Application of the wheat-germ cell-free translation system to produce high temperature requirement A3 (HtrA3) proteases

Overview of Human HtrA Family Proteases and Their Distinctive Physiological Roles and Unique Involvement in Diseases, Especially Cancer and Pregnancy Complications

The mammalian high temperature requirement A (HtrA) proteins are a family of evolutionarily conserved serine proteases, consisting of four homologs (HtrA1-4) that are involved in many cellular processes such as growth, unfolded protein stress response and programmed cell death. In humans, while HtrA1, 2 and 3 are widely expressed in multiple tissues with variable levels, HtrA4 expression is largely restricted to the placenta with the protein released into maternal circulation during pregnancy. This limited expression sets HtrA4 apart from the rest of the family. All four HtrAs are active proteases, and their specific cellular and physiological roles depend on tissue type. The dysregulation of HtrAs has been implicated in many human diseases such as cancer, arthritis, neurogenerative ailments and reproductive disorders. This review first discusses HtrAs broadly and then focuses on the current knowledge of key molecular characteristics of individual human HtrAs, their similarities and differences and their reported physiological functions. HtrAs in other species are also briefly mentioned in the context of understanding the human HtrAs. It then reviews the distinctive involvement of each HtrA in various human diseases, especially cancer and pregnancy complications. It is noteworthy that HtrA4 expression has not yet been reported in any primary tumour samples, suggesting an unlikely involvement of this HtrA in cancer. Collectively, we accentuate that a better understanding of tissue-specific regulation and distinctive physiological and pathological roles of each HtrA will improve our knowledge of many processes that are critical for human health.

Ovarian transcriptomic analysis of black Muscovy duck at the early, peak and late egg-laying stages

Ovarian development is a complex process involving many genes and pathways. A well-developed ovary is essential for poultry to keep high egg production and egg fertility. In order to better understand the mechanism of egg production performance, a comparative transcriptomic analysis was performed on ovaries of black Muscovy ducks at the early (BE), peak (BP) and late laying (BL) stages. 1683 DEGs were identified from BL-vs-BE, BL-vs-BP and BP-vs-BE, and the up-regulated genes were 41, 835, 260, the down-regulated genes were 60, 255, 730, respectively. Besides, there were 32, 20 and 424 DEGs co-expressed in the two comparison groups, and 11 DEGs were co-expressed in the three comparison groups. HOXA10, HtrA3, StAR, ZP2 and TAT were found to be involved in the regulation of ovarian development were significantly differentially expressed at different laying stages, which helped to regulate ovarian maturation and egg production. Moreover, we discovered several important functional pathways, such as steroid hormone biosynthesis and ovarian steroidogenesis, that appear to be much more active in the BP ovary compared to those of the BE and BL. Furthermore, 17 coding and 244 non-coding new transcripts were detected in the three comparison groups, the gene structures were optimized and the gene annotation informations were improved. These findings will provide a solid foundation on ovarian development in black Muscovy ducks and other poultry animals at different laying stages, and help to understand the complex molecular and cellular mechanisms of ovary.

Identification and Modification of Porphyromonas gingivalis Cysteine Protease, Gingipain, Ideal for Screening Periodontitis

Chronic periodontitis is an inflammatory disease caused by the formation of oral microbial biofilms. Periodontitis is associated with general health and not only oral diseases. Porphyromonas gingivalis is a well-known keystone pathogen for periodontitis and is associated with several systemic diseases, such as diabetes mellitus and Alzheimer's disease. We previously developed a system for screening periodontitis using P. gingivalis-specific serum immunoglobulin G (IgG) in an enzyme-linked immunosorbent assay with a sensitivity of 0.774 and a specificity of 0.586 and an area under the receiver operating characteristic curve of 0.708. However, the antigens elicited non-specific responses, since they were obtained from whole extracts of sonicated cultured bacteria. The purpose of this study was to identify antigens ideal for a sensitive and specific serum test. We identified the specific antigens using immunoaffinity columns immobilized with IgG antibodies from periodontitis patients. Liquid chromatography-tandem mass spectrometry identified 29 antigens from the elutes. Recombinant proteins for these candidates were synthesized using the wheat germ cell-free translation system and screened by dot blot analysis with serum from the columns. Three of the 16 candidates that reacted showed strongest affinities upon dot blot analysis; they included outer membrane protein 28, cysteine proteases, lysine gingipain Kgp, and arginine gingipain RgpA. Outer membrane protein 28 was not suitable for screening P. gingivalis infection because of its high false-negative rates. Kgp and RgpA were unstable antigens since they underwent self-digestion. They were made stable by substituting the active cysteine residues in Kgp and RgpA with alanine using site-directed mutagenesis. Using the modified antigens, we demonstrated that the patient serum IgG level against RgpA was the highest among all the antigens expressed in P. gingivalis. Moreover, the N-terminus of recombinant RgpA was excellent in differentiating between diseased and non-diseased states (with sensitivity of 0.85, specificity of 0.9, and area under the curve of 0.915). Although dot blot analysis was the only experiment used, the N-terminus of RgpA is an excellent antigen to immunologically test for P. gingivalis infection, especially for estimating the risks for periodontitis-associated systemic diseases. In conclusion, we have developed a P. gingivalis antigen for screening periodontitis.

Cellular substrates and pro-apoptotic function of the human HtrA4 protease

The human HtrA4 protein, belonging to the HtrA family of proteases/chaperones, participates in oncogenesis and placentation, and plays a role in preeclampsia. As the knowledge concerning the biochemical features of this protein and its role at the molecular level is limited, in this work we characterized the HtrA4 molecule and searched for its cellular function. We found that recombinant HtrA4 composed of the protease and PDZ domains is a trimeric protein of intermediate thermal stability whose activity is considerably lower compared to other human HtrA proteases. By pull-down combined with mass spectrometry we identified a large array of potential HtrA4 partners. Using other experimental approaches, including immunoprecipitation, enzyme-linked immunosorbent assay and fluorescence microscopy we confirmed that HtrA4 formed complexes in vitro and in cellulo with proteins such as XIAP (inhibitor of apoptosis protein), caspases 7 and 9, β-tubulin, actin, TCP1α and S100A6. The recombinant HtrA4 degraded XIAP, the caspases, β-tubulin and actin but not TCP1α or S100A6. Together, these results suggest that HtrA4 may influence various cellular functions, including apoptosis. Furthermore, the panel of potential HtrA4 partners may serve as a basis for future studies of HtrA4 function.

The HtrA3 protease promotes drug-induced death of lung cancer cells by cleavage of the X-linked inhibitor of apoptosis protein (XIAP)

HtrA3 is a proapoptotic protease shown to promote drug-induced cytotoxicity in lung cancer cells and proposed to have an antitumor effect. However, at the molecular level, the role of HtrA3 in cell death induction is poorly understood. There are two HtrA3 isoforms, a long and a short one, termed HtrA3L and HtrA3S. By performing pull down assays, co-immunoprecipitation and ELISA, we showed that HtrA3 formed complexes with the X-linked inhibitor of apoptosis protein (XIAP). The recombinant HtrA3 variants ΔN-HtrA3L and -S, lacking the N-terminal regions that are not essential for protease activity, cleaved XIAP with a comparable efficiency, though ΔN-HtrA3S was more active in the presence of cellular extract, suggesting the existence of an activating factor. Immunofluorescence and proximity ligation assays indicated that HtrA3 partially co-localized with XIAP. Exogenous ΔN-HtrA3L/S promoted apoptotic death of lung cancer cells treated with etoposide and caused a significant decrease of cellular XIAP levels, in a way dependent on HtrA3 proteolytic activity. These results collectively indicate that both HtrA3 isoforms stimulate drug-induced apoptotic death of lung cancer cells via XIAP cleavage and thus help to understand the molecular mechanism of HtrA3 function in apoptosis and in cancer cell death caused by chemotherapy.

RNAi-Based Biocontrol of Wheat Nematodes Using Natural Poly-Component Biostimulants

With the growing global demands on sustainable food production, one of the biggest challenges to agriculture is associated with crop losses due to parasitic nematodes. While chemical pesticides have been quite successful in crop protection and mitigation of damage from parasites, their potential harm to humans and environment, as well as the emergence of nematode resistance, have necessitated the development of viable alternatives to chemical pesticides. One of the most promising and targeted approaches to biocontrol of parasitic nematodes in crops is that of RNA interference (RNAi). In this study we explore the possibility of using biostimulants obtained from metabolites of soil streptomycetes to protect wheat (Triticum aestivum L.) against the cereal cyst nematode Heterodera avenae by means of inducing RNAi in wheat plants. Theoretical models of uptake of organic compounds by plants, and within-plant RNAi dynamics, have provided us with useful insights regarding the choice of routes for delivery of RNAi-inducing biostimulants into plants. We then conducted in planta experiments with several streptomycete-derived biostimulants, which have demonstrated the efficiency of these biostimulants at improving plant growth and development, as well as in providing resistance against the cereal cyst nematode. Using dot blot hybridization we demonstrate that biostimulants trigger a significant increase of the production in plant cells of si/miRNA complementary with plant and nematode mRNA. Wheat germ cell-free experiments show that these si/miRNAs are indeed very effective at silencing the translation of nematode mRNA having complementary sequences, thus reducing the level of nematode infestation and improving plant resistance to nematodes. Thus, we conclude that natural biostimulants produced from metabolites of soil streptomycetes provide an effective tool for biocontrol of wheat nematode.

Antagonism between HTRA3 and TGFβ1 Contributes to Metastasis in Non-Small Cell Lung Cancer

High temperature requirement A3 (HTRA3, long and short isoforms) is a member of the HtrA family and has been implicated as a tumor suppressor in cancer progression in multiple cancer types, yet its molecular functions in non-small cell lung cancer (NSCLC) are not well understood. Here, we report that decreased levels of HTRA3 negatively correlate with elevated TGFβ1 in lung tumor tissue with metastasis. Furthermore, high expression of HTRA3 indicated better prognosis independent of TGFβ1 expression. In NSCLC cell lines, exogenous TGFβ1 significantly downregulated the level of HTRA3, especially the long isoform, during induction of epithelial-mesenchymal transition (EMT). Mechanistically, c-Jun, which is elevated by TGFβ1, directly bound the promoter of HTRA3-L and inhibited its transcription. As a negative feedback loop, overexpression of HTRA3-L attenuated TGFβ1-mediated invasion-metastasis cascades via activation of SMAD2/3 and sensitized cells to anti-PD-L1 treatment. Taken together, our findings suggest that in the early stages of cancer, overexpressed HTRA3 acts as a brake on the oncogenic effects of TGFβ1 and inhibits tumor metastasis. In later stages, the role of HTRA3 is weakened and TGFβ1 efficiently promotes EMT in the absence of the HTRA3 brake. SIGNIFICANCE: This study provides new mechanistic insight of the interaction between HTRA3 and TGFβ in lung cancer by illustrating that HTRA3 is a novel mediator acting as a suppressor of TGFβ1-related oncogenic effects.

HtrA3 is a cellular partner of cytoskeleton proteins and TCP1α chaperonin

The human HtrA3 protease is involved in placentation, mitochondrial homeostasis, stimulation of apoptosis and proposed to be a tumor suppressor. Molecular mechanisms of the HtrA3 functions are poorly understood and knowledge concerning its cellular targets is very limited. There are two HtrA3 isoforms, the long (HtrA3L) and short (HtrA3S). Upon stress, their N-terminal domains are removed, resulting in the more active ΔN-HtrA3. By pull down and mass spectrometry techniques, we identified a panel of putative ΔN-HtrA3L/S substrates. We confirmed that ΔN-HtrA3L/S formed complexes with actin, β-tubulin, vimentin and TCP1α in vitro and in a cell and partially co-localized with the actin and vimentin filaments, microtubules and TCP1α in a cell. In vitro, both isoforms cleaved the cytoskeleton proteins, promoted tubulin polymerization and displayed chaperone-like activity, with ΔN-HtrA3S being more efficient in proteolysis and ΔN-HtrA3L - in polymerization. TCP1α, essential for the actin and tubulin folding, was directly bound by the ΔN-HtrA3L/S but not cleaved. These results indicate that actin, β-tubulin, vimentin, and TCP1α are HtrA3 cellular partners and suggest that HtrA3 may influence cytoskeleton dynamics. They also suggest different roles of the HtrA3 isoforms and a possibility that HtrA3 protease may also function as a co-chaperone.

SIGNIFICANCE

The HtrA3 protease stimulates apoptosis and is proposed to be a tumor suppressor and a therapeutic target, however little is known about its function at the molecular level and very few HtrA3 physiological substrates have been identified so far. Furthermore, HtrA3 is the only member of the HtrA family of proteins which, apart from the long isoform possessing the PD and PDZ domains (HtrA3L), has a short isoform (HtrA3S) lacking the PDZ domain. In this work we identified a large panel (about 150) of the tentative HtrA3L/S cellular partners which provides a good basis for further research concerning the HtrA3 function. We have shown that the cytoskeleton proteins actin, β-tubulin and vimentin, and the TCP1α chaperonin are cellular partners of both HtrA3 isoforms. Our findings indicate that HtrA3 may promote destabilization of the actin and vimentin cytoskeleton and suggest that it may influence the dynamics of the microtubule network, with the HtrA3S being more efficient in cytoskeleton protein cleavage and HtrA3L - in tubulin polymerization. Also, we have shown for the first time that HtrA3 has a chaperone-like, holdase activity in vitro - activity typical for co-chaperone proteins. The proposed HtrA3 influence on the cytoskeleton dynamics may be one of the ways in which HtrA3 promotes cell death and affects cancerogenesis. We believe that the results of this study provide a new insight into the role of HtrA3 in a cell and further confirm the notion that HtrA3 should be considered as a target of new anti-cancer therapies.

Maternal HtrA3 optimizes placental development to influence offspring birth weight and subsequent white fat gain in adulthood

High temperature requirement factor A3 (HtrA3), a member of the HtrA protease family, is highly expressed in the developing placenta, including the maternal decidual cells in both mice and humans. In this study we deleted the HtrA3 gene in the mouse and crossed females carrying zero, one, or two HtrA3-expressing alleles with HtrA3^+/− males to investigate the role of maternal vs fetal HtrA3 in placentation. Although HtrA3^−/− mice were phenotypically normal and fertile, HtrA3 deletion in the mother resulted in intra-uterine growth restriction (IUGR). Disorganization of labyrinthine fetal capillaries was the major placental defect when HtrA3 was absent. The IUGR caused by maternal HtrA3 deletion, albeit being mild, significantly altered offspring growth trajectory long after birth. By 8 months of age, mice born to HtrA3-deficient mothers, independent of their own genotype, were significantly heavier and contained a larger mass of white fat. We further demonstrated that in women serum levels of HtrA3 during early pregnancy were significantly lower in IUGR pregnancies, establishing an association between lower HtrA3 levels and placental insufficiency in the human. This study thus revealed the importance of maternal HtrA3 in optimizing placental development and its long-term impact on the offspring well beyond in utero growth.

Structural insights into the activation mechanisms of human HtrA serine proteases

Human HtrA1-4 proteins belong to the HtrA family of evolutionarily conserved serine proteases and function as important modulators of many physiological processes, including maintenance of mitochondrial homeostasis, cell signaling and apoptosis. Disturbances in their action are linked to severe diseases, including oncogenesis and neurodegeneration. The HtrA1-4 proteins share structural and functional features of other members of the HtrA protein family, however there are several significant differences in structural architecture and mechanisms of action which makes each of them unique. Our goal is to present recent studies regarding human HtrAs. We focus on their physiological functions, structure and regulation, and describe current models of activation mechanisms. Knowledge of molecular basis of the human HtrAs' action is a subject of great interest; it is crucial for understanding their relevance in cellular physiology and pathogenesis as well as for using them as targets in future therapies of diseases such as neurodegenerative disorders and cancer.

Structural and Functional Analysis of Human HtrA3 Protease and Its Subdomains

Human HtrA3 protease, which induces mitochondria-mediated apoptosis, can be a tumor suppressor and a potential therapeutic target in the treatment of cancer. However, there is little information about its structure and biochemical properties. HtrA3 is composed of an N-terminal domain not required for proteolytic activity, a central serine protease domain and a C-terminal PDZ domain. HtrA3S, its short natural isoform, lacks the PDZ domain which is substituted by a stretch of 7 C-terminal amino acid residues, unique for this isoform. This paper presents the crystal structure of the HtrA3 protease domain together with the PDZ domain (ΔN-HtrA3), showing that the protein forms a trimer whose protease domains are similar to those of human HtrA1 and HtrA2. The ΔN-HtrA3 PDZ domains are placed in a position intermediate between that in the flat saucer-like HtrA1 SAXS structure and the compact pyramidal HtrA2 X-ray structure. The PDZ domain interacts closely with the LB loop of the protease domain in a way not found in other human HtrAs. ΔN-HtrA3 with the PDZ removed (ΔN-HtrA3-ΔPDZ) and an N-terminally truncated HtrA3S (ΔN-HtrA3S) were fully active at a wide range of temperatures and their substrate affinity was not impaired. This indicates that the PDZ domain is dispensable for HtrA3 activity. As determined by size exclusion chromatography, ΔN-HtrA3 formed stable trimers while both ΔN-HtrA3-ΔPDZ and ΔN-HtrA3S were monomeric. This suggests that the presence of the PDZ domain, unlike in HtrA1 and HtrA2, influences HtrA3 trimer formation. The unique C-terminal sequence of ΔN-HtrA3S appeared to have little effect on activity and oligomerization. Additionally, we examined the cleavage specificity of ΔN-HtrA3. Results reported in this paper provide new insights into the structure and function of ΔN-HtrA3, which seems to have a unique combination of features among human HtrA proteases.

Activity-modulating monoclonal antibodies to the human serine protease HtrA3 provide novel insights into regulating HtrA proteolytic activities

Mammalian HtrA (high temperature requirement factor A) proteases, comprising 4 multi-domain members HtrA1-4, play important roles in a number of normal cellular processes as well as pathological conditions such as cancer, arthritis, neurodegenerative diseases and pregnancy disorders. However, how HtrA activities are regulated is not well understood, and to date no inhibitors specific to individual HtrA proteins have been identified. Here we investigated five HtrA3 monoclonal antibodies (mAbs) that we have previously produced, and demonstrated that two of them regulated HtrA3 activity in an opposing fashion: one inhibited while the other stimulated. The inhibitory mAb also blocked HtrA3 activity in trophoblast cells and enhanced migration and invasion, confirming its potential in vivo utility. To understand how the binding of these mAbs modulated HtrA3 protease activity, their epitopes were visualized in relation to a 3-dimensional HtrA3 homology model. This model suggests that the inhibitory HtrA3 mAb blocks substrate access to the protease catalytic site, whereas the stimulatory mAb may bind to the PDZ domain alone or in combination with the N-terminal and protease domains. Since HtrA1, HtrA3 and HtrA4 share identical domain organization, our results establish important foundations for developing potential therapeutics to target these HtrA proteins specifically for the treatment of a number of diseases, including cancer and pregnancy disorders.

Soluble full-length expression and characterization of snRNP protein U1-68/70K

The autoantigen U1-68/70K is the dominant diagnostic marker in Mixed Connective Tissue Disease (MCTD) that until recently could not be expressed in its full-length form (Northemann et al., 1995, [16]). Using cell-free expression screening, we successfully produced the snRNP protein U1-68/70K in a soluble full-length form in Escherichia coli cells. The protein length and identity was determined by Western Blot and MS/MS analysis. Additionally, its reactivity in the autoimmune diagnostic was confirmed. Establishment of a cell-free expression system for this protein was important for further elucidation of protein expression properties such as the cDNA construct, expression temperature and folding properties; these parameters can now be determined in a fast and resource-conserving manner.

Serum antibody response to group II chaperonin from Methanobrevibacter oralis and human chaperonin CCT

Both group I (HSP60) and group II (CCT) chaperonins are targets of autoantibodies. Autoimmune reactions to HSP60 have been well characterized, while immune reactions to group II chaperonin have not been clarified. Methanobrevibacter oralis is a suspected periodontal pathogen with group II chaperonin. In this study, serum responses to M. oralis chaperonin, human HSP60, and CCT subunits were examined using sera from patients with periodontitis and autoimmune diseases. In comparison with healthy controls, periodontitis patients showed significantly higher responses to CCT4 and CCT8 on dot blot analysis. Signals for CCT3 and CCT8 in autoimmune disease patients were significantly higher than in controls. Significant differences were also demonstrated by Western blotting in anti-CCT4 response in both patient groups. All subjects showed strong reactivity to M. oralis chaperonin and faint signals to human HSP60. Autoantibodies were raised against CCT rather than HSP60; and CCT3, CCT4, and CCT8 were shown to be the main targets. Host immune systems may be frequently exposed to chaperonins of Archaea in various habitats. Although further studies of the cross-reactivity between M. oralis chaperonin and human CCT are required, anti-CCT autoantibodies may be involved in the pathogenesis of periodontitis and autoimmune diseases.

HtrA3 Is Downregulated in Cancer Cell Lines and Significantly Reduced in Primary Serous and Granulosa Cell Ovarian Tumors

Objective. The high temperature requirement factor A3 (HtrA3) is a serine protease homologous to bacterial HtrA. Four human HtrAs have been identified. HtrA1 and HtrA3 share a high degree of domain organization and are downregulated in a number of cancers, suggesting a widespread loss of these proteases in cancer. This study examined how extensively the HtrA (HtrA1-3) proteins are downregulated in commonly used cancer cell lines and primary ovarian tumors.

Methods. RT-PCR was applied to various cancer cell lines (n=17) derived from the ovary, endometrium, testes, breast, prostate, and colon, and different subtypes of primary ovarian tumors [granulosa cell tumors (n=19), mucinous cystadenocarcinomas (n=6), serous cystadenocarcinomas (n=8)] and normal ovary (n = 9). HtrA3 protein was localized by immunohistochemistry.

Results. HtrA3 was extensively downregulated in the cancer cell lines examined including the granulosa cell tumor-derived cell lines. In primary ovarian tumors, the HtrA3 was significantly lower in serous cystadenocarcinoma and granulosa cell tumors. In contrast, HtrA1 and HtrA2 were expressed in all samples with no significant differences between the control and tumors. In normal postmenopausal ovary, HtrA3 protein was localized to lutenizing stromal cells and corpus albicans. In serous cystadenocarcinoma, HtrA3 protein was absent in the papillae but detected in the mesenchymal cyst wall.

Conclusion. HtrA3 is more extensively downregulated than HtrA1-2 in cancer cell lines. HtrA3, but not HtrA1 or HtrA2, was decreased in primary ovarian serous cystadenocarcinoma and granulosa cell tumors. This study provides evidence that HtrA3 may be the most relevant HtrA associated with ovarian malignancy.

HtrA3 as an early marker for preeclampsia: specific monoclonal antibodies and sensitive high-throughput assays for serum screening

Mammalian HtrA3 (high temperature requirement A3) is a serine protease of the HtrA family. It has two isoforms [long (HtrA3-L) and short (HtrA3-S)] and is important for placental development and cancer progression. Recently, HtrA3 was identified as a potential diagnostic marker for early detection of preeclampsia, a life-threatening pregnancy-specific disorder. Currently there are no high-throughput assays available to detect HtrA3 in human serum. In this study we generated and fully tested a panel of five HtrA3 mouse monoclonal antibodies (mAbs). Three mAbs recognised both HtrA3-L and HtrA3-S and the other two detected HtrA3-L only. All five mAbs were highly specific to HtrA3 and applicable in western blotting and immunohistochemical analysis of endogenous HtrA3 proteins in the mouse and human tissues. Amplified luminescent proximity homogeneous assays-linked immunosorbent assays (AlphaLISAs), were developed to detect HtrA3 isoforms in picomolar levels in serum. The HtrA3 AlphaLISA detected significantly higher serum levels of HtrA3 in women at 13-14 weeks of gestation who subsequently developed preeclampsia compared to gestational-age matched controls. These HtrA3 mAbs are valuable for the development of immunoassays and characterisation of HtrA3 isoform-specific biology. The newly developed HtrA3 AlphaLISA assays are suitable for large scale screening of human serum.