A Mutant of Hepatitis B Virus X Protein (HBxΔ127) Promotes Cell Growth through A Positive Feedback Loop Involving 5-Lipoxygenase and Fatty Acid Synthase

Abstract

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Hepatitis B virus X protein (HBx) contributes to the development of HCC, whereas HBx with COOH-terminal deletion is a frequent event in the HCC tissues. Previously, we identified a natural mutant of HBx-truncated 27 amino acids at the COOH-terminal (termed HBxDelta127), which strongly enhanced cell growth. In the present study, we focused on investigating the mechanism. Accordingly, fatty acid synthase (FAS) plays a crucial role in cancer cell survival and proliferation; thus, we examined the signaling pathways involving FAS. Our data showed that HBxDelta127 strongly increased the transcriptional activities of FAS in human hepatoma HepG2 and H7402 cells. Moreover, we found that 5-lipoxygenase (5-LOX) was responsible for the up-regulation of FAS by using MK886 (an inhibitor of 5-LOX) and 5-LOX small interfering RNA. We observed that HBxDelta127 could upregulate 5-LOX through phosphorylated extracellular signal-regulated protein kinases 1/2 and thus resulted in the increase of released leukotriene B4 (LTB4, a metabolite of 5-LOX) by ELISA. The additional LTB4 could upregulate the expression of FAS in the cells as well. Interestingly, we found that FAS was able to upregulate the expression of 5-LOX in a feedback manner by using cerulenin (an inhibitor of FAS). Collectively, HBxDelta127 promotes cell growth through a positive feedback loop involving 5-LOX and FAS, in which released LTB4 is involved in the up-regulation of FAS. Thus, our finding provides a new insight into the mechanism involving the promotion of cell growth mediated by HBxDelta127.

The Kaposi's Sarcoma-Associated Herpesvirus (KSHV)-Induced 5-Lipoxygenase-Leukotriene B4 Cascade Plays Key Roles in KSHV Latency, Monocyte Recruitment, and Lipogenesis

“…5LO is an emerging target in obesity, insulin resistance, obesity-related fatty liver disease, metabolic dysfunction (118,119), and nonalcoholic fatty liver and nonalcoholic steatohepatitis (120). Since 5LO/LTB4 has been shown to induce lipogenesis in human sebocytes (121), breast cancer cells (60), and hepatitis B virus X protein-mediated development of hepatocellular carcinoma (122) and since 5LO inhibitors are known to directly downregulate lipogenesis in sebocytes (121) and hepatic steatosis (119), we hypothesized that KSHV infection induces the 5LO/LTB4 cascade to enhance lipogenesis (123,124) and favor latency. Our results show that LTB4 promotes FASN transcription and gene expression and silencing of 5LO effectively reduces the protein levels of FASN (Fig.…”

Hepatitis B virus X protein promotes hepatoma cell proliferation via upregulation of MEKK2

“…HBx enhances the proliferation of hepatoma cells Previously, we established two engineered cell lines, namely HepG2-X, which was stably transfected with HBx, and HepG2-P, which was stably transfected with an empty pcD-NA3.0 vector [13] . We examined the growth of HepG2-X cells using the EdU incorporation assay and MTT assay.…”

“…Our laboratory has focused on the investigation of HBx-mediated hepatocarcinogenesis. Our findings show that arachidonic acid metabolism, extracellular signal-related kinases (ERK1/2), sterol regulatory element binding protein 1c, 5-lipoxygenase and fatty acid synthase are involved in HBx-induced cell proliferation [5,12,13] . However, the underlying mechanisms that mediate the effects of HBx on cell proliferation require further investigation.…”

“…HBx strongly enhances the growth of hepatoma cells in a system of stable transfection [5,12,13,32] . In the current study, we further investigated the mechanism that HBx employs to enhance the proliferation of hepatoma cells.…”

“…Previous studies have shown that HBx exhibits either apoptotic or proliferative activities in a context-dependent manner [33,34] . HBx promotes proliferation in stably transfected cells [5,12,13,32] . Therefore, we investigated the HBx-mediated proliferation in a model of stably HBx-transfected hepatoma HepG2-X cells.…”