Author｜Zhang Siwei
54 years ago, Banuch Blumberg, professor of medicine and anthropology at the University of Pennsylvania, discovered hepatitis B virus (HBV) (referred to as hepatitis B virus). Perhaps he did not expect that he would win the Nobel Prize in Physiology or Medicine for this, and he did not expect that for the next half a century, the battle between humans and the hepatitis B virus has been "difficult to resolve." [ cccDNA) and integrated into the human genome to make the virus DNA form stable. This is also the key to HBV's ability to maintain a long-term chronic infection in the body and is difficult to clear." Yang Pengyuan, a researcher at the Institute of Biophysics, Chinese Academy of Sciences, accepted the " Chinese Journal of Science" said in an interview that it is of great significance to study the characteristics of the interaction between hepatitis B virus and the host genome.
Based on this, Yang Pengyuan's research group and Ji Xiong's research group from the School of Life Sciences, Peking University have worked together to systematically explain the characteristics of the interaction between hepatitis B virus cccDNA and the integrated form of HBV-DNA and the host genome using 3C-HTGTS technology, which is HBV infection And related disease treatment provides new potential targets. Related research results were recently published in "Cell Discovery".
Yang Pengyuan (second from the left) is making samples. Photo courtesy of interviewees
reported the first number of cases of Type B infectious disease
Hepatitis B virus infection is one of the major global public health problems. At present, there are about 260 million people chronically infected with hepatitis B virus in the world, and nearly 1 million people die from liver failure, cirrhosis and hepatocellular carcinoma caused by chronic hepatitis B each year.
The National Statutory Epidemic Situation of Infectious Diseases in 2019 issued by the Health Commission pointed out that viral hepatitis is still the number B infectious disease with the number of reported cases of infectious diseases in my country. According to the report data of World Hepatitis Day 2020, there are still about 70 million hepatitis B patients in my country, and the number of patients in need of treatment is about 20 to 30 million.
"With the popularization of hepatitis B vaccine and free vaccination, my country's prevention and control of hepatitis B has a significant effect, and the infection rate of the population is steadily declining, especially the infection rate of children is well controlled." Du Shunda, chief physician of liver surgery at Peking Union Medical College Hospital, told China Science News. However, the problem of hepatitis B infection still cannot be ignored.
It is understood that the relatively high rate of hepatitis B infection is mainly due to the relatively low diagnosis rate (18%) and cure rate (11%) of hepatitis B in my country. The initial symptoms of hepatitis B infection are hidden, which means that many people become infected and the source of infection without knowing it, and once the infection is difficult to cure. Another reason is mother-to-child transmission.
In addition, statistics provided by the International Agency for Research on Cancer of the World Health Organization show that in 2020, liver cancer ranks fifth in the incidence of cancer and the second in mortality in my country. Moreover, previous studies have pointed out that about 80% of liver cancers in my country are related to HBV infection.
"If the hepatitis B virus infection is well controlled, it may be possible to directly reduce the incidence of liver cancer." Du Shunda said.
How does the virus interact with host cells
Compared to hepatitis C virus (HCV), HBV is more difficult to entangle.
Investigating the reason, Yang Pengyuan explained that HBV belongs to the family of hepato-DNA viruses, and cccDNA can synthesize all RNA and proteins required by HBV by using the transcription and translation mechanism of host cells. The existing hepatitis B treatment drugs (nucleoside analogs such as lamivudine) can inhibit HBV replication by inhibiting the function of p protein (HBV polymerase), but they cannot eliminate the cccDNA and integrated forms of the infected cells. Viral DNA.Therefore, when the hepatitis B infection is stopped, the viral DNA can use the transcription and translation mechanism of the host cell to re-synthesize the RNA and protein required by HBV to complete the virus replication.
HCV is a positive-strand RNA virus, and there is no cccDNA-like intermediate during its replication. Hepatitis C Infected patients can effectively reduce HCV RNA levels after taking hepatitis C treatment drugs, thereby eliminating HCV and realizing hepatitis C cure.
Therefore, eliminating the long-term stable viral DNA in the human cell nucleus is the key to hepatitis B treatment. So, this leads to a scientific question: how to stably exist in the host cell of HBV cccDNA and integrated form of viral DNA, and how to effectively eliminate these viral DNA.
"The first step is to clarify the mode and characteristics of the interaction between viral DNA and host cells." Yang Pengyuan said.
For this reason, the two research teams used 3C-HTGTS technology to find that the interaction between HBV cccDNA and the host genome tends to be rich in H3K4me3, H3K9ac, H3K4me1 and H3K27ac and other histone modified HepG2-NTCP cells. Active enhancers and promoters.
3C-HTGTS is also a novel one-to-all chromatin interaction test method adopted by Ji Xiong's research group. "This method only requires one step of restriction enzyme digestion and ligation of the cross-linked chromatin. In theory, any endonuclease that recognizes the 4bp sequence can be used, so that the degree of chromatin fragmentation and the resolution of chromatin interaction detection are higher. "Ji Xiong said.
It is worth mentioning that the researchers also used this method to detect a new form of interaction: in HepAD38 cells stably expressing HBV, it was found that the integrated form of HBV-DNA can form a chromatin circle with the host genomic DNA Structure, and tend to interact with the promoter region of the host gene.
continues to explore the mechanism of virus action
"Although many colleagues at home and abroad have detected that HBV can be integrated in the human genome,But we found for the first time that this integration can further interact with the surrounding human chromatin in the integration area. "Yang Pengyuan said.
research found that HBV cccDNA interacts with the H3K4me1 rich region in the host genome, and then through chromatin immunoprecipitation (ChIP-qPCR) found that there are rich histone H3K4me1 modifications on HBV cccDNA. When knocked When low intracellular lysine-specific methyltransferase 2C/D (KMT2C/D) that mediates histone H3K4me1 generation, HBV RNA transcription is significantly down-regulated, and HBV surface antigen (HBsAg) and E antigen secreted in the supernatant (HBeAg) content was significantly reduced, and the results suggest that HBV cccDNA can mediate transcriptional regulation of the virus through host methyltransferase.
During the interview, the reporter learned that the biggest difficulty they encountered during the research was the availability and ease of use There are too few HBV infection models, especially in small animals.
Fortunately, as early as 2012, the team of Li Wenhui, a researcher at the Beijing Institute of Biological Sciences, discovered that NTCP is a receptor for HBV infection and developed a HepG2-NTCP cell model. This model brings great convenience to HBV infection at the cellular level.
"In this study, we used the HepG2-NTCP cell model. "Yang Pengyuan said that in the future, they will continue to study the mechanism of HBV integration into the human genome and its effective targets for interaction with human chromatin, so as to create conditions for proposing regulatory mechanisms for HBV-induced liver cancer and corresponding new targeting strategies.
related Paper information:
https://doi.org/10.1038/s41421-020-00218-1
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