RELATIONSHIP BETWEEN THE GAAC AND TORC1 PATHWAYS WITH THE EXPRESSION OF AMINOACID PERMEASES ALONG AGING IN BUDDING YEASTS

BIRENBAUM, JOAQUÍN; BERMÚDEZ-MORETTI, MARIANA; GULIAS JUAN FACUNDO; CORREA-GARCÍA, SUSANA; MUÑOZ SEBASTIAN ANIBAL

SALTA

Congreso; Joint LV Annual SAIB Meeting and XIV PABMB Congress; 2019

SAIB PABMB

Protein biosynthesis, lifespan and autophagy induction are processes where the transcription factor Gcn4 has been described as an importantregulator in the budding yeast Saccharomyces cerevisiae. This factor is mainly induced when amino acid starvation occurs. Several Gcn4 targetgenes belong to the GAAC (General Amino Acid Control) or to the TORC1 (Target Of Rapamycin) pathways. Important proteins that aredownstream targets of these regulatory pathways are the amino acid permeases that internalize amino acids through the plasmatic membrane.Uga4 and Bap2 are two amino acid permeases induced by their substrates, γ-aminobutyric acid (GABA) and the branched amino acid leucine,respectively. The aim of this work was to analyse the transcriptional regulation of these permeases and GCN4 in cells deficient in the GAAC(gcn4Δ and leu3Δ cells) and TORC1 (tor1Δ, gln3Δ and sch9Δ cells) pathways, grown in the absence and in the presence of amino acids duringgrowth and along aging. For this purpose we used the lacZ reporter gene assays. We observed that in wild type cells GCN4 expression decreasesafter cells reach the stationary growth phase; and when TORC1 is inhibited by rapamycin, GCN4 expression slightly decreases and then remainsconstant along time. In leu3Δ cells high levels of GCN4 expression are detected at the exponential phase and they drastically diminish duringgrowth; but when these cells are treated with rapamycin GCN4 remains high. The analysis of GCN4 expression in cells deficient in GLN3 andSCH9, two downstream targets of TORC1, showed that this expression varies in opposite direction. These results suggest that GCN4 expressionalong growth depends on the TORC1 pathway. We also found that the expression of Uga4 and Bap2 permeases is differentially regulated in wildtype cells. Whereas UGA4 expression increases along cells aged, even though it has been described that protein translation is generally reducedin aged yeast cells, BAP2 remains low, and Gcn4 seems to be needed for UGA4 full expression. The deficiency in genes of the TORC1 pathwaydoes not affect UGA4 expression, and only in tor1Δ cells we observed an increase in BAP2 expression. Further research must be done tounderstand how Gcn4, Uga4, Bap2 and other permeases such as GAP1, a general amino acid permease, are regulated during aging both attranscriptional and translational levels by the nutrient sensing signaling pathways TORC1 and GAAC.