KIBRA Suppresses Apical Exocytosis through Inhibition of aPKC Kinase Activity in Epithelial Cells

Abstract

Epithelial cells possess apical-basolateral polarity and form tight junctions (TJs) at the apical-lateral border, separating apical and basolateral membrane domains. The PAR3-aPKC-PAR6 complex plays a central role in TJ formation and apical domain development during tissue morphogenesis. Inactivation and overactivation of aPKC kinase activity disrupts membrane polarity. The mechanism that suppresses active aPKC is unknown. KIBRA, an upstream regulator of the Hippo pathway, regulates tissue size in Drosophila and can bind to aPKC. However, the relationship between KIBRA and the PAR3-aPKC-PAR6 complex remains unknown. We report that KIBRA binds to the PAR3-aPKC-PAR6 complex and localizes at TJs and apical domains in epithelial tissues and cells. The knockdown of KIBRA causes expansion of the apical domain in MDCK three-dimensional cysts and suppresses the formation of apical-containing vacuoles through enhanced de novo apical exocytosis. These phenotypes are restored by inhibition of aPKC. In addition, KIBRA directly inhibits the kinase activity of aPKC in vitro. These results strongly support the notion that KIBRA regulates epithelial cell polarity by suppressing apical exocytosis through direct inhibition of aPKC kinase activity in the PAR3-aPKC-PAR6 complex.

KIBRA Regulates Aurora Kinase Activity and Is Required for Precise Chromosome Alignment During Mitosis

“…KIBRA was originally identified as a memory performance-associated protein in humans (28 -32), and this function was recently confirmed in mice (33). The physiological function of KIBRA in non-neuronal cells is much less defined, although KIBRA has been shown to be involved in cell migration in podocytes (34) and NRK cells (35) and in epithelial cell polarity (36). KIBRA also interacts with the motor protein dynein light chain 1 to positively regulate cell growth in breast cancer cells (37).…”

WWC1 (WW and C2 domain containing 1)

“…KIBRA localizes in the apical domain and at cell junctions in epithelial cells (Yoshihama et al, 2011). In brain, KIBRA co-localizes with protein kinase Mzeta (PKMzeta) in the mouse hippocampus (Yoshihama et al, 2009).…”

“…In brain, KIBRA co-localizes with protein kinase Mzeta (PKMzeta) in the mouse hippocampus (Yoshihama et al, 2009). In mouse kidney, KIBRA localizes in the distal tubular epithelial cells (Yoshihama et al, 2011). In migrating cells, KIBRA accumulates in the leading edge (Duning et al, 2008).…”

p120-catenin controls contractility along the vertical axis of epithelial lateral membranes

“…Lgl, Scrib or Dlg proteins) (Yamanaka, 2006). Overexpression of gp135 (also known as CNTN1) or downregulation of KIBRA (also known as WWC1 in mammals) can also induce apical expansion (Nielsen et al, 2000;Yoshihama et al, 2011). For the polarity proteins, apical expansion is driven by mis-targeting of apical membrane proteins to lateral membranes, irrespective of the placement of tight junctions (Tanentzapf and Tepass, 2002).…”

“…Notably, in the latter cases (gp135 and KIBRA KD), the mechanism was shown to not involve mis-targeting to apical or basolateral membranes. Instead, the tight junction is retained at the boundary between apical and lateral membranes but displaced basally by the expanding apical surface (Nielsen et al, 2000;Yoshihama et al, 2011). To determine whether either of these mechanisms was responsible for the p120-KD phenotype, we first examined the effect of p120 KD on the placement of tight junctions relative to the apical surface.…”