Adhesion of Several Cell Lines to Helicobacter pylori CagL Is Mediated by Integrin αVβ6 via an RGDLXXL Motif

Abstract

The Helicobacter pylori type IV secretion system pilus protein CagL mediates interaction with host cells via its RGD motif. Here, we analyzed prerequisites for this interaction within CagL and on host cells. Various human cell lines were tested for adhesion to CagL. HT-29 and 23132/87 cells adhered to immobilized recombinant CagL in an RGD-dependent manner, while 293T (human embryonic kidney) and A549 cells did not. In a competitive ELISA, CagL competed with fibronectin for binding to the ectodomains of integrins αVβ6 and αVβ8 but not of αVβ1, αVβ3, αVβ5 and α5β1. Integrin αVβ6 acts as receptor for several viruses exposing an RGDLXXL motif. CagL also contains an RGDLXXL sequence. We individually mutated Leu79 and Leu82 of this motif to threonine, although both leucines are buried in the hydrophobic core. Surprisingly, the ability of CagL variants L79T and L82T to support adhesion was significantly reduced for 23132/87 cells and lost for MKN-45 and HT-29 cells. The role of integrin αVβ6 in adhesion to CagL was investigated using SW480 cells transfected with the integrin β6 subunit (SW480β6). These cells adhered to CagL in an RGD-dependent manner, while mock-transfected SW480 cells did not. The antibody 3G9 that blocks the function of integrin αVβ6 inhibited adhesion of SW480β6, MKN-45, 23132/87 and HT-29 cells to CagL. In summary, CagL features an RGDLXXL motif facilitating adhesion of several human cell lines via integrin αVβ6. The buried location of Leu79 and Leu82 supports our previously published hypothesis that CagL partly unfolds upon integrin binding.