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

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.

Heat shock factor 1 ameliorates proteotoxicity in cooperation with the transcription factor NFAT.

Heat shock transcription factor 1 (HSF1) is an important regulator of protein homeostasis (proteostasis) by controlling the expression of major heat shock proteins (Hsps) that facilitate protein folding. However, it is unclear whether other proteostasis pathways are mediated by HSF1. Here, we identified novel targets of HSF1 in mammalian cells, which suppress the aggregation of polyglutamine (polyQ) protein. Among them, we show that one of the nuclear factor of activated T cells (NFAT) proteins, NFATc2, significantly inhibits polyQ aggregation in cells and is required for HSF1-mediated suppression of polyQ aggregation. NFAT deficiency accelerated disease progression including aggregation of a mutant polyQ-huntingtin protein and shortening of lifespan in R6/2 Huntington's disease mice. Furthermore, we found that HSF1 and NFAT cooperatively induce the expression of the scaffold protein PDZK3 and αB-crystallin, which facilitate the degradation of polyQ protein. These results show the first mechanistic basis for the observation that HSF1 has a much more profound effect on proteostasis than individual Hsp or combination of different Hsps, and suggest a new pathway for ameliorating protein-misfolding diseases.

A novel mouse HSF3 has the potential to activate nonclassical heat-shock genes during heat shock.

The heat-shock response is characterized by the expression of a set of classical heat-shock genes, and is regulated by heat-shock transcription factor 1 (HSF1) in mammals. However, comprehensive analyses of gene expression have revealed very large numbers of inducible genes in cells exposed to heat shock. It is believed that HSF1 is required for the heat-inducible expression of these genes although HSF2 and HSF4 modulate some of the gene expression. Here, we identified a novel mouse HSF3 (mHSF3) translocated into the nucleus during heat shock. However, mHSF3 did not activate classical heat-shock genes such as Hsp70. Remarkably, overexpression of mHSF3 restored the expression of nonclassical heat-shock genes such as PDZK3 and PROM2 in HSF1-null mouse embryonic fibroblasts (MEFs). Although down-regulation of mHSF3 expression had no effect on gene expression or cell survival in wild-type MEF cells, it abolished the moderate expression of PDZK3 mRNA and reduced cell survival in HSF1-null MEF cells during heat shock. We propose that mHSF3 represents a unique HSF that has the potential to activate only nonclassical heat-shock genes to protect cells from detrimental stresses.

Heat shock transcription factor 1 inhibits expression of IL-6 through activating transcription factor 3.

The febrile response is a complex physiological reaction to disease, including a cytokine-mediated increase in body temperature and the activation of inflammatory systems. Fever has beneficial roles in terms of disease prognosis, partly by suppressing the expression of inflammatory cytokines. However, the molecular mechanisms underlining the fever-mediated suppression of inflammatory gene expression have not been clarified. In this study, we showed that heat shock suppresses LPS-induced expression of IL-6, a major pyrogenic cytokine, in mouse embryonic fibroblasts and macrophages. Heat shock transcription factor 1 (HSF1) activated by heat shock induced the expression of activating transcription factor (ATF) 3, a negative regulator of IL-6, and ATF3 was necessary for heat-mediated suppression of IL-6, indicating a fever-mediated feedback loop consisting of HSF1 and ATF3. A comprehensive analysis of inflammatory gene expression revealed that heat pretreatment suppresses LPS-induced expression of most genes (86%), in part (67%) via ATF3. When HSF1-null and ATF3-null mice were injected with LPS, they expressed much higher levels of IL-6 than wild-type mice, resulting in an exaggerated febrile response. These results demonstrate a novel inhibitory pathway for inflammatory cytokines.

A chromatographic approach for elevating the antibody-dependent cellular cytotoxicity of antibody composites.

Recent studies have shown that antibodies with low fucose content in their oligosaccharides exhibit highly potent antibody-dependent cellular cytotoxicity (ADCC). However, composites of therapeutic antibodies produced by conventional production systems using cell lines such as Chinese hamster ovary (CHO) and SP2/0 do not necessarily contain sufficient amounts of non-fucosylated antibody species. In this study, we combined two lectin-affinity chromatography techniques, Concanavalin A and Lens culinaris agglutinin, to enrich the non-fucosylated species from therapeutic material using the anti-Her2/neu model antibody. Oligosaccharide analysis by matrix-assisted laser desorption/ionization-time of flight MS following peptide-N-glycosidase F digestion suggested that non-fucosylated antibody could be enriched in the purified fraction with efficient removal of high-mannose species. The ADCC activity of the purified fraction was about 100-fold higher than that of the initial material. The chromatographic strategy presented here can be a useful tool to elevate ADCC activity of antibody materials without concentrating high-mannose oligosaccharides.

Analysis of HSF4 binding regions reveals its necessity for gene regulation during development and heat shock response in mouse lenses.

Heat shock transcription factors (HSFs) regulate gene expression in response to heat shock and in physiological conditions. In mammals, HSF1 is required for heat-mediated induction of classic heat shock genes; however, we do not know the molecular mechanisms by which HSF4 regulates gene expression or the biological consequences of its binding to chromatin. Here, we identified that HSF4 binds to various genomic regions, including the introns and distal parts of protein-coding genes in vivo in mouse lenses, and a substantial numbers of the regions were also occupied by HSF1 and HSF2. HSF4 regulated expression of some genes at a developmental stage when HSF1 and HSF2 expression decreased. Although HSF4 binding did not affect expression of many genes, it induces demethylated status of histone H3K9 on the binding regions. Unexpectedly, a lot of HSF4 targets were induced by heat shock treatment, and HSF4 is required for induction of a set of non-classic heat shock genes in response to heat shock, in part by facilitating HSF1 binding through chromatin modification. These results suggest novel mechanisms of gene regulation controlled by HSF4 in non-classic heat shock response and in lens development.

Purification and characterization of a non-S-RNase and S-RNases from styles of Japanese pear (Pyrus pyrifolia).

In this study we biochemically characterized stylar ribonucleases (RNases) of Japanese pear (Pyrus pyrifolia), which exhibits S-RNase-based gametophytic self-incompatibility. We separated the RNase fractions NS-1, NS-2, and NS-3 from stylar extracts of the cultivar Nijisseiki (S(2)S(4)). The RNase in each fraction was purified to homogeneity through a series of chromatographic steps. Chemical analysis of the proteins revealed that the basic RNases in the NS-2 and NS-3 fractions were the S(4)- and S(2)-RNases, respectively. Five additional S-RNases were purified from other cultivars. An acidic RNase in the NS-1 fraction was also purified from other cultivars, and identified as a non-S-allele-associated RNase (non-S-RNase). The non-S-RNase is composed of 203 amino acids, is non-glycosylated and is a N-terminal-pyroglutamylated enzyme of the RNase T(2) family. The substrate specificities and optimum pH levels of the non-S-RNase and S-RNases were similar. Interestingly, the specific activity of the non-S-RNase was 7.5-221-fold higher than those of the S-RNases when tolura yeast RNA was used as the substrate. The specific activity of the S(2)-RNase was 8.8-28.6-fold lower than those of the other S-RNases. These differences in specific activities among the stylar RNases are discussed.

Non-fucosylated therapeutic antibodies: the next generation of therapeutic antibodies.

Therapeutic antibody IgG1 has two N-linked oligosaccharide chains bound to the Fc region. The oligosaccharides are of the complex biantennary type, composed of a trimannosyl core structure with the presence or absence of core fucose, bisecting N-acetylglucosamine (GlcNAc), galactose, and terminal sialic acid, which gives rise to structural heterogeneity. Both human serum IgG and therapeutic antibodies are well known to be heavily fucosylated. Recently, antibody-dependent cellular cytotoxicity (ADCC), a lytic attack on antibody-targeted cells, has been found to be one of the critical effector functions responsible for the clinical efficacy of therapeutic antibodies such as anti-CD20 IgG1 rituximab (Rituxan((R))) and anti-Her2/neu IgG1 trastuzumab (Herceptin((R))). ADCC is triggered upon the binding of lymphocyte receptors (FcgammaRs) to the antibody Fc region. The activity is dependent on the amount of fucose attached to the innermost GlcNAc of N-linked Fc oligosaccharide via an alpha-1,6-linkage, and is dramatically enhanced by a reduction in fucose. Non-fucosylated therapeutic antibodies show more potent efficacy than their fucosylated counterparts both in vitro and in vivo, and are not likely to be immunogenic because their carbohydrate structures are a normal component of natural human serum IgG. Thus, the application of non-fucosylated antibodies is expected to be a powerful and elegant approach to the design of the next generation therapeutic antibodies with improved efficacy. In this review, we discuss the importance of the oligosaccharides attached to the Fc region of therapeutic antibodies, especially regarding the inhibitory effect of fucosylated therapeutic antibodies on the efficacy of non-fucosylated counterparts in one medical agent. The impact of completely non-fucosylated therapeutic antibodies on therapeutic fields will be also discussed.

Defucosylated chimeric anti-CC chemokine receptor 4 IgG1 with enhanced antibody-dependent cellular cytotoxicity shows potent therapeutic activity to T-cell leukemia and lymphoma.

Human IgG1 antibodies with low fucose contents in their asparagine-linked oligosaccharides have been shown recently to exhibit potent antibody-dependent cellular cytotoxicity (ADCC) in vitro. To additionally investigate the efficacy of the human IgG1 with enhanced ADCC, we generated the defucosylated chimeric anti-CC chemokine receptor 4 (CCR4) IgG1 antibody KM2760. KM2760 exhibited much higher ADCC using human peripheral blood mononuclear cells (PBMCs) as effector cells compared with the highly fucosylated, but otherwise identical IgG1, KM3060. In addition, KM2760 also exhibited potent ADCC in the presence of lower concentrations of human PBMCs than KM3060. Because CCR4 is a selective marker of T-cell leukemia/lymphoma, the effectiveness of KM2760 for T-cell malignancy was evaluated in several mouse models. First, to compare the antitumor activity of KM2760 and KM3060, we constructed a human PBMC-engrafted mouse model to determine ADCC efficacy with human effector cells. In this model, KM2760 showed significantly higher antitumor efficacy than KM3060, indicating that KM2760 retains its high potency in vivo. Second, KM2760 suppressed tumor growth in both syngeneic and xenograft mouse models in which human PBMCs were not engrafted. Although murine effector cells exhibited marginal ADCC mediated by KM2760 and KM3060, KM2760 unexpectedly showed higher efficacy than KM3060 in a syngeneic mouse model, suggesting that KM2760 functions in murine effector system in vivo via an unknown mechanism that differs from that in human. These results indicate that defucosylated antibodies with enhanced ADCC as well as potent antitumor activity in vivo are promising candidates for the novel antibody-based therapy.

The absence of fucose but not the presence of galactose or bisecting N-acetylglucosamine of human IgG1 complex-type oligosaccharides shows the critical role of enhancing antibody-dependent cellular cytotoxicity.

An anti-human interleukin 5 receptor (hIL-5R) humanized immunoglobulin G1 (IgG1) and an anti-CD20 chimeric IgG1 produced by rat hybridoma YB2/0 cell lines showed more than 50-fold higher antibody-dependent cellular cytotoxicity (ADCC) using purified human peripheral blood mononuclear cells as effector than those produced by Chinese hamster ovary (CHO) cell lines. Monosaccharide composition and oligosaccharide profiling analysis showed that low fucose (Fuc) content of complex-type oligosaccharides was characteristic in YB2/0-produced IgG1s compared with high Fuc content of CHO-produced IgG1s. YB2/0-produced anti-hIL-5R IgG1 was subjected to Lens culinaris aggulutin affinity column and fractionated based on the contents of Fuc. The lower Fuc IgG1 had higher ADCC than the IgG1 before separation. In contrast, the content of bisecting GlcNAc of the IgG1 affected ADCC much less than that of Fuc. In addition, the correlation between Gal and ADCC was not observed. When the combined effect of Fuc and bisecting GlcNAc was examined in anti-CD20 IgG1, only a severalfold increase of ADCC was observed by the addition of GlcNAc to highly fucosylated IgG1. Quantitative PCR analysis indicated that YB2/0 cells had lower expression level of FUT8 mRNA, which codes alpha1,6-fucosyltransferase, than CHO cells. Overexpression of FUT8 mRNA in YB2/0 cells led to an increase of fucosylated oligosaccharides and decrease of ADCC of the IgG1. These results indicate that the lack of fucosylation of IgG1 has the most critical role in enhancement of ADCC, although several reports have suggested the importance of Gal or bisecting GlcNAc and provide important information to produce the effective therapeutic antibody.