Nutrient availability and the differentiation state determine cell fate in multicellular organisms. The yeast Saccharomyces cerevisiae is a valuable model organism to study how nutrient availability determines cell fate in different growth conditions. In an attempt to understand how metabolism controls cell death and survival in actively dividing and proliferating cells, we have shown that exponential growing yeast cells in the presence of the preferred carbon source glucose (GLU-WT), which inhibits respiration through carbon catabolite repression (CR) pathway, undergo programmed cell death (PCD) in response to acetic acid (AA) treatment. On the contrary, yeast cells grown in raffinose (RAF-WT) are resistant to AA-PCD in a manner dependent on both the activation of mitochondrial retrograde (RTG) pathway, which senses mitochondrial dysfunction, and glucose de-repression of mitochondrial respiration. To study the relationships between CR and RTG pathway in yeast cell death and survival in response to AA, we compared WT cells and a set of yeast mutants lacking negative or positive regulators of either RTG or CR pathway as for their viability after AA treatment. We found that glucose-grown cells lacking MIG1 and HXK2, which repress transcription of mitochondrial respiratory genes in the presence of glucose, undergo AA-PCD as GLU-WT cells, as judged by decrease in viability and increase in DNA fragmentation. On the other hand, differently from RAF-WT cells, raffinose-grown cells lacking transcription factors ADR1 or CAT8, which are activated by alternative carbon sources, or RTG2, a positive regulator of RTG pathway, underwent AA-PCD. Cells lacking HAP4, the regulatory subunit of HAP complex active in raffinose, remain fully resistant to AA-PCD. Interestingly, double knock-out ∆adr1∆rtg2 and ∆cat8∆rtg2 cells were found nearly as much resistant to AA-PCD as RAF-WT cells. RTG pathway activation was studied in raffinose-grown WT and knock-out cells after AA treatment by analyzing the prototypical RTG-target gene CIT2 mRNA level. Results showed that ADR1 and CAT8 are positive regulators of RTG2-dependent transcription and suggest that RTG and CR pathways co-operate in the control of cell fate through interaction between RTG2 and CAT8 or ADR1.
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