The conserved TOR (target of rapamycin) kinase is part of a TORC1 complex that regulates cellular responses to environmental stress, such as amino acid starvation and hypoxia. Dysregulation of Akt-TOR signaling has also been linked to the genesis of cancer, and thus, this pathway presents potential targets for cancer chemotherapeutics. Here we report that rapamycin-sensitive TORC1 signaling is required for the S-phase progression and viability of yeast cells in response to genotoxic stress. In the presence of the DNA-damaging agent methyl methanesulfonate (MMS), TOR-dependent cell survival required a functional S-phase checkpoint. Rapamycin inhibition of TORC1 signaling suppressed the Rad53 checkpoint-mediated induction of ribonucleotide reductase subunits Rnr1 and Rnr3, thereby abrogating MMS-induced mutagenesis and enhancing cell lethality. Moreover, cells deleted for RNR3 were hypersensitive to rapamycin plus MMS, providing the first demonstration that Rnr3 contributes to the survival of cells exposed to DNA damage. Our findings support a model whereby TORC1 acts as a survival pathway in response to genotoxic stress by maintaining the deoxynucleoside triphosphate pools necessary for error-prone translesion DNA polymerases. Thus, TOR-dependent cell survival in response to DNA-damaging agents coincides with increased mutation rates, which may contribute to the acquisition of chemotherapeutic drug resistance.TOR (target of rapamycin) is a phosphatidylinositol 3-kinase-related kinase family member that regulates cellular responses to wide-ranging environmental stresses, including nutrient starvation, growth factor deprivation, and hypoxia (8,20,45). These diverse environmental cues are transmitted by multiprotein TOR complexes through a variety of downstream pathways to regulate cap-dependent mRNA translation, transcriptional stress responses, cell cycle progression from G 1 to S phase, and cell survival. Rapamycin (RAP) is a macrocyclic lactone antibiotic that, in complex with FKBP12 (the Saccharomyces cerevisiae homolog is Fpr1), specifically targets TOR. Since dysregulation of Akt-TOR signaling has been associated with tumorigenesis (7,8), this pathway provides potential targets for cancer chemotherapy, as evidenced by the development of RAP analogs in clinical trials. Yet despite intense investigation of RAP action and the phenotypic consequences of TOR inhibition, the mechanistic basis for the antitumor activity of RAP in preclinical and clinical studies remains unclear.The TOR kinase was initially identified in the yeast S. cerevisiae, in a genetic screen for mutants conferring resistance to RAP. S. cerevisiae carries two closely related Tor1 and Tor2 kinases, while other eukaryotic genomes encode a single kinase, typified by mammalian mTOR (45). As in mammalian cells, TOR signaling in yeast regulates cell growth through the function of distinct multiprotein complexes (29,39,45,46). In yeast, Tor1 or Tor2 participates in the formation of a RAPsensitive TOR complex 1 (TORC1) that consists of Kog1, Lst8, and ...
Summary Age-related cataract (ARC) is a multifactorial disease and the leading cause of visual impairment and blindness worldwide. Genetic predisposition in association with other etiological factors may contribute to ARC. Although, there is some evidence for genetic influence for development of ARC, reports on gene mutations associated with ARC are scanty. In the present work, we identified a genetic variation (F71L) in the exon-2 of CRYAA gene in three unrelated female sporadic cases among 450 ARC patients but not in 144 normal non-cataractous controls. By comparing human recombinant wild-type and F71L-αA-crystallin, further we characterized the functional significance of this missense mutation. Size exclusion chromatography studies revealed that F71L mutation had no significant effect on the apparent molecular mass of αA-crystallin oligomeric complex. Intrinsic tryptophan fluorescence and far- and near-UV CD spectra indicated that F71L missense mutation did not significantly affect the secondary and tertiary structures of αA-crystallin. The ANS fluorescence emission spectra suggested no changes in surface hydrophobicity due to the F71L substitution. While the mutant αA-crystallin displayed almost complete loss (90%) of chaperone-like activity (CLA), in thermal aggregation of carbonic anhydrase, it showed 35-50% less protection in heat-induced aggregation of βL- and γ-crystallins. This is the first report of an αA-F71L mutation being associated with ARC. The results are consistent with the hypothesis that the mechanism of ARC in individuals carrying this mutation (F71L) might be due to the overall loss of in vivo chaperone activity due to interaction with other environmental factors.
Genetically caused deafness is a common trait affecting one in 1000 children and is predominantly inherited in an autosomalrecessive fashion. Several mutations in the GJB2 gene and a deletion of 342 kb in GJB6 gene (delGJB6-D13S1830) have been identified worldwide in patients with hearing impairment. In the present study, 303 nonsyndromic hearing-impaired patients (140 familial; 163 sporadic) were examined clinically and screened for mutations in GJB2 and GJB6 genes. Mutations in GJB2 gene were found in 33 (10.9%) patients of whom six (18.2%) were carriers for the mutant allele. The most frequent mutation was p.W24X accounting for 87% of the mutant alleles. In addition, six other sequence variations were identified in the GJB2 gene viz., c.IVS1+1G>A, c.167delT, c.235delC, p.W77X, p.R127H (polymorphism), p.M163V. None of the samples showed del(GJB6-D13S1830) or any point mutations in GJB6 gene.
A seven-generation family with 30 members affected by highly variable autosomal dominant zonular pulverulent cataracts has been previously described. We have localized the cataracts to a 19-cM interval on chromosome 2q33-q35 including the gamma-crystallin gene cluster. Maximum lod scores are 4.56 (theta=0.02) with D2S157, 3.66 (theta=0.12) with D2S72, and 3.57 (theta=0.052) with CRYG. Sequencing and allele-specific oligonucleotide analysis of the pseudo gammaE-crystallin promoter region from individuals in the pedigree suggest that activation of the gammaE-crystallin pseudo gene is unlikely to cause the cataracts in the family. In addition, base changes in the TATA box but not the Sp1-binding site have been found in unaffected controls and can be excluded as a sole cause of cataracts. In order to investigate the underlying genetic mechanism of cataracts in this family further, exons of the highly expressed gammaC- and gammaD-crystallin genes have been sequenced. The gammaD-crystallin gene shows no abnormalities, but a 5-bp duplication within exon 2 of the gammaC-crystallin gene has been found in one allele of each affected family member and is absent from both unaffected family members and unaffected controls. This mutation disrupts the reading frame of the gammaC-crystallin coding sequence and is predicted to result in the synthesis of an unstable gammaC-crystallin with 38 amino acids of the first "Greek key" motif followed by 52 random amino acids. This finding suggests that the appropriate association of mutant betagamma-crystallins into oligomers is not necessary to cause cataracts and may give us new insights into the genetic mechanism of cataract formation.
Shorter telomere length is associated with hypertensive individuals in Indian population.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.