MAPKKK, or Mitogen-Activated Protein Kinase Kinase Kinase, is a type of enzyme that plays a crucial role in cellular signaling pathways. It is part of the MAPK (Mitogen-Activated Protein Kinase) cascade, which helps cells respond to various external stimuli, such as growth factors and stress signals. MAPKKKs activate MAPKKs (Mitogen-Activated Protein Kinase Kinases), which in turn activate MAPKs. These signaling pathways are essential for regulating various cellular processes, including cell growth, differentiation, and apoptosis (programmed cell death). Dysregulation of MAPKKK activity can lead to various diseases, including cancer, making them important targets for therapeutic research.