Mitotic chromatin condensation is essential for cell division in eukaryotes. Posttranslational modification of the N-terminal tail of histone proteins, particularly by phosphorylation by mitotic histone kinases, may facilitate this process. In mammals, aurora B is believed to be the mitotic histone H3 Ser10 kinase; however, it is not sufficient to phosphorylate H3 Ser10 with aurora B alone. We show that histone H3 is phosphorylated by vaccinia-related kinase 1 (VRK1). Direct phosphorylation of Thr3 and Ser10 in H3 by VRK1 both in vitro and in vivo was observed. Loss of VRK1 activity was associated with a marked decrease in H3 phosphorylation during mitosis. Phosphorylation of Ser10 by VRK1 is similar to that by aurora B. Moreover, expression and chromatin localization of VRK1 depended on the cell cycle phase. Overexpression of VRK1 resulted in a dramatic condensation of nuclei. Our findings collectively support a role of VRK1 as a novel mitotic histone H3 kinase in mammals.Chromatin congregates to chromosomes during mitosis to facilitate the even segregation of genetic information to two daughter cells. In nucleosomes, the combinational modification of histone tails, the so-called "histone code," controls chromatintemplated processes from gene expression to cell fate decision (20,30). Phosphorylation of the N-terminal tail of histone H3 may be responsible for chromatin condensation (21). During mitosis, the N-terminal tail of histone H3 is phosphorylated at several residues, including Thr3 (5, 36), Ser10 (3,7,17,18), Thr11 (37), and Ser28 (12). A correlation between histone H3 Ser10 phosphorylation and chromatin condensation in Aspergillus nidulans (6) and Tetrahymena thermophila (47) is well established. However, in other species, condensation is not accomplished simply by Ser10 phosphorylation, and additional phosphorylation or modification of histone tails is required (21).A number of studies have shown that members of the aurora kinase family are responsible for phosphorylation of histone H3 (3,7,17,18). Mammals contain three isotypes of aurora kinase designated aurora A, B, and C (11). Among these, aurora B is a strong candidate phosphorylator of Ser10 in histone H3 as is evident from data obtained with hesperadin, the aurora B inhibitor (14), which suppressed Ser10 phosphorylation during mitosis (7, 17). However, residual Ser10 phosphorylation was detected, even upon depletion of aurora B in cells, suggesting the presence of an additional histone H3 kinase (29).NIMA (never in mitosis), the histone H3 Ser10 kinase in Aspergillus nidulans (6, 34), triggers chromatin condensation in cells arrested at the interphase (28). In mammals, Nercc1, the functional ortholog of NIMA, was found to be phosphorylating histone H3 (39). Nucleosomal histone kinase 1 (NHK1) from Drosophila melanogaster is the kinase shown to phosphorylate histone protein in chromatin as a substrate. NHK1 phosphorylated H2A at Thr119 in chromatin but not with free histone as the substrate (1). Recent studies showed that NHK1 participates in mit...

Summary Dysregulation of O‐GlcNAc modification catalyzed by O‐GlcNAc transferase (OGT) and O‐GlcNAcase (OGA) contributes to the etiology of chronic diseases of aging, including cancer, cardiovascular disease, type 2 diabetes, and Alzheimer’s disease. Here we found that natural aging in wild‐type mice was marked by a decrease in OGA and OGT protein levels and an increase in O‐GlcNAcylation in various tissues. Genetic disruption of OGA resulted in constitutively elevated O‐GlcNAcylation in embryos and led to neonatal lethality with developmental delay. Importantly, we observed that serum‐stimulated cell cycle entry induced increased O‐GlcNAcylation and decreased its level after release from G2/M arrest, indicating that O‐GlcNAc cycling by OGT and OGA is required for precise cell cycle control. Constitutively, elevated O‐GlcNAcylation by OGA disruption impaired cell proliferation and resulted in mitotic defects with downregulation of mitotic regulators. OGA loss led to mitotic defects including cytokinesis failure and binucleation, increased lagging chromosomes, and micronuclei formation. These findings suggest an important role for O‐GlcNAc cycling by OGA in embryonic development and the regulation of the maintenance of genomic stability linked to the aging process.

The c-myc proto-oncogene plays a key role in the proliferation, differentiation, apoptosis, and regulation of the cell cycle. Recently, it was demonstrated that the 5 nontranslated region (5 NTR) of human c-myc mRNA contains an internal ribosomal entry site (IRES). In this study, we investigated cellular proteins interacting with the IRES element of c-myc mRNA. Heterogeneous nuclear ribonucleoprotein C (hnRNP C) was identified as a cellular protein that interacts specifically with a heptameric U sequence in the c-myc IRES located between two alternative translation initiation codons CUG and AUG. Moreover, the addition of hnRNP C1 in an in vitro translation system enhanced translation of c-myc mRNA. Interestingly, hnRNP C was partially relocalized from the nucleus, where most of the hnRNP C resides at interphase, to the cytoplasm at the G 2 /M phase of the cell cycle. Coincidently, translation mediated through the c-myc IRES was increased at the G 2 /M phase when cap-dependent translation was partially inhibited. On the other hand, a mutant c-myc mRNA lacking the hnRNP C-binding site, showed a decreased level of translation at the G 2 /M phase compared to that of the wild-type message. Taken together, these findings suggest that hnRNP C, via IRES binding, modulates translation of c-myc mRNA in a cell cycle phase-dependent manner.

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B longum KACC 91563 induces apoptosis of mast cells specifically and alleviates food allergy symptoms. Accordingly, B longum KACC 91563 and family 5 extracellular solute-binding protein exhibit potential as therapeutic approaches for food allergies.