Cells were stained with a viability dye (Live/ Dead Blue, Invitrogen, 1:1,000 in PBS) for 10 min on ice in the dark. A volume of 100 μl of PBS was subsequently added to the cell suspension and the pellet was spanned down at 1,800 rpm for five minutes. The supernatant was decanted and cell pellets were subjected to intracellular staining. For intracellular staining, cells were permeabilized with a transcription factor staining buffer set (eBiosciences). Briefly, cell pellets were resuspended in 200 μl permeabilization buffer and incubated on ice in the dark for 20 min. A 200 μl perm-wash buffer was subsequently added to cell suspension and the samples were centrifuged at 1,800 r.p.m. at 4 °C for five minutes. The supernatant was decanted and samples were stained with antibodies in 100 μl perm-wash buffer on ice in the dark for 20 min. Finally, 200 μl of PBS was added to the cell suspension and the samples were centrifuged at 1,800 r.p.m. at 4 °C for five minutes. Cell suspensions were stored in 1% PFA in PBS at 4 °C until
