Itih‐4, a serine protease inhibitor regulated in interleukin‐6–dependent liver formation: role in liver development and regeneration

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Abstract
Inter-α-trypsin inhibitor-4 (Itih-4) is a liver-restricted member of the serine protease inhibitor family with diverse functions as an anti-apoptotic and matrix stabilizing molecule that are important throughout development. We investigate the functional role of Itih-4 in liver formation, regeneration (LR) and examine its role in calcium and hyaluronic acid binding. Itih-4 expression is prominent in early liver development at E9 and later at E16, being restricted to hepatoblasts, immature hepatocytes, and differentiated hepatocytes. We note a marked and differential increase in Itih-4 labeling in proliferating hepatocytes, compared with bile duct cells in liver explant cultures treated with interleukin-6 (IL-6). After partial hepatectomy, maximal Itih-4 expression occurs in a bimodal manner at 30 min and at 12 hr, with a predominant centrizonal distribution. There is no detectable binding of glutathione transferase–fusion Itih-4 protein to calcium and hyaluronic acid, indicating a possible requirement for posttranslational modifications for these functions. These results suggest that in LR, Itih-4 expression corresponds to that of immediate early genes and may contribute to the entry of normally quiescent hepatocytes into the early stages of the cell cycle. The markedly high expression of Itih-4 in early liver development and in explants treated with IL-6 suggests a prominent role for Itih-4 at key points in liver formation.