Distinct regulation of Maf1 for lifespan extension by Protein kinase A and Sch9

Abstract

The Protein kinase A (PKA) and Sch9 regulates cell growth as well as lifespan in Saccharomyces cerevisiae. Maf1 is a RNA polymerase III (Pol III) inhibitor that tailors 5S rRNA and tRNA production in response to various environmental cues. Both PKA and Sch9 have been shown to phosphorylate Maf1 in vitro at similar amino acids, suggesting a redundancy in Maf1 regulation. However, here we find that activating PKA by bcy1 deletion cannot replace Sch9 for Maf1 phosphorylation and cytoplasmic retention; instead, such modulation lowers Maf1 protein levels. Consistently, loss of MAF1 or constitutive PKA activity reverses the stress resistance and the extended lifespan of sch9Δ cells. Overexpression of MAF1 partially rescues the extended lifespan of sch9Δ in bcy1Δsch9Δ mutant, suggesting that PKA suppresses sch9Δ longevity at least partly through Maf1 abundance. Constitutive PKA activity also reverses the reduced tRNA synthesis and slow growth of sch9Δ, which, however, is not attributed to Maf1 protein abundance. Therefore, regulation of lifespan and growth can be decoupled. Together, we reveal that lifespan regulation by PKA and Sch9 are mediated by Maf1 through distinct mechanisms.

The C-Box Region of MAF1 Regulates Transcriptional Activity and Protein Stability

“…Mutation of specific residues in the C-box in MAF1 increased protein turnover via the proteasomal degradation pathway, which, based on our biochemical fractionation, occurs predominantly in the nucleus and with stronger effects on MAF1 s . This discovery is in line with other reports where PKA and Sch9 mutation in yeast leads to Maf1 nuclear accumulation and consequently lowers Maf1 abundance [2,38]. The decreased protein stability in ΔC suggests that this region also helps MAF1 to avoid being recognized by the proteasomal system.…”

“…4A and B), which, as previously shown in both yeast and mammalian cells, correlate with the cytoplasmic/nuclear localization of the protein (Fig. 4C and D) [2,17,19,32]. Based on PhosTag® gel electrophoresis, ΔC is predominantly unphosphorylated, but a monophosphorylated species is also detectable (Fig.…”

“…Protein phosphatase 2A, protein kinase A (PKA), and Sch9 are components of the TOR pathway that modify the phosphorylation of Maf1 to influence its function [2,20]. Mutations of PKA phosphorylation sites in yeast Maf1 result in nuclear accumulation without affecting pol III activity [19].…”

Plasmodium falciparum Maf1 Confers Survival upon Amino Acid Starvation

“…Parasites could remain in the absence of isoleucine for upwards of several days and sustain only a minor loss in viability. This is reminiscent of the stationary-phase dormancy observed in yeast, a process for which Maf1 is necessary to maintain viability during prolonged starvation (18, 29). …”

“…Yeast Maf1 null mutants die under conditions of nutrient limitation or when other factors inhibit TORC1 , due to inability to regulate Pol III transcription (22, 26–28). In yeast, Maf1 is one of the most important genes for maintaining viability during long-term starvation in stationary phase (18, 29). A putative Maf1 ortholog appears to be conserved in the Plasmodium genus.…”