Membrane Targeting of Bazooka/PAR-3 Is Mediated by Direct Binding to Phosphoinositide Lipids

Abstract

Cell polarity in higher animals is controlled by evolutionarily conserved protein complexes, which localize to the cytocortex in a polarized manner. The PAR-3/PAR-6/atypical protein kinase C (aPKC) complex is the first to become asymmetrically localized, and it controls the localization of additional complexes functioning further downstream in the regulation of cell polarity. The first component of the PAR-3/PAR-6/aPKC complex that is localized to the cortex is Bazooka/PAR-3 (Baz), a large scaffolding protein. In most cell types analyzed, loss of Baz function leads to loss of cell polarity. Here we present a structure-function analysis of Baz focusing on its subcellular localization and function in four different polarized Drosophila cell types: the embryonic ectodermal epidermis, the follicular epithelium, embryonic neuroblasts, and the oocyte. We show that the PDZ domains of Baz are dispensable for its correct localization, whereas a conserved region in the C-terminal part of Baz to which no function had been assigned so far is required and sufficient for membrane localization. This region binds to phosphoinositide membrane lipids and thus mediates cortical localization of Baz by direct interaction with the plasma membrane. Our findings reveal a mechanism for the coupling of plasma membrane polarity and cortical polarity.

Localization and Function of Pals1-associated Tight Junction Protein in Drosophila Is Regulated by Two Distinct Apical Complexes

“…Drosophila Genetics-The following mutant alleles were used: PATJ ⌬1 (21), baz (30,31), baz XR11 (32), sdt K85 (33), and crb 11A22 (34). Germ line clones were generated with the mutant alleles recombined with FRT using the dominant female sterile technique (35).…”

“…In contrast, a protein composed of the three PDZ domains of PATJ and a fragment of Baz that accumulates at the apical junctions by direct binding to the plasma membrane (31), is, to a large extent, correctly targeted to the apical junctions (PATJ ⌬L27 -LB(Baz) , Fig. 5D) but does not rescue the PATJ null allele (Fig.…”

Phosphoinositides in Cell Architecture

“…Additional work shows that the interaction between PAR-3 and PTEN was conserved in mammals and necessary for the establishment of epithelial polarity (Feng et al 2008). Interestingly, two recent studies have reported that Baz/PAR-3 can bind directly to PIs in flies and mammals (Wu et al 2007;Krahn et al 2010). There is a PIs specify membrane identity in epithelial cells.…”

Development and Cell Polarity of the C. elegans Intestine

“…From genetic studies on Drosophila ectoderm and mammalian culture cells, it appears that at least four spatially restricted membrane associated protein-scaffolds are required for regulating the maturation of the ZA in epithelial cells: the PAR-3-PAR-6-aPKC (PPC) complex, the Crumbs-Stardust-Patj complex, the Scribble-Dlg-Lgl complex, and the YurtCoracle group (Betschinger et al, 2003;Bilder et al, 2003;Harris and Peifer, 2005;Harris and Peifer, 2007;Krahn et al, 2010a;Krahn et al, 2010b;Laprise et al, 2009;Plant et al, 2003;Tanentzapf and Tepass, 2003;Yamanaka et al, 2003).…”

“…In Drosophila membrane targeting of Bazooka/PAR-3 is mediated by direct binding to phosphoinositide lipids (Krahn et al, 2010b). Recent deletion and point mutation analyses of three LAP proteins, using C. elegans LET-413, human Erbin and human Scribble demonstrate that their LRR domain is crucial for membrane targeting (Legouis et al, 2003).…”