CONCANAVALIN A-INDUCED LIVER-INJURY TRIGGERS HEPATOCYTE PROLIFERATION

Concanavalin A (Con A) injection into mice leads to immune-mediated li ver injury. We studied whether after Con A-induced liver injury, TNF- and IL-6-dependent signaling pathways known to be related to hepatocyt e proliferation are activated. 2 h after Con A injection, maximum TNF- alpha, and after 4-8 h, maximum IL-6 serum levels were found. The rise in aminotransferases and DNA fragmentation started after 4 h; maximum levels were evident after 8 h. 5-Bromo-2'-deoxyuridine staining and n uclear cyclin A expression as markers of the S-phase were first detect ed in hepatocyte nuclei after 24 h, peaking after 48 h. An increase in TNF-dependent nuclear expression of CCAAT/enhancer-binding protein-be ta (C/EBP-beta)/liver-enriched activating protein (LAP) was detected a fter 1 h, whereas an increase in RNA expression was evident only after 4 h. C/EBP-beta/LAP expression returned to normal values before progr ession into the S-phase. DNA binding of signal transducer and activato r of transcription (STAT) 3/acute phase response factor (APRF) increas ed for up to 8 h. As found by supershift experiments, in addition to S TAT3/APRF, STAT1 also binds to the same sequence. During the course of time gel shift experiments, DNA binding of the apoptosis-related STAT 1 started earlier than DNA binding of STAT3/APRF, which regulates hepa tocyte proliferation. However, the subsequent decrease in DNA binding of both factors was comparable. This study demonstrates that after Con A injection, TNF- and IL-6-dependent signals trigger nuclear events r egulating hepatocyte apoptosis and proliferation during liver injury.