The cytoskeleton is thought to play a central role in cellular mechanotransduction. However, the specific mechanisms operative in bone cells have not yet been clearly elucidated. Isolating the roles of the specific cytoskeletal elements could ultimately aid in development of treatments for conditions related to the mechanoresponsiveness of bone (e.g. osteoporosis, space flight). Using an osteoblast-like cell line, the minimum doses of nocodazole (microtubules) and cytochalasin D (actin filaments) that would partially disrupt the cytoskeleton while leaving some elements intact were determined. Cultures were exposed to fluid flow shear, and loaded in the presence or absence of inhibitory drugs at the previously established doses. In untreated cultures, shear stress was associated with significant increases in mRNA levels for collagen I and matrix metalloproteinases I and 3. These increases were maintained in cytochalasin D-treated cultures, but were almost completely abrogated by nocodazole treatment. These results suggest that some mechanotransduction pathways related to bone matrix metabolism are primarily dependent on the microtubule network. (C) 2007 Elsevier Inc. All rights reserved.