Soluble interleukin‐6 receptor strongly increases the production of acute‐phase protein by hepatoma cells but exerts minimal changes on human primary hepatocytes

Abstract

Interleukin-6 (IL-6) interacts with a system of receptors, which include a 80-kDa IL-6-binding subunit (IL-6R) and a transducing element (gp130). The soluble form of IL-6R (sIL-6R) can bind its ligand and induce cellular responses by association with gp130, thus acting as an IL-6 agonist. We and others have previously shown that the responsiveness to IL-6 is different in hepatoma and human primary hepatocytes. We therefore compared the effects of sIL-6R on the two types of cells, and on the B9 hybridoma, another IL-6-sensitive cell line. Human primary hepatocytes, hepatoma cells PLC/PRF/5, and B9 cells were incubated with different concentrations of IL-6, sIL-6-R, or both. The hepatocyte culture supernatants were tested for their content of acute-phase proteins (APP). The proliferation of B9 cells was assessed by a colorimetric method. Results showed that sIL-6R alone markedly increased the production of APP by hepatoma cells in a dose-dependent manner, but affects only minimally primary hepatocytes and the proliferation of B9 cells. The combinations of IL-6R and its ligand enhanced the effects of Il-6 alone in both PLC/PRF/5 and B9 cells, but had no effect on primary hepatocytes. An immunohistochemical study indicated that the cell-surface expression of IL-6R was dramatically lower in hepatoma cells than in primary hepatocytes. In conclusion, our results show that the expression of IL-6R is low in the hepatoma cell PLC/PRF/5 when compared with primary hepatocytes and that this difference can, at least partly, explain their deficient responsiveness to IL-6. On the other hand, it appears that IL-6R expression by primary hepatocytes is sufficient and that circulating sIL-6R is unlikely to play a significant role in the modulation of IL6 effects.

Interleukin 1 receptor antagonist (IL-1Ra) is an acute-phase protein.

“…Human primary hepatocytes were isolated from surgical liver biopsies as previously described (20,21). In brief, liver explants were taken from three patients undergoing partial hepatectomy: two patients for benign tumor, and one patient for local metastasis of colon adenocarcinoma.…”

“…The sIL-1Ra cDNA was excised from the RSET5a expression plasmid as an Xbal and BamHI fragment, and was cloned in pGEM-7 (Promega Corp., Madison, WI) to generate pRAX/B.GEM. The generation of the GAPDH probe was described previously (21). These plasmids were linearized and transcribed with T3 or SP6 RNA polymerase (Promega) to synthesize the 32 P-labeled riboprobes complementary to GAPDH and IL-1Ra mRNAs.…”

Circulating levels of IL-11 and leukaemia inhibitory factor (LIF) do not significantly participate in the production of acute-phase proteins by the liver

“…Primary hepatocytes were isolated as described previously [9,10]. Briefly, liver explants were taken from patients undergoing partial hepatectomy.…”

“…Both LIF and IL-11 share numerous biological effects with IL-6 on different tissues [6][7][8], including stimulation of APP synthesis by hepatoma cells [4,5]. However, results obtained with tumour cells can be difficult to interpret, since they are not always reproducible with human primary hepatocytes [2,9,10].…”

Effects of cortisol on the expression of interleukin-6 and interleukin-1 beta in human osteoblast-like cells

“…There is also a soluble IL-6R (sIL-6R), which is proteolytically cleaved from the membrane-bound IL-6R. It has been shown that the biological activity of IL-6 results from the direct association of either the sIL-6R/IL-6 complex or the IL-6R/IL-6 complex with the membrane-associated protein, gp130, which transduces the IL-6 signal (Mackiewicz et al 1992, Gabay et al 1995. Furthermore, it has been reported that sIL-6R triggers osteoclast formation by IL-6, indicating that the amount of sIL-6R may modulate the IL-6 effect (Tamura et al 1993).…”