Effects of inhibitors on tensile strain-induced expression of MMP-13 mRNA in MC3T3-E1 cells. Cells were seeded at a density of 2 × 105 cells/well on Flex I culture plates and grown in α-MEM medium supplemented with 10% FBS for 24 h. Cells were then cultured in medium containing cycloheximide (10 μM), indomethacin (10 μM), genistein (20 μM), PD098059 (10 μM), or vehicle (control) for 30 min. The cells were cultured with (+) or without (-) loading with tensile strain at 18% elongation at 6 cycles/min for 24 h. Total RNA was extracted from the cells, and expression levels of MMP-13 mRNA were determined by RT-PCR as described in the Materials and methods. (A) Agarose gel electrophoresis of MMP-13 and GAPDH RT-PCR products. (B) MMP-13 mRNA expression levels normalized to GAPDH. The results shown are means ± SD of five independent experiments. **Indicates a significant difference from the strain (+) culture (P < 0.01)as determined by Student's t test.