Disruption of occludin function in polarized epithelial cells activates the extrinsic pathway of apoptosis leading to cell extrusion without loss of transepithelial resistance

Neal E Beeman,Heidi K Baumgartner,Jerome B Schaack,Margaret C Neville,Patricia G Webb

doi:10.1186/1471-2121-10-85

Neal E Beeman, Heidi K Baumgartner + Show 3 more

Open Access

https://doi.org/10.1186/1471-2121-10-85

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Abstract

BackgroundOccludin is a tetraspanin protein normally localized to tight junctions. The protein interacts with a variety of pathogens including viruses and bacteria, an interaction that sometimes leads to its extrajunctional localization.ResultsHere we report that treatment of mammary epithelial monolayers with a circularized peptide containing a four amino acid sequence found in the second extracellular loop of occludin, LHYH, leads to the appearance of extrajunctional occludin and activation of the extrinsic apoptotic pathway. At early times after peptide treatment endogenous occludin and the LYHY peptide were co-localized in extrajunctional patches, which were also shown to contain components of the death inducing signaling complex (DISC), caspases 8 and 3, the death receptor FAS and the adaptor molecule FADD. After this treatment occludin could be immunoprecipitated with FADD, confirming its interaction with the DISC. Extrusion after LYHY treatment was accomplished with no loss of epithelial resistance.ConclusionThese observations provide strong evidence that, following disruption, occludin forms a complex with the extrinsic death receptor leading to extrusion of apoptotic cells from the epithelial monolayer. They suggest that occludin has a protective as well as a barrier forming role in epithelia; pathogenic agents which utilize this protein as an entry point into the cell might set off an apoptotic reaction allowing extrusion of the infected cell before the pathogen can gain entry to the interstitial space.

Highlights

Occludin is a tetraspanin protein normally localized to tight junctions
It is becoming increasingly clear that this structure is the direct or indirect target of many pathogens including Hepatitis C virus [1], Coxsackie virus [2,3], Clostridium perfringens endotoxin [4], enteropathogenic E. coli [5,6], Campylobacter jejuni [7] and others [8] and that the tight junction protein occludin is often involved in host-pathogen interactions that result in infection
To determine whether changes in the tight junction could provide a link to extrusion and apoptosis of epithelial cells, we examined the effects of occludin disruption on mouse mammary epithelial cell monolayers with fully formed junctional complexes

Summary

Introduction

Occludin is a tetraspanin protein normally localized to tight junctions. The protein interacts with a variety of pathogens including viruses and bacteria, an interaction that sometimes leads to its extrajunctional localization. Known as the zonula occludens, form an anastomosing network of protein and lipid strands that apically circumscribe every luminal cell of an epithelium. They form a continuous and selective barrier to paracellular solute flux and ionic current (the gate function) and help maintain the distinct lipid and protein composition of the apical and basolateral cellular membranes (the fence function). Occludin and the claudins are tetraspanin proteins with two extracellular loops and are considered to form the variable permeability barrier between the luminal and interstitial spaces separated by the epithelium. The work presented here suggests that occludin can have an important direct interaction with the extrinsic apoptotic pathway in the mammary epithelium

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