Proinflammatory cytokines up-regulate synthesis and secretion of urinary trypsin inhibitor in human hepatoma HepG2 cells

Background and Aims: The urinary trypsin inhibitor (UTI), a wide range protein inhibitor synthesized by hepatocytes, is considered to play an important role not only in the protection of organ injury during severe inflammation but also in the inhibition of tumor invasion and metastasis. However, the precise mechanisms underlying control of its synthesis, secretion, and processing remain unclarified. The aim of this study is to determine whether human hepatoma HepG2 cells secrete UTI in free form and whether its synthesis and secretion are regulated by proinflammatory cytokines. Methods: Cultured HepG2 cells were stimulated using different concentrations of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). The concentration of free UTI in the medium was measured by ELISA and the intracellular UTI precursor was identified by western blotting. UTI mRNA expression was studied by reverse transcription polymerase chain reaction (RT-PCR). Results: HepG2 cells constantly secreted free UTI and this secretion was significantly up-regulated by IL-6, IL-1β, and TNF-α. IL-6, IL-1β, and TNF-α enhanced the synthesis of the intracellular UTI precursor protein, and IL-1β up-regulated UTI mRNA expression. Conclusions: HepG2 cells constantly secrete free UTI. The proinflammatory cytokines, IL-1β, IL-6, and TNF-α, up-regulate UTI synthesis and secretion by up-regulating UTI mRNA expression.