Pro-migratory and TGF-β-activating functions of αvβ6 integrin in pancreatic cancer are differentially regulated via an Eps8-dependent GTPase switch

J Pathol. 2017 Sep;243(1):37-50. doi: 10.1002/path.4923. Epub 2017 Aug 7.

Abstract

The integrin αvβ6 is up-regulated in numerous carcinomas, where expression commonly correlates with poor prognosis. αvβ6 promotes tumour invasion, partly through regulation of proteases and cell migration, and is also the principal mechanism by which epithelial cells activate TGF-β1; this latter function complicates therapeutic targeting of αvβ6, since TGF-β1 has both tumour-promoting and -suppressive effects. It is unclear how these different αvβ6 functions are linked; both require actin cytoskeletal reorganization, and it is suggested that tractive forces generated during cell migration activate TGF-β1 by exerting mechanical tension on the ECM-bound latent complex. We examined the functional relationship between cell invasion and TGF-β1 activation in pancreatic ductal adenocarcinoma (PDAC) cells, and confirmed that both processes are αvβ6-dependent. Surprisingly, we found that cellular functions could be biased towards either motility or TGF-β1 activation depending on the presence or absence of epidermal growth factor receptor pathway substrate 8 (Eps8), a regulator of actin remodelling, endocytosis, and GTPase activation. Similar to αvβ6, we found that Eps8 was up-regulated in >70% of PDACs. In complex with Abi1/Sos1, Eps8 regulated αvβ6-dependent cell migration through activation of Rac1. Down-regulation of Eps8, Sos1 or Rac1 suppressed cell movement, while simultaneously increasing αvβ6-dependent TGF-β1 activation. This latter effect was modulated through increased cell tension, regulated by Rho activation. Thus, the Eps8/Abi1/Sos1 tricomplex acts as a key molecular switch altering the balance between Rac1 and Rho activation; its presence or absence in PDAC cells modulates αvβ6-dependent functions, resulting in a pro-migratory (Rac1-dependent) or a pro-TGF-β1 activation (Rho-dependent) functional phenotype, respectively. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Keywords: Eps8; Rac1; Rho; TGF-β1; motility; αvβ6.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Antigens, Neoplasm / genetics
  • Antigens, Neoplasm / metabolism*
  • Carcinoma, Pancreatic Ductal / enzymology*
  • Carcinoma, Pancreatic Ductal / genetics
  • Carcinoma, Pancreatic Ductal / pathology
  • Cell Line, Tumor
  • Cell Movement* / drug effects
  • Coculture Techniques
  • Cytoskeletal Proteins / genetics
  • Cytoskeletal Proteins / metabolism
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Integrins / genetics
  • Integrins / metabolism*
  • Neoplasm Invasiveness
  • Pancreatic Neoplasms / enzymology*
  • Pancreatic Neoplasms / genetics
  • Pancreatic Neoplasms / pathology
  • Phenotype
  • RNA Interference
  • SOS1 Protein / genetics
  • SOS1 Protein / metabolism
  • Signal Transduction
  • Stromal Cells / enzymology
  • Stromal Cells / pathology
  • Transfection
  • Transforming Growth Factor beta1 / metabolism*
  • Tumor Microenvironment
  • rac1 GTP-Binding Protein / genetics
  • rac1 GTP-Binding Protein / metabolism*
  • rho GTP-Binding Proteins / antagonists & inhibitors
  • rho GTP-Binding Proteins / metabolism*

Substances

  • ABI1 protein, human
  • Adaptor Proteins, Signal Transducing
  • Antigens, Neoplasm
  • Cytoskeletal Proteins
  • EPS8 protein, human
  • Enzyme Inhibitors
  • Integrins
  • RAC1 protein, human
  • SOS1 Protein
  • TGFB1 protein, human
  • Transforming Growth Factor beta1
  • integrin alphavbeta6
  • rac1 GTP-Binding Protein
  • rho GTP-Binding Proteins