Article

Mst4 and Ezrin Induce Brush Borders Downstream of the Lkb1/Strad/Mo25 Polarization Complex

Hubrecht Institute, KNAW and University Medical Centre, Utrecht, The Netherlands.
Developmental Cell (Impact Factor: 10.37). 05/2009; 16(4):551-62. DOI: 10.1016/j.devcel.2009.01.016
Source: PubMed

ABSTRACT The human Lkb1 kinase, encoded by the ortholog of the invertebrate Par4 polarity gene, is mutated in Peutz-Jeghers cancer syndrome. Lkb1 activity requires complex formation with the pseudokinase Strad and the adaptor protein Mo25. The complex can induce complete polarization in a single isolated intestinal epithelial cell. We describe an interaction between Mo25alpha and a human serine/threonine kinase termed Mst4. A homologous interaction occurs in the yeast Schizosaccharomyces pombe in the control of polar tip growth. Human Mst4 translocates from the Golgi to the subapical membrane compartment upon activation of Lkb1. Inhibition of Mst4 activity inhibits Lkb1-induced brush border formation, whereas other aspects of polarity such as the formation of lateral junctions remain unaffected. As an essential event in brush border formation, Mst4 phosphorylates the regulatory T567 residue of Ezrin. These data define a brush border induction pathway downstream of the Lkb1/Strad/Mo25 polarization complex, yet separate from other polarity events.

Download full-text

Full-text

Available from: Peter Hornbeck, Jun 22, 2015
0 Followers
 · 
202 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The apicobasal polarity of enterocytes determines where the brush border membrane (apical membrane) will form, but how this apical membrane faces the lumen is not well understood. The electrical signal across the epithelium could serve as a coordinating cue, orienting and polarizing enterocytes. Here we show that applying a physiological electric field (EF) to intestinal epithelial cells, to mimic the natural EF created by the transepithelial potential difference, directed phosphorylation of the actin-binding protein ezrin, increased expression of intestinal alkaline phosphatase (ALPI, a differentiation marker) and remodelled the actin cytoskeleton selectively on the cathode side. In addition, an applied EF also activated ERK1/2 and LKB1, key molecules in apical membrane formation. Disruption of the tyrosine-protein kinase transmembrane receptor Ror2 suppressed activation of ERK1/2 and LKB1 significantly and subsequently inhibited apical membrane formation in enterocytes. Our findings indicate that the endogenous EF created by the TEP may act as an essential coordinating signal for apical membrane formation at a tissue level, through activation of LKB1 mediated by Ror2/ERK signalling.
    Development 06/2014; 127(15). DOI:10.1242/jcs.146357 · 6.27 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The tumor suppressor Lkb1/STK11/Par-4 is a key regulator of cellular energy, proliferation, and polarity, yet its mechanisms of action remain poorly defined. We generated mice harboring a mutant Lkb1 knockin allele that allows for rapid inhibition of Lkb1 kinase. Culturing embryonic tissues, we show that acute loss of kinase activity perturbs epithelial morphogenesis without affecting cell polarity. In pancreas, cystic structures developed rapidly after Lkb1 inhibition. In lung, inhibition resulted in cell-autonomous branching defects. Although the lung phenotype was rescued by an activator of the Lkb1 target adenosine monophosphate-activated kinase (AMPK), pancreatic cyst development was independent of AMPK signaling. Remarkably, the pancreatic phenotype evolved to resemble precancerous lesions, demonstrating that loss of Lkb1 was sufficient to drive the initial steps of carcinogenesis ex vivo. A similar phenotype was induced by expression of mutant K-Ras with p16/p19 deletion. Combining culture of embryonic tissues with genetic manipulation and chemical genetics thus provides a powerful approach to unraveling developmental programs and understanding cancer initiation.
    The Journal of Cell Biology 12/2012; 199(7):1117-30. DOI:10.1083/jcb.201208080 · 9.69 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ezrin is a multifunctional protein that connects the actin cytoskeleton to the extracellular matrix through transmembrane proteins. High ezrin expression is associated with lung metastasis and poor survival in cancer. We screened small molecule libraries for compounds that directly interact with ezrin protein using surface plasmon resonance to identify lead compounds. The secondary functional assays used for lead compound selection included ezrin phosphorylation as measured by immunoprecipitation and in vitro kinase assays, actin binding, chemotaxis, invasion into an endothelial cell monolayer, zebrafish and Xenopus embryonic development, mouse lung organ culture and an in vivo lung metastasis model. Two molecules, NSC305787 and NSC668394, that directly bind to ezrin with low micromolar affinity were selected based on inhibition of ezrin function in multiple assays. They inhibited ezrin phosphorylation, ezrin-actin interaction and ezrin-mediated motility of osteosarcoma (OS) cells in culture. NSC305787 mimicked the ezrin morpholino phenotype, and NSC668394 caused a unique developmental defect consistent with reduced cell motility in zebrafish. Following tail vein injection of OS cells into mice, both molecules inhibited lung metastasis of ezrin-sensitive cells, but not ezrin-resistant cells. The small molecule inhibitors NSC305787 and NSC668394 demonstrate a novel targeted therapy that directly inhibits ezrin protein as an approach to prevent tumor metastasis.
    Oncogene 06/2011; 31(3):269-81. DOI:10.1038/onc.2011.245 · 8.56 Impact Factor