JNK1, also known as c-Jun N-terminal kinase 1, is a member of the mitogen-activated protein kinase (MAPK) family of enzymes that play essential roles in cellular signaling pathways. JNK1 is primarily involved in the cellular response to stress. JNK1 is activated by a complex signaling cascade involving upstream kinases, such as MEKK1, MLK3, and ASK1. Activation typically occurs in response to stress stimuli, which trigger the assembly of a multi-protein complex known as the MAPKKK-MAPKK-MAPK module. This complex leads to the phosphorylation and activation of JNK1, which then phosphorylates its downstream targets. Upon activation, it phosphorylates specific substrates, including transcription factors such as c-Jun, ATF2, and p53, leading to changes in gene expression that help cells adapt to stress. JNK1 plays a dual role in regulating cell death (apoptosis) and survival. Depending on the cellular context and stimuli, JNK1 can either promote or inhibit apoptosis. JNK1 is also involved in inflammatory and immune responses. It can regulate the production of cytokines, chemokines, and other inflammatory mediators, as well as modulate the activation and function of immune cells.