Chronic treatment with interleukin-1β attenuates contractions by decreasing the activities of CPI-17 and MYPT-1 in intestinal smooth muscle

Abstract

Interleukin-1β (IL-1β) is a proinflammatory cytokine that plays a central role in inflammatory bowel disease (IBD). In order to elucidate the mechanism of motility disorders frequently observed in IBD, we investigated the long term effects of IL-1β on rat ileal smooth muscle contractility by using an organ culture system. When ileal smooth muscle strips were cultured with IL-1β (10 ng/ml), contractions elicited by high K+ and carbachol were inhibited in a time-dependent manner. IL-1β more strongly inhibited the carbachol-induced contractions than high K+ with decreasing myosin light chain phosphorylation. In the α-toxin- permeabilized ileal muscle, carbachol with GTP or guanosine 5′-3-O-(thio) triphosphate increased the Ca2+ sensitivity of contractile elements, and this G protein-coupled Ca2+ sensitization was significantly reduced in the IL-1β-treated ileum. Among the functional proteins involved in the smooth muscle Ca2+ sensitization, CPI-17 expression was significantly reduced after the culture with IL-1β, whereas the expressions of RhoA, ROCK-I, ROCK-II, MYPT-1, myosin light chain kinase, and myosin phosphatase (PP1) were unchanged. The phosphorylation level of CPI-17 by carbachol was low in accordance with the decrease in CPI-17 expression due to IL-1β treatment. In contrast, constitutively phosphorylated MYPT-1 was also decreased in the IL-1β-treated muscles. These results suggest that long term treatment with IL-1β decreases either CPI-17 expression or MYPT-1 phosphorylation, which may result in an increase in myosin phosphatase activity to reduce force generation. Based on these findings, we consider IL-1β to be an important mediator of gastrointestinal motility disorders in IBD, and CPI-17 and MYPT-1 are key molecules in the decreased smooth muscle contractility due to IL-1β. © 2003 by The American Society for Biochemistry and Molecular Biology, Inc.