αV-Integrins Are Required for Mechanotransduction in MDCK Epithelial Cells

The properties of epithelial cells within tissues are regulated by their immediate microenvironment, which consists of neighboring cells and the extracellular matrix (ECM). Integrin heterodimers orchestrate dynamic assembly and disassembly of cell-ECM connections and thereby convey biochemical and mechanical information from the ECM into cells. However, the specific contributions and functional hierarchy between different integrin heterodimers in the regulation of focal adhesion dynamics in epithelial cells are incompletely understood. Here, we have studied the functions of RGD-binding αV-integrins in a Madin Darby Canine Kidney (MDCK) cell model and found that αV-integrins regulate the maturation of focal adhesions (FAs) and cell spreading. αV-integrin-deficient MDCK cells bound collagen I (Col I) substrate via α2β1-integrins but failed to efficiently recruit FA components such as talin, focal adhesion kinase (FAK), vinculin and integrin-linked kinase (ILK). The apparent inability to mature α2β1-integrin-mediated FAs and link them to cellular actin cytoskeleton led to disrupted mechanotransduction in αV-integrin deficient cells seeded onto Col I substrate

BAMBI is a novel HIF1-dependent modulator of TGF beta-mediated disruption of cell polarity during hypoxia

Hypoxia and loss of cell polarity are common features of malignant carcinomas. Hypoxia-inducible factor 1 (HIF1) is the major regulator of cellular hypoxia response and mediates the activation of similar to 300 genes. Increased HIF1 signaling is known to be associated with epithelial-mesenchymal transformation. Here, we report that hypoxia disrupts polarized epithelial morphogenesis of MDCK cells in a HIF1 alpha-dependent manner by modulating the transforming growth factor-beta (TGF beta) signaling pathway. Analysis of potential HIF1 targets in the TGF beta pathway identified the bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI), a transmembrane glycoprotein related to the type I receptors of the TGF beta family, whose expression was essentially lost in HIF1-depleted cells. Similar to what was observed in HIF1-deficient cells, BAMBI-depleted cells failed to efficiently activate TGF beta signaling and retained epithelial polarity during hypoxia. Taken together, we show that hypoxic conditions promote TGF beta signaling in a HIF1-dependent manner and BAMBI is identified in this pathway as a novel HIF1-regulated gene that contributes to hypoxia-induced loss of epithelial polarity.Peer reviewe

Seeing an Unseen Science

No abstrac

Seeing an Unseen Science.

Karl Matlin explores the origins of cell biology in this review of Carol Moberg'

Moberg CL (2012) Entering an Unseen World. New York: Rockefeller University Press. 499 p. ISBN 978-0874700633 (hardcover). US$40.00.

<p>Moberg CL (2012) Entering an Unseen World. New York: Rockefeller University Press. 499 p. ISBN 978-0874700633 (hardcover). US$40.00.</p

Multilayering and loss of apical polarity in MDCK cells transformed with viral K-ras

Abstract. The effects of viral Kirsten ras oncogene expression on the polarized phenotype of MDCK cells were investigated. Stable transformed MDCK cell lines expressing the v-K-ras oncogene were generated via infection with a helper-independent retroviral vector construct. When grown on plastic substrata, transformed cells formed continuous monolayers with epithelial-like morphology. However, on permeable filter supports where normal cells form highly polarized monolayers, transformed MDCK cells detached from the substratum and developed multilayers. Morphological analysis of the multilayers revealed that oncogene expression perturbed the polarized organization of MDCK cells such that the transformed cells lacked an apical-basal axis around which the cytoplasm i

Endosomal fractions from viral K-<i>ras</i>-transformed MDCK cells reveal transformation specific changes on two-dimensional gel maps

We have investigated the effects of viral Kirsten ras oncogene expression in Madin-Darby canine kidney (MDCK) II epithelial cell on the differential protein expression of organelle proteins. MDCK cells, stably transformed via infection with a helper-independent retroviral vector construct, were grown on permeable filter supports. Whereas normal cells form highly polarized monolayers, ras-transformed cells display an unpolarized phenotype, detaching from the substratum and developing multilayers (Schoenenberger, C.-A. et al., J. Cell Biol. 1991, 112, 873–889). We postulate that this breakdown of epithelial polarity reflects disturbed intracellular protein transport and sorting, namely, proteins will no longer be sorted correctly in intracellular organelles and will therefore not reach their appropriate target membrane. Here we emphasize the role of endosomes as sorting platform in epithelial cells. We found significant differences in the molecular composition of endosomes from normal vs. oncogenic transformed epithelial cells, strengthening previous evidence indicating that oncogenic transformation results in abnormal expression of normal genes (Celis, J. E., Olsen, E., Electrophoresis 1994, 15, 309–344) as well as the expression of new ones (Huber, L. A. et al., Electrophoresis 1994, 15, 468–473)