The LKB1 serine/threonine protein kinase was initially identified as a tumor suppressor gene mutated in human Peutz-Jeghers syndrome (PJS), a condition resulting in the growth of numerous intestinal polyps classed as hamartomas. LKB1 exists as a heterotrimeric complex with two other proteins, Ste20-related adaptor protein (STRAD) and MO25. Together, this complex can phsophorylate and activate the AMP-activate protein kinase (AMPK). Following AMPK activation by LKB1, AMPK then phosphorylates TSC1 and TSC2, key components of the metabolism-regulating TOR signaling pathway, which antagonizes the activation for the TOR pathway. LKB1 has also been shown to play a fundamental role in controlling the spatial orientation of structures required to maintain an ordered, polarized epithelium.
