The Granulocyte Receptor Carcinoembryonic Antigen-Related Cell Adhesion Molecule 3 (CEACAM3) Directly Associates with Vav to Promote Phagocytosis of Human Pathogens

Abstract

The human granulocyte-specific receptor carcinoembryonic antigen-related cell adhesion molecule (CEACAM)3 is critically involved in the opsonin-independent recognition of several bacterial pathogens. CEACAM3-mediated phagocytosis depends on the integrity of an ITAM-like sequence within the cytoplasmic domain of CEACAM3 and is characterized by rapid stimulation of the GTPase Rac. By performing a functional screen with CEACAM3-expressing cells, we found that overexpression of a dominant-negative form of the guanine nucleotide exchange factor Vav, but not the dominant-negative versions SWAP70, Dock2, or ELMO1 interfered with CEACAM3-initiated phagocytosis. Moreover, small interfering RNA-mediated silencing of Vav reduced uptake and abrogated the stimulation of Rac in response to bacterial CEACAM3 engagement. In Vav1/Vav2-deficient cells, CEACAM3-mediated internalization was only observed after re-expression of Vav. Vav colocalized with CEACAM3 upon bacterial infection, coimmunoprecipitated in a complex with CEACAM3, and the Vav Src homology 2 domain directly associated with phosphorylated Tyr230 of CEACAM3. In primary human granulocytes, TAT-mediated transduction of dominant-negative Vav, but not SWAP70, severely impaired the uptake of CEACAM3-binding bacteria. These data support the view that, different from canonical ITAM signaling, the CEACAM3 ITAM-like sequence short-wires bacterial recognition and Rac stimulation via a direct association with Vav to promote rapid phagocytosis and elimination of CEACAM-binding human pathogens.

CEACAM3: An innate immune receptor directed against human-restricted bacterial pathogens

“…This is in line with previous reports showing that Syk is not activated upon CEACAM stimulation in human phagocytic cells (Hauck et al, 1998). A molecular explanation for this surprising finding is provided by the fact that the cytoplasmic domain of CEACAM3 can directly interact with the guanine-nucleotide exchange factor (GEF) Vav (Schmitter et al, 2007a). In particular, phosphorylated Tyr-230 of CEACAM3 selectively associates with the SH2 domain of Vav, suggesting a short circuit between bacterial engagement of CEACAM3 and the local stimulation of guanine nucleotide exchange activity (Fig.…”

“…Indeed, the recruitment of Vav appears as the critical molecular event required for CEACAM3-initiated GTP loading of Rac (Schmitter et al, 2007a). Interference with either Rac or Vav in primary human granulocytes blocks the efficient uptake of Opa-expressing gonococci (Schmitter et al, 2004(Schmitter et al, , 2007a. GTPloaded Rac operates as a master regulator of actin polymerization and NADPH oxidase function in phagocytes, suggesting that the signaling events initiated by CEACAM3 are responsible for the uptake as well as Signaling connections of CEACAM3.…”

“…2). Indeed, the recruitment of Vav appears as the critical molecular event required for CEACAM3-initiated GTP loading of Rac (Schmitter et al, 2007a). Interference with either Rac or Vav in primary human granulocytes blocks the efficient uptake of Opa-expressing gonococci (Schmitter et al, 2004(Schmitter et al, , 2007a.…”

Defining the Roles of Human Carcinoembryonic Antigen-Related Cellular Adhesion Molecules during Neutrophil Responses to Neisseria gonorrhoeae

“…The central importance of neutrophils in the pathogenesis of gonorrhea has prompted focused research seeking to characterize molecular mechanisms of neutrophil-expressed CEACAM functions in response to N. gonorrhoeae infection (3,20,31). This work has largely been conducted in transfected epithelial cell lines in an effort to study individual CEACAMs in the absence of coexpressed CEACAMs and/or other potential receptors on the neutrophil (3,20,32).…”

Rho GTPases as pathogen targets: Focus on curable sexually transmitted infections

“…59,65,66 Recent studies indicate that the CEACAM3-ITAM sequence associates directly with Vav, a Rac GEF, thus promoting the phagocytosis and elimination of CEACAM-bound bacteria. 67 Interestingly, Vav directly associates via its Src homology 2 (SH2) domain with a phosphorylated tyrosine residue within the ITAM-like sequence of the receptor. Homologous SH2 domains are also found in the adaptor molecules Nck1 and Nck2, and mediate their interaction with CEACAM3 in a complex with the Rac effector WAVE2.…”