Transcription factor cooperativity with heat shock factor 1

SIRT1 Mediates Neuroprotective and Neurorescue Effects of Camel α-Lactalbumin and Oleic Acid Complex on Rotenone-Induced Parkinson's Disease

Parkinson's disease (PD) is the second most common devastating neurodegenerative disorder. Presently used therapies for PD have severe side effects and are limited to only temporary improvement. Therefore, a new therapeutic approach to treat PD urgently needs to be developed. α-Lactalbumin, the most abundant milk protein in camel milk, has been attributed to various medicinal properties. This study intended to investigate the neuroprotective efficacy of the camel α-lactalbumin and oleic acid (CLOA) complex. One mechanism postulated to underlie neuroprotection by the CLOA complex is the induction of silent information regulatory protein (SIRT1). SIRT1 is known to be involved in several pathological and physiological processes, and it has been suggested that SIRT1 plays a protective role in PD. Oxidative stress, inflammation, mitochondrial dysfunction, and apoptosis are involved in PD pathogenesis. Our results revealed that SIRT1 inhibits oxidative stress by maintaining HIF-1α in a deacetylated state. SIRT1 upregulates the expression of FOXO3a and HSF-1, thus inhibiting apoptosis and maintaining the homeostasis of cellular proteins. Increased SIRT1 expression reduces the levels of TNF-α, IL-6, and IL-8, which in turn inhibits neuroinflammation. In addition to SIRT1, the CLOA complex also enhances the expression of survivin and leptin and promotes the survival of neuroblastoma cells. Altogether, our results suggest that the CLOA complex might be a novel therapeutic molecule that could ameliorate neuronal cell damage in PD.

Heat Shock Signaling in Land Plants: From Plasma Membrane Sensing to the Transcription of Small Heat Shock Proteins

Heat stress events are major factors limiting crop productivity. During summer days, land plants must anticipate in a timely manner upcoming mild and severe temperature. They respond by accumulating protective heat-shock proteins (HSPs), conferring acquired thermotolerance. All organisms synthetize HSPs; many of which are members of the conserved chaperones families. This review describes recent advances in plant temperature sensing, signaling, and response. We highlight the pathway from heat perception by the plasma membrane through calcium channels, such as cyclic nucleotide-gated channels, to the activation of the heat-shock transcription factors (HSFs). An unclear cellular signal activates HSFs, which act as essential regulators. In particular, the HSFA subfamily can bind heat shock elements in HSP promoters and could mediate the dissociation of bound histones, leading to HSPs transcription. Although plants can modulate their transcriptome, proteome, and metabolome to protect the cellular machinery, HSP chaperones prevent, use, and revert the formation of misfolded proteins, thereby avoiding heat-induced cell death. Remarkably, the HSP20 family is mostly tightly repressed at low temperature, suggesting that a costly mechanism can become detrimental under unnecessary conditions. Here, the role of HSP20s in response to HS and their possible deleterious expression at non-HS temperatures is discussed.

KDM4B histone demethylase and G9a regulate expression of vascular adhesion proteins in cerebral microvessels

Intercellular adhesion molecule 1 (ICAM1) mediates the adhesion and transmigration of leukocytes across the endothelium, promoting inflammation. We investigated the epigenetic mechanism regulating ICAM1 expression. The pro-inflammatory cytokine TNF-α dramatically increased ICAM1 mRNA and protein levels in human brain microvascular endothelial cells and mouse brain microvessels. Chromatin immunoprecipitation revealed that TNF-α reduced methylation of histone H3 at lysines 9 and 27 (H3K9 and H3K27), well-known residues involved in gene suppression. Inhibition of G9a and EZH2, histone methyltransferases responsible for methylation at H3K9 and H3K27, respectively as well as G9a overexpression demonstrated the involvement of G9a in TNF-α-induced ICAM1 expression and leukocyte adhesion and transmigration. A specific role for KDM4B, a histone demethylase targeting H3K9me2, in TNF-α-induced ICAM1 upregulation was validated with siRNA. Moreover, treating mice with a KDM4 inhibitor ML324 blocked TNF-α-mediated neutrophil adhesion. Similarly, TNF-α-induced VCAM1 expression was suppressed by G9a overexpression and KDM4B knockdown. Collectively, we demonstrated that modification of H3K9me2 by G9a and KDM4B regulates expression of vascular adhesion molecules, and that depletion of these proteins or KDM4B reduces inflammation-induced leukocyte extravasation. Thus, blocking ICAM1 or KDM4B could offer a novel therapeutic opportunity treating brain diseases.

KDM7A histone demethylase mediates TNF-α-induced ICAM1 protein upregulation by modulating lysosomal activity

Intercellular adhesion molecule1 (ICAM1) is involved in adhesion and transmigration of leukocytes across endothelium, promoting brain inflammation and leading to brain diseases. Here, we studied the mechanism that regulates ICAM expression in response to proinflammatory cytokine tumor necrosis factor alpha (TNF-α). ICAM1 mRNA and protein levels in human brain microvascular endothelial cells dramatically increased after TNF-α treatment. TNF-α also upregulated histone demethylases KDM1B and KDM7A responsible for demethylation of H3K9me2, a well-known repression marker. Knockdown of KDM7A by a small interfering RNA reduced the ICAM1 protein level and leukocyte adhesion without an effect on ICAM1 mRNA expression. In contrast, a KDM1B knockdown did not affect TNF-α-induced ICAM1 expression. Thus, KDM7A-mediated ICAM1 protein upregulation is likely related to protein stability, not a histone-mediated epigenetic mechanism. Experiments with cycloheximide supported the role of KDM7A in ICAM1 protein stabilization. Further experiments suggest that KDM7A regulates ICAM1 protein stability via a lysosome-dependent pathway. Lysosome inhibitors increased the TNF-α-induced ICAM1 protein level and restored KDM7A knockdown-induced downregulation of ICAM1. In contrast, the KDM7A knockdown had no effect on proteasome-mediated ICAM1 degradation. We also found that the transcription factor EB protein level reduced in response to TNF-α but increased by the KDM7A knockdown. Immunocytochemical analysis revealed weak lysosome formation with high ICAM1 immunoreactivity after TNF-α treatment, but KDM7A knockdown reversed this response, resulting in strong lysosome formation with ICAM1 protein clustering in lysosomes. Taken together, our results show that KDM7A mediates TNF-α-induced ICAM1 protein upregulation and is mediated by induction of KDM7A, which regulates the TFEB-mediated lysosomal activity.

Analysis of the heat shock factor complex in mammalian HSP70 promoter

The heat shock response is characterized by the induction of heat shock proteins (HSPs) and is one of prominent mechanisms that regulate proteostasis capacity in the cell. In mammals, heat shock factor 1 (HSF1) regulates the expression of HSPs transcriptionally in both unstressed and stressed cells. Recent reports show that the HSF1-RPA complex constitutively gains access to nucleosomal DNA in part by recruiting a histone chaperone and a chromatin-remodeling component. Here, we describe the strategies to substitute endogenous HSF1 with ectopically expressed HSF1 or its mutant and to detect the occupancy of HSF1 transcription complex including RPA in vivo on two heat shock response elements located close together in the human or mouse HSP70 promoters by chromatin immunoprecipitation assay with high sensitivity and specificity.

ATF1 modulates the heat shock response by regulating the stress-inducible heat shock factor 1 transcription complex

The heat shock response is an evolutionally conserved adaptive response to high temperatures that controls proteostasis capacity and is regulated mainly by an ancient heat shock factor (HSF). However, the regulation of target genes by the stress-inducible HSF1 transcription complex has not yet been examined in detail in mammalian cells. In the present study, we demonstrated that HSF1 interacted with members of the ATF1/CREB family involved in metabolic homeostasis and recruited them on the HSP70 promoter in response to heat shock. The HSF1 transcription complex, including the chromatin-remodeling factor BRG1 and lysine acetyltransferases p300 and CREB-binding protein (CBP), was formed in a manner that was dependent on the phosphorylation of ATF1. ATF1-BRG1 promoted the establishment of an active chromatin state and HSP70 expression during heat shock, whereas ATF1-p300/CBP accelerated the shutdown of HSF1 DNA-binding activity during recovery from acute stress, possibly through the acetylation of HSF1. Furthermore, ATF1 markedly affected the resistance to heat shock. These results revealed the unanticipated complexity of the primitive heat shock response mechanism, which is connected to metabolic adaptation.

Heat shock factor 2 is required for maintaining proteostasis against febrile-range thermal stress and polyglutamine aggregation

HSF2 regulates proteostasis capacity against febrile-range thermal stress, which provides temperature-dependent mechanisms of cellular adaptation to thermal stress. Furthermore, HSF2 has a strong impact on disease progression of Huntington's disease R6/2 mice, suggesting that it could be a promising therapeutic target for protein misfolding diseases.

Heat shock response is characterized by the induction of heat shock proteins (HSPs), which facilitate protein folding, and non-HSP proteins with diverse functions, including protein degradation, and is regulated by heat shock factors (HSFs). HSF1 is a master regulator of HSP expression during heat shock in mammals, as is HSF3 in avians. HSF2 plays roles in development of the brain and reproductive organs. However, the fundamental roles of HSF2 in vertebrate cells have not been identified. Here we find that vertebrate HSF2 is activated during heat shock in the physiological range. HSF2 deficiency reduces threshold for chicken HSF3 or mouse HSF1 activation, resulting in increased HSP expression during mild heat shock. HSF2-null cells are more sensitive to sustained mild heat shock than wild-type cells, associated with the accumulation of ubiquitylated misfolded proteins. Furthermore, loss of HSF2 function increases the accumulation of aggregated polyglutamine protein and shortens the lifespan of R6/2 Huntington's disease mice, partly through αB-crystallin expression. These results identify HSF2 as a major regulator of proteostasis capacity against febrile-range thermal stress and suggest that HSF2 could be a promising therapeutic target for protein-misfolding diseases.