Academic journal article Genetics

A Functional Analysis Reveals Dependence on the Anaphase-Promoting Complex for Prolonged Life Span in Yeast

Academic journal article Genetics

A Functional Analysis Reveals Dependence on the Anaphase-Promoting Complex for Prolonged Life Span in Yeast

Article excerpt

ABSTRACT

Defects in anaphase-promoting complex (APC) activity, which regulates mitotic progression and chromatin assembly, results in genomic instability, a hallmark of premature aging and cancer. We investigated whether APC-dependent genomic stability affects aging and life span in yeast. Utilizing replicative and chronological aging assays, the APC was shown to promote longevity. Multicopy expression of genes encoding Snf1p (MIG1) and PKA (PDE2) aging-pathway components suppressed apc5^sup CA^ phenotypes, suggesting their involvement in APC-dependent longevity. While it is known that PKA inhibits APC activity and reduces life span, a link between the Snf1p-inhibited Mig1p transcriptional modulator and the APC is novel. Our mutant analysis supports a model in which Snf1p promotes extended life span by inhibiting the negative influence of Mig1p on the APC. Consistent with this, we found that increased MIG1 expression reduced replicative life span, whereas mig1Δ mutations suppressed the apc5^sup CA^ chronological aging defect. Furthermore, Mig1p and Mig2p activate APC gene transcription, particularly on glycerol, and mig2Δ, but not mig1Δ, confers a prolonged replicative life span in both APC5 and acp5^sup CA^ cells. However, glucose repression of APC genes was Mig1p and Mig2p independent, indicating the presence of an uncharacterized factor. Therefore, we propose that APC-dependent genomic stability is linked to prolonged longevity by the antagonistic regulation of the PKA and Snf1p pathways.

THE anaphase-promoting complex (APC), an evolutionarily conserved, large multi-protein complex that is essential for yeast viability, functions as a ubiquitin-protein ligase (E3; ZACHARIAE and NASMYTH 1999; HARPER et al. 2002). The APC controls progression through mitosis by targeting mitotic inhibitors for degradation and this activity is regulated at the protein level by a complex network of interactions (KOTANI et al. 1998; RUDNER and MURRAY 2000). One notable example of APC regulation is the negative influence of RAS/protein kinase A (PKA) signaling on the yeast APC (YAMASHITA et al. 1996; KOTANI et al. 1998; IRNIGER et al. 2000; BOLTE et al. 2003). PKA phosphorylates the APC subunits Cdc27p and Apc1p, which is sufficient to inactivate the APC (KOTANI et al. 1998). PKA signaling is considered to play a role in maintaining chromosomal stability (MATYAKHINA et al. 2002). Defects that alter APC activity are associated with cancer development in humans (PRAY et al. 2002; LIU et al. 2003; WANG et al. 2003; SONG et al. 2004). Recently, we isolated and described a mutation in the Apc5p APC subunit that rendered cells temperature sensitive (ts) at 37°, predisposed to chromosome loss, and chromatin assembly defective in vitro (HARKNESS et al. 2002, 2003). These observations suggest that the APC is also critical for chromosome maintenance, chromatin metabolism, and genomic stability during mitosis.

Recent studies have demonstrated the striking involvement of chromatin in the aging process (reviewed in CAMPISI 2000; CHANG and MIN 2002; HEKIMI and GUARENTE 2003). Chromatin is a complex molecular structure composed of nucleosomal repeats in which 147 bp of DNA are wrapped around two copies of the four core histones, H2A, H2B, H3, and H4 (LUGER et al. 1997; RICHMOND and DAVEY 2003). The critical components within chromatin that are central to the control of many cellular processes are the histones. Chromatin-associated histones are post-translationally modified by a variety of activities and these modifications are responsible for the control of a vast number of cellular activities (VAN LEEUWEN and GOTTSCHLING 2002; FISCHLE et al. 2003). Deacetylation of lysine residues within histone N-terminal tails is believed to play a large role in gene silencing by creating conformational changes within chromatin that render it resistant to transcription factors (GRUNSTEIN 1997; EBERHARTER and BECKER 2002). Silencing of the yeast rDNA locus, in particular, represses rDNA recombination, reducing the formation of extrachromosomal rDNA circles (ERCs), and this is believed to enhance replicative life span, a measure of how many daughter cells a given mother cell can produce (KENNEDY et al. …

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