MAPK8 and breast cancer: In contrast, DDR2 triggers p38 and ERK1/2 (but not JNK) to activate MMP-13 expression in chondrocytes [61,159,160], p38 and JNK (but not ERK1/2) to activate IL-12 production [161], ERK2 in breast cancer cells [162], and p38 MAP kinase or ERK1/2 to activate transcription factor Runx 2 during osteoblast differentiation [51,163].