Protein Extraction and Western Blot

After treatments, cells or liver tissues were washed with sterile phosphate-buffered saline for 3 times and then subjected to total protein extraction by using an radio-immunoprecipitation assay (RIPA) kit from Sigma-Aldrich (Cat. No. R0278). For secreted protein, culture media were collected and centrifuged for RIPA extraction. Then protein samples were quantified with bicinchoninic acid assay (BCA) reagent from Bio-Rad (Cat. No. 5000001). Western blot analyses of all proteins were performed as described using β-actin as the internal control.