The effects of Ser-339 mutation on ERK1/2 phosphorylation.
A, Time-dependent ERK1/2 phosphorylation in HEK293 cells expressing APJ (upper) or APJ-S339A (middle) after 100 nM apelin-36 stimulation for different lengths of time. The time-dependent curves of the two groups were quantified and the results shown in the lower panel. B, Concentration-dependent ERK1/2 phosphorylation in HEK293 cells expressing APJ (upper) or APJ-S339A (middle) after apelin-36 stimulation at different concentrations for 5 min. The concentration-dependent effects in the two groups were quantified and the results are shown in the lower panel. C and D, ERK1/2 phosphorylation in HEK293 cells expressing APJ or APJ-S339A (upper) after 100 nM apelin-36 stimulation for 15 min (C) or 5 min (D). ERK1/2 phosphorylation in HEK293 cells expressing APJ or APJ-S339A after 100 nM ELA-32 treatment for 15 min (E) or 5 min (F). The P-ERK/T-ERK ratio of the two groups was quantified and is shown in the lower panels. The density of the bands corresponding to 44 and 42 kDa was quantified with an imaging densitometer, normalized to total ERK. The data correspond to the means ± S.E. from five independent experiments. APJ-S339A group compared with WT APJ group, ***P < 0.001; ns, no significant difference, P > 0.05.