Activation of MAP kinases during differentiation of PLB and PLB-D cells by 1,25(OH)₂D₃. Kinetics of JNK, ERK, or p38 MAP kinase phosphorylation were analyzed by immunoblot analysis with phospho-specific antibodies (p-JNK, p-ERK, or p-p38) in PLB and PLB-D cells during differentiation by 1,25(OH)₂D₃. The levels of JNK, ERK, or p38 MAP kinase in each sample were evaluated by immunoblotting anti-JNK, anti-ERK, or anti-p38 MAP kinase antibodies, respectively. Results are representative of 3 experiments.