Esophageal cancer-related gene-4 (ECRG4) interactions with the innate immunity receptor complex

Objective and design: The human c2orf40 gene encodes a tumor suppressor gene called esophageal cancer-related gene-4 (ECRG4) with pro- and anti-inflammatory activities that depend on cell surface processing. Here, we investigated its physical and functional association with the innate immunity receptor complex.

Methods: Interactions between ECRG4 and the innate immunity receptor complex were assessed by flow cytometry, immunohistochemistry, confocal microscopy, and co-immunoprecipitation. Phage display was used for ligand targeting to cells that overexpress the TLR4–MD2–CD14.

Results: Immunoprecipitation and immunohistochemical studies demonstrate a physical interaction between ECRG4 and TLR4–MD2–CD14 on human granulocytes. Flow cytometry shows ECRG4 on the cell surface of a subset of CD14⁺ and CD16⁺ leukocytes. In a cohort of trauma patients, the C-terminal 16 amino acid domain of ECRG4 (ECRG4^133–148) appears to be processed and shed, presumably at a thrombin-like consensus sequence. Phage targeting this putative ligand shows that this peptide sequence internalizes into cells through the TLR4/CD14/MD2 complex, but modulates inflammation through non-canonical, NFκB signal transduction.

Conclusions: ECRG4 is present on the surface of human monocytes and granulocytes. Its interaction with the human innate immunity receptor complex supports a role for cell surface activation of ECRG4 during inflammation and implicates this receptor in its mechanism of action.