Fig. 8. Inhibition of JNK activation suppresses the increased proliferative response to LPA in GSK3β-negative cells.

A, the effect of the JNK inhibitor SP600125 on LPA-induced c-Jun phosphorylation. GSK-3β-negative cells were starved and incubated with SP600125 at the indicated concentrations. One hour later the cells were stimulated with 10 μM LPA for 30 min. Cells were lysed in SDS sample buffer and analyzed by immunoblotting for c-Jun phosphorylation using phospho-specific (p-c-Jun) antibodies. GAPDH, glyceraldehyde-3-phosphate dehydrogenase. B, the effect of the JNK inhibitor on LPA-mediated cell proliferation. GSK3β-negative MEFs were prepared and plated as described for Fig. 7B. After attachment and starvation, cells were incubated with LPA (10 μM) in the presence of the indicated concentration of SP600125 that was added 1 h before the addition of LPA. Cell numbers were determined at 24-h intervals by counting in a hemocytometer. The data are presented as means ± S.D. of duplicate assays from three independent experiments. Statistical differences between cells treated with vehicle (Me₂SO) and SP600125 are indicated by an asterisk (p < 0.01).