Helicobacter pylori Exploits Host Membrane Phosphatidylserine for Delivery, Localization, and Pathophysiological Action of the CagA Oncoprotein

Abstract

When delivered into gastric epithelial cells via type IV secretion, Helicobacter pylori CagA perturbs host cell signaling and thereby promotes gastric carcinogenesis. However, the mechanisms of CagA delivery, localization, and action remain poorly understood. We show that direct contact of H. pylori with epithelial cells induces externalization of the inner leaflet enriched host phospholipid, phosphatidylserine, to the outer leaflet of the host plasma membrane. CagA, which is exposed on the bacterial surface via type IV secretion, interacts with the externalized phosphatidylserine to initiate its entry into cells. CagA delivery also requires energy-dependent host cell processes distinct from known endocytic pathways. Within polarized epithelial cells, CagA is tethered to the inner leaflet of the plasma membrane through interaction with phosphatidylserine and binds the polarity-regulating host kinase PAR1/MARK to induce junctional and polarity defects. Thus, host membrane phosphatidylserine plays a key role in the delivery, localization, and pathophysiological action of CagA.

Structural insights into Helicobacter pylori oncoprotein CagA interaction with β1 integrin

“…Although the same amount of proteins were incubated, CagA 1-273 , CagA 1-291 (covering D1), CagA 303-456 (proximal part of the SLB and D2′), and CagA 392-733 (containing the distal part of the SLB and D2′′) were found to interact more strongly with AGS cells than CagA 369-448 (containing only D2′). The binding of the fragment CagA 392-733 on AGS cells might be attributed to the presence of the PS-binding patch at its surface, because PS is externalized during H. pylori infection (25). The CagA translocation assay shows that the purified CagA 303-456 fragment inhibited CagA translocation by H. pylori (Fig.…”

“…CSP3 includes residues R624 and R626, which were previously found to interact with phosphatidylserine (PS) (25) (Fig. 3).…”

“…Secondary structure elements are indicated above the sequences and colored according to the domain: D2′, cyan; SLB, pink; D2′′, purple; D3, green; and D4, yellow. Blue dots are positioned below residues R624 and R626, involved in PS binding (25). S1).…”

“…CSP3 contains residues that were shown to be involved in the binding to PS. The binding of CagA CSP3 might contribute to tether CagA at the inner leaflet membrane, where PS is more abundant (25). Another important area is CSP4, which was shown to constitute the binding interface with α5β1 integrin.…”

The phospholipid code: a key component of dying cell recognition, tumor progression and host–microbe interactions

“…This enables CagA to subsequently modify host cell signaling to induce the formation of gastric carcinoma. 83 Thus, pathogen-derived effector molecules that exhibit phospholipid detector properties can exploit the extracellular phospholipid code on host cells to gain cellular entry.…”