Mammalian homologues of C. elegans PAR-1 are asymmetrically localized in epithelial cells and may influence their polarity

Abstract

The establishment of polarity in the embryo is fundamental for the correct development of an organism [1]. The first cleavage of the Caenorhabditis elegans embryo is asymmetric with certain cytoplasmic components being distributed unequally between the daughter cells [2-4]. Using a genetic screen, Kemphues and co-workers have identified six par genes (partition-defective) [5,6], which are involved in the process of asymmetric division. One of these genes encodes a highly conserved protein, PAR-1, which is a serine/threonine kinase that localizes asymmetrically to the posterior part of the zygote and to those blastocysts that give rise to the germ line [7-9]. We reasoned that the mammalian homologue of PAR-1 (mPAR-1) might be involved in the process of polarization of epithelial cells, which consist of apical and basolateral membrane domains. We found that mPAR-1 was expressed in a wide variety of epithelial tissues and cell lines and was associated with the cellular cortex. In polarized epithelial cells, mPAR-1 was asymmetrically localized to the lateral domain. A fusion protein lacking the kinase domain had the same localization as the full-length protein but its prolonged expression acted in a dominant-negative fashion: lateral adhesion of the transfected cells to neighbouring cells was diminished, resulting in the former cells being 'squeezed out' from the monolayer. Moreover, the polarity of these cells was disturbed resulting in mislocalization of E-cadherin. Thus, in the C. elegans embryo and in epithelial cells, polarity appears to be governed by similar mechanisms.

Conformational instability of the MARK3 UBA domain compromises ubiquitin recognition and promotes interaction with the adjacent kinase domain

“…These k ex values indicate that exchange occurs in the fast limit [i.e., k ex Ͼ Ͼ ␦ , where ␦ ϭ N *␦ , ␦ , and ␦ are frequency (rad/s) and chemical shift differences (ppm) between states, respectively, and N is Larmor frequency of the 15 N nucleus] so that neither the populations of the exchanging states nor the chemical shifts for each probe in each state could be reliably estimated. In this limit, it is only possible to extract the exchange rate constant k ex ϭ k A ϩ k B and the product p A p B (␦ ) 2 , where p A and p B are the fractional populations of interconverting sites A and B, respectively. In what follows, we have assumed that the populations of each state are equal (p A ϭ p B ϭ 0.5) so that the minimum chemical shift differences between each state, ␦ , could be obtained for each probe.…”

“…P rotein kinases in the Par-1/MARK family are the subject of intense interest because of the crucial roles they play in establishing cell polarity (1)(2)(3)(4), regulating the cell cycle progression (5)(6)(7), and controlling microtubule dynamics (8)(9)(10)(11). Functional orthologs of Par-1 have been described from yeast to mammals (1-3, 8, 12).…”

Polarity-Regulating Kinase Partitioning-Defective 1/Microtubule Affinity-Regulating Kinase 2 Negatively Regulates Development of Dendrites on Hippocampal Neurons

“…In mammals, there are several Par1-related proteins (Tassan and Le Goff, 2004), and Par1b is the best characterized. The polarity-regulating function of Par1 is evolutionarily conserved, and it has been shown that Par1 is important in the regulation of apical-basolateral polarity of epithelial cells (Bohm et al, 1997;Cohen et al, 2004a,b;Hurov et al, 2004;Suzuki et al, 2004). Illenberger et al (1996) discovered the serine/threonine kinase microtubule affinity regulating kinase (MARK) as an ortholog of C. elegans Par1, which phosphorylates several microtubule-binding proteins (MAPs).…”

“…In mammalian epithelial cells, Par1/MARK localizes predominantly at basolateral membranes and is excluded from apical areas (Bohm et al, 1997). Par1/MARK is phosphorylated by atypical protein kinase C (aPKC) (Hurov et al, 2004;Kusakabe and Nishida, 2004;Suzuki et al, 2004), and then moves to the cytosol.…”

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

“…Originally identified in Caenorhabdhitis elegans as a critical player in early embryonic polarity, Par-1 has since been shown to regulate cell polarity in yeast, Drosophila, Xenopus, and several mammalian cell types (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Par-1 is a regulator of microtubule stability, the Wnt signaling pathway and also plays a role in vesicular trafficking (2,8,12,(14)(15)(16)(17)(18)(19).…”