HEK293T cells were transfected with cerulean-vector, cerulean-UCR1C, or cerulean-UCR1C R/A. Forty-eight hours later, cell lysates were harvested, and 1.5 mg total protein was applied for immunoprecipitation using protein A-agarose beads, and anti-PDE4B pan-antibody or anti-UCR1 antibody. Relative PDE activities of endogenous PDE4 long isoforms (anti-UCR1 IP) are shown in (A), and endogenous PDE4B (anti-PDE4B IP) in (B). The data were shown as mean± s.e.m from two independent experiments.