The tumor suppressor Lgl1 forms discrete complexes with NMII-A, and Par6α–aPKCζ that are affected by Lgl1 phosphorylation

Abstract

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.

The Scribble–Dlg–Lgl Module in Cell Polarity Regulation

“…Lgl also binds to Myosin II and negatively regulates Myosin II function in Drosophila and mammalian cells (Strand et al 1994(Strand et al , 1995Betschinger et al 2005). In mammalian cells, a recent study has revealed that Lgl forms alternative complexes with aPKC (PKCζ) or Myosin II and that phosphorylation of Lgl by aPKC affects its ability to inhibit Myosin II filament formation in polarized migrating cells (Dahan et al 2014). In Drosophila the interaction of Lgl with Myosin II has a role in PCP in Drosophila embryo ventral epidermis (Kaplan and Tolwinski 2010); however the function for this regulation in other types of polarity is unclear.…”

aPKCζ affects directed cell migration through the regulation of myosin light chain phosphorylation

“…27 Phosphorylation of Lgl1 by aPKCz affects its cellular localization and prevents its interaction with NMIIA, thus affecting the cellular organization of the acto-NMIIA cytoskeleton. 26 Together, these results strongly indicate that aPKCz plays an important role in cell migration. Nevertheless, little is known about the mechanism by which aPKCz affects cell migration and how it mediates extracellular signals to the cytoskeleton.…”

“…We have recently shown that Lgl1 binds NMIIA, inhibiting its ability to form filaments, and that phosphorylation of Lgl1 by aPKCz prevents its interaction with NMIIA both in vitro and in vivo, thus removing the inhibition of NMIIA filament assembly. 26,27 Furthermore, phosphorylation of Lgl1 by aPKCz affects its cellular localization and is important for the cellular organization of the acto-NMII cytoskeleton. 26 We therefore propose that in the absence of aPKCz, Lgl1 is not phosphorylated and binds with NMIIA constitutively, inhibiting its activity.…”

“…26,27 Furthermore, phosphorylation of Lgl1 by aPKCz affects its cellular localization and is important for the cellular organization of the acto-NMII cytoskeleton. 26 We therefore propose that in the absence of aPKCz, Lgl1 is not phosphorylated and binds with NMIIA constitutively, inhibiting its activity. Because NMIIA is required for focal adhesion maturation, its inhibition leads to the small number of focal adhesions observed in aPKCz ¡/¡ cells.…”

“…25 Recently we showed that aPKCz is important for establishing front-rear polarization of migrating cells by regulating the tumor suppressor lethal giant larvae 1 (Lgl1). 26 Lgl1 regulates the polarity of migrating cells by controlling the assembly state of NMII isoform A (NMIIA), its cellular localization, and focal adhesion assembly. 27 Phosphorylation of Lgl1 by aPKCz affects its cellular localization and prevents its interaction with NMIIA, thus affecting the cellular organization of the acto-NMIIA cytoskeleton.…”