Vol. 181, No. 3, 1991 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS December 31, 1991 Pages 1192-l 200 HSP27 IS A MEDIATOR OF SUSTAINED SMOOTH MUSCLE CONTRACTION IN RESPONSETO BOMBESIN Khalil N. Biter 1 *. Mark S. Kaminski2, Nabil Hailat 3, Kemp B. Cease 2 and John R. Strahler 3 ‘Division of Pediatric Gastroenterology, University of Michigan Medical Center, Ann Arbor, MI 48109-0658 3Division of Pediatric Hematology University of Michigan Medical Center, Ann Arbor, MI 48 109 2 Department of Internal Medicine, Division of Hematology/Oncology, University of Michigan Medical Center, Ann Arbor, MI 48109-0724 Received November 13, 1991 We have identified the low MW 27 kD heat shock protein as a major phosphoprotein constituent of smooth muscleand have investigated its potential role in agonistinduced smooth musclecontraction. The neuropeptides bombesin and substance P, which are presentin neurons of the anorectai region, induce contraction of isolated smooth muscle cells from this region by activating different intracellular pathways. SubstanceP-induced contraction is 1,4,5-inositol trisphosphate (IPs)/calmodulindependent, while contraction induced by bombesin is mediated by a protein kinase C (PKC) -dependent pathway. The sustained contraction induced by bon&sin or exogenousPKC was blocked by preincubation of cells with monoclonal antibodies to hsp27, while the transient contraction induced by substance P or IP3 was unaffected by the antibodies. Preincubation with isotype matched control antibodies had no inhibitory effect on contraction induced in responseto the agents used. These data support a novel role for hsp27 in the non calmoduhn mediated sustained contraction inducedby bombesin or PKC. a 1991 Academic Press, Inc. Agonist inducedcontraction in a number of smooth muscle cells hasbeenassociated with a rise in intracellular Ca++concentration [Ca++i] (1,2,3,4,5). The rise in [Ca++i] activates the calmodulin-dependent enzyme, myosin light chain kinase (6, 7, 8), which results in phosphorylation of 20 kD myosin light chains (mlc). It is known that the interaction of actin and myosin, which resultsin contraction through a calmodulindependent process, is regulatedby actin ATPase activity induced by phosphorylationof myosin light chain. Numerous proteins have been shown to act as substrates for PKC but the precise pathway leading to muscle contraction in response to PKC mediatedagonists is not well understood. We have investigated the hypothesis * To whom correspondence should be addressed. 0006291X/91 $1.50 Copyright 0 1991 by Academic Press, Inc. All rights of reproduction in any form reserved. 1192