Associates with scaffold proteins JNK interacting proteins as well as their upstream kinases JNKK1 and JNKK2 following their activation. Modifies the activity of numerous proteins that reside at the mitochondria or act in the nucleus. Downstream molecules that are activated by JNK include c-Jun, ATF2, ELK1, SMAD4, p53 and HSF1. Involved in apoptosis, neurodegeneration, cell differentiation and proliferation, inflammatory conditions and cytokine production mediated by AP-1 (activation protein 1) such as RANTES, IL-8 and GM-CSF.