Liver kinase�B1 restoration promotes exosome secretion and motility of lung cancer cells

Liver kinase B1 (LKB1) regulates a variety of cellular functions, including cell polarity, energy metabolism and cell growth, by targeting multiple signaling pathways such as AMPK/mTOR and p53. LKB1 functions as a tumor suppressor in sporadic cancers including lung cancer. Extracellular vesicles such as exosomes secreted by cancer cells modulate the tumor microenvironment and progression by targeting both tumor cells (autocrine actions) and other types of cells associated with tumors (paracrine actions). While the roles of LKB1 in cellular signaling in general is well-studied, its specific role in exosome-mediated signaling remains to be explored. To this purpose, we reintroduced LKB1 into H460 and A549 lung cancer cells that are endogenously deficient in LKB1 expression. Notably, we found that while restoration of LKB1 significantly reduced lung cancer cell growth as expected, it greatly promoted cell motility and enhanced the release of exosomes. In addition, exosomes isolated from H460 cells with stable restoration of LKB1 had much higher ability in stimulating lung cancer cell migration than did those from H460 cells lacking LKB1. Mechanistically, restoration of LKB1 in H460 cells inhibited cellular expression and exosomal secretion of migration-suppressing microRNAs (miRNAs), including miR-125a, miR-126 and let7b. Taken together, the present study revealed a new role for LKB1 in promoting cell motility by downregulating migration-suppressing miRNA expression and exosome secretion.