Transglutaminase 2 regulates mallory body inclusion formation and injury-associated liver enlargement.
OBJECTIVE
Mallory body (MB) inclusions are a characteristic feature of several liver disorders and share similarities with cytoplasmic inclusions observed in neural diseases and myopathies. MBs consist primarily of keratins 8 and 18 (K8/K18), require a K8-greater-than-K18 ratio for their formation, and contain glutamine-lysine cross-links generated by transglutaminase (TG). We hypothesized that protein transamidation is essential for MB formation.


METHODS
Because TG2 is the most abundant hepatocyte TG, we tested our hypothesis using TG2(-/-) and their wild-type counterpart mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), an established MB inducer. Keratin cross-linking was further examined using recombinant proteins or transgenic mice that overexpress K8 or K18.


RESULTS
TG2(-/-) livers have markedly reduced TG2 activity as compared with TG2(+/+) livers. The DDC-fed TG2(-/-) mice have dramatic decreases in MB formation and liver hypertrophy response as contrasted with DDC-fed TG2(+/+) mice. Despite similar hepatocellular damage, TG2(-/-) mice had more gallstones, jaundice, and ductal proliferation than wild-type mice. Inhibition of MB formation in TG2(-/-) mice was associated with marked attenuation of ubiquitination and K8-containing protein cross-linking. MB formation and resolution paralleled the generation then disappearance of cross-linked K8, respectively. K8 is a preferential TG2 substrate when compared to K18, as examined in vitro or in DDC-fed transgenic mice that overexpress K8 or K18.


CONCLUSIONS
We demonstrate an essential role for TG2 in determining injury-mediated liver enlargement and the necessity of K8 and TG2 for generating cross-linked keratins and MBs. The role of TG in inclusion formation might extend to nonkeratin intermediate filament protein-related diseases.
Strnad
Pavel
P
Department of Medicine, Palo Alto VA Medical Center, Palo Alto, California, USA.
Harada
Masaru
M
Siegel
Matthew
M
Terkeltaub
Robert A
RA
Graham
Robert M
RM
Khosla
Chaitan
C
Omary
M Bishr
MB
D000818:Animals; D004195:Disease Models, Animal; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000648:ultrastructure*; D006529:Hepatomegaly / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D015151:Immunoblotting; D002479:Inclusion Bodies / Q000648:ultrastructure*; D053538:Keratin-18 / Q000096:biosynthesis / Q000235:genetics; D053533:Keratin-8 / Q000096:biosynthesis / Q000235:genetics; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D016133:Polymerase Chain Reaction; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D012313:RNA / Q000235:genetics*; D011503:Transglutaminases / Q000235:genetics* / Q000378:metabolism
D053538:Keratin-18; D053533:Keratin-8; D012313:RNA; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins