http://www.klinikaikozpont.u-szeged.hu/pedia/images/pdf/CME_TEL/Full-Text/25.pdf

The Hallmarks of Aging

Phosphatidylinositol 3-kinases (PI3Ks) evolved from a single enzyme that regulates vesicle trafficking in unicellular eukaryotes into a family of enzymes that regulate cellular metabolism and growth in multicellular organisms. In this review, we examine how the PI3K pathway has evolved to control these fundamental processes, and how this pathway is in turn regulated by intricate feedback and crosstalk mechanisms. In light of the recent advances in our understanding of the function of PI3Ks in the pathogenesis of diabetes and cancer, we discuss the exciting therapeutic opportunities for targeting this pathway to treat these diseases.

The evolution of phosphatidylinositol 3-kinases as regulators of growth and metabolism

The nematode Caenorhabditis elegans ages and dies in a few weeks, but humans can live for 100 years or more. Assuming that the ancestor we share with nematodes aged rapidly, this means that over evolutionary time mutations have increased lifespan more than 2,000-fold. Which genes can extend lifespan? Can we augment their activities and live even longer? After centuries of wistful poetry and wild imagination, we are now getting answers, often unexpected ones, to these fundamental questions.

The genetics of ageing

Is human life expectancy approaching its limit? Many--including individuals planning their retirement and officials responsible for health and social policy--believe it is, but the evidence presented in the
 Policy Forum
 suggests otherwise. For 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year, an extraordinary constancy of human achievement. Mortality experts have repeatedly asserted that life expectancy is close to an ultimate ceiling; these experts have repeatedly been proven wrong. The apparent leveling off of life expectancy in various countries is an artifact of laggards catching up and leaders falling behind.

/pdf/broken-limits-to-life-expectancy-3fna6yf8to.pdf

Broken Limits to Life Expectancy

E3 ligases confer specificity to ubiquitination by recognizing target substrates and mediating transfer of ubiquitin from an E2 ubiquitinconjugating enzyme to substrate. The activity of most E3s is specified by a RING domain, which binds to an E2∼ubiquitin thioester and activates discharge of its ubiquitin cargo. E2-E3 complexes can either monoubiquitinate a substrate lysine or synthesize polyubiquitin chains assembled via different lysine residues of ubiquitin. These modifications can have diverse effects on the substrate, ranging from proteasome-dependent proteolysis to modulation of protein function, structure, assembly, and/or localization. Not surprisingly, RING E3mediated ubiquitination can be regulated in a number of ways. RING-based E3s are specified by over 600 human genes, surpassing the 518 protein kinase genes. Accordingly, RING E3s have been linked to the control of many cellular processes and to multiple human diseases. Despite their critical importance, our knowledge of the physiological partners, biological functions, substrates, and mechanism of action for most RING E3s remains at a rudimentary stage.

/pdf/ring-domain-e3-ubiquitin-ligases-2zqhjd6kca.pdf

RING Domain E3 Ubiquitin Ligases

We have found that mutations in the gene daf-2 can cause fertile, active, adult Caenorhabditis elegans hermaphrodites to live more than twice as long as wild type. This lifespan extension, the largest yet reported in any organism, requires the activity of a second gene, daf-16. Both genes also regulate formation of the dauer larva, a developmentally arrested larval form that is induced by crowding and starvation and is very long-lived. Our findings raise the possibility that the longevity of the dauer is not simply a consequence of its arrested growth, but instead results from a regulated lifespan extension mechanism that can be uncoupled from other aspects of dauer formation. daf-2 and daf-16 provide entry points into understanding how lifespan can be extended.

A C. elegans mutant that lives twice as long as wild type

The spindle assembly checkpoint

Budding yeast initiates anaphase by activating the Cdc20-dependent anaphase-promoting complex (APC). The mitotic activity of Cdc28 (Cdk1) is required to activate this form of the APC, and mutants that are impaired in mitotic Cdc28 function have difficulty leaving mitosis. This defect can be explained by a defect in APC phosphorylation, which depends on mitotic Cdc28 activity in vivo and can be catalyzed by purified Cdc28 in vitro. Mutating putative Cdc28 phosphorylation sites in three components of the APC, Cdc16, Cdc23, and Cdc27, makes the APC resistant to phosphorylation both in vivo and in vitro. The nonphosphorylatable APC has normal activity in G1, but its mitotic, Cdc20-dependent activity is compromised. These results show that Cdc28 activates the APC in budding yeast to trigger anaphase. Previous reports have shown that the budding yeast Cdc5 homologue, Plk, can also phosphorylate and activate the APC in vitro. We show that, like cdc28 mutants, cdc5 mutants affect APC phosphorylation in vivo. However, although Cdc5 can phosphorylate Cdc16 and Cdc27 in vitro, this in vitro phosphorylation does not occur on in vivo sites of phosphorylation.

/pdf/phosphorylation-by-cdc28-activates-the-cdc20-dependent-42qufef1lz.pdf

Phosphorylation by Cdc28 Activates the Cdc20-Dependent Activity of the Anaphase-Promoting Complex

Transcriptional silencing at the budding yeast silent mating type (HM) loci and telomeric DNA regions requires Sir2, a conserved NAD-dependent histone deacetylase, Sir3, Sir4, histones H3 and H4, and several DNA-binding proteins Silencing at the yeast ribosomal DNA (rDNA) repeats requires a complex containing Sir2, Net1, and Cdc14 Here we show that the native Sir2/Sir4 complex is composed solely of Sir2 and Sir4 and that native Sir3 is not associated with other proteins We further show that the initial binding of the Sir2/Sir4 complex to DNA sites that nucleate silencing, accompanied by partial Sir2-dependent histone deacetylation, occurs independently of Sir3 and is likely to be the first step in assembly of silent chromatin at the HM loci and telomeres The enzymatic activity of Sir2 is not required for this initial binding, but is required for the association of silencing proteins with regions distal from nucleation sites At the rDNA repeats, we show that histone H3 and H4 tails are required for silencing and rDNA-associated H4 is hypoacetylated in a Sir2-dependent manner However, the binding of Sir2 to rDNA is independent of its histone deacetylase activity Together, these results support a stepwise model for the assembly of silent chromatin domains in Saccharomyces cerevisiae

/pdf/steps-in-assembly-of-silent-chromatin-in-yeast-sir3-2u6gn2cp7n.pdf

Steps in Assembly of Silent Chromatin in Yeast: Sir3-Independent Binding of a Sir2/Sir4 Complex to Silencers and Role for Sir2-Dependent Deacetylation

http://www.med.uottawa.ca/rudnerlab/Adam_Rudner_Lab/Publications_files/Mol%20Cell%20Proteomics%202005%20Denison.pdf

Adam D. Rudner

Papers

A C. elegans mutant that lives twice as long as wild type

The spindle assembly checkpoint

Phosphorylation by Cdc28 Activates the Cdc20-Dependent Activity of the Anaphase-Promoting Complex

Steps in Assembly of Silent Chromatin in Yeast: Sir3-Independent Binding of a Sir2/Sir4 Complex to Silencers and Role for Sir2-Dependent Deacetylation

A Proteomic Strategy for Gaining Insights into Protein Sumoylation in Yeast