Retrograde Response to Mitochondrial Dysfunction Is Separable from TOR1/2 Regulation of Retrograde Gene Expression

Sergio Giannattasio,Zhengchang Liu,Janet Thornton,Ronald A Butow

doi:10.1074/jbc.m509187200

Abstract

Retrograde (RTG) signaling senses mitochondrial dysfunction and initiates readjustments of carbohydrate and nitrogen metabolism through nuclear accumulation of the heterodimeric transcription factors, Rtg1/3p. The RTG pathway is also linked to target of rapamycin (TOR) signaling, among whose activities is transcriptional control of nitrogen catabolite repression (NCR)-sensitive genes. To investigate the connections between these two signaling pathways, we have analyzed rapamycin sensitivity of the expression of the RTG target gene CIT2 and of two NCR-sensitive genes, GLN1 and DAL5, in respiratory-competent (rho+) and -incompetent (rho0) yeast cells. Here we have presented evidence that retrograde gene expression is separable from TOR regulation of RTG- and NCR-responsive genes. We showed that expression of these two classes of genes is differentially regulated by glutamate starvation whether in response to mitochondrial dysfunction or induced by rapamycin treatment, as well by glutamine or histidine starvation. We also showed that Lst8p, a component of the TOR1/2 complexes and a negative regulator of the RTG pathway, has multiple roles in the regulation of RTG- and NCR-sensitive genes. Lst8p negatively regulates CIT2 and GLN1 expression, whereas DAL5 expression is independent of Lst8p function. DAL5 expression depends on the GATA transcription factors Gln3p and Gat1p. Gat1p is translocated to the nucleus only upon TOR inhibition by rapamycin. Altogether, these data show that Rtg1/3p, Gln3p, and Gat1p can be differentially regulated through different nutrient-sensing pathways, such as TOR and retrograde signaling, and by multiple factors, such as Lst8p, which is suggested to have a role in connecting the RTG and TOR pathways.

Highlights

Piration-deficient cells that provide key metabolites such as acetyl-CoA and oxaloacetate to mitochondria to compensate for the block of the Krebs cycle
Separation of the Retrograde and target of rapamycin (TOR) Pathways—The retrograde pathway was originally defined in comparisons of gene expression between respiratory-competent ␳ϩ cells and respiratory-incompetent petite cells grown in rich medium [39]
To gain insight into how the retrograde and TOR signaling pathways are integrated under these growth conditions, we examined the expression of two RTG target genes, CIT2 and DLD3, and two nitrogen catabolite repression (NCR)-responsive genes, GLN1 and DAL5, in ␳ϩ and ␳° cells before and after the addition of rapamycin to the medium

Summary

Introduction

Piration-deficient cells that provide key metabolites such as acetyl-CoA and oxaloacetate to mitochondria to compensate for the block of the Krebs cycle. The glyoxylate cycle gene, CIT2, encoding an isoform of citrate synthase, and DLD3, encoding a cytoplasmic lactate dehydrogenase, are among the genes activated in respiratory-deficient cells [3, 4] Their expression is positively regulated by the heterodimeric transcription factors Rtg1p and Rtg3p and Rtg2p, a novel cytoplasmic protein with an N-terminal ATP binding domain that is required for the relocalization of Rtg1/3p from the cytoplasm to the nucleus when the retrograde pathway is activated [5]. Analysis of different mutant alleles of LST8 that result in constitutive activation of RTG target gene expression reveals that Lst8p acts at two distinct sites, one upstream and the other downstream of Rtg2p [15, 16] The former site is believed to involve the role of Lst8p on the activity or assembly of the SPS (Ssy1p, Ptr3p, and Ssy5p) amino acid-sensing system, affecting the ability of cells to sense external glutamate [17]. S228c PSY142 ZLY98407 ZLY98573 ZLY98405 ZLY98577 ZLY98832 SGY127 SGY121 SGY164 BY4741 JTY413 ZLY98711 ZLY98713 ZLY98715 TSY279 TSY328 TSY1112

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