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Vol. 20, Issue 21, 4500-4508, November 1, 2009

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Cdc42 Regulates Fc Receptor-mediated Phagocytosis through the Activation and Phosphorylation of Wiskott-Aldrich Syndrome Protein (WASP) and Neural-WASP

Haein Park^*, and Dianne Cox^*,

Departments of *Anatomy and Structural Biology and Developmental and Molecular Biology, Albert Einstein College of Medicine, Yeshiva University, Bronx, NY 10461

Submitted March 20, 2009; Revised August 28, 2009; Accepted August 31, 2009
Monitoring Editor: Carole Parent

Cdc42 is a key regulator of the actin cytoskeleton and activator of Wiskott-Aldrich syndrome protein (WASP). Although several studies have separately demonstrated the requirement for both Cdc42 and WASP in Fc receptor (FcR)-mediated phagocytosis, their precise roles in the signal cascade leading to engulfment are still unclear. Reduction of endogenous Cdc42 expression by using RNA-mediated interference (short hairpin RNA [shRNA]) severely impaired the phagocytic capacity of RAW/LR5 macrophages, due to defects in phagocytic cup formation, actin assembly, and pseudopod extension. Addition of wiskostatin, a WASP/neural-WASP (N-WASP) inhibitor showed extensive inhibition of phagocytosis, actin assembly, and cell extension identical to the phenotype seen upon reduction of Cdc42 expression. However, using WASP-deficient bone marrow-derived macrophages or shRNA of WASP or N-WASP indicated a requirement for both WASP and N-WASP in phagocytosis. Cdc42 was necessary for WASP/N-WASP activation, as determined using a conformation-sensitive antibody against WASP/N-WASP and partial restoration of phagocytosis in Cdc42 reduced cells by expression of a constitutively activated WASP. In addition, Cdc42 was required for proper WASP tyrosine phosphorylation, which was also necessary for phagocytosis. These results indicate that Cdc42 is essential for the activation of WASP and N-WASP, leading to actin assembly and phagocytic cup formation by macrophages during FcR-mediated phagocytosis.

Address correspondence to: Haein Park (hapark{at}aecom.yu.edu).

Abbreviations used: BMM, bone marrow-derived macrophage; CSA, conformation-sensitive WASP/N-WASP antibody; EigG, erythrocytes opsonized with immunoglobulin G; FcR, Fc receptor; shRNA, short hairpin RNA; WASP, Wiskott-Aldrich syndrome protein; N-WASP, neural Wiskott-Aldrich syndrome protein.