STE20-type kinases MST3 and MST4 promote the progression of hepatocellular carcinoma: Evidence from human cell culture and expression profiling of liver biopsies

Cell-intrinsic insulin signaling defects in human iPS cell-derived hepatocytes in type 2 diabetes

Hepatic insulin resistance is central to type 2 diabetes (T2D) and metabolic syndrome, but defining the molecular basis of this defect in humans is challenging because of limited tissue access. Utilizing inducible pluripotent stem cells differentiated into hepatocytes from control individuals and patients with T2D and liquid chromatography with tandem mass spectrometry-based (LC-MS/MS-based) phosphoproteomics analysis, we identified a large network of cell-intrinsic alterations in signaling in T2D. Over 300 phosphosites showed impaired or reduced insulin signaling, including losses in the classical insulin-stimulated PI3K/AKT cascade and their downstream targets. In addition, we identified over 500 phosphosites of emergent, i.e., new or enhanced, signaling. These occurred on proteins involved in the Rho-GTPase pathway, RNA metabolism, vesicle trafficking, and chromatin modification. Kinome analysis indicated that the impaired phosphorylation sites represented reduced actions of AKT2/3, PKCθ, CHK2, PHKG2, and/or STK32C kinases. By contrast, the emergent phosphorylation sites were predicted to be mediated by increased action of the Rho-associated kinases 1 and 2 (ROCK1/2), mammalian STE20-like protein kinase 4 (MST4), and/or branched-chain α-ketoacid dehydrogenase kinase (BCKDK). Inhibiting ROCK1/2 activity in T2D induced pluripotent stem cell-derived hepatocytes restored some of the alterations in insulin action. Thus, insulin resistance in the liver in T2D did not simply involve a loss of canonical insulin signaling but the also appearance of new phosphorylations representing a change in the balance of multiple kinases. Together, these led to altered insulin action in the liver and identified important targets for the therapy of hepatic insulin resistance.

Therapeutic Potential of STE20-Type Kinase STK25 Inhibition for the Prevention and Treatment of Metabolically Induced Hepatocellular Carcinoma

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is a rapidly growing malignancy with high mortality. Recently, metabolic dysfunction-associated steatohepatitis (MASH) has emerged as a major HCC catalyst; however, signals driving transition of MASH to HCC remain elusive and treatment options are limited. Herein, we investigated the role of STE20-type kinase STK25, a critical regulator of hepatocellular lipotoxic milieu and MASH susceptibility, in the initiation and progression of MASH-related HCC.

METHODS

The clinical relevance of STK25 in HCC was assessed in publicly available datasets and by RT-qPCR and proximity ligation assay in a validation cohort. The functional significance of STK25 silencing in human hepatoma cells was evaluated in vitro and in a subcutaneous xenograft mouse model. The therapeutic potential of STK25 antagonism was examined in a mouse model of MASH-driven HCC, induced by a single diethylnitrosamine injection combined with a high-fat diet.

RESULTS

Analysis of public databases and in-house cohorts revealed that STK25 expression in human liver biopsies positively correlated with HCC incidence and severity. The in vitro silencing of STK25 in human hepatoma cells suppressed proliferation, migration, and invasion with efficacy comparable to that achieved by anti-HCC drugs sorafenib or regorafenib. STK25 knockout in human hepatoma cells also blocked tumor formation and growth in a subcutaneous xenograft mouse model. Furthermore, pharmacologic inhibition of STK25 with antisense oligonucleotides-administered systemically or hepatocyte-specifically-efficiently mitigated the development and exacerbation of hepatocarcinogenesis in a mouse model of MASH-driven HCC.

CONCLUSION

This study underscores STK25 antagonism as a promising therapeutic strategy for the prevention and treatment of HCC in the context of MASH.

Targeting STK26 and ATG4B: miR-22-3p as a modulator of autophagy and tumor progression in HCC

Drug-induced protective autophagy significantly affects the efficacy of anticancer therapies. Enhancing tumor cell sensitivity to treatment by inhibiting autophagy is essential for effective cancer therapy. Our study, analyzing data from The Cancer Genome Atlas (TCGA) public database, HCC cell lines, and liver cancer tissue samples, found that miR-22-3p is expressed at low levels in HCC and is significantly associated with clinicopathological features and patient prognosis. Functional assays and xenograft models demonstrated that miR-22-3p suppresses HCC progression. Moreover, Western blot analysis and the LC3B double reporter (mRFP1-EGFP-LC3B) confirmed that miR-22-3p inhibits autophagy in HCC cells. Further investigation identified Sterile 20-like kinase 26 (STK26) and Autophagy Related 4B Cysteine Peptidase (ATG4B) as targets of miR-22-3p. STK26, which is overexpressed in HCC, promotes malignant characteristics such as proliferation, migration, and invasion. Additionally, STK26 facilitates autophagy in HCC by phosphorylating ATG4B at serine 383. miR-22-3p inhibits autophagy by targeting STK26 and ATG4B, thus preventing the phosphorylation of ATG4B at serine 383. Sorafenib treatment increases the levels and phosphorylation of STK26 and ATG4B, inducing protective autophagy. The combination of miR-22-3p with sorafenib demonstrated enhanced antitumor effects both in vitro and in vivo. In conclusion, our findings suggest that miR-22-3p inhibits HCC progression by regulating the expression of STK26 and ATG4B, potentially through autophagy inhibition, thereby increasing sensitivity to sorafenib treatment. This offers a new therapeutic approach for effective HCC.

Mechanisms coupling lipid droplets to MASLD pathophysiology

Hepatic steatosis, the buildup of neutral lipids in lipid droplets (LDs), is commonly referred to as metabolic dysfunction-associated steatotic liver disease when alcohol or viral infections are not involved. Metabolic dysfunction-associated steatotic liver disease encompasses simple steatosis and the more severe metabolic dysfunction-associated steatohepatitis, characterized by inflammation, hepatocyte injury, and fibrosis. Previously viewed as inert markers of disease, LDs are now understood to play active roles in disease etiology and have significant nonpathological and pathological functions in cell signaling and function. These dynamic properties of LDs are tightly regulated by hundreds of proteins that coat the LD surface, controlling lipid metabolism, trafficking, and signaling. The following review highlights various facets of LD biology with the primary goal of discussing key mechanisms through which LDs promote the development of advanced liver diseases, including metabolic dysfunction-associated steatohepatitis.

7-Hydroxyflavone improves nonalcoholic fatty liver disease by acting on STK24

The escalating incidence of nonalcoholic fatty liver disease (NAFLD) is closely associated with a high-fat diet, leading to a decline in quality of life and significant health impairment. 7-Hydroxyflavone (7-HY) is a flavonoid known for its anti-inflammatory, anticarcinogenic, and antioxidant effects. This study aims to assess the ameliorative effects of 7-HY on NAFLD induced by a high-fat diet and elucidate underlying mechanisms. Oleic acid/palmitic acid-induced HepG2 cells and C57BL/6 mice on a high-fat diet were utilized as in vitro and in vivo models. In animal experiments, 7-HY was utilized as a dietary supplement. The 15-week in vivo experiment monitored body weight, body fat percentage, glucose tolerance, insulin tolerance, and metabolic indexes. Commercial kits assessed triglyceride (TG) and total cholesterol levels in cells, liver tissue, and blood. Discovery Studio identified potential targets of 7-HY, compared with NAFLD-associated targets in the GeneCards database. Results indicated 7-HY mitigated fat accumulation, hepatic steatosis, and oxidative stress induced by a high-fat diet. Furthermore, 7-HY showed potential efficacy in ameliorating abnormal glucose metabolism and promoting energy metabolism. Reverse target finding and molecular docking demonstrated a robust interaction between 7-HY and serine/threonine kinase 24 (STK24). Subsequent experimental results confirmed 7-HY's ability to inhibit TG deposition in HepG2 cells through interaction with STK24. In conclusion, 7-HY demonstrated the capacity to alleviate high-fat diet-induced NAFLD, presenting a novel strategy for the prevention and treatment of NAFLD.

Genetic Ablation of STE20-Type Kinase MST4 Does Not Alleviate Diet-Induced MASLD Susceptibility in Mice

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its advanced subtype, metabolic dysfunction-associated steatohepatitis (MASH), have emerged as the most common chronic liver disease worldwide, yet there is no targeted pharmacotherapy presently available. This study aimed to investigate the possible in vivo function of STE20-type protein kinase MST4, which was earlier implicated in the regulation of hepatocellular lipotoxic milieu in vitro, in the control of the diet-induced impairment of systemic glucose and insulin homeostasis as well as MASLD susceptibility. Whole-body and liver-specific Mst4 knockout mice were generated by crossbreeding conditional Mst4fl/fl mice with mice expressing Cre recombinase under the Sox2 or Alb promoters, respectively. To replicate the environment in high-risk subjects, Mst4-/- mice and their wild-type littermates were fed a high-fat or a methionine-choline-deficient (MCD) diet. Different in vivo tests were conducted in obese mice to describe the whole-body metabolism. MASLD progression in the liver and lipotoxic damage to adipose tissue, kidney, and skeletal muscle were analyzed by histological and immunofluorescence analysis, biochemical assays, and protein and gene expression profiling. In parallel, intracellular fat storage and oxidative stress were assessed in primary mouse hepatocytes, where MST4 was silenced by small interfering RNA. We found that global MST4 depletion had no effect on body weight or composition, locomotor activity, whole-body glucose tolerance or insulin sensitivity in obese mice. Furthermore, we observed no alterations in lipotoxic injuries to the liver, adipose, kidney, or skeletal muscle tissue in high-fat diet-fed whole-body Mst4-/- vs. wild-type mice. Liver-specific Mst4-/- mice and wild-type littermates displayed a similar severity of MASLD when subjected to an MCD diet, as evidenced by equal levels of steatosis, inflammation, hepatic stellate cell activation, fibrosis, oxidative/ER stress, and apoptosis in the liver. In contrast, the in vitro silencing of MST4 effectively protected primary mouse hepatocytes against ectopic lipid accumulation and oxidative cell injury triggered by exposure to fatty acids. In summary, these results suggest that the genetic ablation of MST4 in mice does not mitigate the initiation or progression of MASLD and has no effect on systemic glucose or insulin homeostasis in the context of nutritional stress. The functional compensation for the genetic loss of MST4 by yet undefined mechanisms may contribute to the apparent discrepancy between in vivo and in vitro phenotypic consequences of MST4 silencing.