Atypical Protein Kinase C Is Involved in the Evolutionarily Conserved Par Protein Complex and Plays a Critical Role in Establishing Epithelia-Specific Junctional Structures

Abstract

We have previously shown that during early Caenorhabditis elegans embryogenesis PKC-3, a C. elegans atypical PKC (aPKC), plays critical roles in the establishment of cell polarity required for subsequent asymmetric cleavage by interacting with PAR-3 [Tabuse, Y., Y. Izumi, F. Piano, K.J. Kemphues, J. Miwa, and S. Ohno. 1998. Development (Camb.). 125:3607–3614]. Together with the fact that aPKC and a mammalian PAR-3 homologue, aPKC-specific interacting protein (ASIP), colocalize at the tight junctions of polarized epithelial cells (Izumi, Y., H. Hirose, Y. Tamai, S.-I. Hirai, Y. Nagashima, T. Fujimoto, Y. Tabuse, K.J. Kemphues, and S. Ohno. 1998. J. Cell Biol. 143:95–106), this suggests a ubiquitous role for aPKC in establishing cell polarity in multicellular organisms. Here, we show that the overexpression of a dominant-negative mutant of aPKC (aPKCkn) in MDCK II cells causes mislocalization of ASIP/PAR-3. Immunocytochemical analyses, as well as measurements of paracellular diffusion of ions or nonionic solutes, demonstrate that the biogenesis of the tight junction structure itself is severely affected in aPKCkn-expressing cells. Furthermore, these cells show increased interdomain diffusion of fluorescent lipid and disruption of the polarized distribution of Na+,K+-ATPase, suggesting that epithelial cell surface polarity is severely impaired in these cells. On the other hand, we also found that aPKC associates not only with ASIP/PAR-3, but also with a mammalian homologue of C. elegans PAR-6 (mPAR-6), and thereby mediates the formation of an aPKC-ASIP/PAR-3–PAR-6 ternary complex that localizes to the apical junctional region of MDCK cells. These results indicate that aPKC is involved in the evolutionarily conserved PAR protein complex, and plays critical roles in the development of the junctional structures and apico-basal polarization of mammalian epithelial cells.

Loss of Cell Adhesion Causes Hydrocephalus in Nonmuscle Myosin II-B–ablated and Mutated Mice

“…In contrast, Even-Faitelson and Ravid (2006) have reported that phosphorylation of the NMHC II-B in the nonhelical tail by an aPKC results in cortical localization of both NM II-B and aPKC in a prostate cancer cell line. The requirement of aPKC in cell-cell adhesion has been demonstrated both in cultured cells (Suzuki et al, 2001, Nunbhakdi-Craig et al, 2002 and neuroepithelial cells in the developing mouse brain (Manabe et al, 2002). As noted above, the importance of aPKC in maintaining adherens junctions in the neocortex was demonstrated by conditional loss of this enzyme, which also resulted in hydrocephalus, although at a much later time (P3) than we report here (Imai et al, 2006).…”

Down-regulated expression of atypical PKC-binding domain deleted asip isoforms in human hepatocellular carcinomas

“…Although L-02 was originally derived from normal human liver tissue, we can not exclude the possibility, to some extent, that the cell line studied here has undergone malignant transformation. Since Asip localizes at the tight junctions of polarized epithelial cells and may play a critical role in the development of the junctional structures and apico-basal polarization of mammalian epithelial cells [7], [19]. The expression of exon 17b deleted variants might be related to highly organized cell-cell contact and its down-regulation or absence occurred if the contacts among cells were disrupted.…”

Role of Rho family GTPases in epithelial morphogenesis

“…Interestingly, whereas overexpression of kinase-dead aPKC or truncated versions of Par-6 or JAM interferes with the establishment of new tight junctions, it does not appear to alter the morphology or composition of mature junctions (Joberty et al 2000;Ebnet et al 2001;Itoh et al 2001;Suzuki et al 2001;Yamanaka et al 2001). This suggests that the role of the Par-aPKC complex may be restricted to tight junction development rather than maintenance.…”