Abstract
BackgroundThe cell adhesion and tumor suppressor protein E-cadherin is an important factor in the establishment and maintenance of epithelial integrity. E-cadherin is a single transmembrane protein, which consists of an intracellular domain (IC), a transmembrane domain (TD), and five extracellular domains (EC). EC domains form homophilic interactions in cis and trans that require calcium binding to the linker region between the EC domains. In our previous studies, we identified the serine protease high temperature requirement A (HtrA) from the human pathogen and class-I carcinogen Helicobacter pylori (H. pylori) as a bacterial E-cadherin-cleaving protease that targets the linker region of the EC domains, thereby disrupting gastric epithelial integrity. However, it remains unclear how calcium binding to the E-cadherin linker regions affects HtrA-mediated cleavage.ResultsInvestigating the influence of calcium on the HtrA-mediated cleavage of recombinant E-cadherin (rCdh1) in vitro, we tested different concentrations of calcium ions and the calcium chelator ethylenediaminetetraacetic acid (EDTA). Calcium efficiently reduced HtrA-mediated E-cadherin fragmentation. Conversely, the addition of EDTA strongly increased cleavage, resulting in a ladder of defined E-cadherin fragments. However, calcium ions did not affect HtrA oligomerization and protease activity as monitored by degradation of the universal protease substrate casein. Finally, addition of ethyleneglycol-bis-tetraacetic acid (EGTA) slightly enhanced E-cadherin cleavage during H. pylori infection of gastric epithelial cells.ConclusionsOur results suggest that calcium blocks HtrA-mediated cleavage by interfering with the accessibility of calcium-binding regions between the individual EC domains, which have been identified as cleavage sites of HtrA.Electronic supplementary materialThe online version of this article (doi:10.1186/s13099-016-0112-6) contains supplementary material, which is available to authorized users.
Highlights
The cell adhesion and tumor suppressor protein E-cadherin is an important factor in the establishment and maintenance of epithelial integrity
Depletion of calcium ions enhances high temperature requirement A (HtrA)‐mediated E‐cadherin cleavage The bacterial protease HtrA secreted by H. pylori mediates efficient E-cadherin ectodomain (NTF, N-terminal fragment) shedding to open intercellular adhesion of polarized epithelial cells [27, 33]
These target sites are located between the individual extracellular domains (EC) domains (Fig. 1a, open arrows). Since these motifs are known to bind calcium ions [3, 5, 8], which are crucially important for the adhesive properties of E-cadherin, we investigated whether calcium ions affect HtrA-mediated cleavage of E-cadherin
Summary
The cell adhesion and tumor suppressor protein E-cadherin is an important factor in the establishment and maintenance of epithelial integrity. EC domains form homophilic interactions in cis and trans that require calcium binding to the linker region between the EC domains. We identified the serine protease high temperature requirement A (HtrA) from the human pathogen and class-I carcinogen Helicobacter pylori (H. pylori) as a bacterial E-cadherin-cleaving protease that targets the linker region of the EC domains, thereby disrupting gastric epithelial integrity. It remains unclear how calcium binding to the E-cadherin linker regions affects HtrA-mediated cleavage. Epithelial cadherin (E-cadherin, Cdh1) is the key molecule of adherens junctions and is implicated in the establishment of intercellular adhesion and tumor suppression of human epithelia [2, 3].
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