Contact inhibition is the ability of cells to inhibit motility and proliferation after forming cell-cell contacts. Our long-term goal is to understand the molecular mechanism underlying contact inhibition in normal epithelial cells. Epithelial cell-cell contacts are mainly formed by E-cadherin-based adherens junctions, which function as a focal point of many signaling pathways regulating various cellular behaviors, including most likely, contact inhibition. We recently reported that translocation of a protein complex to cell-cell contacts is pivotal to the establishment of contact inhibition. These complexes, defined here as """"""""Pak:PIX complexes"""""""", minimally contain the Rac/cdc42 effector molecules p21-activated kinase 1 (Pak1) and the Rac/cdc42-guanine exchange factor betaPIX. In subconfluent cells, Pak:PIX complexes are in focal contacts, where they regulate cell motility and morphology. How they are recruited to cell-cell contact sites and how this translocation can regulate proliferation, is however unknown. The objective of this proposal is to characterize the mechanisms by which Pak:PIX complexes translocate from focal contacts to cell-cell contacts when cells become confluent, and to determine how this affects mitogenic signaling through the MEK-ERK pathway. The central hypothesis is that, upon E-cadherin-mediated activation of phosphatidyl inositol-3-kinase, Pak:PIX complexes are recruited to cell-cell contacts. This translocation may uncouple mitogenic signaling.
In aim 1, we will characterize the translocation of Pak:PIX complexes and will identify new binding partners, in aim 2, we will further define the role of E-cadherin, and in aim 3, we will investigate how Pak:PIX complexes control contact inhibition by regulating the mitogenic MEK-ERK signaling pathway. The proposed research is important, as it will help to understand how localized, subcellular dynamic regulation of Rho effector proteins integrates the many signals that cells receive from their extracellular environment. The experiments outlined in this proposal will specifically address the mechanism that regulates the cell density-dependent localization of Pak:PIX complexes, which is crucial for contact inhibition. Identification of the mechanism underlying contact inhibition will allow us to identify specific target molecules that can be employed for diagnostic purposes or drug design. We anticipate that the results of our studies will yield novel and fundamental insights into the biology of epithelial morphogenesis. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM076363-03
Application #
7254943
Study Section
Special Emphasis Panel (ZRG1-ICI-G (01))
Program Officer
Flicker, Paula F
Project Start
2006-07-01
Project End
2011-06-30
Budget Start
2007-07-01
Budget End
2008-06-30
Support Year
3
Fiscal Year
2007
Total Cost
$260,703
Indirect Cost
Name
University of Chicago
Department
Surgery
Type
Schools of Medicine
DUNS #
005421136
City
Chicago
State
IL
Country
United States
Zip Code
60637
Eastburn, Dennis J; Zegers, Mirjam M; Mostov, Keith E (2012) Scrib regulates HGF-mediated epithelial morphogenesis and is stabilized by Sgt1-HSP90. J Cell Sci 125:4147-57
deLeon, Orlando; Puglise, Jason M; Liu, Fengming et al. (2012) Pak1 regulates the orientation of apical polarization and lumen formation by distinct pathways. PLoS One 7:e41039
Jia, Liwei; Liu, Fengming; Hansen, Steen H et al. (2011) Distinct roles of cadherin-6 and E-cadherin in tubulogenesis and lumen formation. Mol Biol Cell 22:2031-41
Torres, Jacqueline; Funk, Holly M; Zegers, Mirjam M P et al. (2011) The syntaxin 4 N terminus regulates its basolateral targeting by munc18c-dependent and -independent mechanisms. J Biol Chem 286:10834-46
Liu, Fengming; Jia, Liwei; Thompson-Baine, Ann-Marie et al. (2010) Cadherins and Pak1 control contact inhibition of proliferation by Pak1-betaPIX-GIT complex-dependent regulation of cell-matrix signaling. Mol Cell Biol 30:1971-83
Hunter, Michael P; Zegers, Mirjam M (2010) Pak1 regulates branching morphogenesis in 3D MDCK cell culture by a PIX and beta1-integrin-dependent mechanism. Am J Physiol Cell Physiol 299:C21-32
Zegers, Mirjam (2008) Roles of P21-activated kinases and associated proteins in epithelial wound healing. Int Rev Cell Mol Biol 267:253-98