title: Ras-related GTPases Rap1 and RhoA collectively induce the phagocytosis of serum-opsonized zymosan particles in macrophages.
abstract: Phagocytosis occurs primarily through two main processes in macrophages: the Fcγ receptor- and the integrin αMβ2-mediated processes. Complement C3bi-opsonized particles are known to be engulfed through integrin αMβ2-mediated process, which is regulated by RhoA GTPase. C3 toxin fused with Tat-peptide (Tat-C3 toxin), an inhibitor of the Rho GTPases, was shown to markedly inhibit the phagocytosis of serum (C3bi)-opsonized zymosans (SOZs). However, 8CPT-2Me-cAMP, an activator of exchange protein directly activated by cAMP (Epac, Rap1 guanine nucleotide exchange factor), restored the phagocytosis of the SOZs that was previously inhibited by the Tat-C3 toxin. In addition, a constitutively active form of Rap1 GTPase (CA-Rap1) also restored the phagocytosis that was previously reduced by a dominant negative form of RhoA GTPase (DN-RhoA). This suggests that Rap1 can replace the function of RhoA in the phagocytosis. Inversely, CA-RhoA rescued the phagocytosis that was suppressed by DN-Rap1. These findings suggest that both RhoA and Rap1 GTPases collectively regulate the phagocytosis of SOZs. In addition, filamentous actin was reduced by the Tat-C3 toxin, which was again restored by 8CPT-2Me-cAMP. Small interfering profilin suppressed the phagocytosis, suggesting that profilin is essential for the phagocytosis of SOZs. Furthermore, 8CPT-2Me-cAMP increased the co-immunoprecipitation of profilin with Rap1, whereas Tat-C3 toxin decreased that of profilin with RhoA. Co-immunoprecipitations of profilin with actin, Rap1, and RhoA GTPases were augmented in the presence of GTPγS rather than GDP. Therefore, we propose that both Rap1 and RhoA GTPases regulate the formation of filamentous actin through the interaction between actin and profilin, thereby collectively inducing the phagocytosis of SOZs in macrophages.
authors.affiliation: Department of Biochemistry, College of Medicine, Hallym University, Chuncheon, Kangwon-Do 200-702, Republic of Korea.
authors.forename: Jae-Gyu
authors.initials: JG
authors.lastname: Kim
authors.forename: Mi-Young
authors.initials: MY
authors.lastname: Moon
authors.forename: Hee-Jun
authors.initials: HJ
authors.lastname: Kim
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Dong-Keun
authors.initials: DK
authors.lastname: Song
authors.forename: Jun-Sub
authors.initials: JS
authors.lastname: Kim
authors.forename: Jae-Yong
authors.initials: JY
authors.lastname: Lee
authors.forename: Jaebong
authors.initials: J
authors.lastname: Kim
authors.forename: Sung-Chan
authors.initials: SC
authors.lastname: Kim
authors.forename: Jae-Bong
authors.initials: JB
authors.lastname: Park
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003179:Complement C3b / Q000494:pharmacology*; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology*; D051304:Profilins / Q000235:genetics / Q000378:metabolism; D015054:Zymosan / Q000494:pharmacology*; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein
chemical_list: D051304:Profilins; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003179:Complement C3b; D015054:Zymosan; D000242:Cyclic AMP; C526380:RhoA protein, mouse; D020827:rap1 GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein