Murine Cardiotrophin-1 Stimulates the Acute-Phase Response in Rat Hepatocytes and H35 Hepatoma Cells

Abstract

Mouse cardiotrophin-1 (CT-1) is a hypertrophy-inducing factor for cardiac myocytes and interacts with cell surface receptors that incorporate the signaling molecule gp 130. Because other cytokines utilizing this receptor subunit stimulate acute-phase protein synthesis, we tested cardiotrophin-1 in in vitro assays of protein synthesis by primary rat hepatocytes, rat hepatoma cells (H35), and human hepatoma cells (HepG2). CT-1 showed a dose-dependent induction of protein synthesis by primary rat hepatocytes, with effective concentrations ranging from 0.1 to 100 ng/ml. Production of a number of acute-phase proteins, including α₁-cysteine proteinase inhibitor (α₁-CPI), ;₁-proteinase inhibitor (α₁-Pi), α₂-macroglobulin, and α₁-acid glycoprotein, was markedly increased at 48 and 72 h of cytokine stimulation. In rat H35 cells, CT-1 stimulated α₁-Pi and α₁-CPI protein production and upregulated α₁-CPI mRNA levels with similar potency. Compared with other IL-6-type human cytokines at optimal concentrations in parallel assays, CT-1 induced similar levels of acute-phase proteins as human oncostatin M (OM) and leukemia inhibitory factor (LIF), whereas human IL-6 induced the greatest levels of α₁-CPI or α₁-Pi production by H35 cells. When tested on human HepG2 cells, murine CT-1 was far less effective, in that it stimulated α₁-antichymotrypsin production only at very high concentrations (100 ng/ml) but did not alter haptoglobin or α₁-Pi. Human OM and IL-6 were effective at lower concentrations and induced much higher levels of acute-phase protein synthesis, whereas LIF activity was similar to that of CT-1. These results show that murine CT-1 is a strong acute-phase mediator for rat hepatocytes in vitro and its activity is similar to LIF on rat hepatocytes, H35 cells, and HepG2 cells.