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Abstract Mechanical stimulation of bone induces new bone formation in vivo and increases the metabolic activity and gene expression of osteoblasts in culture. We investigated the role of the actin cytoskeleton and actin-membrane interactions in the transmission of mechanical signals leading to altered gene expression in cultured MC3T3-E1 osteoblasts. Application of fluid shear to osteoblasts caused reorganization of actin filaments into contractile stress fibers and involved recruitment of β 1 -integrins and α-actinin to focal adhesions. Fluid shear also increased expression of two proteins linked to mechanotransduction in vivo, cyclooxygenase-2 (COX-2) and the early response gene product c-fos. Inhibition of actin stress fiber development by treatment of cells with cytochalasin D, by expression of a dominant negative form of the small GTPase Rho, or by microinjection into cells of a proteolytic fragment of α-actinin that inhibits α-actinin-mediated anchoring of actin filaments to integrins at the plasma membrane each blocked fluid-shear-induced gene expression in osteoblasts. We conclude that fluid shear-induced mechanical signaling in osteoblasts leads to increased expression of COX-2 and c-Fos through a mechanism that involves reorganization of the actin cytoskeleton. Thus Rho-mediated stress fiber formation and the α-actinin-dependent anchorage of stress fibers to integrins in focal adhesions may promote fluid shear-induced metabolic changes in bone cells. mechanotransduction α-actinin gene expression Footnotes Address for reprint requests: F. M. Pavalko, Dept. of Physiology and Biophysics, Indiana University School of Medicine, 635 Barnhill Dr., Indianapolis, IN 46202-5120. This work was supported by National Institute of General Medical Sciences Grant GM-4733 and a Grant-in-Aid from the American Heart Association (F. M. Pavalko), by National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) Grant AR-43222 and National Aeronautics and Space Administration Grant NAG5-4917 (R. L. Duncan), by NIAMS Grant T32 AR-07581 (D. B. Burr), and by NIAMS Grant AR-43730 (C. H. Turner). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “ advertisement ” in accordance with 18 U.S.C. §1734 solely to indicate this fact. Copyright © 1998 the American Physiological Society
AJP - Cell Physiology – The American Physiological Society
Published: Dec 1, 1998
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