engleski

Dictyostelium IqgD is a Rho-regulated IQGAP involved in large-scale endocytosis

IqgD is an IQGAP-related protein from amoeba 𝘋𝘪𝘤𝘵𝘺𝘰𝘴𝘵𝘦𝘭𝘪𝘶𝘮 𝘥𝘪𝘴𝘤𝘰𝘪𝘥𝘦𝘶𝘮. IQGAPs are evolutionarily conserved, multidomain proteins that serve as scaffolds to integrate diverse signaling pathways. Consequently, they regulate various cellular processes such as migration, adhesion, and vesicle trafficking [1]. IQGAP proteins directly bind actin filaments via their calponin homology domain (CHD). They can further cross-link them into bundles, and this F-actin-cross-linking activity is dependent on the dimerization and oligomerization of IQGAP molecules. Oligomerization is facilitated by binding of active Cdc42 and Rac1, members of the Rho family GTPases, to the GAP-related domain (GRD). IQGAPs also regulate actin dynamics via interaction with nucleation-promoting factor N-WASP and actin- assembly factors Arp2/3 complex and formin Dia1, thus promoting the generation of protrusive structures at the cell leading edge [2]. 𝘋𝘪𝘤𝘵𝘺𝘰𝘴𝘵𝘦𝘭𝘪𝘶𝘮 IqgD is a fimbrin-related RasGAP that contains a CHD duplex, a coiled-coil region, a GRD/RasGAP domain, and a RasGAP_C-terminal (RGCt) extension [3]. It is the only 𝘋𝘪𝘤𝘵𝘺𝘰𝘴𝘵𝘦𝘭𝘪𝘶𝘮 IQGAP that possesses an actin-binding domain and presumably binds actin filaments. We show by confocal microscopy that fluorescently labelled IqgD in live 𝘋𝘪𝘤𝘵𝘺𝘰𝘴𝘵𝘦𝘭𝘪𝘶𝘮 cells localizes to the entire cell cortex. However, it is enriched at the membrane patches that are primed for macropinocytosis and subsequently enclose nascent macropinosomes. Similarly, IqgD is also strongly enriched at the base of the phagocytic cup during large particle engulfment. As the protrusion of the cup advances, IqgD translocates to the distal parts of the cup and reaches maximal intensity at the site of phagosome sealing. Soon after internalization is completed, the IqgD signal disperses. Next, we examined its presumed interactions with actin via CHD, and with Ras and Rho GTPases involved in large-scale endocytosis, via GRD. Using yeast two-hybrid assay we demonstrated a direct interaction between IqgD and Rac1A and Rac1C GTPases. Interestingly, while IqgD showed a higher affinity for constitutively active Rac1A, it prefers binding to dominant-negative Rac1C. Interaction with endogenous actin was demonstrated using Co-IP. The presented data strongly suggest that 𝘋𝘪𝘤𝘵𝘺𝘰𝘴𝘵𝘦𝘭𝘪𝘶𝘮 protein IqgD regulates actin cytoskeleton in large protrusions such as macropinocytic and phagocytic cups and that Rho GTPases Rac1A and Rac1C regulate its activity.

IqgD ; IQGAP ; Rho ; actin ; Dictyostelium

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