2.6. Western Blot
To obtain total protein lysates, cells were homogenized in RIPA buffer (1% NP40, 0.5% sodium deoxycholate, 0.1% SDS, 1 mM EDTA, 1 mM EGTA, 1 mM Na3VO4, 20 mM NaF, 0.5 mM DTT, 1 mM PMSF, and protease inhibitor cocktail in PBS pH 7.4) and centrifuged at 12,000 g for 15 min at 4°C. Protein concentrations were estimated by Coomassie Plus Protein Assay Reagent (Pierce, IL, USA). Fifty micrograms of the resulting cytosolic protein extracts were heat-denatured in Laemmli sample loading buffer, separated by 10% sodium dodecyl sulfate polyacrylamide gel electrophoresis, and electroblotted onto a nitrocellulose membrane. For immunoblotting, membranes were blocked with 5% nonfat dry milk in saline buffer overnight at 4°C, and the following antibodies were used: anti-β-actin (sc-130657, Santa Cruz Biotechnology, CA, USA, 43 kDa) and anti-matrix metallopeptidase 9 (MMP9) (sc-6841, Santa Cruz Biotechnology, CA, USA, 92 kDa). Each primary antibody was diluted appropriately in blocking buffer and then added to the blots for 1 h at room temperature. The blots were washed three times in the washing buffer and covered with the horseradish peroxidase-linked secondary antibody at a 1 : 2000 dilution for 1 h. Blots were incubated with enhanced chemiluminescence (ECL) detection system (Amersham Biosciences, Bucks, UK) and exposed to radiographic film (Fuji Hyperfilm, Tokyo, Japan). ImageJ was used to analyze the intensity of the blots. The level of β-actin was used as internal standard.