous non-histone proteins of the chromatin was measured, spermine stimulated both the initial rates and the final extent of transphosphorylation, even in the presence of optimal concentration of NaCl. By contrast, spermine or spermidine had no effect on the chromatin- and non-histone-protein-associated protein kinase reactions determined with lysine-rich histones as substrates. Chemically NN-dimethylated dephosphophosvitin was a less active substrate for the chromatin-associated protein kinase, but its phosphorylation was more markedly stimulated by spermine in comparison with unmodified dephosphophosvitin. These observations hint that the polyamine stimulations of the various protein kinase reactions may be due to effects on the conformations of the non-histone protein substrates rather than on the kinases themselves.

Acidic-phosphoprotein phosphatase activity of rat ventral prostate nuclei: apparent lack of effect of androgens

A protein phosphatase activity has been demonstrated in nuclei of rat ventral prostate utilizing 32P-labelled phosvitin as a model acidic phosphoprotein substrate. This phosphoprotein phosphatase has a pH optimum of 6.7, is unaffected by the sulphydryl protecting agent 2-mercaptoethanol, and requires a divalent cation for maximal activity. Of the various divalent cations tested, Mg2+ is the most effective in reactivating the EDTA-inhibited enzyme. The phosphatase is inhibited by sodium flouride, sodium oxalate, N-ethylmaleimide, ATP and ADP but is relatively insensitive to ammonium molybdate. Increased ionic strength of the reaction medium also causes a reduction in the enzyme activity, e.g., by 48% at 200 mM sodium chloride. The activity of the acidic phosphoprotein phosphatase did not change significantly at 48 h or 96 h post-orchiectomy when expressed per unit of nuclear protein. However, it is reduced by approx. 30% at these times after castration if based on DNA content. The decline in activity per nucleus reflects the decrease in the realtive nuclear protein content observed at 48 h or 96 h post-orchiectomy. This suggests that the decline in the phosphorylation of prostatic nuclear acidic proteins which occurs upon androgen withdrawal is not due to increased nuclear phosphatase activity.

Increased activity of rat liver nucleolar protein kinase following triiodothyronine administration

Triiodothyronine (T3) administration to thyroidectomized rats induces a significant increase in the nucleolus-associated protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) activity. The general properties of the protein kinase solubilized from liver nucleoli have been investigated. Mg2+ (20 mM) is essential for the reaction and an appropriate concentration of NaCl (100 mM) is required to achieve maximal phosphorylation rates. The optimal pH for casein phosphorylation is 7.6. The kinase phosphorylates casein more efficiently than phosvitin and displays an almost undetectable activity towards histones and protamine. No significant stimulation of the kinase activity by cyclic AMP has been detected. The apparent Km values for casein and ATP are 1.5 mg/ml and 1.5-10(-5) M, respectively, and are not affected by the hormone administration.

The differential response of prostatic nucleolar and extra-nucleolar protein phosphokinase activities following androgen deprivation

Protein phosphokinase activities of nucleolar and extra-nucleolar compartments of rat ventral prostate nuclei were measured using the model acidic phosphoprotein, dephosphophosvitin, as substrate. Following orchiectomy, the activity in both of these fractions declined; however, the kinase activity of the nucleolus decreased at a much greater rate than that in the extra-nucleolar portion of the nucleus. Testosterone maintenance of castrated animals prevented this decline in activity. The regulation of protein phosphokinases which phosphorylate prostatic nucleolar acidic proteins may be an important mechanism in the androgen mediated activation of the nucleolus in this target tissue.