ETOC: Lgl1 interacts directly with NMII-A, inhibiting its filament assembly. It excludes NMII-A from the cell leading edge. Depletion of Lgl1 affects the size and number of focal adhesions, cell polarity, and the rate of migrating cells. These results indicate that Lgl1 regulates the polarity of migrating cells by controlling NMII-A filament assembly.

Non-muscle myosin IIA (NMII-A) and the tumor suppressor lethal giant larvae 1 (Lgl1) play a central role in the polarization of migrating cells. Mammalian Lgl1 interacts directly with NMII-A, inhibiting its ability to assemble into filaments in vitro. Lgl1 also regulates the cellular localization of NMII-A, the maturation of focal adhesions and cell migration. In Drosophila, phosphorylation of Lgl affects its association with the cytoskeleton. Here we show that phosphorylation of mammalian Lgl1 by aPKCf prevents its interaction with NMII-A both in vitro and in vivo, and affects its inhibition of NMII-A filament assembly. Phosphorylation of Lgl1 affects its cellular localization and is important for the cellular organization of the acto-NMII cytoskeleton. We further show that Lgl1 forms two distinct complexes in vivo, Lgl1-NMIIA and Lgl1-Par6a-aPKCf, and that the formation of these complexes is affected by the phosphorylation state of Lgl1. The complex Lgl1-Par6a-aPKCf resides in the leading edge of the cell. Finally, we show that aPKCf and NMII-A compete to bind directly to Lgl1 at the same domain. These results provide new insights into the mechanism regulating the interaction between Lgl1, NMII-A, Par6a and aPKCf in polarized migrating cells.

No abstract

Cell motility is an essential cellular process for a variety of biological events. It requires cross-talk between the signaling and the cytoskeletal systems. Despite the recognized importance of aPKCz for cell motility, there is little understanding of the mechanism by which aPKCz mediates extracellular signals to the cytoskeleton. In the present study, we report that aPKCz is required for the cellular organization of acto-non-muscle myosin II (NMII) cytoskeleton, for proper cell adhesion and directed cell migration. We show that aPKCz mediates EGF-dependent RhoA activation and recruitment to the cell membrane. We also show that aPKCz mediates EGFdependent myosin light chain (MRLC) phosphorylation that is carried out by Rho-associated protein kinase (ROCK), and that aPKCz is required for EGF-dependent phosphorylation and inhibition of the myosin phosphatase targeting subunit (MYPT). Finally, we show that aPKCz mediates the spatial organization of the acto-NMII cytoskeleton in response to EGF stimulation. Our data suggest that aPKCz is an essential component regulator of acto-NMII cytoskeleton organization leading to directed cell migration, and is a mediator of the EGF signal to the cytoskeleton.