MALLORY DENK BODY FORMATION IS ASSOCIATED WITH AN INCREASE OF THE IMMUNOPROTEASOME AND A DECREASE OF THE 26S PROTEASOME

Abstract

Mallory Denk body (MDB) formation is seen in the liver cells of alcoholic patients and in other non‐alcoholic diseases. Proteasome inhibition is hypothesized to be the one of causes of MDB formation. Mice fed the drug diethyl‐1, 4‐dihydro‐2, 4, 6‐trimethyl‐3, 5‐pyridinedicarboxylate (DDC) for 10 weeks is the experimental model used to study MDB formation. 20S proteasome chymotrypsin‐like activity was not changed in the liver of mice refed DDC. However, ATP‐stimulated 26S proteasome chymotrypsin‐like activity was decreased by DDC feeding. These results confirm the reduction of 26S‐dependent ubiquitin‐proteasome proteolysis, which is reflected in the accumulation of ubiquitinated cytokeratins. Three constitutively expressed subunits of the 20S proteasome are known to be replaced by the inducible subunits of the immunoproteasome LMP2, LMP7, and MECL‐1 when stimulated with IFNg. There was an up regulation of LMP2, LMP7 and MECL‐1 protein levels and gene expression in the liver of mice fed DDC. Gene expression and protein levels of FAT10, a member of the ubiquitin‐like modifier family, which is also induced by IFNg and TNFa, were induced by DDC feeding. The marked up regulation of FAT10 could account for the block of cytokeratin turnover by the 26S proteasome. These results support the concept that the proteasome population is switched from the 26S proteasome to the immunoproteasome. The lack of 26S proteasome formation causes an accumulation of altered cytokeratin proteins. Protein aggresomes such as MDB then form. Supported by NIH/NIAAA Grants 8116 and P50‐011999 Alcohol Center Grant, Liver/Pancreas.