Rap2A links intestinal cell polarity to brush border formation

Abstract

The microvillus brush border at the apex of the highly polarized enterocyte allows the regulated uptake of nutrients from the intestinal lumen. Here, we identify the small G protein Rap2A as a molecular link that couples the formation of microvilli directly to the preceding cell polarization. Establishment of apicobasal polarity, which can be triggered by the kinase LKB1 in single, isolated colon cells, results in enrichment of PtdIns(4,5)P(2) at the apical membrane. The subsequent recruitment of phospholipase D1 allows polarized accumulation of phosphatidic acid, which provides a local cue for successive signalling by the guanine nucleotide exchange factor PDZGEF, the small G protein Rap2A, its effector TNIK, the kinase MST4 and, ultimately, the actin-binding protein Ezrin. Thus, epithelial cell polarization is translated directly into the acquisition of brush borders through a small G protein signalling module whose action is positioned by a cortical lipid cue.

Cellular and Physiological Roles for Phospholipase D1 in Cancer

“…PLD function has been studied using biochemical, cell biological, and now physiological approaches. Potential roles for PLD in general or for PLD1 specifically have been reported in numerous physiological settings including ones relevant to cancer such as survival signaling (8 -11), control of cell polarity (12,13), Ras activation (14 -19), and cell migration (13, 20 -26). Moreover, a PLD1 single nucleotide polymorphism (SNP) associates with the risk of non-small cell lung cancer and increased PLD1 expression and/or PLD activity have been reported in multiple types of cancer (27)(28)(29)(30)(31)(32)(33), although the mechanisms underlying this increase and the specific advantage this confers to the tumor cells are not known.…”

“…Another early step involves loss of polarization for epithelial cells. PLD1 has been linked to epithelial cell polarization downstream of the tumor suppressor LKB1 via effects on the small GTPase Rap2A and the actin-binding protein Ezrin (12) and for motile cells such as neutrophils via control of recruitment of Rac1 to the leading edge of the cell and subsequent actin cytoskeletal reorganization (13). An important subsequent step involves increasing invasive capacity to facilitate movement into the vascular or lymphatic circulation.…”

Myosin Vb and rab11a regulate ezrin phosphorylation in enterocytes

“…Proteins move up and down the microvilli membrane in response to signals and microvilli generate vesicles that are shed into the apical lumen (McConnell et al, 2009) where they regulate epithelial-microbial interactions (Shifrin et al, 2012). Interestingly, (part of) the molecular pathway(s) for the development of microvilli has been demonstrated to constitute a separate branch of the epithelial cell polarity program driven by the serine/threonine liver kinase B1 (LKB1) (Gloerich et al, 2012;ten Klooster et al, 2009). Whether the apically enriched Rab11a-positive recycling endosomes play a direct role in the development and organization of microvilli at the apical plasma membrane is not known.…”

“…Several kinases have been implicated in the direct T567 phosphorylation of ezrin in intestinal epithelial cells, including protein kinase B2/Akt2 (Shiue et al, 2005), atypical protein kinase C-iota (aPKCi) (Wald et al, 2008), mammalian Sterile 20 (Ste20)-like kinase-4 (Mst4) (Gloerich et al, 2012;ten Klooster et al, 2009), lymphocyte-oriented kinase (LOK) and Ste20-like kinase (SLK) (Viswanatha et al, 2012). Knockdown of each of these kinases in various intestinal epithelial cell models inhibits microvillus development at the apical plasma membrane (Gloerich et al, 2012;Shiue et al, 2005;ten Klooster et al, 2009;Viswanatha et al, 2012;Wald et al, 2008). Some of these kinases have been reported to localize to the apical microvillus membrane (Shiue et al, 2005;Viswanatha et al, 2012).…”

Smad1 stabilization and delocalization in response to the blockade of BMP activity

“…Here, we have uncovered a novel regulatory mechanism in response to the blockade of BMP activity. This not only occurs in in vitro cultured cells but also in the cells of the mouse intestine villi, which undergo rapid turnover [33,44]. The stem cells in the crypts generate new enterocytes, which undergo transient proliferation, then terminal differentiation, and finally move up from the crypt to the villi top, where they die by apoptosis [33].…”