Purification of cytosolic cAMP-independent protein kinases from rat ventral prostate

Casein kinase 2 as a potentially important enzyme in the nervous system

Protein kinase CK2 is a ubiquitous and pleiotropic seryl/threonyl protein kinase which is highly conserved in evolution indicating a vital cellular role for this kinase. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. Special attention has been devoted to phosphorylation status and structure of these enzymic molecules, however, their regulation and roles remain intriguing. Until recently, CK2 was believed to represent a kinase especially required for cell cycle progression in non-neural cells. At present, with respect to recent findings, four essential features suggest potentially important roles for this enzyme in specific neural functions: (1) CK2 is much more abundant in brain than in any other tissue; (2) there appear to be a myriad of substrates for CK2 in both synaptic and nuclear compartments that have clear implications in development, neuritogenesis, synaptic transmission, synaptic plasticity, information storage and survival; (3) CK2 seems to be associated with mechanisms underlying long-term potentiation in hippocampus; and (4) neurotrophins stimulate activity of CK2 in hippocampus. In addition, some data are suggestive that CK2 might play a role in processes underlying progressive disorders due to Alzheimer's disease, ischemia, chronic alcohol exposure or immunodeficiency virus HIV. The present review focuses mainly on the latest data concerning the regulatory mechanisms and the possible neurophysiological functions of this enzyme.

Nuclear casein kinase 2 (CK-2) activity in human normal, benign hyperplastic, and cancerous prostate

In previous work, we had observed that chromatin-associated nonhistone protein phosphorylation, catalyzed by intrinsic protein kinase reaction in chromatin preparations from human benign prostatic hyperplasia (BPH) prostate samples was markedly elevated, compared with the normal prostate chromatin samples [Rayan et al: Cancer Res 45:2277-2282, 1985]. The properties of this protein kinase reaction were suggestive of the involvement of casein kinase(s). By employing the specific synthetic substrate for casein kinase 2 (CK-2) for assays in cellular fractions, we have shown that this protein kinase is present in human prostate chromatin. Its activity is increased in BPH chromatin by about 25-fold, as compared with its activity in the normal prostate chromatin. This suggests that CK-2 is a possible mediator of the enhanced phosphorylation of chromosomal proteins in BPH chromatin. By comparison, CK-2 activity in chromatin preparations from prostatic carcinoma samples was markedly less elevated than that of the BPH chromatin. Immunohistochemical analysis of the enzyme in human frozen sections of prostate tissue samples showed that the enzyme immunostaining was diffuse in the cytoplasm, but more intense in the nucleus, especially in the nucleoli. In general, the staining corresponded with the enzymic data. However, sections from prostatic carcinoma samples appeared to show differential staining, depending on the Gleason's grade of the sample. The samples with higher Gleason's grade showed less intense immunostain in the nucleus, compared with samples of lower Gleason's grade. Further, regions of sections in samples with higher Gleason's grade did not show any immunostaining. These differences in the characteristics of CK-2 expression in prostatic carcinoma samples may be potentially significant, but need to be evaluated further for their significance to the pathobiology of prostatic neoplasia.

Association of casein kinase 2 with nuclear chromatin in relation to androgenic regulation of rat prostate

Casein kinase 2 (CK-2) is a ubiquitous messenger-independent protein serine/threonine kinase that has been implicated in growth control. We have studied the activity and subcellular location of CK-2 in adult rat ventral prostate in relation to androgen withdrawal and administration. Androgen deprivation by castration results in a faster decline in CK-2 activity associated with prostatic nuclei than that in the cytosol. Nuclear CK-2 associated with chromatin is reduced at an even greater rate than that in the total nucleus. Reversal of these events by administration of a single dose of 5 alpha-dihydrotestosterone to adult rats castrated 144 hr previously was accompanied by a differential early enhancement of chromatin-associated CK-2 activity, with a concomitant decrease in the CK-2 activity present in the cytosol. Changes in the nuclear CK-2 activity correlated with the immunostainable enzyme protein in the nucleus. We propose that androgens evoke translocation of CK-2 from the cytoplasm to the nucleus (nucleoplasm) where its enhanced association with the chromatin constituents takes place. Conversely, withdrawal of circulating androgens due to castration evokes a dissociation of CK-2 from chromatin and eventual translocation of nucleoplasmic CK-2 to the cytoplasm. Modulations in the association of CK-2 with nuclear chromatin may represent an important mechanism of post-transcriptional regulation of nuclear CK-2 in relation to androgen action in the prostate.

Casein kinases: pleiotropic mediators of cellular regulation

The present review on casein kinases focuses mainly on the possible metabolic role of CK-2, with special emphasis on its behavior in pathological tissues. From these data at least three ways to regulate CK-2 activity emerge: (i) CK-2 activity changes during embryogenesis, being high at certain stages of development and showing basal activity values at others; (ii) CK-2 activity can be enhanced in vitro by treatment of tissue culture cells with various growth factors and serum and (iii) CK-2 activity is constitutively enhanced in rapidly proliferating cells. The regulated CK-2 activity changes during embryogenesis cannot be explained as yet. In the case of the constitutive high expression of CK-2 in tumors, genetic changes may be responsible, e.g. through alterations of the regulatory genetic elements and/or regulation by specific transcription factors. In the case of serum induction, no genetic changes are necessarily involved; the observed changes may be entirely due to a signal transduction pathway where CK-2 could be phosphorylated by another kinase(s). CK-2 cDNAs from various organisms have been isolated and characterized. From the deduced amino acid sequence it turns out that CK-2 subunits are highly conserved during evolution. The relationship between CK-2 alpha from humans and plants is still 73%. Similar relationships are reported for the beta-subunit. Chromosomal assignment of CK-2 alpha shows two gene loci, one of which is a pseudogene. They are located on different chromosomes. Expression of the CK-2 subunits in Escherichia coli and the Baculo expression system is shown. The recombinant subunits can self-assemble to a functional holoenzyme in vitro. Biochemical and biophysical analysis of the recombinant beta-subunit suggests it to be trifunctional in association with the alpha-subunit affecting: (i) stability, (ii) enzyme specificity and (iii) enzyme activity. The question where CK-2 and its subunits are located throughout the cell cycle has also been addressed, mainly because of the large discrepancies that still exist between results obtained by different investigators. Tissue-specific expression of CK-2 at the mRNA and at the protein level has also been given attention. The fact that the enzyme activity is surprisingly high in brain and low in heart and lung may be indicative of involvement of CK-2 in processes other than proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and identification of a novel cellular protein that potently activates Ca2+/phospholipid-dependent protein kinase (protein kinase C)

A novel heat-stable cellular protein that significantly stimulated Ca2+/phospholipid-dependent protein kinase (protein kinase C, PKC) was identified. It is ubiquitous and has a molecular mass of over 150 kDa, and was shown to be specific for PKC. It activates PKC in the absence and presence of phospholipids; however, its maximal stimulatory potential was achieved when optimal amounts of phospholipids were also present in the reaction medium. Thus, in comparison with classical cofactors such as phospholipid, where activation of PKC mainly involves interaction with the regulatory domain of PKC, the mechanism of activation of PKC by the activator appears to involve several binding sites.

Monoclonal antibodies against nuclear casein kinase NII (PK-N2)

A monoclonal antibody was produced against the nuclear casein kinase II (PK-N2) isolated from rat liver. The antibody was of the IgM class, and showed immunoreactivity towards the higher molecular weight subunit (41K Da) of the protein kinase in Western blots. The antibody was equally reactive towards the PK-N2 isolated from rat ventral prostate indicating that it can recognize the enzyme from different tissues of the rat. The antibody also detected the cytosolic casein kinase II (CK-2) suggesting significant similarity of the antigenic domains in the two forms of this protein kinase. No binding was detected with the nuclear or cytosolic casein kinase I (PK-N1 and CK-1). The antibody did not inhibit the enzyme activity or directly precipitate the enzyme, but when coupled to an affinity matrix and cross-linked with dimethylpimelimidate, it was capable of removing nearly all the PK-N2 activity from solution.

Tissue-specific decline in cytosolic casein kinase II of the ventral prostate in aging rats

An age-associated decline in the activity of cytosolic casein kinase II in the rat ventral prostate was observed. The decrease in specific and total activity of casein kinase II of prostatic cytosol obtained from 12-month old rats compared with that from 3-month old rats was 50% and 70%, respectively. This decrease was tissue specific since no such alteration in enzymic activity was found in liver, lung, or heart. The decline in activity was not due to an increase in the concentration of a casein kinase inhibitor or to altered androgenic status with aging. Rather, the reduction in the activity of the enzyme was commensurate with the decrease in the total concentration of the enzyme protein as determined by an ELISA using anti-casein kinase II antibodies. The activity of casein kinase II in the nuclear fraction of the rat prostate was not altered in aging animals. It may be concluded that the cytosolic form of casein kinase II in the prostate of older animals is regulated at the transcriptional level (but not via the androgen-receptor complex mechanism). An alternative explanation for this observation may relate to altered stability of the enzyme in the prostate of older animals.

Polyamine-like effects of aminoglycosides on various messenger-independent protein kinase reactions

Gentamicin and several other aminoglycoside antibiotics in millimolar concentrations directly stimulate the phosphorylation of casein by purified preparations of cAMP- and Ca2+-independent protein kinases PK-C2 (equivalent to cytosolic casein kinase II) and its nuclear counterpart PK-N2 from rat liver and ventral prostate. These stimulatory effects of aminoglycoside antibiotics were similar to those exerted by the aliphatic polyamine spermine. Phosphorylation of casein by purified preparations of messenger-independent protein kinases PK-C1 (equivalent to cytosolic casein kinase I) and its nuclear counterpart PK-N1 was much less enhanced by spermine and the aminoglycoside antibiotics tested. Stimulations of PK-N2 reactions evoked by gentamicin or spermine (at 0.5 and 1.0 mM) were not additive. Several amino sugars tested were without effect on these protein kinases. Methylglyoxal bis(guanylhydrazone) which is known to block the stimulatory effects of polyamines on certain other enzymes did not alter spermine-stimulated phosphorylation of casein catalyzed by PK-N2 preparations.

Purification of nuclear cAMP-independent protein kinases from rat ventral prostate

Two nuclear cAMP-independent protein kinases (designated PK-N1 and PK-N2) were purified from rat ventral-prostate and liver. The yield of enzyme units was 4-5% and 7-9% for each enzyme from the prostatic nuclei and liver nuclei, respectively. The average fold purification for prostatic nuclear protein kinase N1 and N2 was 1360 and 1833, respectively. The respective average specific activity of the two enzymes towards casein was 81,585 and 110,000 nmol 32P incorporated/hr/mg of enzyme. Protein kinase N1 comprised one polypeptide of Mr 35,000 which underwent phosphorylation in the presence of Mg2+ + ATP. Protein kinase N2 comprised two polypeptides Mr 40,000 and 30,000 of which only the Mr 30,000 polypeptide was autophosphorylated. Both enzymes were active towards casein, phosvitin, dephosphophosvitin, spermine-binding protein, and non-histone proteins in vitro. Little activity was detected towards histones. Both enzymes were stimulated by 150-200 mM NaCl. MgCl2 requirement varied with the protein substrate but was between 2-4 mM for both enzymes. With dephosphophosvitin as substrate, the apparent Km for ATP for N1 protein kinase was 0.01 mM. GTP did not replace ATP in this reaction. Protein kinase N2 was active in the presence of ATP or GTP. The apparent Km was 0.01 mM for ATP, but 0.1 mM for GTP.