Caffeine alleviates acute liver injury by inducing the expression of NEDD4L and deceasing GRP78 level via ubiquitination.

BACKGROUND: Acute liver injury is liver cell injury that occurs rapidly in a short period of time. Caffeine has been shown to maintain hepatoprotective effect with an unclear mechanism. Endoplasmic reticulum stress (ERS) has significant effects in acute liver injury. Induction of GRP78 is a hallmark of ERS. Whether or not caffeine's function is related to GRP78 remains to be explored. METHODS: Acute liver injury model was established by LPS-treated L02 cells and in vivo administration of LPS/D-Gal in mice. Caffeine was pre-treated in L02 cells or mice. Gene levels was determined by real-time PCR and western blot. Cell viability was tested by CCK-8 assay and cell apoptosis was tested by flow cytometry. The interaction of GRP78 and NEDD4L was determined by Pull-down and co-immunoprecipitation (Co-IP) assay. The ubiquitination by NEDD4L on GRP78 was validated by in vitro ubiquitination assay. RESULTS: Caffeine protected liver cells against acute injury induced cell apoptosis and ERS both in vitro and in vivo. Suppression of GRP78 could block the LPS-induced cell apoptosis and ERS. NEDD4L was found to interact with GRP78 and ubiquitinate its lysine of 324 site directly. Caffeine treatment induced the expression of NEDD4L, resulting in the ubiquitination and inhibition of GRP78. CONCLUSION: Caffeine mitigated the acute liver injury by stimulating NEDD4L expression, which inhibited GRP78 expression via ubiquitination at its K324 site. Low dose of caffeine could be a promising therapeutic treatment for acute liver injury.

HBx regulates transcription factor PAX8 stabilization to promote the progression of hepatocellular carcinoma.

Transcription factor PAX8 expression is upregulated in several types of cancers. However, little is known about the function of PAX8 in the progression of hepatoma and its regulatory mechanisms. Here, we show that PAX8 silencing inhibits the proliferation and clonogenicity of hepatoma cells and its growth in vivo. The HBV X protein (HBx) does not directly interacts, but stabilizes PAX8 by inhibiting proteasome-dependent ubiquitination and degradation. Furthermore, the E3 ubiquitin ligase complex component Skp2 through its LRR domain directly interacts with the Prd domain of PAX8 and targets PAX8 by recognizing its lysine 275 for ubiquitination and degradation in hepatoma cells. In addition, HBx directly interacts and is colocalized with Skp2 to inhibit its recognition and subsequent ubiquitination and degradation of PAX8 in hepatoma cells. Moreover, HBx upregulates the expression and phosphorylation of Aurora A, a serine-threonine kinase, which interacts with and phosphorylates PAX8 at S209 and T277, compromising the Skp2-recognized PAX8 ubiquitination and destabilization. Thus, HBx stabilizes PAX8 protein by inhibiting the Skp2 targeted PAX8 ubiquitination and enhancing the Aurora A-mediated its phosphorylation, contributing to the progression of hepatoma. Our findings suggest that PAX8 may a new target for design of therapies and uncover new insights into the pathogenesis of hepatoma.

Integrated analysis of microRNA and mRNA expression profiles in HBx-expressing hepatic cells.

AIM: To identify the miRNA-mRNA regulatory network in hepatitis B virus X (HBx)-expressing hepatic cells. METHODS: A stable HBx-expressing human liver cell line L02 was established. The mRNA and miRNA expression profiles of L02/HBx and L02/pcDNA liver cells were identified by RNA-sequencing analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis was performed to investigate the function of candidate biomarkers, and the relationship between miRNA and mRNA was studied by network analysis. RESULTS: Compared with L02/pcDNA cells, 742 unregulated genes and 501 downregulated genes were determined as differentially expressed in L02/HBx cells. Gene ontology analysis suggested that the differentially expressed genes were relevant to different biological processes. Concurrently, 22 differential miRNAs were also determined in L02/HBx cells. Furthermore, integrated analysis of miRNA and mRNA expression profiles identified a core miRNA-mRNA regulatory network that is correlated with the carcinogenic role of HBx. CONCLUSION: Collectively, the miRNA-mRNA network-based analysis could be useful to elucidate the potential role of HBx in liver cell malignant transformation and shed light on the underlying molecular mechanism and novel therapy targets for hepatocellular carcinoma.