Research
We are interested in how bacteria or viruses are detected by the immune system, and how those responses are connected to various inflammatory and infectious diseases.
The immune system consists of two evolutionarily different but closely related arms, innate and adaptive immune responses. Harmony between these two immune responses is required for efficient combat against hazardous pathogens and cancers. Our laboratory focuses on the mechanisms of the innate immune system, its connection to the adaptive immune response, and disease pathogenesis resulting from dysregulation of innate immune responses.
left: Epithelium of human colon. Photograph courtesy of Dr. Cecile Chalouni. Also see her recent work in Nature Cell Biology 6, 1069 (2004)
2nd from left: Photograph courtesy of Dr. Ayano Satoh. Also see her recent work in Science (2005) 307(5712):1095
2nd from right: Salmonella on intestinal epithelium. Photograph courtesy of Dr. Jorge Galan. See our relevant publications in Cell 110, 191-202.
right: Crypts at terminal ileum. See our relevant publications in Science 307, 731-4.
Toll-like receptors (TLR)
A variety of microbial products are detected by a family of germline-encoded cell surface receptors called Toll-like receptors (TLRs). TLRs are evolutionarily conserved proteins that recognize specific pathogens or pathogen associated molecular patterns (PAMPs) and trigger signaling cascades leading to host immune responses and inflammation. One of our goals is to determine the molecular mechanisms involved in TLR signaling and its role in disease pathogenesis. We have shown that TLR plays role in the infectious and inflammatory diseases.
TLRs are receptor to detect pathogens such as virus or bacteria. Upon recognition of microbes the cascade of signaling is activated to induce various immune response genes.
Photograph is an Intestine of Crohn’s disease patient.
Paneth cells in the small intestine (ileum) can regulate bacterial flora by secreting anti-bacterial compounds. Photograph shows isolated mouse ileum containing Paneth cells.
Discovery of MHC Class I transactivator (CITA)
MHC (HLA in human) is the most important gene family discovered in modern medical history and Nobel prizes were given three times in this field. MHC genes are critical for infectious diseases, cancer, inflammatory disorders and transplantation medicine.
MHC class I and class II are required for antigen presentation to CD8 and CD4 T cells respectively. While CIITA (MHC class II transactivator) has been long known, the mechanism of expression of MHC class I genes had been largely unknown until our recent discovery of NLRC5/CITA (PNAS 2010 107:13794). CIITA can strongly induce MHC class II and related genes such as invariant chain, whereas another NLR family protein, NLRC5, can specifically associate with and activate promoters of both classical (HLA-A, B, C) and non-classical (HLA-E, F, G) MHC class I genes. In addition to MHC class I, NLRC5 can induce the expression of related genes in the MHC class I pathway, including beta2-microglobulin, TAP1 and LMP2. Therefore, NLRC5/CITA and CIITA regulate a concerted expression of genes in MHC class I and class II pathways, respectively (reviewed in Microbes Infect 2012 14:477 and Nat Rev Immunol 2012 12:813-20). We found that mice lacking NLRC5 gene display largely impaired expression of MHC class I, resulting in impaired CD8 T cell responses (J Immunol 2012 189:516). We also found that NLRC5 moves into the nucleus in cells and activates promoter of MHC class I genes by cooperating with other transcription factors (BBRC 2012 418: 786, Immunol2012 188:4951).
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How cancer is escaping from human immune system?
Low expression of NLRC5 is the main cause of cancer immunoescape.
How to predict the effect of immune checkpoint therapy on cancers
Checkpoint blockade immunotherapy has emerged as excellent strategies to treat patients with various cancers, as demonstrated by Nobel prize to Drs James Allison and Tasku Honjo. Although anti-CTLA-4, PD-1 or PD-L1/2 antibodies have been documented in a variety of cancers, responses are usually observed in a minority of patients. Considering the substantial risk of autoimmune side effects and the high cost of the treatment, it is critical to develop methods to identify the patients who can benefit from checkpoint blockade therapies. While various technologies have been assessed for predicting responses to checkpoint blockade therapies, their predictive power and usefulness as potential biomarkers were limited.
NLRC5 is a critical transactivator for the expression of MHC class I, which is required for activation of cytotoxic T cells and elimination of cancer cells. By analyzing gene expression in skin cancer (melanoma) patients, we identified that the patients group with high expression of NLRC5 is likely to respond to immucheckpoint blockade therapies. By combining NLRC5 expression with other biomarkers, we could increase the prediction power. We also found that similar method is useful to predict patients’ 5-years survival. These results suggest that NLRC5 tumor expression, alone or together with other biomarkers constitutes a valuable predictive biomarker for both prognosis and response to anti-CTLA-4 and anti-PD-1 blockade immunotherapy in cancer patients.
Press release: https://www.hokudai.ac.jp/news/2021/02/post-789.html (JPN)
The paper was published in Scientific Reports.
Pic: Immune cells attacking cancer cells
The innate immune system directly recognize pathogens such as virus or bacteria. The activation of innate immunity will allow antigen-specific immune responses by lymphocytes – adaptive immunity.
NLR proteins
Another gene family that plays critical role in the host defense against pathogens are the NLR protein family. This cytoplasmic protein family is characterized by two motifs: a nucleotide binding domain (NBD or NOD) and leucine-rich repeats (LRRs). NLRs belong to a very diverse protein family. Our efforts are focused on elucidating the function of this protein family, especially on their mechanisms of pathogen detection and downstream signaling cascades, as well as their significance in fighting infectious diseases.
Many NLRs are inside cells (cytoplasm) and detect bacteria or bacterial products. The activation of NLRs cause cytokine production and inflammatory responses.
NOD2: the highest risk factor in Crohn's disease
Crohn’s disease is a chronic inflammatory condition of the intestine. NOD2, an NLR family protein, is a sensor of a moiety of the bacterial cell wall. NOD2 mutations are the strongest genetic risk factor of Crohn’s disease in the small bowel (ileum). Nod2 is highly expressed in ileal Paneth cells, which produce anti-bacterial compounds. We are the first group to show the role of NOD2 in the host defense against bacteria in the intestine (Science 2005 307:731). Moreover, we found that NOD2 is critical for the bacterial killing activity of Paneth cells (PNAS 2009 106:15813). Indeed, we showed that mice lacking NOD2 gene have increased loads of bacteria in the ileum (PNAS 2009 106:15813). These findings led us to develop a novel ileal Crohn’s disease model using NOD2-mutant mice (PNAS 2010 41:182). This model strikingly recapitulates many characteristics seen in actual Crohn’s disease and is a powerful tool for Crohn’s disease research and drug development.
NLRC5 / CITA (MHC class I transactivator) is required for MHC class I expression. See our recent work in Nature Rev Immunol 12:813-20 (2012).
Revealed: How SARS-CoV-2 escapes from our immune system?
Our group composed of researchers at Hokkaido University in Japan and the Texas A&M University in the United States have found SARS-CoV-2 can knock out an important molecular pathway linked to an immune complex called MHC class I. The finding should help scientists better understand how COVID-19 infection takes hold.
We have used a bioinformatics approach to look at how SARS-CoV-2, the virus that causes COVID-19, changes gene expression in the immune systems of COVID-19 patients compared to uninfected individuals. This is a useful way to look into the function of complicated cell signalling pathways that trigger immune responses to fight off harmful bacteria and viruses.
MHC (major histocompatibility complex) class I molecules are a central weapon in the immune response against viruses. When a virus infects a cell, the cell facilitates the expression of viral antigens on the surface of infected cells, drawing the attention of immune cells called cytotoxic T cells. These immune cells zero in on and destroy the infected cells, together with the invading virus inside them. In addition to analyzing gene expression in COVID-19 patients, we also infected human cell lines with the SARS-CoV-2 virus to validate their findings. The results showed that a protein from the SARS-CoV-2 virus, called ORF 6, suppresses a host cell protein, called NLRC5, responsible for activating the MHC class I pathway.
The study showed this happens in two ways. ORF6 hampers cell signalling, which turns off the expression of NLRC5. ORF6 also blocks the function of NLRC5.Other infectious viruses, including HIV and MERS, are known to also target the MHC class I pathway. Researchers believed that SARS-CoV-2 probably did as well, but this study is the first to unravel the mechanism.Further research could help find and test drugs that block the activity of the ORF6 viral protein, to restore host cell ability to activate the major histocompatibility complex. If successful, such drugs could encourage the host immune system to clear the virus itself, effectively boosting immune responses.
Press release news from Hokkaido University and Texas A&M University:
(HU) https://www.global.hokudai.ac.jp/blog/revealed-how-sars-cov-2-evades-our-immune-system/
(Texas A&M) https://vitalrecord.tamhsc.edu/why-does-the-covid-19-virus-escape-from-our-immune-system/
Interviewed by local newspapers and media, including Yomiuri Shinbun, Hokkaido Shinbun; for US media including EurekAlert and Drug Target Review, etc.
Left: SARS-CoV-2 on the surface of cells
Bottom left: Article from Hokkaido Shinbun.
Bottom right: SARS-CoV-2 suppressed by NLRC5 (credit: JS Yoo, Kobayashi)
While many patients’ lives are saved by organ transplantation, mismatching of HLA (MHC in human) may cause serious side effects including rejection of transplanted organs and graft versus host diseases (GVHD).
MHC class I proteins are necessary to fight against pathogenic virus and intracellular bacteria. Photograph is Ebola virus, one of the most deadly virus and cause Ebola hemorrhagic fever.
Cancer cells are characterized with uncontrolled proliferation. The immune system eliminates cancer cells using MHC class I and cytotoxic T cells.