Serine/threonine-protein kinase TAO3, also known as cutaneous T-cell lymphoma-associated antigen HD-CL-09, CTCL-associated antigen HD-CL-09, Dendritic cell-derived protein kinase, JNK / SAPK-inhibitory kinase, Jun kinase-inhibitory kinase, Kinase from chicken homolog A, Thousand and one amino acid protein 3, JIK, TAOK3 and MAP3K18, is cytoplasm and peripheral membrane protein which belongs to the protein kinase superfamily, STE Ser/Thr protein kinase family and STE20 subfamily. Protein kinases are pivotal regulators of cell signaling that modulate each other's functions and activities through site-specific phosphorylation events. TAOK3 / JIK contains one protein kinase domain. TAOK3 / JIK is ubiquitously expressed at a low level, and highly expressed in peripheral blood leukocytes (PBLs), thymus, spleen, kidney, skeletal muscle, heart and liver. TAOK3 / JIK inhibits the basal activity of Jun kinase. It is negatively regulated by epidermal growth factor (EGF). When overexpressed, TAOK3 / JIK may activate ERK1 / ERK2 and JNK / SAPK.