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The present study aimed to evaluate the inhibitory effects of an irinotecan derivative, ZBH‑1208, on brain tumors, and to explore the underlying molecular mechanisms. To determine the effects of ZBH‑1208, a brain tumor mouse model was established by transplanting B22 cells. Subsequently, the visceral indices of immune organs and white blood cell counts were determined, and the effects of ZBH‑1208 on the expression levels of cell cycle‑related proteins were assessed by western blotting. The tumor inhibition rates of 20 and 40 mg/kg ZBH‑1208 were 11.7 and 54.1%, respectively. Compared with the negative control group, ZBH‑1208 barely affected visceral indices or white blood cell count. Furthermore, the expression levels of p53, p21, cyclin‑dependent kinase 7 (CDK7), Wee1, phosphorylated (p)‑cell division cycle 2 (CDC2) (Tyr15), p‑CDC2 (Thr161) and cyclin B1 proteins were upregulated, whereas the expression levels of cyclin E were downregulated, and those of CDC2, CDK2 and CDC25C were barely altered. In conclusion, the present study demonstrated that ZBH‑1208 suppressed the growth of B22 mouse brain tumor xenografts, but did not affect their visceral indices or white blood cell counts. It was suggested that ZBH‑1208 exerted its effects by regulating the expression of p53, p21, Wee1, p‑CDC2 (Tyr15) and cyclin E proteins.

Quantitative measurement of enzyme activity is a valuable approach to study how cells function. We present a method to measure the activity of the enzyme Cdk1/cyclin B. This enzyme is required by all eukaryotic cells to enter mitosis. Therefore, a biochemical assay to measure Cdk1/cyclin B activity can be used to identify cell populations that are in mitosis or to detect inhibitors of Cdk1/Cyclin B in vitro. A key distinction of the method presented here, compared to others, is that it uses a recombinant protein, a specific antibody, and a western blot apparatus, which makes the technique available to cell and molecular biology laboratories who do not wish to use radioisotopes, which are commonly required for other protein kinase assays.

Helicobacter pylori at multiplicity of infection (MOI ≥ 50) have been shown to cause apoptosis in RAW264.7 monocytic macrophage cells. Because chronic gastric infection by H. pylori results in the persistence of macrophages in the host's gut, it is likely that H. pylori is present at low to moderate, rather than high numbers in the infected host. At present, the effect of low-MOI H. pylori infection on macrophage has not been fully elucidated. In this study, we investigated the genome-wide transcriptional regulation of H. pylori-infected RAW264.7 cells at MOI 1, 5 and 10 in the absence of cellular apoptosis. Microarray data revealed up- and down-regulation of 1341 and 1591 genes, respectively. The expression of genes encoding for DNA replication and cell cycle-associated molecules, including Aurora-B kinase (AurkB) were down-regulated. Immunoblot analysis verified the decreased expression of AurkB and downstream phosphorylation of Cdk1 caused by H. pylori infection. Consistently, we observed that H. pylori infection inhibited cell proliferation and progression through the G1/S and G2/M checkpoints. In summary, we suggest that H. pylori disrupts expression of cell cycle-associated genes, thereby impeding proliferation of RAW264.7 cells, and such disruption may be an immunoevasive strategy utilized by H. pylori.

The maintenance of T cell memory is critical for the development of rapid recall responses to pathogens, but may also have the undesired side effect of clonal expansion of T effector memory (T(EM)) cells in chronic autoimmune diseases. The mechanisms by which lineage differentiation of T cells is controlled have been investigated, but are not completely understood. Our previous work demonstrated a role of the voltage-gated potassium channel Kv1.3 in effector T cell function in autoimmune disease. In the present study, we have identified a mechanism by which Kv1.3 regulates the conversion of T central memory cells (T(CM)) into T(EM). Using a lentiviral-dominant negative approach, we show that loss of function of Kv1.3 mediates reversion of T(EM) into T(CM), via a delay in cell cycle progression at the G2/M stage. The inhibition of Kv1.3 signaling caused an up-regulation of SMAD3 phosphorylation and induction of nuclear p21(cip1) with resulting suppression of Cdk1 and cyclin B1. These data highlight a novel role for Kv1.3 in T cell differentiation and memory responses, and provide further support for the therapeutic potential of Kv1.3 specific channel blockers in T(EM)-mediated autoimmune diseases.

Objective: The expression of cytokine-associated genes in dendritic cells (DCs) derived from umbilical cord blood (UCB) and adult peripheral blood (APB) was comprehensively compared in order to elucidate the difference in DC function between newborns and adults., Study Design: Immature DCs were obtained from UCB and APB of healthy human donors. Several cytokines were added to generate mature DCs. Gene expression was compared using cDNA microarray containing 553 cytokine-associated genes. Eleven genes with differential expression were selected and determined their expression levels in DCs by quantitative real-time RT-PCR., Results: The expression of the Th1 response-related genes (IL-12B and IL-18) and chemokine genes (CXCL9, CXCL13, CCL18 and CCL24) was significantly lower in UCB-DCs than in APB-DC in both maturation states. On the other hand, calgranulins A and B, which are speculated to induce immune tolerance, showed higher expression in UCB-DCs. The expression of cell cycle-related genes (CDC2 and cyclin B1) was significantly higher in UCB-DCs than in APB-DCs, and immature UCB-DCs proliferated more rapidly than immature APB-DCs., Conclusion: The expression of genes related to immune responses was significantly different between UCB- and APB-DCs, which may cause a decreased DC-mediated immunity and an increased susceptibility to infection in newborns.

CCR7 and its ligands, CCL19 and CCL21, are responsible for directing the migration of T cells and dendritic cells into lymph nodes, where these cells play an important role in the initiation of the immune response. Recently, we have shown that systemic application of CCL19-IgG is able to inhibit the colocalization of T cells and dendritic cells within secondary lymphoid organs, resulting in pronounced immunosuppression with reduced allograft rejection after organ transplantation. In this study, we demonstrate that the application of sustained high concentrations of either soluble or immobilized CCL19 and CCL21 elicits an inhibitory program in T cells. We show that these ligands specifically interfere with cell proliferation and IL-2 secretion of CCR7(+) cells. This could be demonstrated for human and murine T cells and was valid for both CD4(+) and CD8(+) T cells. In contrast, CCL19 had no inhibitory effect on T cells from CCR7 knockout mice, but CCR7(-/-) T cells showed a proliferative response upon TCR-stimulation similar to that of CCL19-treated wild-type cells. Furthermore, the inhibition of proliferation is associated with delayed degradation of the cyclin-dependent kinase (CDK) inhibitor p27(Kip1) and the down-regulation of CDK1. This shows that CCR7 signaling is linked to cell cycle control and that sustained engagement of CCR7, either by high concentrations of soluble ligands or by high density of immobilized ligands, is capable of inducing cell cycle arrest in TCR-stimulated cells. Thus, CCR7, a chemokine receptor that has been demonstrated to play an essential role during activation of the immune response, is also competent to directly inhibit T cell proliferation.

The majority of cancer therapeutics induces DNA damage to kill cells. Normal proliferating cells undergo cell cycle arrest in response to DNA damage, thus allowing DNA repair to protect the genome. DNA damage induced cell cycle arrest depends on an evolutionarily conserved signal transduction network in which the Chk1 kinase plays a critical role. In mammalian cells, the p53 and RB pathways further augment the cell cycle arrest response to prevent catastrophic cell death. Given the fact that most tumor cells suffer defects in the p53 and RB pathways, it is likely that tumor cells would depend more on the Chk1 kinase to maintain cell cycle arrest than would normal cells. Therefore Chk1 inhibition could be used to specifically sensitize tumor cells to DNA-damaging agents. We have previously shown that siRNA-mediated Chk1 knockdown abrogates DNA damage-induced checkpoints and potentiates the cytotoxicity of several DNA-damaging agents in p53-deficient cell lines. In this study, we have developed 2 potent and selective Chk1 inhibitors, A-690002 and A-641397, and shown that these compounds abrogate cell cycle checkpoints and potentiate the cytotoxicity of topoisomerase inhibitors and gamma-radiation in p53-deficient but not in p53-proficient cells of different tissue origins. These results indicate that it is feasible to achieve a therapeutic window with 1 or more Chk1 inhibitors in potentiation of cancer therapy based on the status of the p53 pathway in a wide spectrum of tumor types., (Copyright 2006 Wiley-Liss, Inc.)

The G2 to M phase transition in perch oocytes is regulated by maturation promoting factor (MPF), a complex of Cdc2 and cyclin B. In Anabas testudineus, a fresh water perch, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, the maturation inducing hormone (MIH), induced complete germinal vesicle breakdown (GVBD) of oocytes at 21 h. An unusual cyclin, p30 cyclin B, has been identified in oocyte extract using both monoclonal and polyclonal antibodies. Surprisingly, Cdc2 could not be identified, although a Northern blot with Cdc2 cDNA demonstrated expression of the gene. Purification of MPF through an immunoaffinity column followed by SDS-PAGE showed three proteins, Cdc2, cyclin B, and a 20 kDa fragment, indicating earlier failure in immunodetection may be due to the interference by this fragment. In uninduced oocytes, p30 cyclin B was present, and its expression was increased by MIH. MIH increased p30 cyclin B accumulation at 3 h, a high level which was maintained between 9 and 21 h, but an effective increase in GVBD and H1 kinase activation could only be observed between 15 and 21 h. This delay in active MPF formation was found to be related to the activation of Cdc25, phosphorylation of which was detected at 12 h, and a substantial increase occurred during 15-18 h. Sodium orthovanadate, a tyrosine phosphatase inhibitor, inhibited H1 kinase activity and GVBD, suggesting the requirement of Cdc25 activity in MPF activation. Our results show occurrence of pre-MPF in uninduced oocytes and its conversion to active MPF requires dephosphorylation by Cdc25, the existence of which has not yet been shown in fish.

We report on the in vivo uptake of antibodies into plant protoplasts. When protoplasts of sunflower, Arabidopsis or tobacco were incubated in vivo with an antibody, this antibody was detected by immunofluorescence in the cytoplasm and/or the nucleus, depending on the location of the target protein. Furthermore, when protoplasts were cultured in the presence of antibodies, specific effects were observed. Incubation with antibodies raised against p34cdc2 led to a strong inhibition of the division rate, and a decrease in the average DNA content of protoplasts. With antibodies against HaWLIM1, a LIM domain protein of the CRP type, a negative effect on actin organisation was observed. We conclude that antibodies can penetrate plant protoplasts in vivo, and thus may be used as powerful tools for the study of protein function.

In order to obtain recombinant antibody fragments that bind the cell-cycle protein CDC2a from Arabidopsis thaliana (CDC2aAt), two phage display libraries of single-chain variable (scFv) fragments were constructed. One library was derived from mice immunized with recombinant CDC2aAt N-terminally fused to a His6-tag (His-CDC2aAt) and the other was made out of an anti-PSTAIRE hybridoma cell line. Six specific His-CDC2aAt-binding phage clones (3D1, 3D2, 3D10, 3D25, 4D21 and 4D47) were isolated by panning. The isolated monoclonal phage clones, as well as the soluble scFv fragments produced in the periplasm of Escherichia coli, bind His-CDC2aAt in ELISA and on Western blots. Moreover, four clones (3D1, 3D2, 3D10 and 4D21) detect specifically CDC2aAt from Arabidopsis cell suspensions on Western blots. Clone 4D21 binds the PSTAIRE epitope, whereas the 3D1, 3D2 and 3D10 clones bind, as yet unidentified, epitopes of CDC2aAt. Furthermore, the accumulation and antigen-binding activity of these scFv fragments in a reducing environment were assessed. No interaction could be shown between the scFv fragments and CDC2aAt in a yeast two-hybrid assay. However, after transient expression of the scFv fragments in the cytosol of tobacco leaves, three of six scFv fragments (3D1, 3D2 and 3D10) accumulated in the plant cytosol and ELISA results indicate that these scFv fragments retained antigen-binding activity.

A key regulator of the cell cycle is a highly conserved protein kinase whose catalytic subunit, p34cdc2, is encoded by cdc2 gene. Immunoblotting with a polyclonal antibody raised against PSTAIRE sequence (found in the N-terminal region of all cdc2 and cdc2 related proteins throughout the phylogenetic scale including higher plants), was used to study the presence of p34cdc2 in onion scale leaves and root tip cells. p34cdc2 homologues are beyond the detection level in scale leaves. PSTAIRE antibody was used to estimate p34cdc2 kinase protein levels during cell cycle in highly synchronous population of Allium cepa L. root meristem cells. p34cdc2 kinase protein showed gradual increase in their levels from S phase to G2 phase boundary. Immunoprecipitation followed by in vitro histone H1 kinase assays also depicted that its kinase activity increased parallel to the increase in p34cdc2 level.

We have shown previously that M-phase phospho-epitopes accumulate in neuronal tau proteins incorporated into the hallmark neurofibrillary tangles (NFT) of Alzheimer's disease (AD). In M phase, the epitopes are produced by cdc2/cyclin B1 kinase by a highly conserved mechanism believed to be quiescent in terminally differentiated neurons of adult brain. To determine whether an M-phase mechanism is possible in AD neurons, we first investigated the presence of cdc2 and cyclin B1 in AD. Both proteins were enriched in neurons with NFT and in neurons susceptible to NFT. An antibody specific for catalytically active cdc2 stained numerous NFT-containing neurons in AD but did not react with normal neurons. Double-labeling studies showed that active cdc2 and cyclin B1 coexist in AD neurons and co-localize with AD-specific mitotic phospho-epitopes. Mitotic kinase purified from AD and normal brain, using the yeast p13suc1 protein as affinity ligand, showed higher histone H1 phosphorylation activity in AD. Accordingly, the levels of cdc2 and cyclin B1 in p13suc1 fractions from AD were higher than normal. Consistent with a physiological relationship between NFT and mitotic kinase, NFT proteins co-purified with and became phosphorylated by the p13suc1-bound kinase in vitro. Furthermore, cdc2/cyclin B1 is the only one of several proline-directed kinases that created the TG/MC mitotic phospho-epitopes in recombinant tau in vitro. These findings suggest that aberrantly reexpressed cdc2/cyclin B1 in NFT-bearing neurons in AD brain contributes to the generation of M-phase phospho-epitopes in NFT.

The cell cycle is driven by the sequential activation of a family of cyclin-dependent kinases (CDK) in association with cyclins. In mammalian cells the timing of activation of cyclin A-associated kinase activity coincides with the onset of DNA synthesis in S-phase. Using in vitro replication of SV40 origin-containing DNA as a model system, we have analyzed the proteins associated with DNA during initiation of DNA replication in S-phase cell extracts. This analysis reveals that, in addition to replication initiation proteins, cyclin A and cdk2 are also specifically associated with DNA. The association of cyclin A and cdk2 with DNA during initiation is cell cycle regulated and occurs specifically in the presence of SV40 origin-containing plasmid and SV40 T antigen (the viral replication initiator protein). The interactions among proteins involved in initiation play an important role in DNA replication. We therefore investigated the ability of cyclin A and cdk2 to associate with replication initiation proteins. Under replication initiation conditions, cyclin A and cdk2 from S-phase extracts specifically associate with SV40 T antigen. Further, the interaction of cyclin A-cdk2 with SV40 T antigen is mediated via cyclin A, and purified recombinant cyclin A associates directly with SV40 T antigen. Taken together, our results suggest that cyclin A and cdk2 are components of the SV40 replication initiation complex, and that protein-protein interactions between cyclin A-cdk2 and T antigen may facilitate the association of cyclin A-cdk2 with the complex.

Activated Xenopus egg extracts are capable of undergoing cell-free cell cycling. Using these activated extracts, we previously showed that purified, bacterially expressed oncogenic human RasH protein arrests cell cycle progression. Because oncogenic Ras activates many serine/threonine protein kinases in Xenopus oocytes and egg extracts, it is possible that induction of cell cycle arrest involves the action of oncogenic Ras-activated kinases. Thus, the identification of the physiological substrates for oncogenic Ras-activated kinases is important for elucidating the molecular mechanism underlying oncogenic Ras-induced cell cycle arrest. We used 32P-orthophosphate as a label to identify the potential substrates. Our results demonstrated that the 32P-labeling of both a 32 and a 33 kDa protein were greatly enhanced by oncogenic Ras during the incubation of activated Xenopus egg extracts. The enhanced labeling correlated with the induced cell cycle arrest and was contributed by serine phosphorylation. Moreover, the 33 kDa protein was detected only in the presence of oncogenic Ras and was a serine-hyperphosphorylated form of the 32 kDa protein. Furthermore, new protein synthesis was not required for the enhanced labeling, consistent with the concept that the enhanced serine phosphorylation of the 32 kDa protein is by oncogenic Ras-activated protein kinases. In addition to serine phosphorylation, our results also suggested that an as yet unidentified modification of the 32 kDa protein might also be induced by oncogenic Ras. Our results suggest that the 32 kDa protein is a potential physiological substrate for oncogenic Ras-activated protein kinases.

We here describe an alternative way to microinjection by which cellular transport of immunoglobulins through surface membranes can be achieved after binding to specific surface receptors either induced or constutively present, or via Fc receptors (Ig-mediated). In this report, the internalisation of two antibodies in two different cellular systems is analysed: the anti-p21ras monoclonal antibody (MoAb) after surface Ig binding on murine placental cells and anti-cdc2 MoAb that binds directly to its surface receptor expressed on the human promyelocytic leukemia cell line HL-60. In both cases, binding and internalisation is followed by Electron Microscopy (EM) and function is assessed by different assays. The first involves abrogation of class II antigen expression induced by Interferon-gamma (IFN-gamma) and 5-Azacytidine (5-AzaC) known to be mediated by activation of the ras pathway. The second involves growth cessation of HL-60 cells after antibody adsorption when a G1-S-specific culture supernatant containing anti-cdc2 activity is employed, whereas no growth hindrance is observed when a G2-M-specific anti-cdc2 MoAb is used. Thus, the antibodies do not follow the lysosyme pathway and do not lose their functional activity. This method may be applied in the future in order to achieve biological or clinical therapies.

An immunoprecipitation assay was used to identify protein kinases which are physically associated with neurofilaments (NF) in mouse brain extracts. Using this approach, we show that a cdc2-related kinase is associated with NF. The cdc2-related kinase was found to be distinct from cdk5 and the authentic cdc2 by a number of criteria. Firstly, it has a molecular mass on SDS-PAGE gels of 34 kDa, similar to that of cdc2, but differing from cdk5 (31 kDa). Secondly, it is not recognized by an antibody specific for cdk5. Thirdly, it is recognized by an antibody raised against the C-terminal region of authentic cdc2, but not by an antibody specific for the PSTAIRE motif. Using immunoblotting, we further show that the cdc2-related kinase copurifies with NF isolated from rat tissues. In vitro kinase assays further demonstrated that immunoprecipitated cdc2-related kinase phosphorylates recombinant NF-H protein. Phosphorylation of NF-H by the cdc2-like activity was not affected by 3 microM olomoucine but was inhibited by 10 microM of this kinase inhibitor. Phosphoamino acid analysis of in vitro phosphorylated NF-H indicates that the immunoprecipitated cdc2-related kinase phosphorylates serine residues.

Since malignant cell proliferation occurs at the expense of cell differentiation, we examined the possibility of differentiating malignant cells from mature cells by altering the regulation of the cell cycle. Using the human promyelocytic leukemia cell line HL-60, which expresses p34cdc2, the product of the cdc2 gene that controls the cell cycle, we showed that guided internalization of an anti-cdc2 monoclonal antibody could initiate differentiation not yet described for other cells of myeloid malignant origin. Experimental cellular manipulation may be employed as a method of inducing in vitro differentiation for transplantation purposes.

Intercellular adhesion molecules (ICAM)-1 and -3 coexist on T lymphocytes and are counter-receptors for the integrin LFA-1. Signaling through ICAM-3 stimulates a number of T cell functions and involves phosphorylation of Fyn, Lck, CD45, and other proteins. In contrast, this type of specific signaling event has not been described for signaling through ICAM-1. Here, tyrosine phosphorylation of cellular proteins was examined after cross-linking of ICAM-1. Tyrosine phosphorylation of the 34-kDa cdc2 protein kinase was induced transiently after stimulation of the leukemic T cell line, Molt-3, or peripheral blood T cells. Stimulation through ICAM-1 had no effect on constitutive presence of cdc2 or phosphorylation of cdc2 on threonine. cdc2 kinase activity was constitutive in peripheral blood T cells, and transient inhibition of kinase activity after ICAM-1 stimulation correlated kinetically with phosphorylation of cdc2 on tyrosine.

The meiotic maturation of Xenopus oocytes triggered by progesterone requires new protein synthesis to activate both maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAP kinase). Injection of mRNA encoding mutant p34cdc2 (K33R) that can bind cyclins but lacks protein kinase activity strongly inhibited progesterone-induced activation of both MPF and MAP kinase in Xenopus oocytes. Similar results were obtained by injection of GST-p34cdc2 K33R protein or by injection of a monoclonal antibody (A17) against p34cdc2 that blocks its activation by cyclins. Both the dominant-negative p34cdc2 and monoclonal antibody A17 blocked the accumulation of p39mos and activation of MAP kinase in response to progesterone, as well as blocking the appearance of MPF, although they did not inhibit the translation of p39mos mRNA. These results suggest that: (i) activation of free p34cdc2 by newly made proteins, probably cyclin(s), is normally required for the activation of both MPF and MAP kinase by progesterone in Xenopus oocytes; (ii) the activation of translation of cyclin mRNA normally precedes, and does not require either MPF or MAP kinase activity; and (iii) de novo synthesis and accumulation of p39mos is probably both necessary and sufficient for the activation of MAP kinase in response to progesterone.

The immunoreactivity of cortical and brainstem-type Lewy bodies has been investigates with antibodies to the cyclin-dependent kinase 5 (cdk5), to the extracellular regulated kinase 1 (ERK-1), and to the cdc2p34 kinase and with antibodies specific for phosphorylation epitopes typical of paired helical filament-tau (PHF-tau). Both cortical and brainstem-type Lewy bodies in diffuse Lewy body disease and brainstem-type Lewy bodies in Parkinson's disease were found to be immunoreactive for cdk5 but not for cdc2p34 or ERK-1 or with the PHF-tau antibodies. Double immunolabeling showed that cdk5-positive Lewy bodies were also ubiquitin immunoreactive and that cdk5 antibodies labeled as many Lewy bodies as ubiquitin antibodies in adequately fixed tissue. The cdk5 immunoreactivity of Lewy bodies was abolished by preabsorption of the antibody with a cdk5 peptide. The antibodies to cdk5 labeled a single 33-kd species on Western blots of human brain homogenates, with a similar intensity in control, diffuse Lewy body disease, and Alzheimer's disease, and this cdk5 species was found mainly in the particulate fraction of brain homogenates. This observation suggests that cdk5 might be a protein kinase involved in the phosphorylation of a molecular component of Lewy bodies, for example, neurofilament proteins known to be present in these inclusions.

We have monitored the tyrosine (Y15) phosphorylated and dephosphorylated forms of p34cdc2 from Schizosaccharomyces pombe as cells proceed through the cell cycle. Y15 is dephosphorylated in G1 before start and becomes phosphorylated only after cells pass start and enter late G1. This transition is associated with a switch from one checkpoint which restrains mitosis in pre-start G1, by a mechanism independent from Y15 phosphorylation, to a second checkpoint acting post-start during late G1 and S phase operating through Y15 phosphorylation. The pre-start checkpoint may act by preventing formation of the p34cdc2/p56cdc13 complex. The complex between Y15-phosphorylated p34cdc2 and p56cdc13 accumulates during S phase and G2, but the level generated is not solely dependent on the amount of p34cdc2 and p56cdc13 present in the cell. The extent of p56cdc13 breakdown at the end of mitosis may be determined by the amount complexed with p34cdc2. We have also shown that an insoluble form of p34cdc2 is associated with the progression of the cell through late G1 into S phase.

p34cdc2 protein kinase is a component of M phase-promoting factor (MPF), which plays an important role in controlling the mitotic and meiotic cell cycle. p34cdc2 contains a unique 16 amino acid sequence (PSTAIR) that is conserved from fission yeast to human. Using polyclonal anti-PSTAIR antibody, we detected the p34cdc2 homologue in the central nervous system of adult mice by western blotting. By immunohistochemical technique, we found that the p34cdc2 homologue was located in the nucleoli of neurons and glia in the central and peripheral nervous systems. In the central nervous system, positive cells were widely distributed from the cerebral cortex to the spinal cord. Immunoreactive cells were also detected in retina and pituitary. The evidence that the p34cdc2 is present in neurons which have lost the ability of cell division predicts another function of p34cdc2 family proteins besides the one that has generally recognized.

Mice and rabbits were injected with various forms of a 16 amino acid synthetic peptide representing PSTAIR, the evolutionarily conserved region of the protein kinase p34cdc2, for polyclonal antisera and hybridoma-monoclonal antibody production. Antisera from mice injected with an unconjugated monomeric form of the peptide showed no reaction to the peptide. Of four animals injected with the monomeric form of the peptide conjugated to keyhole limpet hemocyanin via m-maleimidobenzoyl-N-hydroxysulfosuccinimide (MBS), antisera from only one mouse had a very low titer to the peptide, and all four animals produced antibody to the MBS bridge. Both mice injected with an octameric multiple antigen peptide (MAP) of PSTAIR produced antisera reactive to the octameric MAP form of the peptide in ELISA and also to the cdc2 protein expressed in bacteria in an immunoblotting assay. Splenocytes from one mouse injected with the octameric MAP form of the peptide were successfully used for hybridoma-monoclonal antibody production. A monoclonal antibody was produced that reacted with octamer, monomer and cdc2-expressed protein and specifically with the carboxyl terminus of the 16 amino acid peptide.

Glial fibrillary acidic protein (GFAP) is a component of glial filaments specific to astroglia. We now report the spatial and temporal distributions of four phosphorylated sites in the GFAP molecule during mitosis of astroglial cells, determined by antibodies which can distinguish phosphorylated epitopes from non-phosphorylated-epitopes. Immunofluorescence microscopy showed that the Ser8 residues in the entire cytoplasmic glial filament system are initially phosphorylated when the cells enter mitosis. In cytokinesis, the phosphoSer8 residues become dephosphorylated, whereas Thr7, Ser13 and Ser34 in glial filaments at the cleavage furrow become the preferred sites of phosphorylation. The cdc2 kinase purified from mitotic cells can phosphorylate GFAP at Ser8 but not at Thr7, Ser13 or Ser34, in vitro. These results suggest that cdc2 kinase acts as a glial filament kinase only at the G2-M phase transition while other glial filament kinases are probably activated at the cleavage furrow before final separation of the daughter cells.

Studies on the functional and structural properties of the cdc2 kinase, a key cell-cycle regulator, have been possible thanks to the availability of cdc2-specific immunoreagents. In an attempt to elucidate the biochemical regulation of the cdc2 kinase in more detail, we have raised a series of novel mouse monoclonal antibodies against human recombinant cdc2 protein. The five Mab reported here can be subclassified into two groups according to their interspecies cross-reactivity and distinct immunoprecipitation patterns. Thus, the target epitopes of Mab POH-1, POH-2 and POH-7 (group 1) appear to be limited to a few mammalian species and the fraction of cdc2 immunoprecipitable by these Mab from cellular extracts is considerably enhanced by denaturation. In contrast, the POH-3 and POH-8 (group 2) Mab recognize a denaturation-sensitive epitope on cdc2 which is present in all tested mammalian species. More importantly, each of the two groups of Mab immunoprecipitate forms of cdc2 associated with a characteristic set of cellular proteins, none of which appears to be cyclin A or cyclin B. None of the antibodies precipitated a histone-H1 or casein-kinase activity, although an activity which phosphorylated some of the coprecipitated proteins was coprecipitated with the group 2 Mab. These novel Mab did not interfere with the association of cdc2 with cyclin A in vitro and efficient immunoprecipitation of a panel of cdc2 mutant proteins suggests that the target epitopes may not involve amino acid residues essential for currently known cdc2 functions. The results of the present study provide evidence for the existence of additional forms of the cdc2 protein in exponentially growing human cells, distinct from both the monomeric and the cyclin-bound cdc2 identified so far.

In yeast, the protein kinase p34cdc2 plays a role in regulating both the G2 to M and G1 to S phase transitions. The discovery of multiple homologues of the protein in cells of higher eukaryotic organisms suggests that different cell cycle regulatory events may be performed by different kinases in such cells. Here, the synthesis and metabolism of the human forms of these proteins are described in a normal human cell type, peripheral blood T lymphocytes that have been stimulated to enter the cell cycle in vitro. Using a carboxyl-terminus antiserum specific for true p34cdc2, the protein could first be found in T cells at about 24 to 30 h after stimulation, just before the initiation of DNA synthesis. Three forms of the enzyme could be resolved by denaturing gel electrophoresis: an unphosphorylated form with an apparent molecular mass of 34,500 daltons and two phosphorylated derivatives. In cells synchronized at G2/M phase with nocodazole, p34 was almost entirely in the unphosphorylated form whereas the phosphorylated derivatives were more predominant in cultures arrested at the G1/S border with aphidicolin. The relationship of p34 synthesis to the phosphorylation of p110Rb, an event known to be associated with passage through late G1 and/or the G1/S phase transition, was also investigated. It was noted that p110Rb phosphorylation began before p34 synthesis first became detectable. Furthermore, it appeared that the two events could be largely uncoupled by treating cells with deferoxamine (10 microM), an iron chelating agent that arrests T cells at a point in late G1 phase but substantially before the G1 to S phase transition. Under these conditions, p110Rb phosphorylation was almost completely accomplished in the absence of significant p34 synthesis, a finding that suggests that most or all of p110 phosphorylation is performed by kinases other than p34. Because of this observation, extracts were next examined for p34-like molecules using an antibody against the so-called PSTAIRE domain found in all cdc2 homologues identified to date. A species of protein with a mobility slightly less than true p34 was found, even in resting T cells. Upon stimulation, this protein increased slightly in amount, and a second protein with a mobility greater than p34, a putative p33cdk2, was seen. Not only was the appearance of these proteins not inhibited by deferoxamine but they accumulated in cultures treated with the drug, suggesting that p33, and not p34, may be the G1 phase kinase for p110Rb.(ABSTRACT TRUNCATED AT 400 WORDS)

A homologue of the ubiquitous eukaryotic cell cycle regulatory gene, cdc2, has been cloned from Pisum sativum, the garden pea. A novel immunological strategy was devised and implemented for screening PCR products generated by degenerate oligonucleotide primers. We used PCR to construct a deletion derivative of an Escherichia coli expression plasmid carrying the Schizosaccharomyces pombe cdc2 gene. The deleted segment encoded the domain recognized by monoclonal antibody MAb-J4, a reagent which also detects a single protein in extracts of all plant species we have examined. PCR products, generated by appropriate cdc2 primers, were ligated into new restriction sites flanking the deletion, reconstituting the deleted epitope. This strategy, first validated on a cloned yeast cdc2 template as control, was applied to the highly efficient cloning of a cDNA segment comprising 60% of the pea cdc2 homologue. DNA sequencing revealed strong amino acid sequence conservation among the cdc2 gene products from pea, yeast and animal cells. Genomic Southern analysis indicated that the cdc2 gene occurs as a single copy in pea. An additional cdc2-like clone was recovered which displays amino acid sequence similarity with that of pea cdc2. The reported cloning and screening strategy, though limited by the availability of appropriate immunological reagents, provides not only an efficient means of screening heterogeneous PCR products generated by degenerate probes and/or low stringency PCR, but also product verification by immunological criteria.

Faithful and efficient transcription initiation at the mouse ribosomal gene promoter requires besides RNA polymerase I (pol I) four polypeptide trans-acting factors, termed TIF-IA, TIF-IB, TIF-IC, and mUBF. We have partially purified these proteins from cultured Ehrlich ascites cells and show that in the presence of TIF-IA and TIF-IB, pol I directs very low amounts of specific transcripts. Neither TIF-IC nor mUBF on their own significantly stimulate the efficiency of template utilization. However, both factors together strongly activate transcription. Interestingly, factor TIF-IB - the murine homologue of human SL1 - fails to program a human extract to transcribe the murine template, but requires its homologous RNA polymerase I. This finding implicates that not only some rDNA transcription factors but also pol I exhibits species-specific differences. The growth-related factor TIF-IA, on the other hand, stimulates both mouse and human rDNA transcription. This regulatory factor whose amount or activity fluctuates according to the proliferation rate of the cells, is functionally inactivated by antibodies against cdc2 protein kinase. This result together with the observation that transcription is stimulated by ATP-gamma S, an ATP analogue which is a substrate for protein kinases but not for protein phosphatases, strongly suggests that post-translational protein modification is involved in rDNA transcription regulation.

At the onset of mitosis, eukaryotic cells display an abrupt increase in a Ca2(+)- and cyclic nucleotide-independent histone H1 kinase activity, referred to as growth-associated or M phase-specific H1 kinase. The molecular basis for this activity is generally attributed to a kinase complex that consists of the p34cdc2 protein and cyclin, and exhibits maturation-promoting factor (MPF) activity. In the present study, we show that more than one kinase contributes to M phase-specific H1 kinase activity. When mature Xenopus oocyte extract prepared with ATP gamma S and NaF was fractionated by gel filtration, two prominent peaks of H1 kinase activity were detected, with apparent molecular masses of 600 and 150 kDa. The 150-kDa kinase copurified with the p34cdc2 protein and was immobilized by the suc 1 gene product p13 and anti-cyclin B2, which are specific for the cdc2 kinase complex. However, the 600-kDa kinase did not satisfy any of these criteria, thus identifying it as a novel M phase-specific H1 kinase. Only the 600-kDa kinase was recognized by the mitosis-specific monoclonal antibody, MPM-2, which inhibits Xenopus oocyte maturation and immunodepletes MPF activity. Furthermore, not only did the full activation of this kinase (MPM-2 kinase) coincide with the activation of MPF during the cell cycle, but also MPM-2 kinase-positive fractions obtained by gel filtration accelerated progesterone-induced oocyte maturation. It is, therefore, likely that MPM-2 kinase is a positive regulator in the M phase induction pathway.

The cdc2 kinase is a key regulator of the eukaryotic cell cycle. The activity of its catalytic subunit, p34cdc2, is controlled by cell cycle dependent interactions with other proteins as well as by phosphorylation--dephosphorylation reactions. In this paper, we examine the phosphorylation state of chicken p34cdc2 at various stages of the cell cycle. By peptide mapping, we detect four major phosphopeptides in chicken p34cdc2; three phosphorylation sites are identified as threonine (Thr) 14, tyrosine (Tyr) 15 and serine (Ser) 277. Analysis of synchronized cells demonstrates that phosphorylation of all four sites is cell cycle regulated. Thr 14 and Tyr 15 are phosphorylated maximally during G2 phase but dephosphorylated abruptly at the G2/M transition, concomitant with activation of p34cdc2 kinase. This result suggests that phosphorylation of Thr 14 and/or Tyr 15 inhibits p34cdc2 kinase activity, in line with the location of these residues within the putative ATP binding site of the kinase. During M phase, p34cdc2 is also phosphorylated, but phosphorylation occurs on a threonine residue distinct from Thr 14. Finally, phosphorylation of Ser 277 peaks during G1 phase and drops markedly as cells progress through S phase, raising the possibility that this modification may contribute to control the proposed G1/S function of the vertebrate p34cdc2 kinase.

Using probes obtained by PCR amplification, we have cloned Drosophila cDNAs encoding structural homologs of the p34cdc2 cell cycle kinase. Southern blot experiments and in situ hybridization to polytene chromosomes demonstrated that the isolated cDNAs, were derived from two distinct genes, Dm cdc2 (31E) and Dm cdc2c (92F). Northern blot and in situ hybridization experiments revealed that these two genes are coexpressed during embryogenesis and that expression is correlated with cell proliferation. However, despite the similarity in structure and expression, the two gene products differed in functional assays in yeasts. Expression of Dm cdc2 in Schizosaccharomyces pombe and Saccharomyces cerevisiae rescued cell cycle arrest caused by mutations in cdc2+ and CDC28, the genes encoding the p34cdc2 kinase homologs of these yeasts. In contrast, the Dm cdc2c gene product did not restore cell cycle progression. Thus, in addition to the identification of a functional homolog in Drosophila, our results indicate the presence of a closely related cognate of the p34cdc2 cell cycle kinase.

Changes in protein kinase activities are thought to contribute to the alteration of gene expression after heat shock and related stresses. In an attempt to identify enzymes which might be involved in both chromatin structure modification and transcriptional switch in heat-shocked cells, we have studied protein kinase activities in heat-shocked cell lysates with two exogenous substrates: a tetramer of a heptapeptide (heptapeptide 4) corresponding to the RNA polymerase II C-terminal domain (CTD), and the histone H1. Heat-shock and arsenite stress were found to stimulate strongly CTD kinase activity. H1 kinase activity was also stimulated but more weakly. Stimulation of CTD and H1 kinases occurs mainly at the early phase of recovery and by a process which is independent of protein synthesis. The stress-induced H1 kinase is shown to contain a molecule related to the mitotic-promoting factor (MPF) Cdc2 component. On the other hand, though Cdc2-related protein has also been reported to be part of a CTD kinase complex, we show that the stress-induced CTD kinase activity corresponds to a distinct entity. It is proposed that stress activation of CTD kinase might be involved in changing the specificity of RNA polymerase II.

Recent advances in the understanding of the molecular basis of cell cycle control, particularly that of mitotic control, are reviewed with respect to what is known about cell cycle control in early mouse embryos. The behaviour of the murine homologue of cdc2+, a component of Maturation Promotion Factor (MPF), is described at these early stages.

We investigated plant cell division by testing for the presence and involvement in progress through the division cycle of the protein p34cdc2, a key participant in division control in other eukaryotes. A protein of the same m(r) 34,000 has structural similarity indicated by its reaction with three sorts of antibody raised against (1) cell division-specific regions within a 16-amino acid internal sequence that is perfectly conserved in p34cdc2 from all known sources, (2) the carboxy-terminal 127 amino acids of human p34cdc2 linked to beta-galactosidase, and (3) whole p34cdc2 of fission yeast. Participation of p34 in the division cycle of the green plant Chlamydomonas is indicated by phosphorylation of the protein only in proliferating cells. There is a consistent fivefold increase relative to other proteins when cells become committed to division and a maximum of phosphorylation at the time of nuclear division under conditions that alter by twofold the time of these events. A p34 protein is detectable in oats and Arabidopsis and in remote taxa, including red and brown algae. We conclude that the plant kingdom shares a division control involving p34cdc2 that was probably established in the common ancestral eukaryote prior to divergence of any of the major eukaryote taxa.