HSF1Base: A Comprehensive Database of HSF1 (Heat Shock Factor 1) Target Genes

HSF1 (heat shock factor 1) is an evolutionarily conserved master transcriptional regulator of the heat shock response (HSR) in eukaryotic cells. In response to high temperatures, HSF1 upregulates genes encoding molecular chaperones, also called heat shock proteins, which assist the refolding or degradation of damaged intracellular proteins. Accumulating evidence reveals however that HSF1 participates in several other physiological and pathological processes such as differentiation, immune response, and multidrug resistance, as well as in ageing, neurodegenerative demise, and cancer. To address how HSF1 controls these processes one should systematically analyze its target genes. Here we present a novel database called HSF1Base (hsf1base.org) that contains a nearly comprehensive list of HSF1 target genes identified so far. The list was obtained by manually curating publications on individual HSF1 targets and analyzing relevant high throughput transcriptomic and chromatin immunoprecipitation data derived from the literature and the Yeastract database. To support the biological relevance of HSF1 targets identified by high throughput methods, we performed an enrichment analysis of (potential) HSF1 targets across different tissues/cell types and organisms. We found that general HSF1 functions (targets are expressed in all tissues/cell types) are mostly related to cellular proteostasis. Furthermore, HSF1 targets that are conserved across various animal taxa operate mostly in cellular stress pathways (e.g., autophagy), chromatin remodeling, ribosome biogenesis, and ageing. Together, these data highlight diverse roles for HSF1, expanding far beyond the HSR

The Evolutionary and Functional Divergence of the Atg8 Autophagy Protein Superfamily

Autophagy is a highly conserved self-degradation process of eukaryotic cells which is required for the efective elimination of damaged and unnecessary cytosolic constituents. Defects in the process can cause the intracellular accumulation of such damages, thereby leading to the senescence and subsequent loss of the afected cell. Defective autophagy hence is implicated in the development of various degenerative processes, including cancer, neurodegenerative diseases, diabetes, tissue atrophy and fbrosis, and immune defciency, as well as in accelerated aging. The autophagic process is mediated by numerous autophagy-related (ATG) proteins, among which the ATG8/LC3/GABARAP (Microtubule-associated protein 1A/1B-light chain 3/Gammaaminobutyric acid receptor-associated protein) superfamily has a pivotal role in the formation and maturation of autophagosome, a key (macro) autophagic structure (the autophagosome sequesters parts of the cytoplasm which are destined for breakdown). While in the unicellular yeast there is only a single ATG8 protein, metazoan systems usually contain more ATG8 paralogs. ATG8 paralogs generally display tissue-specifc expression patterns and their functions are not strictly restricted to autophagy. For example, GABARAP proteins also play a role in intracellular vesicle transport, and, in addition to autophagosome formation, ATG8 also functions in selective autophagy. In this review, we summarize the functional diversity of ATG8/LC3/GABARAP proteins, using tractable genetic models applied in autophagy research

Suppression of AMPK/aak-2 by NRF2/SKN-1 down-regulates autophagy during prolonged oxidative stress

NF-E2-related factor 2 (NRF2) transcription factor has a fundamental role in cell homeostasis maintenance as one of the master regulators of oxidative and electrophilic stress responses. Previous studies have shown that a regulatory connection exists between NRF2 and autophagy during reactive oxygen species-generated oxidative stress. The aim of the present study was to investigate how autophagy is turned off during prolonged oxidative stress, to avoid overeating and destruction of essential cellular components. AMPK is a key cellular energy sensor highly conserved in eukaryotic organisms, and it has an essential role in autophagy activation at various stress events. Here the role of human AMPK and its Caenorhabditis elegans counterpart AAK-2 was explored upon oxidative stress. We investigated the regulatory connection between NRF2 and AMPK during oxidative stress induced by tert-butyl hydroperoxide (TBHP) in HEK293T cells and C. elegans. Putative conserved NRF2/protein skinhead-1 binding sites were found in AMPK/aak-2 genes by in silico analysis and were later confirmed experimentally by using EMSA. After addition of TBHP, NRF2 and AMPK showed a quick activation; AMPK was later down-regulated, however, while NRF2 level remained high. Autophagosome formation and Unc-51-like autophagy activating kinase 1 phosphorylation were initially stimulated, but they returned to basal values after 4 h of TBHP treatment. The silencing of NRF2 resulted in a constant activation of AMPK leading to hyperactivation of autophagy during oxidative stress. We observed the same effects in C. elegans demonstrating the conservation of this self-defense mechanism to save cells from hyperactivated autophagy upon prolonged oxidative stress. We conclude that NRF2 negatively regulates autophagy through delayed down-regulation of the expression of AMPK upon prolonged oxidative stress. This regulatory connection between NRF2 and AMPK may have an important role in understanding how autophagy is regulated in chronic human morbidities characterized by oxidative stress, such as neurodegenerative diseases, certain cancer types, and in metabolic diseases.-Kosztelnik, M., Kurucz, A., Papp, D., Jones, E., Sigmond, T., Barna, J., Traka, M. H., Lorincz, T., Szarka, A., Banhegyi, G., Vellai, T., Korcsmaros, T., Kapuy, O. Suppression of AMPK/aak-2 by NRF2/SKN-1 down-regulates autophagy during prolonged oxidative stress

The Small-Molecule Enhancers of Autophagy AUTEN-67 and -99 Delay Ageing in <i>Drosophila</i> Striated Muscle Cells

Autophagy (cellular self-degradation) plays a major role in maintaining the functional integrity (homeostasis) of essentially all eukaryotic cells. During the process, superfluous and damaged cellular constituents are delivered into the lysosomal compartment for enzymatic degradation. In humans, age-related defects in autophagy have been linked to the incidence of various age-associated degenerative pathologies (e.g., cancer, neurodegenerative diseases, diabetes, tissue atrophy and fibrosis, and immune deficiency) and accelerated ageing. Muscle mass decreases at detectable levels already in middle-aged patients, and this change can increase up to 30–50% at age 80. AUTEN-67 and -99, two small-molecule enhancers of autophagy with cytoprotective and anti-ageing effects have been previously identified and initially characterized. These compounds can increase the life span in wild-type and neurodegenerative model strains of the fruit fly Drosophila melanogaster. Adult flies were treated with these AUTEN molecules via feeding. Fluorescence and electron microscopy and Western blotting were used to assess the level of autophagy and cellular senescence. Flying tests were used to measure the locomotor ability of the treated animals at different ages. In the current study, the effects of AUTEN-67 and -99 were observed on striated muscle cells using the Drosophila indirect flight muscle (IFM) as a model. The two molecules were capable of inducing autophagy in IFM cells, thereby lowering the accumulation of protein aggregates and damaged mitochondria, both characterizing muscle ageing. Furthermore, the two molecules significantly improved the flying ability of treated animals. AUTEN-67 and -99 decrease the rate at which striated muscle cells age. These results may have a significant medical relevance that could be further examined in mammalian models

Longevity pathways converge on autophagy genes to regulate life span in Caenorhabditis elegans

Aging is a multifactorial. process with many mechanisms contributing to the decline. Mutations decreasing insulin/IGF-1 (insulin-like growth factor-1) or TOR (target of rapamycin) kinase-mediated signaling, mitochondrial activity and food intake each extend life span in divergent animal phyla. Understanding how these genetically distinct mechanisms interact to control longevity is a fundamental and fascinating problem in biology. Here we show that mutational inactivation of autophagy genes, which are involved in the degradation of aberrant, damaged cytoplasmic constituents accumulating in all aging cells, accelerates the rate at which the tissues age in the nematode Caenorhabditis elegans. According to our results Drosophila flies deficient in autophagy are also short-lived. We further demonstrate that reduced activity of autophagy genes suppresses life span extension in mutant nematodes with inherent dietary restriction, aberrant insulin/IGF-1 or TOR signaling, and lowered mitochondrial respiration. These findings suggest that the autophagy gene cascade functions downstream of and is inhibited by different longevity pathways in C elegans, therefore, their effects converge on autophagy genes to slow down aging and lengthen life span. Thus, autophagy may act as a central regulatory mechanism of animal aging