['Recently we reported that fluid shear stress promotes endothelial cell differentiation from a mouse embryo mesenchymal progenitor cell line C3H10T1/2. However, it is not clear whether the transforming growth factor-beta 1 (TGF-beta1) system is associated with shear-induced endothelial differentiation. The purpose of this study was to determine the effect of shear stress on the expression of TGF-beta1 and its signaling molecules in C3H10T1/2 cells.', 'Murine C3H10T1/2 cells were incubated on collagen Type 1-coated dishes, and subjected to a steady fluid shear stress of 15 dyn/cm(2) for 6, 12, and 24 h. The mRNA levels for TGF-beta1, TGF-beta receptors (TGF-beta R), and Smad molecules were determined with real-time PCR analysis and normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA levels.', 'TGF-beta1 mRNA expression was down-regulated by 60% and 66% in shear stress-treated cells at 12 and 24 h, respectively, compared with static control group (P < 0.01). In addition, shear stress significantly decreased TGF-beta R1 mRNA levels by 30% and 50% in shear stress-treated cells at 12 and 24 h, respectively (P < 0.01). For TGF-beta R2, shear stress at 6, 12, and 24 h significantly reduced its expression by 93%, 95% and 97%, respectively, compared with static controls (P < 0.01). Furthermore, shear stress significant decreased mRNA levels of positive signaling molecules Smad2, Smad3, and Smad4 in a time-dependent manner (P < 0.01). However, shear stress significantly increased negative signaling molecule Smad7 mRNA levels by 100% at 24 h treatment compared with static control group (P < 0.01).'] Does fluid shear stress regulate the expression of TGF-beta1 and its signaling molecules in mouse embryo mesenchymal progenitor cells?