Role of STE20-Type Kinases in Liver Lipid Metabolism and Hepatocarcinogenesis: Insights from In Vitro and In Vivo Studies

Abstract

Metabolic dysfunction-associated steatotic liver disease (MASLD) has emerged as a leading cause of chronic liver disease worldwide, affecting approximately 30% of the adult population. Up to 20% of individuals with MASLD progress to metabolic dysfunction-associated steatohepatitis (MASH), which is characterized by hepatic inflammation, fibrosis, and cell damage in the form of ballooning degeneration and apoptosis, in addition to hepatic fat infiltration. Patients with MASH are at high risk of developing cirrhosis, liver failure, and hepatocellular carcinoma (HCC), which is one of the most fatal and fastest-growing cancers. Thus, understanding the molecular pathogenesis of MASLD, and the signals that trigger the transition of simple steatosis to MASH and MASH-related HCC, are of high clinical importance. Our previous studies have identified several STE20-type kinases including STK25, MST3, and MST4 as important regulators of MASLD/MASH susceptibility. Here, we examined the possible role of STE20 kinases TAOK1 and TAOK3 in hepatocellular lipotoxicity and MASLD. We found that the expression levels of TAOK1 and TAOK3 in human liver biopsies positively correlated with key hallmarks of MASLD (i.e., hepatic steatosis, inflammation, and ballooning). The subcellular localization of TAOK1 and TAOK3 in human and mouse hepatocytes was confined to intracellular lipid droplets. Knockdown of TAOK1 or TAOK3 alleviated lipotoxicity in cultured human hepatocytes by accelerating lipid catabolism (mitochondrial β-oxidation and triacylglycerol secretion), suppressing lipid anabolism (fatty acid influx and lipogenesis), and mitigating oxidative/endoplasmic reticulum stress; the opposite changes were detected in TAOK1- or TAOK3-overexpressing cells. However, in contrast to the in vitro observations, genetic deficiency of TAOK3 in obese mice failed to inhibit diet-induced liver steatosis, inflammation, fibrosis, or systemic metabolic disturbances. Interestingly, the hepatic mRNA abundance of several TAOK3-related kinases, which have been previously implicated in MASLD development, was elevated in Taok3–/– vs. wild-type mice. We also investigated the role of STE20-type kinase STK25 in the initiation and progression of MASH-related HCC. Analysis of publicly available databases and in-house cohorts revealed that STK25 expression in human liver biopsies positively correlated with the incidence and severity of HCC. We found that 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, either globally across all peripheral tissues or specifically in hepatocytes, efficiently mitigated the development and exacerbation of hepatocarcinogenesis in a mouse model of MASH-driven HCC. Collectively, this thesis suggests that (1) TAOK1 and TAOK3 are critical regulatory nodes controlling hepatocellular lipotoxicity; (2) the lack of hepatic phenotype in Taok3 knockout mice in vivo may be attributable to the liver-specific compensation response for the genetic loss of TAOK3 by related STE20-type kinases; and (3) antagonizing STK25 signaling is a promising therapeutic strategy for the prevention and treatment of HCC in the context of MASH.