Essential role in G1 cell cycle arrest. Phosphorylates and activates members of the AMPK-related subfamily of protein kinases. Tumor suppressor.serine/threonine kinase 11,with two alternatively spliced isoforms,expressed in all tissues,strongly homolog of Xenopus early embryonic kinase 1 (XEEK1),tumor suppressor gene in hamartomas syndrome and in left sided colon carcinogenesis,mutated in sporadic testicular cancer,malignant melanomas and laryngeal tumors,playing a minor role in the development of ovarian carcinoma.LKB1 is a potential target for atherosclerosis and cancer and is shown to be mutated in patients with Peutz-Jeghers cancer syndrome. Tissue specificity: Ubiquitously expressed. Strongest expression in testis and fetal liver.