The tumor suppressor Lgl1 regulates front-rear polarity of migrating cells

Cell migration is a highly integrated, multistep process that plays an important role in physiological and pathological processes. The migrating cell is highly polarized, with complex regulatory pathways that integrate its component processes spatially and temporally.(1) The Drosophila tumor suppressor, Lethal (2) giant larvae (Lgl), regulates apical-basal polarity in epithelia and asymmetric cell division.(2) But little is known about the role of Lgl in establishing cell polarity in migrating cells. Recently, we showed that the mammalian Lgl1 interacts directly with non-muscle myosin IIA (NMIIA), inhibiting its ability to assemble into filaments in vitro.(3) Lgl1 also regulates the cellular localization of NMIIA, the maturation of focal adhesions, and cell migration.(3) We further showed that phosphorylation of Lgl1 by aPKC prevents its interaction with NMIIA and is important for Lgl1 and acto-NMII cytoskeleton cellular organization.(4) Lgl is a critical downstream target of the Par6-aPKC cell polarity complex; we showed that Lgl1 forms two distinct complexes in vivo, Lgl1-NMIIA and Lgl1-Par6-aPKC in different cellular compartments.(4) We further showed that aPKC and NMIIA compete to bind directly to Lgl1 through the same domain. These data provide new insights into the role of Lgl1, NMIIA, and Par6-aPKC in establishing front-rear polarity in migrating cells. In this commentary, I discuss the role of Lgl1 in the regulation of the acto-NMII cytoskeleton and its regulation by the Par6-aPKC polarity complex, and how Lgl1 activity may contribute to the establishment of front-rear polarity in migrating cells.