for 15 min at 37°C. After stimulation, cells were immediately placed on ice, 1 ml ice-cold DPBS were added quickly before centrifugation at 300 x g for 5 min. The pellets were lysed for 30 min at 4°C with 150 µl lysis buffer (RIPA, Thermo Scientific, USA) including phosphatase inhibitor PhosSTOP (Sigma-Aldrich, USA) as well as protease inhibitor (Sigma-Aldrich, USA).