The difference in murine CDC2 kinase activity between cytoplasmic and nuclear fractions during the cell cycle

Increased c-Fos/activator protein-1 confers resistance against anergy induction on antigen-specific T cell

We have studied the contribution of c-Fos/activator protein-1 (AP-1) to antigen-specific T cell response with reference to T cell anergy by increasing c-Fos/AP-1 in vivo and in vitro. First, after injection of a high dose of staphylococcus enterotoxin B (SEB), clonal deletion of SEB-reactive V(beta)8(+) CD4 T cells occurred both in control B6 and H2-c-fos transgenic (fos) mice, whereas proliferation of T cells against SEB was profoundly depressed in B6 but not in fos mice. Second, the keyhole limpet hemocyanin-specific CD4 T(h)1 cell clone produced decreasing amounts of IL-2 in response to increasing amounts of concanavalin A (Con A) in vitro, whereas the decrease was less significant in the T(h)1 clones stably transfected with c-fos gene. Electrophoretic mobility shift assay with nuclear protein from the transformants showed that overexpression of the c-fos gene compensated the amounts of AP-1 in the nuclei of Con A-treated T(h)1 clones. Thus, increased c-Fos/AP-1 confers resistance against anergy induction on antigen-specific T cells.

cDNA cloning and chromosomal mapping of genes encoding novel protein kinases termed PKU-alpha and PKU-beta, which have nuclear localization signal

We have cloned cDNAs for novel serine/threonine protein kinases (PK), termed PKU-alpha and PKU-beta, by screening a bacteriophage expression library for kinase activity. Sequence analysis of PKU-alpha and PKU-beta genes revealed that their open reading frames (ORF) were 2151 and 2361 nucleotides (nt) encoding polypeptides of 717 and 787 amino acid (aa) residues, respectively. The deduced aa sequences of PKU-alpha and PKU-beta contained typical serine/threonine PK domains at the C-terminal region and were 86% identical to each other, indicating that they belong to the same PK family. Northern analysis reveals that they are expressed in nearly all human tissues and in cultured cells. The genes for PKU-alpha and PKU-beta were mapped to chromosome 17q23 and 8p12-p22, respectively, by fluorescence in situ hybridization. The proteins encoded by both cDNAs contain a putative nuclear localization signal (NLS) in their N-terminal region. These signals are likely to function in nuclear localization. Glutathione S-transferase (GST)-fusions to regions of PKU-alpha and beta containing the NLS were efficiently localized to the nucleus. In addition, PKU-beta transiently expressed in COS-1 cells was predominantly nuclear. PKU-alpha and PKU-beta differ: a consensus sequence for a nt binding motif is present near the NLS of PKU-beta. These results suggest that PKU-alpha and beta may phosphorylate serine and/or threonine residues on similar proteins, but their activities are regulated through distinct interactions with a nuclear component.

A role for phosphorylation in the proteolytic processing of the human NF-kappa B1 precursor

A precursor, p105, for one of the subunits (p50) of the NF-kappa B transcription factor, plays an important role in inducible expression of diverse cellular genes. p105 also functions as a cytoplasmic inhibitor for NF-kappa B, and the proteolytic processing of its inhibitory C-terminal region is required for generation of active NF-kappa B. Here, it is reported that the human p105 C-terminal region is phosphorylated in vivo on Ser894 and Ser908, which are potential phosphorylation sites in vitro for proline-directed serine/threonine kinases such as cyclin-dependent kinase. Furthermore, the mutation of these in vivo phosphorylation sites retards p105 processing in vivo, suggesting that p105 processing is regulated in a phosphorylation-dependent manner.

Mouse p87wee1 kinase is regulated by M-phase specific phosphorylation

We have cloned a mouse wee1 kinase cDNA (mwee1). The clone is 2258 bp in length and its open reading frame corresponds to 646 amino acid residues. The molecular weight of this kinase is 87 kDa in SDS-PAGE, which is about 1.7-fold larger than the human p50wee1 kinase reported previously. In a cell cycle, the mouse wee1 kinase is phosphorylated at M-phase, and an in vitro study using a mitotic extract revealed that phosphorylation occurs in the N-terminal domain, which is absent from the human wee1 kinase, resulting in inactivation of the kinase activity. The N-terminal domain or entire molecule is extensively phosphorylated by cdc2-cyclin B kinase. Furthermore, the activity of the wee1 kinase was reduced by phosphorylation with the mitotic extract which contained cdc2-cyclin B kinase.

Ubiquitin-activating enzyme, E1, is phosphorylated in mammalian cells by the protein kinase Cdc2

The ubiquitin-activating enzyme (E1) is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates. E1 was found to be phosphorylated in cells of a mouse mammary carcinoma cell line, FM3A. Peptide mapping of trypsin digests of labeled E1 indicated that two oligopeptides were mainly phosphorylated in vivo. The same oligopeptides were also labeled in vitro on Cdc2 kinase-mediated phosphorylation of E1, affinity-purified from the same cell line. The Cdc2 kinase is a key enzyme playing a pivotal role in G2/M transition in the cell cycle. The phosphorylation of one of the two oligopeptides was prominent at the G2/M phase of the cell cycle, and dependent upon the Cdc2 kinase activity in vivo since it was significantly reduced in tsFT210, a mutant cell line deficient in Cdc2 kinase. Mutation analysis indicated that the serine residue at the fourth position of the E1 enzyme was a phosphorylation site of Cdc2 kinase. These findings suggest that E1 is a target of Cdc2 kinase in the cell, implying that the ubiquitin system may be dynamically involved in cell cycle control through phosphorylation of this key enzyme.

Inhibition of DNA topoisomerase II by ICRF-193 induces polyploidization by uncoupling chromosome dynamics from other cell cycle events

ICRF-193, a novel noncleavable, complex-stabilizing type topoisomerase (topo) II inhibitor, has been shown to target topo II in mammalian cells (Ishida, R., T. Miki, T. Narita, R. Yui, S. Sato, K. R. Utsumi, K. Tanabe, and T. Andoh. 1991. Cancer Res. 51:4909-4916). With the aim of elucidating the roles of topo II in mammalian cells, we examined the effects of ICRF-193 on the transition through the S phase, when the genome is replicated, and through the M phase, when the replicated genome is condensed and segregated. Replication of the genome did not appear to be affected by the drug because the scheduled synthesis of DNA and activation of cdc2 kinase followed by increase in mitotic index occurred normally, while VP-16, a cleavable, complex-stabilizing type topo II inhibitor, inhibited all these processes. In the M phase, however, late stages of chromosome condensation and segregation were clearly blocked by ICRF-193. Inhibition at the stage of compaction of 300-nm diameter chromatin fibers to 600-nm diameter chromatids was demonstrated using the drug during premature chromosome condensation (PCC) induced in tsBN2 baby hamster kidney cells in early S and G2 phases. In spite of interference with M phase chromosome dynamics, other mitotic events such as activation of cdc2 kinase, spindle apparatus reorganization and disassembly and reassembly of nuclear envelopes occurred, and the cells traversed an unusual M phase termed "absence of chromosome segregation" (ACS)-M phase. Cells then continued through further cell cycle rounds, becoming polyploid and losing viability. This effect of ICRF-193 on the cell cycle was shown to parallel that of inactivation of topo II on the cell cycle of the ts top2 mutant yeast. The results strongly suggest that the essential roles of topo II are confined to the M phase, when the enzyme decatenates intertwined replicated chromosomes. In other phases of the cycle, including the S phase, topo II may thus play a complementary role with topo I in controlling the torsional strain accumulated in various genetic processes.

Abundant existence of 40kD-cdc2-related protein in rat thyroid cells

The cdc2 kinase family is known to be one of the important factors for cell proliferation in both yeast and mammalian cells. By using polyclonal antibodies against PSTAIRE region of cdc2HS, we studied the amount of cdc2-related kinases in the rat thyroid cell line, FRTL-5, during the cell cycle. The immunoreactive protein with molecular weight 34kD was hardly detectable, instead, 40kD protein exists constantly in amount through G0 phase to S phase. Further, it did not decrease when the cells were cultured in serum- and hormone-free medium. Moreover, we observed an increase of this protein in the nuclear fraction as the cells enter S phase. On the contrary, we could not detect any immunoreactive 40kD protein in primary cultures of rat thyroid cells. These results may indicate abundant existence of this protein might concern cell cycle regulation of FRTL-5 or its immortal feature.

Cell cycle dependent distribution of proliferating cell nuclear antigen/cyclin and cdc2-kinase in mouse T-lymphoma cells

The aim of the present study was to investigate bromodeoxyuridine (BrdU) uptake and coordinated distribution of proliferating cell nuclear antigen (PCNA) and p34-cdc2-kinase, two important proteins involved in cell cycle regulation and progression. Flow cytometric analysis of marker proteins in freshly plated mouse T-lymphoma cells (Yac-1 cells), using fluorescein isothiocyanate (FITC)-labeled specific antibodies, showed PCNA distributed throughout the cell cycle with increased intensity in S-phase. PCNA is essential for cells to cycle through S-phase and its synthesis is initiated during late G1-phase before incorporation of BrdU and remains high during active DNA replication. The intensity of PCNA fluorescence increases with the duration of incubation after plating. The cdc2-kinase was detectable in all phases of the cell cycle and the G2-M-phase appears to have the maximum concentrations. The cell cycle analysis of high dose colcemid (2 micrograms/ml) treated Yac-1 cells showed an aneuploid or hypodiploid population. Although the G2-M-phase seems to be the dominating population in aneuploid cells, the concentrations of cdc2-kinase were variable in this phase of cell cycle. The colcemid treatment at 25 ng/ml arrested 96% of cells in S-phase and G2-M-phase, but PCNA expression was evident in a portion of the cell population in G2-M-phase. Although cells blocked in M-phase seem to have high levels of cdc2-kinase, colcemid renders them inactive. From these data, it appears that the down regulation and/or inactivation of cdc2-kinase could be responsible for the colcemid arrest of cells in M-phase.

Negative regulation of mitosis by the fission yeast protein phosphatase ppa2

To understand the role of the type 2A-like protein phosphatase in the cell division cycle, we investigated the mutant phenotypes obtained when the fission yeast ppa1+ and ppa2+ phosphatase genes (which encode polypeptides with approximately 80% identity to mammalian type 2A phosphatases) were either deleted or overexpressed. We also investigated the in vivo effect of okadaic acid, an inhibitor of protein serine/threonine phosphatases, on cell division. We show that ppa2+ interacts genetically with the cell cell regulators cdc25+ and wee1+, as a ppa2 deletion is lethal when combined with wee1-50 but partially suppresses the conditional lethality of cdc25-22 mutation. Evidence that ppa2+ negatively controls the entry into mitosis, possibly through the regulation of cdc2 tyrosine phosphorylation, is presented. ppa2 phosphatase is abundant in the cytoplasm, in contrast to the type 1-like phosphatase dis2, which is enriched in the nucleus. Overproduced ppa1 or ppa2 proteins accumulate in the cytoplasm near the nuclear periphery, and cells arrest in interphase. Okadaic acid-treated cells, like a ppa2 deletion, are short in length and display protein hyperphosphorylation. Cytokinesis is also inhibited, producing binucleated cells. We show that ppa2 is the genetic locus controlling okadaic acid sensitivity. The ppa2 deletion reveals the same hyperphosphorylated proteins as okadaic acid. When a strain deleted for ppa2 is treated with okadaic acid, cell size is reduced further to that of wee1-50 mutant strain or overexpressing the cdc25+ gene product, suggesting functional relationship of ppa2 with the cdc25 tyrosine phosphatase and/or the wee1 kinase in cell cycle control.

Mitotic regulation of protein phosphatases by the fission yeast sds22 protein

BACKGROUND

Cell cycle progression requires the activity of protein kinases and phosphatases at critical points in the cell cycle in all eukaryotes. We have previously reported that the dis2(+) and sds2(+) genes of fission yeast encode redundant catalytic subunits of a type 1-like protein phosphatase. The sds22(+) gene was shown to be essential for cell viability and to interact genetically with dis2(+) and sds21(+).

RESULTS

Here we show by immunoprecipitation that the sds22 protein physically interacts with the dis2 and sds21 proteins, and that sds22-associated phosphatase activity has altered substrate specificity, The loss of sds22 function by a temperature sensitive mutation leads to cell cycle arrest at mid-mitosis, at which point cdc2-dependent histone Hl kinase activity is high while sds22-dependent H1 phosphatase activity is low. To examine the unusual properties of sds22 protein structure, we analyzed a collection of sds22 deletion and point mutants by a variety of functional criteria.

CONCLUSION

We propose that sds22 is a regulatory subunit of the dis2/sds21 phosphatase catalytic subunits and that sds22-bound phosphatase carries a key phosphatase activity essential for the progression from metaphase to anaphase. Mutational analysis indicates that dis2/sds21 interacts with the central repetitive domain of sds22, while the C-terminal and central regions of sds22 may be involved in subcellular targeting and the N-terminus is important for stability.

Cyclin-dependent kinase 2 (cdk2) in the murine Cdc2 kinase TS mutant

Kinases of the mammalian cdc2 family including cdk2 (cyclin-dependent kinase 2) are thought to be involved in both the G2/M transition and DNA replication. To investigate the role of cdc2 kinase and cdk2 in cell cycle progression, murine tsFT210 cells bearing a temperature-sensitive cdc2 mutation were used. These kinases were purified by column chromatography, using a peptide with the consensus phosphorylation site of cdc2 kinase as the substrate. In this mutant, cdc2 kinase activity was temperature sensitive and cdk2 activity was not. At the restrictive temperature, the mutant was only arrested in the G2 phase and not in the G1-S phase, suggesting that cdk2 did not compensate for cdc2 kinase at the G2/M transition but did function at the G1-S phase. This suggestion was supported by the finding that transfection of cdk2 cDNA did not improve the growth of the mutant cell line at the restrictive temperature, although transfection of cdc2 cDNA did.

The cell cycle regulator, human p50weel, is a tyrosine kinase and not a serine/tyrosine kinase

The human weel protein, a homologue of the yeast weel protein, was expressed in E. coli and purified to homogeneity. The purified weel protein phosphorylated the tyrosine residue of cdc2 kinase in HeLa cell extracts in the presence of human cyclin B1. It also phosphorylated the tyrosine but not the threonine residue in the peptide of the amino-terminal of cdc2 kinase, although both these residues have been shown to be phosphorylated in higher eukaryotes in vivo. Furthermore, serine and tyrosine residues of the yeast weel protein are reportedly autophosphorylated in vitro, however the tyrosine residue of the human weel protein was autophosphorylated whereas the serine and threonine residues were not. These data indicate that human p50weel is tyrosine kinase and that it phosphorylated the tyrosine residue of the amino-terminal of cdc2 kinase in the presence of cyclin B1 and that the threonine residue is phosphorylated by another, unknown kinase.

M-phase-specific histone H1 kinase in fish oocytes. Purification, components and biochemical properties

We demonstrate, for the first time in fish, that a Ca(2+)-independent and cyclic-nucleotide-independent histone H1 kinase activity oscillates according to the cell cycle of the oocyte, peaking at the first and the second meiotic metaphase with a transient drop between them. The kinase, M-phase-specific histone H1 kinase (M-H1K), was purified from mature carp oocytes by using two exogenous substrates for assaying its activity: histone H1 and a synthetic peptide (SP peptide, KKAAKSPKKAKK) containing the sequence KSPKK, which includes the consensus sequence of the site phosphorylated by a serine/threonine-specific protein kinase encoded by the fission yeast cdc2+ gene (cdc 2 kinase). The M-H1K and maturation-promoting factor (MPF) activities coincided closely throughout four steps of purification, strongly suggesting the identity of M-H1K and MPF. The final preparation was purified 5000-fold with a recovery of 4%, when histone H1 was used for the kinase assay, and 10,000-fold with a recovery of 7% when SP peptide was used. The purified molecular mass of the kinase was estimated to be 100 kDa by gel filtration and contained four proteins of 33, 34, 46 and 48 kDa. Anti-PSTAIR antibody recognizing cdc2 kinase cross-reacted with the 33-kDa and 34-kDa proteins, while the 46-kDa and 48-kDa bands cross-reacted with monoclonal antibodies raised against cyclin B. The 33-kDa protein was also recognized by an antibody against a goldfish cdk2 (Eg1) kinase, a cdc2-related kinase which has the PSTAIR sequence and binds to p13suc1 but does not form a complex with cyclin B. M-H1K activity corresponded well to the 34-kDa, 46-kDa and 48-kDa proteins but not to the 33-kDa protein. These results strongly suggest that M-H1K consists of cdc2 kinase forming a complex with cyclin B, and that cdk2 kinase is not a component of M-H1K, although it is found in the highly purified M-H1K. The purified M-H1K utilized Mg2+, Mn2+, ATP and GTP, and had a wide pH optimum ranging over 8.0-10.5. The kinase was thermolabile and sensitive to freezing/thawing.

A temperature-sensitive CHO-K1 cell mutant (tsTM13) defective in chromosome decondensation and spindle deconstruction in M phase

A temperature-sensitive CHO-K1 cell mutant, tsTM13, exhibited a delayed cell cycle progression from metaphase to telophase at a nonpermissive temperature and was finally arrested from anaphase to telophase. Metaphase chromosomes were overcondensed and chromosome disjunction in anaphase was uncoordinated. In telophase, sister chromatids were segregated and cytokinesis was completed, but chromosome structure remained in a condensed state and the spindle was not deconstructed. The level of phosphorylation of histones H1 and H3 remained high in the later stages of mitosis and the activity of histone H1 kinase was also maintained at a high level. These results strongly suggest that the pleiotropic defects of tsTM13 cells in mitosis are associated with a lack of inactivation of activated histone H1 kinase.

Microtubule destabilization by cdc2/H1 histone kinase: phosphorylation of a "pro-rich region" in the microtubule-binding domain of MAP-4

Microtubule-associated protein-4 (MAP-4), a major MAP in proliferating cells, consists of a microtubule-binding domain and a projection domain protruding from the microtubule wall. The former contains a Pro-rich region and an assembly-promoting (AP) sequence region which is common to the neuron-specific MAPs, MAP-2 and tau1. In this paper, we describe the phosphorylation of the Pro-rich region of MAP-4 and the suppression of its assembly-promoting activity by cdc2/H1 histone kinase. This inactivation of MAP-4 may cause disassembly of the interphase microtubular network at the end of the G2 phase of the cell cycle.