Mos is a germ cell-specific serine/threonine kinase and is required for Xenopus oocyte maturation. Active Mos stimulates a mitogen-activated protein kinase (MAPK) by directly phosphorylating and activating MAPK kinase (MKK). We report here that the Xenopus homolog of the ␤ subunit of casein kinase II (CKII␤) binds to and regulates Mos. The Mos-interacting region of CKII␤ was mapped to the C terminus. Mos bound to CKII␤ in somatic cells ectopically expressing Mos and CKII␤ as well as in unfertilized Xenopus eggs. CKII␤ inhibited Mos-mediated MAPK activation in rabbit reticulocyte lysates and repressed MKK activation by v-Mos in a coupled kinase assay. In addition, microinjection of CKII␤ mRNA into Xenopus oocytes inhibited progesterone-induced meiotic maturation and MAPK activation, presumably by binding of CKII␤ to Mos and thereby inhibiting MAPK activation. Moreover, this inhibitory phenotype could be rescued by another protein that binds to CKII␤, CKII␣. The ability of ectopic CKII␤ to inhibit meiotic maturation and the detection of a complex between endogenous Mos and CKII␤ suggest that CKII␤ may act as an inhibitor of Mos during oocyte maturation, perhaps setting a threshold beyond which Mos protein must accumulate before it can activate the MAPK pathway.Mos is a germ cell-specific serine/threonine kinase and is present at a very low level in fully grown (stage VI) Xenopus oocytes (46,53,55,65). During oocyte maturation, mos translation is activated by progesterone secreted from the follicle cells (64,65). Oocytes are then released from the prophase arrest of meiosis I and undergo a sequence of events including nuclear envelope breakdown (commonly known as germinal vesicle breakdown [GVBD]), completion of meiosis I, extrusion of the first polar body, meiosis II entry, and subsequent metaphase II arrest as unfertilized eggs (reviewed in reference 45). Upon fertilization, Mos protein is degraded and does not reappear during embryonic development (39,80).Mos is essential for progesterone-induced oocyte maturation. Microinjection of antisense mos oligonucleotides into Xenopus oocytes blocks progesterone-induced GVBD and the activation of maturation-promoting factor (MPF) (31, 65). MPF is a universal M-phase regulator that drives meiotic progression and consists of the p34 cdc2 protein kinase and the cyclin B protein (reviewed in references 32 and 49). In the absence of progesterone, injected Mos protein or mos mRNA can activate MPF and induce GVBD (64,65,82). These results suggest that Mos is necessary and sufficient to initiate meiosis. Mos is also needed for the later stage of oocyte maturation. Extracts of unfertilized eggs in meiosis II contain an activity, cytostatic factor (CSF), that causes metaphase II arrest and can be assayed by the induction of cleavage arrest when injected into blastomeres of dividing embryos (45). Mos has CSF activity, and immunodepletion of Mos from unfertilized Xenopus egg extracts abolishes CSF (15,66,82). Mos is also important for the meiosis II arrest in mice. Female mice lacki...

In order to investigate the in vivo functions of protein kinase CK2 (CK2), the expression of Myc-tagged versions of the subunits, Myc-CK2␣ and Myc-CK2␤, was carried out in Chinese hamster ovary cells (CHO cells) and in 3T3 L1 fibroblasts. Cell proliferation in these cells was examined. CHO 3 H]thymidine incorporation, it was found that expression of Myc-CK2␤ prolonged the G 1 phase and inhibited up-regulation of cyclin D1 expression during G 1 . In addition, a lower mitotic index and lower mitotic cyclin-dependent kinase activities were detected in Myc-CK2␤-expressing cells. Detailed analysis of stable cells that were synchronously released into the cell cycle revealed that the expression of Myc-CK2␤ inhibited cells entering into mitosis and prevented the activation of mitotic cyclin-dependent kinases. Taken together, results from both transient and stable expression of CK2 subunits strongly suggest that CK2 may be involved in the control of cell growth and progression of the cell cycle. Casein kinase 2 (CK2)1 is a ubiquitous, multifunctional eukaryotic serine/threonine protein kinase that phosphorylates many different substrates including metabolic enzymes, structural proteins, transcription factors, and proto-oncoproteins (1). The holoenzyme form of CK2 is a heterotetramer, composed of ␣, ␣Ј, and ␤ subunits combined to form ␣ 2 ␤ 2 , ␣␣Ј␤ 2 , and ␣Ј 2 ␤ 2 . The ␣ and ␣Ј subunits are catalytically active, whereas the ␤ subunit is thought to be a regulatory subunit that stimulates the catalytic activity of ␣ or ␣Ј subunits and may also influence substrate specificity (for reviews, see Refs. 1-4). CK2 exhibits remarkable evolutionary conservation of primary structure in all eukaryotes from yeast to human, e.g. the identity of amino acid sequences of ␣ and ␤ subunits between human and Drosophila melanogaster is 90 and 88%, respectively. The amino acid sequences of the ␤ subunits of human, pig, and chicken are even identical, underscoring this point (5-6).The physiological role of CK2 has been explored in yeast and in a number of mammalian cell types, and these studies suggest that the enzyme is involved in cell growth and progression of the cell cycle. For example, genetic studies in Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Dictyostelium discoideum (7-9) showed that CK2 activity is essential for cell viability, e.g. the simultaneous disruption of the genes encoding the catalytic subunits, cka1 and cka2, in S. cerevisiae is lethal (7). An essential role of CK2 in control of cell cycle progression has also been demonstrated in the yeast S. cerevisiae (10). Through the use of mutant strains temperaturesensitive for the CK2 gene, the function of CK2 during the cell cycle was analyzed. It was shown that following a shift to the nonpermissive temperature, the mutant strains arrested within a single cell cycle and showed a dual arrest phenotype consisting of 50% of cells in G 1 and 50% cells in G 2 /M. Further analysis by flow cytometry of pheromone-synchronized cells confirmed that CK2 is required at a...

Mos is a germ cell-specific serine/threonine protein kinase that activates mitogen-activated protein kinase (MAPK) through MAPK kinase (MKK).

BackgroundHigh mobility group-box 3 (HMGB3) has been shown to affect tumor initiation and progression. This research aimed to investigate the role of HMGB3 in gastric cancer (GC) cell proliferation, migration, invasion, chemoresistance, and its potential molecular mechanisms.Material/MethodsGC MGC803 and BGC823 cells were transfected with siRNA targeting the HMGB3 gene. The expressions of HMGB3 protein in MGC803 and BGC823 cells after transfection were detected by Western blot assays. We detected cell proliferation and cell cycle by MTT and flow cytometry assay. Cell migration and invasion were determined by wound scratch and transwell assay. MGC803 and BGC823 cells were treated with various concentrations of oxaliplatin, cisplatin, and paclitaxel. After 24 hours of drug exposure, we performed MTT assays to investigate chemoresistance in both groups. Western blot assays were used to detect related proteins expression.ResultsSilencing of HMGB3 inhibited cell proliferation and induced G0/G1 phase arrest of GC cells partly via modulating p53 and p21 pathways, and downregulating Bcl-2/Bax ratio. RNA interference of HMGB3 inhibited cell invasion and migration by downregulating MMP2 and MMP9. Silencing of HMGB3 enhanced sensitive to cisplatin and paclitaxel, and reduced sensitive to oxaliplatin.ConclusionsThese findings suggest the importance of HMGB3 in the regulation of growth, migration, and apoptosis of GC, improve our understanding of the mechanisms of GC pathogenesis, and may promote the development of novel targeted therapies.