Lipopolysaccharide Induces Cholangiocyte Proliferation Via An Interleukin–6-Mediated Activation of P44/P42 Mitogen–Activated Protein Kinase

Abstract

The biliary epithelium is exposed to mediators of inflammation such as bacterial endotoxin or lipopolysaccharide (LPS) in a variety of inflammatory conditions. These conditions are also characterized by cholangiocyte proliferation and a predisposition to malignancy. Furthermore, LPS can enhance the expression of interleukin–6 (IL–6), a known biliary mitogen. However, the effects of LPS on cholangiocyte proliferation or IL–6 secretion are unknown. Thus, our aims were to determine if LPS stimulates cholangiocyte proliferation by IL–6-dependent signaling pathways. H69 cells derived from normal human intrahepatic cholangiocytes proliferated in response to LPS. Cholangiocytes responded to LPS (and other inflammatory cytokines such as tumor necrosis factor α [TNF–α] and IL–1β) by increased secretion of IL–6, which had a mitogenic effect on H69 cells. Preincubation with anti-IL–6 neutralizing antibodies inhibited LPS–induced proliferation. Furthermore, cholangiocytes possessed the IL–6 receptor complex subunits and intact signaling mechanisms leading to activation of signal transducers and activators of transcription (STAT) factors. Although both p38 and p44/p42 mitogen–activated protein kinases (MAPKs) were constitutively present and active in cholangiocytes, IL–6 increased p44/p42, but not p38 MAPK activity. PD098059 inhibited activation of p44/p42 MAPK in cholangiocytes and completely blocked DNA synthesis in response to IL–6 or LPS. These studies identify a critical role for the p44/p42 MAPK in cholangiocyte proliferation and demonstrate that the proliferative response of cholangiocytes to inflammatory mediators such as LPS involves IL–6-mediated activation of the p44/p42 MAPK pathway