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PubMed1981

Interrelationships between protein kinases and spectrin phosphorylation in human erythrocytes.

Casein kinase and histone kinase(s) are solubilized from human erythrocyte membranes by buffered ionic solutions (0.1 mM EDTA and subsequent 0.8 M NaCl, pH 8) containing 0.2% Triton X-100. Casein kinase is separated from histone kinase(s) by submitting the crude extracts directly to chromatography on a phosphocellulose column, eluted with a continuous linear gradient of potassium phosphate buffer, pH 7.0, containing 0.2% Triton X-100. Under these conditions, the membrane-bound casein kinase activity is almost completely recovered into a quite stable preparation, free of histone kinase activity. In contrast, it undergoes a dramatic loss of activity when the extraction and the subsequent phosphocellulose chromatography are carried out with buffers which do not contain Triton X-100. Isolated spectrin, the most abundant membrane protein, is phosphorylated, in the presence of [gamma-32P]ATP, only by casein kinase while histone kinase is ineffective. Only the smaller subunit (band II) of isolated spectrin (and not the larger one (band I) is involved in such a phosphorylation process, as in the endogenous phosphorylation occurring in intact erythrocytes.

Casein Kinases↗
PubMed1992

Effect of triiodothyronine on cAMP-dependent and cAMP-independent protein kinase activities in developing chick embryo liver.

1. Changes in liver cytosol cAMP-dependent kinase and cAMP-independent growth-related quercetin-inhibited casein kinase activities during chick embryo development were studied. 2. Both kinase activities were found to increase continuously during the experimental period. 3. Upon treatment of embryos with triiodothyronine, an activation of cAMP-dependent kinase A and cAMP-independent casein kinase was observed which was most pronounced on days 12 and 14.

Animals↗
PubMed1997

The 96 kDa protein kinase activated by oncogenic Ras in Xenopus egg extracts is also activated by constitutively active Mek: activation requires serine/threonine phosphorylation.

In the Xenopus egg and oocyte system, oncogenic Ras protein can induce cell cycle arrest. The effect of oncogenic Ras on the cell cycle seems to be mediated by the Raf-Mek-Erk pathway of Ras signal transduction since constitutively active Raf, Mek, or Erk can mimic the effect of oncogenic Ras protein and since specific inhibition of these kinases can block the effect of oncogenic Ras. Using activated Xenopus egg extracts, we previously reported that the cell cycle arrest induced by oncogenic Ras correlates with the activation of a 96 kDa protein that phosphorylates histone h2b in vitro. This result raised the possibility that the 96 kDa kinase (designated as p96h2bk) is a potential target of the Raf-Mek-Erk pathway that links the pathway to the control of the cell cycle. We report here that constitutively active Mek1 could activate p96h2bk in the absence of oncogenic Ras. Moreover, inhibition of endogenous Mek by a specific inhibitor, PD 098059, suppressed the activation of p96h2bk by oncogenic Ras. These results are consistent with the concept that p96h2bk is a component or target of the Raf-Mek-Erk pathway. Furthermore, we have shown that activation of p96h2bk requires serine/threonine phosphorylation of p96h2bk.

Animals↗
PubMed2003

Efficient production of cloned bovine embryos using cdc2 kinase inhibitor.

This study was carried out to compare the effects of the combination of ionomycin with a H1-histone kinase inhibitor (dimethylaminopurine, DMAP) or cdc2 kinase inhibitor (sodium pyrophosphate, SPP) on the development of reconstituted bovine eggs. For this study, the enucleated bovine oocytes were injected with a presumptive primordial germ cell pre-treated with 1% sodium citrate, and randomly allocated into three activation groups: Group 1 (ionomycin 5 microm, 5 min), Group 2 (ionomycin + DMAP 1.9 mm, 3 h), and Group 3 (ionomycin + SPP 2 mm, 3 h). The reconstituted eggs were compared on the rates of cleavage and development with the blastocyst stage and the ploidy of embryos at 96 h post-activation. Cleavage rates and blastocyst development in Groups 1, 2 and 3 were 7 and 0%, 63 and 17%, and 53 and 14%, respectively. The chromosomal composition differed significantly (p < 0.05) among treatments. Although the embryos in Group 1 had significantly lower developments, 60% of embryos evaluated had diploid chromosomal sets. In contrast, approximately 60% of embryos in Group 2 had abnormal ploidy (21% polyploid and 38% mixoploid). In Group 3, the appearance of abnormal chromosome sets was reduced with the proportion of diploid embryos being increased to 86% (19 of 22), significantly higher (p < 0.05) than in Group 2. It can be concluded that the use of SPP with ionomycin reduces greatly the incidence of chromosomal abnormalities, and may be applicable for the activation of nuclear transplant bovine embryos.

Adenine↗
PubMed1997

Roscovitine, a novel cyclin-dependent kinase inhibitor, characterizes restriction point and G2/M transition in tobacco BY-2 cell suspension.

Although the developmental programs of plants and animals differ, key regulatory components of their cell cycle have been conserved. Particular attention has been paid to the role of the complexes between highly conserved cyclin and cyclin-dependent kinases in regulating progression through the cell cycle. The recent demonstration that roscovitine is a potent and selective inhibitor of the animal cyclin-dependent kinases cdc2 (CDK1), CDK2 and CDK5 prompted an investigation into its effects on progression through the plant cell cycle. Roscovitine induced arrests both in late G1 and late G2 phase in BY-2 tobacco cell suspensions. Both block were fully reversible when roscovitine was used at concentrations similar to those used in the animal system. Stationary-phase cells subcultured in the presence of roscovitine were arrested at a 2C DNA content. This arrest was more efficient without exogenous addition of plant growth regulator. Roscovitine induced a block in G1 earlier than that induced by aphidicolin. S-phase synchronized cells treated with roscovitine were arrested at a 4C DNA content at the G2/ M transition. The expression analysis of a mitotic cyclin (NTCYC1) indicated that the roscovitine-induced G2 block probably occurs in late G2. Finally, cells in metaphase were insensitive to roscovitine. The purified CDK/cyclin kinase activities of late G1 and early M arrested cells were inhibited in vitro by roscovitine. The implications of these experimental observations for the requirement for CDK activity during progression through the plant cell cycle are discussed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1993

Phosphatidylinositol 3-kinase activity is important for progesterone-induced Xenopus oocyte maturation.

In somatic cells, phosphatidylinositol 3-kinase (PI3 kinase) is a critical intermediary in growth factor-induced mitogenesis. We have examined the role of this enzyme in meiotic maturation of Xenopus laevis oocytes. PI3 kinase activity was present in immunoprecipitates of the p85 subunit of PI3 kinase from immature oocytes and markedly increased following progesterone stimulation. Injection of bacterially expressed protein corresponding to the C-terminal SH2 domain of p85 (SH2-C) inhibited progesterone-induced PI3 kinase activation and meiotic maturation. Injection of protein corresponding to the N-terminal SH2 domain or the SH3 domain of p85 did not inhibit PI3 kinase activation or maturation. SH2-C did not inhibit oocyte maturation induced by c-mos RNA injection. In addition, radiolabelled SH2-C was used to probe oocyte lysates, revealing that a novel 200-kDa protein bound to SH2-C. This protein may be an important mediator of progesterone-induced lipid metabolism in oocytes.

Animals↗
PubMed1992

Induction of cyclin mRNA and cyclin-associated histone H1 kinase during liver regeneration.

Cyclins and cyclin-associated cdc kinases are key regulators of oocyte maturation (Maller, J. L. (1990) in The Biology and Medicine of Signal Transduction (Nishizuka, Y., Endo, M., and Tanaka, C., eds) pp. 323-328, Raven Press, New York), yeast cell cycles (Nurse, P. (1990) Nature 344, 503-508), DNA replication in cell-free systems (D'Urso, F., Marraccino, R. L., Marshak, R. R., and Roberts, J. M. (1990) Science 250, 786-791), and amphibian cell proliferative transitions (Hunt, T. (1991) Nature 350, 462-463). The extent to which these regulatory molecules participate in the growth control of differentiated epithelial cells like hepatocytes is unknown. Therefore, we investigated the expression of "G1" (E, C, and D) and "G2/M" (A, B1, and B2) cyclin mRNAs, the relative levels of cyclin A- and B1-associated histone H1-kinase activity, and the appearance of cyclin-associated kinases (p32/p33cdk2 and p33/p34cdc2) in regenerating rat liver and in control tissues from sham hepatectomized rats. To do this, we exploited a battery of human cyclin cDNAs and cyclin antisera that recognize rat molecules. The results suggest an apparent sequence of regeneration-specific changes: 1) elevated and induced expression of cyclins E (2.1 kilobases (kb)) and C (4 kb), and D mRNAs (4 kb), within 12 h, respectively; 2) induction of cyclins A (3.4 and 1.8 kb), B1 (2.5 and 1.8 kb), and B2 (1.9 kb) mRNAs at 24 h; 3) induction of cyclin A- and B1-associated nuclear histone H1 kinase at 24 h; and 4) enhanced levels of PSTAIRE-containing proteins of Mr approximately 32-33 and 33-34 kDa in nuclear extracts from 24-h regenerating liver that co-immunoprecipitate with cyclin A and B1 antisera, respectively. These observations provide an intellectual framework that unifies the biology of hepatocyte mitogenesis, proto-oncogene expression, and the machinery of the cell cycle.

Animals↗
PubMed1994

The release from metaphase arrest in blue mussel oocytes.

In Mytilus edulis, shed oocytes are arrested at metaphase I of meiosis until fertilization. We previously suggested (Dubé and Dufresne, J. Exp. Zool. 256:323-332, 1990) that such a metaphase arrest depends upon a continuous synthesis of short-lived proteins, the destruction of which is sufficient to induce meiosis resumption. We further investigated the mechanism of metaphase release in blue mussel oocytes as triggered either by fertilization or by inhibition of protein synthesis (emetine) or phosphorylation (6-dimethylaminopurine, 6-DMAP). Treatment of unfertilized oocytes (UF) with emetine induces completion of the first meiotic cycle including extrusion of the polar body, followed by chromosome decondensation and by the formation of large membrane-bound nuclei, as visualized by Hoechst staining and transmission electron microscopy (TEM). Inhibition of protein phosphorylation with 6-DMAP induces directly chromosome decondensation and the formation of multiple nuclei surrounded by nuclear membrane. These interphasic nuclei exhibit continuous 3H-thymidine incorporation. p13 precipitation of p34 and associated proteins reveals "putative" cyclins in UF, no longer detected after metaphase/anaphase transition due to fertilization or emetine treatment. In the presence of 6-DMAP, new migrating forms are observed. The phosphorylated p34cdc2 homolog becomes dephosphorylated after fertilization or emetine treatment, whereas 6-DMAP induces its phosphorylation on tyrosine. Histone H1 kinase activity is reduced after these treatments, compared to the UF sample. Our results suggest that the metaphase/anaphase transition triggered by fertilization in blue mussel oocytes is induced by the rapid destruction of a set of continuously synthesized proteins accompanied by decreased histone H1 kinase activity. These events can be mimicked by inhibiting protein synthesis. Inhibition of protein phosphorylation would drive the cell to interphase without commitment to meiosis I.

Adenine↗
PubMed1995

Protein kinase activities in Leishmania aethiopica: control by growth, transformation and inhibitors.

Promastigotes of L. aethiopica express an ectokinase activity preferring histone V-S as substrate. A soluble kinase activity utilizing protamine and histone V-S, as well as a particulate fraction associated kinase activity preferring protamine are also expressed. The soluble histone kinase activity, but not the ectokinase, was expressed at a higher level in cells from late phases of growth, as compared to early log phase cultures. Transformation of L. aethiopica to an amastigote-like stage, resulted in almost complete loss of the kinase activities, with retained viability of the cells. Formycin-ATP only weakly inhibited the kinases while effectively inhibiting cell growth and thymidine incorporation. Staurosporin efficiently blocked the kinase activities and cell growth without affecting thymidine incorporation.

Alkaloids↗
PubMed1992

Association of human cyclin E with a periodic G1-S phase protein kinase.

G1 cyclins control the G1 to S phase transition in the budding yeast, Saccharomyces cerevisiae. Cyclin E was discovered in the course of a screen for human complementary DNAs that rescue a deficiency of G1 cyclin function in budding yeast. The amounts of both the cyclin E protein and an associated protein kinase activity fluctuated periodically through the human cell cycle; both were maximal in late G1 and early S phases. Cyclin E-associated kinase activity was correlated with the appearance of complexes containing cyclin E and the cyclin-dependent kinase Cdk2. Thus, the cyclin E-Cdk2 complex may constitute a human G1-S phase-specific regulatory protein kinase.

CDC2-CDC28 Kinases↗
PubMed1994

Meiosis-specific cell cycle regulation in maturing Xenopus oocytes.

Meiotic cell cycles differ from mitotic cell cycles in that the former lack S-phase in the interphase between meiosis I and meiosis II. To obtain clues for mechanisms involved in the cell cycle regulation unique to meiosis, we have examined changes in chromosomal morphology and H1 kinase activity during a meiotic period from metaphase I (MI) to metaphase II (MII) in Xenopus oocytes. Using populations of oocytes that underwent germinal vesicle breakdown (GVBD) within a 10 minute interval, we found that the kinase activity declined gradually during the 60 minute period after GVBD and then increased steadily during the following 80 minute interval, showing remarkable differences from the rapid drop and biphasic increase of the kinase activity in intermitotic periods (Solomon et al. (1990) Cell 63, 1013-1024; Dasso and Newport (1990) Cell 61, 811-823). We also found that the exit from MI lagged, by more than 30 minutes, behind the time of lowest H1 kinase activity, whereas the two events took place concomitantly at the end of meiosis II and mitosis. Consequently, the H1 kinase activity was already increasing during the first meiotic division. When H1 kinase activation at MII was delayed by a transient inhibition of protein synthesis after GVBD, oocytes were able to support formation of interphase nuclei and DNA replication between the first meiotic division and the MII arrest, indicating that the cell cycle entered S-phase between meiosis I and meiosis II. These results strongly suggest that the machinery required for entering S-phase has been established in maturing oocytes by the end of meiosis I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Protein kinases in the lactating mammary gland.

Protein kinases in the cytosol of whole bovine lactating mammary gland were separated by phosphocellulose chromatography. Five protein kinases (identified as histone kinase and casein kinases A, B, C, and D) were characterized and compared with kinases from other tissues. The histone kinase activity was identified as cyclic AMP-dependent protein kinase. The casein kinases differed in their activities toward a variety of proteins (alpha s1-casein, native and dephosphorylated beta-casein, and alpha-lactalbumin) and peptides. Based on substrate specificity studies and the inhibitory effects of heparin, 2,3-diphosphoglycerate, and guanosine triphosphate, kinases B, C, and D were tentatively identified as glycogen synthase kinase-3, casein kinase I, and casein kinase II, respectively.

Animals↗
PubMed1983

Cyclic adenosine 3':5'-monophosphate-dependent and -independent protein kinases in human leukemic cells.

The pattern of protein kinase activity in leukemic cells from patients with chronic myelocytic leukemia, acute myeloblastic leukemia, acute monocytic leukemia, chronic lymphocytic leukemia, and acute lymphoblastic leukemia was studied and compared with normal peripheral blood granulocytes and lymphocytes. Our data showed that: (a) histone kinase activity was slightly lower in leukemic cells than in normal cells, whereas casein kinase activity was 2- to 3-fold higher in leukemic cells; (b) cyclic adenosine 3':5'-monophosphate stimulated 1.4- to 1.6-fold histone kinase activity of both normal and leukemic cells, whereas it did not stimulate casein kinase activity; (c) the ratio of histone kinase activities to casein kinase activities correlated directly with the maturation of the white blood cells; and (d) histone and casein kinase activities of extracts from normal and leukemic cells behaved similarly on chromatography on phosphocellulose and casein/Sepharose 4B. These results suggest that the increase in casein kinase activity is not due to the appearance of a new type of casein kinase but to an increase of the casein kinases 1 and 2 present in normal cells.

Casein Kinases↗