XBP1 Positively Regulates MANF Expression In The Liver Tissue Of Chronic Hepatitis B

Hepatitis B is caused by hepatitis B virus. A part of hepatitis B patients develop into liver cirrhosis and hepatocellular carcinoma. It was reported that ER stress and unfolded protein response(UPR) are activated in hepatitis B. MANF is a secreting protein sensitive to ER stress. MANF can protect cells from apoptosis induced by ER stress. Recently, we found that MANF negatively regulates NF-kB by interacting with p65. The purpose of this study is to investigate the relationship of UPR gene XBP1 expression and MANF in hepatitis B. The main results are as follows:1. Expressions of ER stress markers in liver tissues of hepatitis B patients.Immunohistochemistry and Q-PCR assays were used to detect the expressions of ER stress markers BIP, CHOP. We found that both BIP and CHOP were upregulated in hepatitis B, and the levels of BIP and CHOP in G4S4 stage were higher than that in G1S1 stage.2. Expressions of XBP1 and MANF in the liver of hepatitis BThe protein and mRNA levels of XBP1 and MANF were detected by using immunohistochemistry and Q-PCR assays. We found that XBP1 and MANF wereincreased in hepatitis B and the amount of both proteins was increased along with the severity of disease.3. Interaction of XBP1 and MANF in the liver tissue of hepatitis BImmunofluorescence staining showed that XBP1/XBP1 s localized with MANF in the liver tissues. CO-immunoprecipitation assay also showed that XBP1 and MANF interaction with in the liver tissue.4. Inhibition of IRE1-XBP1 signal on MANF expressionSTF-083010 was used to inhibit IRE1 nuclease activity. XBP1s-si RNA was used to knockdown XBP1 s. Western blot assay showed that the level of IRE1 was not changed, but the levels of XBP1 s and MANF were decreased after STF-083010 treatment. Meanwhile, knockdown of endogenous XBP1 s also reduced MANF expression. These results suggest that IRE1-XBP1 signal up-regulate MANF.Taken together, ER stress was induced in hepatitis B. The expressions of XBP1 and MANF were up-regulated in the liver tissues of hepatitis B. XBP1 interacted with MANF and IRE1-XBP1 signal up-regulate MANF.