Fig. 1. JNK and ERK are differentially regulated by growth factors.

Swiss 3T3 cells were starved in serum-free medium and incubated with LPA (1 μM), S1P (1 μM), or EGF (20 ng/ml). Cells were lysed in SDS sample buffer at 0, 5, 10, 30, and 60 min post-treatment and analyzed by immunoblotting for JNK and ERK phosphorylation using phospho-specific (p-Erk and p-JNK) antibodies. Starved Swiss 3T3 were subjected to UV light irradiation using an UV cross-linker at 10, 20, 40, and 80 J/m² (J). UV light-irradiated cells were re-fed serum-free medium and returned to a CO₂ incubator for 30 min before the cells were lysed and analyzed for JNK and ERK phosphorylation. Reprobing with anti-JNK1 antibody was included to show similar levels of loading among samples. For this and all other illustrations in the paper, similar results were obtained from three independent experiments.