DDX39B facilitates the malignant progression of hepatocellular carcinoma via activation of SREBP1-mediated de novo lipid synthesis

DDX39B protects against sorafenib-induced ferroptosis by facilitating the splicing and cytoplasmic export of GPX4 pre-mRNA in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the main histological subtype of primary liver cancer and remains one of the most common solid malignancies globally. Ferroptosis was recently defined as an iron-catalyzed form of regulated necrosis. Because cancer cells exhibit higher iron requirements than noncancer cells, treatment with ferroptosis-inducing compounds may be a feasible strategy for cancer therapy. However, cancer cells develop acquired resistance to evade ferroptosis, and the mechanisms responsible for ferroptosis resistance are not fully clarified. In the current study, we reported that DDX39B was downregulated during sorafenib-induced ferroptosis in a dose- and time-dependent manner. Exogenous introduction of DDX39B ensured the survival of HCC cells upon exposure to sorafenib, while the opposite phenomenon was observed in DDX39B-silenced HCC cells. Mechanistically, we demonstrated that DDX39B increased GPX4 levels by promoting the splicing and cytoplasmic translocation of GPX4 pre-mRNA, which was sufficient to detoxify sorafenib-triggered excess lipid ROS production, lipid peroxidation accumulation, ferrous iron levels, and mitochondrial damage. Inhibition of DDX39B ATPase activity by CCT018159 repressed the splicing and cytoplasmic export of GPX4 pre-mRNA and synergistically assisted sorafenib-induced ferroptotic cell death in HCC cells. Taken together, our data uncover a novel role for DDX39B in ferroptosis resistance by modulating the maturation of GPX4 mRNA via a posttranscriptional approach and suggest that DDX39B inhibition may be a promising therapeutic strategy to enhance the sensitivity and vulnerability of HCC cells to sorafenib.

The switch triggering the invasion process: Lipid metabolism in the metastasis of hepatocellular carcinoma

ABSTRACT

In humans, the liver is a central metabolic organ with a complex and unique histological microenvironment. Hepatocellular carcinoma (HCC), which is a highly aggressive disease with a poor prognosis, accounts for most cases of primary liver cancer. As an emerging hallmark of cancers, metabolic reprogramming acts as a runaway mechanism that disrupts homeostasis of the affected organs, including the liver. Specifically, rewiring of the liver metabolic microenvironment, including lipid metabolism, is driven by HCC cells, propelling the phenotypes of HCC cells, including dissemination, invasion, and even metastasis in return. The resulting formation of this vicious loop facilitates various malignant behaviors of HCC further. However, few articles have comprehensively summarized lipid reprogramming in HCC metastasis. Here, we have reviewed the general situation of the liver microenvironment and the physiological lipid metabolism in the liver, and highlighted the effects of different aspects of lipid metabolism on HCC metastasis to explore the underlying mechanisms. In addition, we have recapitulated promising therapeutic strategies targeting lipid metabolism and the effects of lipid metabolic reprogramming on the efficacy of HCC systematical therapy, aiming to offer new perspectives for targeted therapy.

NAMPT promotes the malignant progression of HBV-associated hepatocellular carcinoma through activation of SREBP1-mediated lipogenesis

Metabolic reprogramming is a hallmark of cancer. The nicotinamide phosphoribosyltransferase (NAMPT)-mediated salvage pathway maintains sufficient cellular NAD levels and is required for tumorigenesis and development. However, the molecular mechanism by which NAMPT contributes to HBV-associated hepatocellular carcinoma (HCC) remains not fully understood. In the present study, our results showed that NAMPT protein was obviously upregulated in HBV-positive HCC tissues compared with HBV-negative HCC tissues. NAMPT was positively associated with aggressive HCC phenotypes and poor prognosis in HBV-positive HCC patients. NAMPT overexpression strengthened the proliferative, migratory, and invasive capacities of HBV-associated HCC cells, while NAMPT-insufficient HCC cells exhibited decreased growth and mobility. Mechanistically, we demonstrated that NAMPT activated SREBP1 (sterol regulatory element-binding protein 1) by increasing the expression and nuclear translocation of SREBP1, leading to the transcription of SREBP1 downstream lipogenesis-related genes and the production of intracellular lipids and cholesterol. Altogether, our data uncovered an important molecular mechanism by which NAMPT promoted HBV-induced HCC progression through the activation of SREBP1-triggered lipid metabolism reprogramming and suggested NAMPT as a promising prognostic biomarker and therapeutic target for HBV-associated HCC patients.

Valine promotes milk synthesis by regulating PKM2 nuclear accumulation and histone H3 acetylation through the TAS1R1-mTOR-DDX39B signaling pathway

Valine, a branched-chain amino acid found in dairy cows, has been recognized for its critical role in milk synthesis. However, the precise effect of valine on lactation in dairy cows remains an area of investigation. In our study, bovine mammary epithelial cells (BMECs) were isolated to explore the mechanism through which valine enhances milk synthesis. The results showed that 100 μM valine significantly boosted the milk synthesis via TAS1R1-mTOR-DDX39B signaling pathway in BMECs. Subsequent investigations revealed that DDX39B governs the accumulation of PKM2 in the nuclei of BMECs. This nuclear buildup of PKM2 weakened the interaction between HDAC3 and histone H3, leading to an increase in the acetylation levels of histone H3. In an vivo context, the 0.25 % valine-enriched drinking water notably elevated in the expression of milk protein and fat in these mice. Further examination showed that 0.25 % valine drinking water considerably augmented the protein expression levels of DDX39B, PKM2, and p-mTOR in the mice mammary glands. In summary, our results suggest that valine, by modulating the TAS1R1-mTOR-DDX39B signaling pathway, directs the accumulation of PKM2 in the nucleus. This, in turn, escalates the acetylation levels of histone H3, promoting the synthesis of both milk protein and fat.