D-MEKK1 mediates the activation of JNK by cadmium and arsenite. S2 cells were incubated, as indicated, in the absence ("-") or presence of 15 μg per well of dsRNA specific to either D-ASK, D-MLK, D-MEKK1, or D-TAK or a mixture of all of them ("ALL") for 4 days followed by treatments, as indicated, with either 200 μM CdCl2 or 200 μM NaAsO2 for 2 hours, 200 mM resveratrol for 1 h, or 50 mM LPS for 10 min. Cells were harvested and analyzed for MAP kinase phosphorylation in immunoblot analyses using phosphoepitope-specific antibodies as indicated. Immunoblotblot analysis using an antibody recognizing JNK indicates equal protein loading (A). An experiment representative of 3 repetitions is shown. The levels of respective JNKKK mRNAs under conditios of RNAi using a mixture of dsRNAs specific for all four JNKKKs were detected in RT-PCR analyses and presented in (B). RT-PCR using primers specific for D-JNK demonstrates the lack of non-specific interference with D-JNK mRNA.