Updated FTP location. HUVEC were infected retroviral vectors expressing mCherry-GPNMB or mCherry. The cells were lysed with Pierce IP lysis buffer. The lysates after immunoprecipitation using anti-mCherry antibody (ab213511, Abcam) was transferred into a new microcentrifuge tube for “tube gel digestion”, a modified in-gel digestion procedure, to generate dithiothreitol-reduced iodoacetamide-alkylated tryptic peptides for nano-flow liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS).