LKB1, a member of the serine/threonine kinase family, is a tumor suppressor. Physically associates with p53, it regulates specific p53 dependent apoptosis pathways. LKB1 protein is present in both the cytoplasm and nucleus of living cells and translocates to mitochondria during apoptosis. Restoring LKB1 activity into cancer cell lines defective for its expression results in a G1 cell cycle arrest.Mutations in LKB1 gene are associated with Peutz Jeghers syndrome, an autosomal dominant disorder characterized by the growth of polyps in the gastrointestinal tract, pigmented macules on the skin and mouth, and other neoplasms. LKB1 functions as a master upstream protein kinase, regulating AMPK related kinases as well as AMPK. In vitro, LKB1 has been observed to directly phosphorylate threonine 172 of AMPKa, an event that is correlated with activation of this kinase. LKB1 has also been found to play a role in chromatin remodeling, cell cycle arrest, Wnt signaling, cell polarity, and energy metabolism.