Investigation of E-cadherin dynamics in cancer cell adhesion and metastasis

E-cadherin is a cell adhesion protein required for epithelial tissue integrity. In many cancer cells mis-regulation of E-cadherin adhesions causes increased progression and invasion of cancer. Alteration in E-cadherin dynamics could therefore serve as an early molecular biomarker of metastasis. In this project, I used E-cadherin FRAP to asses real time dynamics of cadherin junctions in a pancreatic cancer mice model of in a variety of micro-environments. My data showed that p53 mutation drives metastasis through mobilizing E-cadherin in junctions. Also, I used FRAP as a pharmaco-dynamic marker to assess the effect of an anti-invasive drug (dasatinib) in pancreatic tumours in vivo. Moreover, my E-cadherin FRAP data along with cross-linking experiments and disruption of E-cadherin interactions by mutation provided a comprehensive framework for understanding E-cadherin dynamics at cell-cell. Here, I have identified four distinct populations of E-cadherin within regions of cell-cell contact and characterized the interactions governing their mobility using FRAP. These pancreatic cancer cells had the immobile fraction (Fi) of E-cadherin-GFP comprised adhesive and non-adhesive populations. The remaining mobile fraction (Fm) also comprised of non-adhesive and adhesive populations, one population moves at the rate of pure diffusion, and therefore represents free E-cadherin monomers. The other population moves more slowly, and represents E-cadherin monomers turning over within immobile complexes. Inclusion of E-cadherin into either adhesive population requires cis-, trans-, and actin interactions. The signaling pathways in cells dramatically affect the fractions of these cadherin components. I showed that understanding the dynamics of these four populations of E-cadherins could be used to design or interpretation of future pharmacological and genetic experiments to probe the function of E-cadherin in development, disease progression, and response to therapy

In-depth proteomics identifies a role for autophagy in controlling reactive oxygen species mediated endothelial permeability

Endothelial cells (ECs) form the inner layer of blood vessels and physically separate the blood from the surrounding tissue. To support tissues with nutrients and oxygen, the endothelial monolayer is semipermeable. When EC permeability is altered, blood vessels are not functional, and this is associated with disease. A comprehensive knowledge of the mechanisms regulating EC permeability is key in developing strategies to target this mechanism in pathologies. Here we have used an in vitro model of human umbilical vein endothelial cells mimicking the formation of a physiologically permeable vessel and performed time-resolved in-depth molecular profiling using stable isotope labeling by amino acids in cell culture mass spectrometry (MS)-proteomics. Autophagy is induced when ECs are assembled into a physiologically permeable monolayer. By using siRNA and drug treatment to block autophagy in combination with functional assays and MS proteomics, we show that ECs require autophagy flux to maintain intracellular reactive oxygen species levels, and this is required to maintain the physiological permeability of the cells

Intravital FRAP imaging using an E-cadherin-GFP mouse reveals disease- and drug-dependent dynamic regulation of cell-cell junctions in live tissue

E-cadherin-mediated cell-cell junctions play a prominent role in maintaining the epithelial architecture. The disruption or deregulation of these adhesions in cancer can lead to the collapse of tumor epithelia that precedes invasion and subsequent metastasis. Here we generated an E-cadherin-GFP mouse that enables intravital photobleaching and quantification of E-cadherin mobility in live tissue without affecting normal biology. We demonstrate the broad applications of this mouse by examining E-cadherin regulation in multiple tissues, including mammary, brain, liver, and kidney tissue, while specifically monitoring E-cadherin mobility during disease progression in the pancreas. We assess E-cadherin stability in native pancreatic tissue upon genetic manipulation involving Kras and p53 or in response to anti-invasive drug treatment and gain insights into the dynamic remodeling of E-cadherin during in situ cancer progression. FRAP in the E-cadherin-GFP mouse, therefore, promises to be a valuable tool to fundamentally expand our understanding of E-cadherin-mediated events in native microenvironments