MAP kinase kinase kinase kinases (MAP4Ks) belong to the mammalian Ste20-like family of serine/threonine kinases. MAP4Ks including MAP4K1/HPK1, MAP4K2/GCK, MAP4K3/GLK, MAP4K4/HGK, MAP4K5/KHS, and MAP4K6/MINK have been reported to induce JNK activation through activating the MAP3K-MAP2K cascade.