We previously identified SIRT2, an nicotinamide adenine dinucleotide (NAD)-dependent tubulin deacetylase, as a protein downregulated in gliomas and glioma cell lines, which are characterized by aneuploidy. Other studies reported SIRT2 to be involved in mitotic progression in the normal cell cycle. We herein investigated whether SIRT2 functions in the mitotic checkpoint in response to mitotic stress caused by microtubule poisons. By monitoring chromosome condensation, the exogenously expressed SIRT2 was found to block the entry to chromosome condensation and subsequent hyperploid cell formation in glioma cell lines with a persistence of the cyclin B/cdc2 activity in response to mitotic stress. SIRT2 is thus a novel mitotic checkpoint protein that functions in the early metaphase to prevent chromosomal instability (CIN), characteristics previously reported for the CHFR protein.We further found that histone deacetylation, but not the aberrant DNA methylation of SIRT2 5 0 untranslated region is involved in the downregulation of SIRT2. Although SIRT2 is normally exclusively located in the cytoplasm, the rapid accumulation of SIRT2 in the nucleus was observed after treatment with a nuclear export inhibitor, leptomycin B and ionizing radiation in normal human fibroblasts, suggesting that nucleo-cytoplasmic shuttling regulates the SIRT2 function. Collectively, our results suggest that the further study of SIRT2 may thus provide new insights into the relationships among CIN, epigenetic regulation and tumorigenesis. Oncogene (2007) 26, 945-957.

No abstract

Precise chromosome transmission in cell division cycle is maintained by a number of genes. The attempt made in the present study was to isolate temperature-sensitive (ts) fission yeast mutants that display high loss rates of minichromosomes at permissive or semipermissive temperature (designated mis). By colony color assay of 539 ts strains that contain a minichromosome, we have identified 12 genetic loci (misl-misl2) and determined their phenotypes at restrictive temperature. Seven of them are related to cell cycle block phenotype at restrictive temperature, three of them in mitosis. Unequal distribution of regular chromosomes in the daughters is extensive in mis6 and misl2. Cells become inviable after rounds of cell division due to missegregation. The phenotype of mis5 is DNA replication defect and hypersensitivity to UV ray and hydroxyurea. mis5+ encodes a novel member of the ubiquitous MCM family required for the onset of replication. The mis5+ gene is essential for viability and functionally distinct from other previously identified members in fission yeast, cdc21+, ndal+, and nda4+. The mislI mutant phenotype was the cell division block with reduced cell size. Progression of the G1 and G2 phases is blocked in mislI. The cloned misl I gene is identical to prp2+, which is essential for RNA splicing and similar to a mammalian splicing factor U2AF65. (Hieter et al., 1985;Koshland et al., 1985) were employed to identify a number of mutations producing increased rates of chromosome loss or nondisjunction (Liras et al., 1978;Maine et al., 1984;Hartwell and Smith, 1985;Kouprina et al., 1988Kouprina et al., , 1993Hoyt et al., 1990;Spencer et al., 1990). They were designated mcm (Maine et al., 1984), ctf (Spencer et al., 1990), cin (Hoyt et al., 1990), or chl (Liras et al., 1978Kouprina et al., 1988Kouprina et al., , 1993. A significant number of these genes turned out to be nonessential for cell viability, probably because they had overlapping functions. More than 100 ctfmutants were isolated and mapped in -50 genetic loci (Spencer et al., 1990). The MCM2, MCM3, and MCM5 gene products are the members of a gene family required for the onset of DNA replication (Gibson et al., 1990;Chen et al., 1992), whereas MCM1 encodes a transcription factor (Passmore et al., 1988(Passmore et al., , 1989Jarvis et al., 1989). CIN8 and KIP1 (CIN9) code for kinesin-like motor proteins Roof et al., 1992;Saundes and Hoyt, 1992). CTF13 and CTF14 code for proteins CBF3C and CBF3A bound to the essential centromere region (Doheny et al., 1993;Goh and Kilmartin, 1993;Jiang et al., 1993 INTRODUCTION MATERIALS AND METHODS Media and Genetic MethodsS. pombe strains used were 972 h-, 975h+, JY6 (h+ leul his2), and SP6/ HM123 (h-leul). Standard genetic procedures for tetrad dissection, random spore and heterozygous diploid analyses as described by Gutz et al. (1974) were followed. Media used were YPD (1% yeast extract, 2% polypeptone, 2% glucose) and EMM2 (minimal medium;Mitchison, 1970). Media containing 1.6% agar were used for plating unless o...

The 20S cyclosome complex (also known as the anaphase-promoting complex) has ubiquitin ligase activity and is required for mitotic cyclin destruction and sister chromatid separation. The formation and activation of the 20S cyclosome complex is regulated by an unknown mechanism. Here we show that Cut4 (ref. 6) is an essential component of the cyclosome in fission yeast. Cut4 shares sequence similarity with BimE, a protein that regulates mitosis in Aspergillus nidulans. Mutations in cut4 result in hypersensitivity to cyclic AMP and to stress-inducing heavy metals, inhibition of the onset of anaphase, disruption of the 20S complex, and inhibition of mitotic cyclin ubiquitination. These phenotypes are fully suppressed by cAMP phosphodiesterase and the protein kinase A (PKA) regulatory subunit and weakly suppressed by Sti1 (an activator of the Hsp70 and Hsp90 chaperones). Suppression correlates with the amount of 20S complex, indicating that cyclosome formation and activation is inhibited by the cAMP/PKA pathway.

The incidence of liver cancer has increased in recent years. Worldwide, liver cancer is common: more than 600000 related deaths are estimated each year. In the USA, about 27170 deaths due to liver cancer are estimated for 2016. Liver cancer is highly resistant to conventional chemotherapy and radiotherapy. For all stages combined, the 5-year survival rate is 15-17%, leaving much to be desired for liver cancer prevention and therapy. Heterogeneity, which can originate from genomic instability, is one reason for poor outcome. About 80-90% of liver cancers are hepatocellular carcinoma (HCC), and recent cancer genome sequencing studies have revealed frequently mutated genes in HCC. In this review, we discuss the cause of the tumor heterogeneity based on the functions of genes that are frequently mutated in HCC. We overview the functions of the genes that are most frequently mutated (e.g. TP53, CTNNB1, AXIN1, ARID1A and WWP1) that portray major pathways leading to HCC and identify the roles of these genes in preventing genomic instability. Notably, the pathway analysis suggested that oxidative stress management may be critical to prevent accumulation of DNA damage and further mutations. We propose that both chromosome instability (CIN) and microsatellite instability (MIN) are integral to the hepatic carcinogenesis process leading to heterogeneity in HCC and that the pathways leading to heterogeneity may be targeted for prognosis, prevention and treatment.