The mammalian microtubule-associated serine/threonine (MAST) kinases are a highly conserved subfamily of AGC kinases that are implicated as therapeutic targets for cancer and diabetes. However, the ac Show more
The mammalian microtubule-associated serine/threonine (MAST) kinases are a highly conserved subfamily of AGC kinases that are implicated as therapeutic targets for cancer and diabetes. However, the activity, regulation, and substrates of MAST kinases are poorly understood. We examined the biochemical activity of Mast2, as a representative of the MAST family. The domain of unknown function (DUF1908) is necessary for Mast2 kinase activity in vitro, while the PDZ domain is dispensable. Mast2 kinase activity does not appear to be compatible with the AGC kinase model of T-loop phospho-activation. Instead, it contains a unique insertion that is likely stabilized by ion-pair interactions. The C terminus of the kinase domain contains motifs regulated by mechanistic target of rapamycin (mTOR) in other AGC kinases, and mutation of these conserved residues reduces Mast2 kinase activity. Consistent with mTOR regulation, Mast2 purified from insulin-stimulated cells has increased activity compared to serum-starved cells, and this increase in activity is dependent on mTOR. Finally, stable Show less
Compromised hepatic fatty acid oxidation (FAO) has been observed in human MASH patients and animal models of MASLD/MASH. It remains poorly understood how and when the hepatic FAO pathway is suppressed Show more
Compromised hepatic fatty acid oxidation (FAO) has been observed in human MASH patients and animal models of MASLD/MASH. It remains poorly understood how and when the hepatic FAO pathway is suppressed during the progression of MASLD towards MASH. Hepatic ChREBP⍺ is a classical lipogenic transcription factor that responds to the intake of dietary sugars. We examined its role in regulating hepatocyte fatty acid oxidation (FAO) and the impact of hepatic Chrebpa deficiency on sensitivity to diet-induced MASLD/MASH in mice. We discovered that hepatocyte ChREBP⍺ is both necessary and sufficient to maintain FAO in a cell-autonomous manner independently of its DNA-binding activity. Supplementation of synthetic PPAR⍺/δ agonist is sufficient to restore FAO in Chrebp Our findings support the protective role of hepatocyte ChREBPa against diet-induced MASLD/MASH in mouse models in part via promoting CYP2C50-driven FAO. Show less