To identify potential phosphorylation sites of STAT6, RAW 264.7 cells were overexpressed with STAT6-HA. 48 hours after transfection, cells were treated with 10 μM etoposide for 2 h, then lysed for immunoprecipitation using anti-HA beads. Immunoprecipitates were separated by SDS–PAGE and then Coomassie blue staining was carried out. Bands of interest were cut from the gel and then in-gel digestion was performed using sequencing grade-modified trypsin. The peptides were analyzed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) with nano-LC combined with Orbitrap Q Exactive mass spectrometer