Tubular cells in culture were fixed with frozen methanol and permeabilized with PBS plus BSA 2% and triton 0.5% solution. Cells were marked with a rabbit anti-p21 monoclonal antibody (ab109199, Abcam, 1/200).Secondary antibody was Alexa Fluor 488 goat anti rabbit (A11008, Invitrogen, 1/1000). Nucleus was marked with DAPI (Invitrogen thermofischer scientific, 1/2000).