Glucose and SIRT2 reciprocally mediate the regulation of keratin 8 by lysine acetylation.

Lysine acetylation is an important posttranslational modification that regulates microtubules and microfilaments, but its effects on intermediate filament proteins (IFs) are unknown. We investigated the regulation of keratin 8 (K8), a type II simple epithelial IF, by lysine acetylation. K8 was basally acetylated and the highly conserved Lys-207 was a major acetylation site. K8 acetylation regulated filament organization and decreased keratin solubility. Acetylation of K8 was rapidly responsive to changes in glucose levels and was up-regulated in response to nicotinamide adenine dinucleotide (NAD) depletion and in diabetic mouse and human livers. The NAD-dependent deacetylase sirtuin 2 (SIRT2) associated with and deacetylated K8. Pharmacologic or genetic inhibition of SIRT2 decreased K8 solubility and affected filament organization. Inhibition of K8 Lys-207 acetylation resulted in site-specific phosphorylation changes of K8. Therefore, K8 acetylation at Lys-207, a highly conserved residue among type II keratins and other IFs, is up-regulated upon hyperglycemia and down-regulated by SIRT2. Keratin acetylation provides a new mechanism to regulate keratin filaments, possibly via modulating keratin phosphorylation.

Energy determinants GAPDH and NDPK act as genetic modifiers for hepatocyte inclusion formation.

Genetic factors impact liver injury susceptibility and disease progression. Prominent histological features of some chronic human liver diseases are hepatocyte ballooning and Mallory-Denk bodies. In mice, these features are induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) in a strain-dependent manner, with the C57BL and C3H strains showing high and low susceptibility, respectively. To identify modifiers of DDC-induced liver injury, we compared C57BL and C3H mice using proteomic, biochemical, and cell biological tools. DDC elevated reactive oxygen species (ROS) and oxidative stress enzymes preferentially in C57BL livers and isolated hepatocytes. C57BL livers and hepatocytes also manifested significant down-regulation, aggregation, and nuclear translocation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDH knockdown depleted bioenergetic and antioxidant enzymes and elevated hepatocyte ROS, whereas GAPDH overexpression decreased hepatocyte ROS. On the other hand, C3H livers had higher expression and activity of the energy-generating nucleoside-diphosphate kinase (NDPK), and knockdown of hepatocyte NDPK augmented DDC-induced ROS formation. Consistent with these findings, cirrhotic, but not normal, human livers contained GAPDH aggregates and NDPK complexes. We propose that GAPDH and NDPK are genetic modifiers of murine DDC-induced liver injury and potentially human liver disease.