RTKN-1/Rhotekin shields endosome-associated F-actin from disassembly to ensure endocytic recycling

Abstract

Cargo sorting and the subsequent membrane carrier formation require a properly organized endosomal actin network. To better understand the actin dynamics during endocytic recycling, we performed a genetic screen in C. elegans and identified RTKN-1/Rhotekin as a requisite to sustain endosome-associated actin integrity. Loss of RTKN-1 led to a prominent decrease in actin structures and basolateral recycling defects. Furthermore, we showed that the presence of RTKN-1 thwarts the actin disassembly competence of UNC-60A/cofilin. Consistently, in RTKN-1–deficient cells, UNC-60A knockdown replenished actin structures and alleviated the recycling defects. Notably, an intramolecular interaction within RTKN-1 could mediate the formation of oligomers. Overexpression of an RTKN-1 mutant form that lacks self-binding capacity failed to restore actin structures and recycling flow in rtkn-1 mutants. Finally, we demonstrated that SDPN-1/Syndapin acts to direct the recycling endosomal dwelling of RTKN-1 and promotes actin integrity there. Taken together, these findings consolidated the role of SDPN-1 in organizing the endosomal actin network architecture and introduced RTKN-1 as a novel regulatory protein involved in this process.

AP-1 Recruits SMAP-1/SMAPs to the trans-Golgi Network to Promote Sorting in Polarized Epithelia

“…However, the mechanism controlling the localization of SMAPs is still not well understood. Here, by using a well-established in vivo membrane trafficking investigation model ( Chen et al, 2018 ; Chen et al, 2019 ; Gao et al, 2020 ; Zhang et al, 2020 ; Yan et al, 2021 ), we showed that the integrity of AP-1 adaptor is necessary for the TGN positioning of SMAP-1. Although we did not specifically identify which AP-1 subunit governs the TGN localization of SMAP-1, our results suggested that in addition to CALM, SMAP-1 underlies an additional clathrin assembly mechanism, enriching the understanding of AP-1/clathrin coat assembly.…”

PACSIN proteins in vivo: Roles in development and physiology

“…119 A recent study identified RTKN-1/ Rhotekin, an effector of the Rho GTPase, as a new molecule necessary for endosomal recycling via the regulation of endosome-associated F-actin structures in the intestine of C. elegans. 122 Interestingly, targeting of RTKN-1 to endosomes appears to depend on SDPN-1, stressing out the importance of SDPN-1 for the normal physiology of the intestine in worms via the intertwined functions of endosomal recycling and actin cytoskeleton. 122 Another level of regulation for SDPN-1 is brought by phosphoinositides, and specifically, phosphoinositide PI(4,5)P2.…”

“…122 Interestingly, targeting of RTKN-1 to endosomes appears to depend on SDPN-1, stressing out the importance of SDPN-1 for the normal physiology of the intestine in worms via the intertwined functions of endosomal recycling and actin cytoskeleton. 122 Another level of regulation for SDPN-1 is brought by phosphoinositides, and specifically, phosphoinositide PI(4,5)P2. PI(4,5)P2 plays a central role in endosomal recycling 123 and interestingly, in C. elegans with mutated Arf-6 and CNT-1, also known to regulate endosomal recycling, the expression of SDPN-1 was altered in the intestinal basolateral recycling endosomes due to changed concentrations of PI (4,5)P2 in this location.…”

“… 122 Interestingly, targeting of RTKN‐1 to endosomes appears to depend on SDPN‐1, stressing out the importance of SDPN‐1 for the normal physiology of the intestine in worms via the intertwined functions of endosomal recycling and actin cytoskeleton. 122 …”

“…In the absence of SDPN‐1, this process is perturbed leading to trapping of the recycling cargo 119 . A recent study identified RTKN‐1/Rhotekin, an effector of the Rho GTPase, as a new molecule necessary for endosomal recycling via the regulation of endosome‐associated F‐actin structures in the intestine of C. elegans 122 . Interestingly, targeting of RTKN‐1 to endosomes appears to depend on SDPN‐1, stressing out the importance of SDPN‐1 for the normal physiology of the intestine in worms via the intertwined functions of endosomal recycling and actin cytoskeleton 122 …”