Cells were cultured in DME (Invitrogen) supplemented with 10% fetal bovine serum and 100 U/ml penicillin/streptomycin (Invitrogen) at 37°C in a humidified 5% CO2 incubator. For transfections, cells in 60-mm-diameter dishes or on fibronectin-coated coverslips were incu- bated with a mixture of DNA and LipofectAMINE 2000 (Invitrogen) according to the manufacturer’s instructions. The cDNA for MLC was subcloned into pCMV-myc (Takara Bio Inc.). Mutant constructs of MLC were generated using a QuikChange site-directed mutagenesis kit (Agilent Technologies) according to the manufacturer’s protocol. In this myc-tagged MLC mutant, Ser1/Ser2 were replaced by alanines, and expressed in NIH3T3 cells. In some experimental conditions, 16 h after replating onto fibronectin-coated coverslips, cells were treated with 50 ng/ml PDGF for 20 min. Cells were fixed 24–48 h after transfection using 3.7% paraformaldehyde in PBS for 15 min, permeabilized using 0.2% Triton X-100 in PBS for 2 min, blocked with 2% BSA in PBS, and co-stained for MLC (green), TRIO (red), and actin (blue). Images were captured by Zeiss LSM 710 confocal microscope with Plan-Apochromat 63X objective.