CAB39(Calcium binding protein 39) also known as MO25, CGI-66 plays a crucial role in the regulation of the serine/threonine kinase LKB1, which is a key tumor suppressor involved in cellular energy homeostasis and metabolism. The interaction between CAB39 and LKB1 is vital for proper localization and activation of LKB1, as CAB39 facilitates LKB1 translocation from the nucleus to the cytoplasm, thereby enhancing tumor suppressor functions. Dysregulation of this complex can lead to impaired LKB1 activity, contributing to the development of Peutz-Jeghers Syndrome and increasing the risk of various cancers.