Atypical PKC Phosphorylates PAR-1 Kinases to Regulate Localization and Activity

Abstract

The establishment and maintenance of cellular polarity are essential biological processes that must be maintained throughout the lifetime of eukaryotic organisms. The Par-1 protein kinases are key polarity determinants that have been conserved throughout evolution. Par-1 directs anterior-posterior asymmetry in the one-cell C. elegans embryo and the Drosophila oocyte. In mammalian cells, Par-1 may regulate epithelial cell polarity. Relevant substrates of Par-1 in these pathways are just being identified, but it is not yet known how Par-1 itself is regulated. Here, we demonstrate that human Par-1b (hPar-1b) interacts with and is negatively regulated by atypical PKC. hPar-1b is phosphorylated by aPKC on threonine 595, a residue conserved in Par-1 orthologs in mammals, worms, and flies. The equivalent site in hPar-1a, T564, is phosphorylated in vivo and by aPKC in vitro. Importantly, phosphorylation of hPar-1b on T595 negatively regulates the kinase activity and plasma membrane localization of hPar-1b in vivo. This study establishes a novel functional link between two central determinants of cellular polarity, aPKC and Par-1, and suggests a model by which aPKC may regulate Par-1 in polarized cells.

PAK5 Kinase Is an Inhibitor of MARK/Par-1, Which Leads to Stable Microtubules and Dynamic Actin

“…MAP kinase/ERK provides an example where dimerization of the catalytic domain regulates signaling (Cobb and Goldsmith, 2000). A further variation is that of Par-1b (homologous to MARK2) whose phosphorylation at Thr595 by aPKC creates a 14-3-3 binding site and subsequent inhibition (Hurov et al, 2004;Suzuki et al, 2004). Such control sequences tend to lie outside the core of the catalytic domain, unlike our present case where the catalytic core domain of PAK5 can bind and inhibit the core domain of MARK2.…”

Linking epithelial polarity and carcinogenesis by multitasking Helicobacter pylori virulence factor CagA

“…This CagA activity is mediated by specific interaction of CagA with PAR1 (Saadat et al, 2007: Zeaiter et al, 2008 (Figure 1), one of the six PAR proteins isolated in C. elegans. PAR1 is a serine/ threonine kinase that has a central function in the establishment and maintenance of the basolateral membrane domain in epithelial cells (Hurov et al, 2004;Suzuki et al, 2004) (Figure 2a). Mammalian PAR1 was originally identified as a microtubule affinityregulating kinase (MARK) based on its ability to phosphorylate MAPs such as tau, MAP2 and MAP4 (Drewes et al, 1997).…”

“…The causal link between LKB1 and the cancer-prone PeutzJeghers syndrome supports the idea that defects in epithelial polarity are required for the development of epithelial tumors. PAR1 is also phosphorylated by the aPKC/PAR3/PAR6 complex (Hurov et al, 2004;Suzuki et al, 2004). This PAR1 phosphorylation creates a docking site for 14-3-3, the mammalian ortholog of C. elegans PAR5.…”

Loss of the Par-1b/MARK2 polarity kinase leads to increased metabolic rate, decreased adiposity, and insulin hypersensitivity in vivo

“…Two critical regulators of Par-1, LKB1 (Par-4) and atypical PKC / (aPKC), have been identified in multiple systems. LKB1 catalyzes phosphorylation of an activation loop Thr residue in the kinase domain of the Par-1, whereas aPKC phosphorylates a conserved Thr residue in the ''spacer'' domain of the Par-1 kinases (20)(21)(22). In contrast to the activating phosphorylation catalyzed by LKB1, aPKC negatively regulates localization and activity of Par-1 (22)(23)(24)(25).…”