MAPK3 and neoplasm: After 0.5 h exposure of WB-F344 cells to 10 nM TPA (12-O-tetradecanoylphorbol 13-acetate), which was used as a positive control and known GJIC inhibitor and tumor promoter, rapidly and significantly increased (~30-fold increase) the levels of phosphorylated, i.e., activated, MAPK-Erk1 and 2 (Figure 4; original, uncropped and unadjusted images in Figures S6–S9).