Studies of yeast have shown that the SIR2 gene family is involved in chromatin structure, transcriptional silencing, DNA repair, and control of cellular life span. Our functional studies of human SIRT2, a homolog of the product of the yeast SIR2 gene, indicate that it plays a role in mitosis. The SIRT2 protein is a NADdependent deacetylase (NDAC), the abundance of which increases dramatically during mitosis and is multiply phosphorylated at the G 2 /M transition of the cell cycle. Cells stably overexpressing the wild-type SIRT2 but not missense mutants lacking NDAC activity show a marked prolongation of the mitotic phase of the cell cycle. Overexpression of the protein phosphatase CDC14B, but not its close homolog CDC14A, results in dephosphorylation of SIRT2 with a subsequent decrease in the abundance of SIRT2 protein. A CDC14B mutant defective in catalyzing dephosphorylation fails to change the phosphorylation status or abundance of SIRT2 protein. Addition of 26S proteasome inhibitors to human cells increases the abundance of SIRT2 protein, indicating that SIRT2 is targeted for degradation by the 26S proteasome. Our data suggest that human SIRT2 is part of a phosphorylation cascade in which SIRT2 is phosphorylated late in G 2 , during M, and into the period of cytokinesis. CDC14B may provoke exit from mitosis coincident with the loss of SIRT2 via ubiquitination and subsequent degradation by the 26S proteasome.As the founding member of a vast gene family with members present in archaebacteria, eubacteria, and eukaryotes, SIR2 was first described in the budding yeast as a gene mediating the transcriptional silencing of the silent mating type (MAT) loci HML and HMR (14,19). Additional functions for SIR2 in budding have been described, including the silencing of subtelomeric genes (telomere position effect [TPE]) and the regulation of transcription and recombination in the multiple tandem copies of ribosomal DNA (rDNA) (for a review, see reference 12). Guarente, Sinclair, and coworkers have shown that the SIR2 gene may suppress aging in budding yeast, through a mechanism involving the suppression of extrachromosomal rDNA circles (ERCs) derived from errant intralocus recombination and suggested that SIR2-related genes in other organisms may be involved in the aging process as well, even in multicellular eukaryotes (13). The mechanism by which SIRT (an acronym for SIR2 related) genes retard aging in metazoans may involve caloric restriction (CR) instead of the ERCs found in yeast (22). Support for this hypothesis has recently come from the key finding that providing the nematode Caenorhabditis elegans with two copies of one of its SIR2-related genes (the gene normally found on chromosome IV) can extend the worm's life span by ϳ50% (36). This extension of life span function is seen only for one of the three SIR2-related genes, Sir-2.1, encoding a large nuclear protein orthologous to that coded for by the SIR2-related gene known as SIRT1 in humans and SIR2␣ in mice. Neither of the other two SIRT genes in the worm (ort...

A noninvasive screening test would significantly facilitate early detection of epithelial ovarian cancer. This study used a combination of high-throughput selection and arraybased serologic detection of many antigens indicative of the presence of cancer, thereby using the immune system as a biosensor. This high-throughput selection involved biopanning of an ovarian cancer phage display library using serum immunoglobulins from an ovarian cancer patient as bait. Protein macroarrays containing 480 of these selected antigen clones revealed 65 clones that interacted with immunoglobulins in sera from 32 ovarian cancer patients but not with sera from 25 healthy women or 14 patients having other benign or malignant gynecologic diseases. Sequence analysis data of these 65 clones revealed 62 different antigens. Among the markers, we identified some known antigens, including RCAS1, signal recognition protein-19, AHNAK-related sequence, nuclear autoantogenic sperm protein, Nijmegen breakage syndrome 1 (Nibrin), ribosomal protein L4, Homo sapiens KIAA0419 gene product, eukaryotic initiation factor 5A, and casein kinase II, as well as many previously uncharacterized antigenic gene products. Using these 65 antigens on protein microarrays, we trained neural networks on two-color fluorescent detection of serum IgG binding and found an average sensitivity and specificity of 55% and 98%, respectively. In addition, the top 6 of the most specific clones resulted in an average sensitivity and specificity of 32% and 94%, respectively. This global approach to antigenic profiling, epitomics, has applications to cancer and autoimmune diseases for diagnostic and therapeutic studies. Further work with larger panels of antigens should provide a comprehensive set of markers with sufficient sensitivity and specificity suitable for clinical testing in high-risk populations. (Cancer Res 2006; 66(2): 1181-90)

Human SIRT2 is a cytoplasmic NAD-dependent deacetylase implicated in the mitotic regulation of microtubule dynamics by its association with the class II histone deacetylase 6 (HDAC6). We have previously reported that SIRT2 is multiply phosphorylated in a cell cycle dependent pattern. Here, we demonstrate that HDAC6 binds to both phosphorylated and unphosphorylated forms of SIRT2 and that tubulin binds only to the SIRT2-HDAC6 complex. Tubulin does not bind to either HDAC6 or SIRT2 individually. In addition, we show that replacement of specific serines with alanines in either isoform of SIRT2 regulates its enzymatic activity. We also found that overexpression of isoform2 was deleterious to cell survival. SIRT2 was found to be phosphorylated at serines 368 and 372, outside the conserved core domain of the Sir2 protein family. Double replacement of S368A and S372A reduced SIRT2 deacetylase activity by 44% compared to wildtype activity. Replacements of other serine, threonine, and tyrosine residues, which did not alter the phosphorylation pattern, had varying effects on SIRT2 deacetylase activity but no effect on tubulin/HDAC6 binding.