AMPK/LKB1 signaling in epithelial cell polarity and cell division.

Cells must coordinate diverse processes including cell division, cell migration, and cell polarity with the cell's metabolic status. How single molecules coordinate these seemingly distinct cell biological events remains relatively unexplored. AMP-activated protein kinase (AMPK) sits at a unique position as a proposed energy sensor that can interface with diverse signaling molecules ranging from LKB1 to mammalian target of rapamycin (mTOR), affecting processes from ribosomal biogenesis to actin regulation. Determining biologically relevant direct kinase targets remains challenging. Alternatively, one can genetically inactivate a kinase and subsequently characterize cellular and whole animal phenotypes without the kinase's activity. Recent genetic studies inactivating AMPK activity in Drosophila indicate unanticipated roles for AMPK as a regulator of epithelial polarity, consistent with known roles of an upstream activator, LKB1 as a PAR (portioning defective) mutant in Caenorhabditis elegans and polarity regulator. Additional genetic analyses demonstrate that both AMPK and LKB1 function are required for faithful chromosomal segregation during mitosis. At least some of these apparently divergent phenotypes may be mediated through myosin regulatory light chain, and presumably the acto-myosin complex, which can affect both polarity and cell division. Chromosomal integrity defects could also be consistent with LKB1's role as a known human tumor suppressor gene. Elucidating the molecular players that interface with AMPK and their potential energy dependent regulation remains an important challenge to fully understand AMPK signaling.