PTRN‐1/CAMSAPpromotesCYK‐1/formin‐dependent actin polymerization during endocytic recycling

Abstract

Cargo sorting and membrane carrier initiation in recycling endosomes require appropriately coordinated actin dynamics. However, the mechanism underlying the regulation of actin organization during recycling transport remains elusive. Here we report that the loss of PTRN-1/CAMSAP stalled actin exchange and diminished the cytosolic actin structures. Furthermore, we found that PTRN-1 is required for the recycling of clathrin-independent cargo hTAC-GFP The N-terminal calponin homology (CH) domain and central coiled-coils (CC) region of PTRN-1 can synergistically sustain the flow of hTAC-GFP We identified CYK-1/formin as a binding partner of PTRN-1. The N-terminal GTPase-binding domain (GBD) of CYK-1 serves as the binding interface for the PTRN-1 CH domain. The presence of the PTRN-1 CH domain promoted CYK-1-mediated actin polymerization, which suggests that the PTRN-1-CH:CYK-1-GBD interaction efficiently relieves autoinhibitory interactions within CYK-1. As expected, the overexpression of the CYK-1 formin homology domain 2 (FH2) substantially restored actin structures and partially suppressed the hTAC-GFP overaccumulation phenotype in mutants. We conclude that the PTRN-1 CH domain is required to stimulate CYK-1 to facilitate actin dynamics during endocytic recycling.

An EHBP-1-SID-3-DYN-1 axis promotes membranous tubule fission during endocytic recycling

“…Through confocal stack imaging of intestinal epithelial cells from intact living animals ( Fig 1B), we found that, in both sid-3 mutants, the number and size of hTAC-GFP-labeled intracellular structures increased significantly (~9-fold increase in total area) ( Fig 1C-1C''). This phenotype is typical of basolateral recycling mutants [5,12,[28][29][30]. We further assayed the accumulation of FGT-1, the worm homolog of another clathrin-independent recycling cargo, GLUT1 [8], and observed that SID-3 deficiency led to substantial intracellular aggregation of FGT-1-positive structures (~7.8-fold increase in total area) (S1A and S1A ' Fig).…”

Epidermal PAR-6 and PKC-3 are essential for larval development of C. elegans and organize non-centrosomal microtubules

“…Thus, the combined defects in NOCA-1 and PTRN-1 localization we observed upon PAR-6 depletion may partially explain the growth defects. The roles of PTRN-1 may not be limited to microtubule regulation, as a recent study demonstrated that PTRN-1 stimulates actin polymerization during endocytic recycling in the intestine ( Gong et al, 2018 , p. 1).…”

Actin-dependent endosomal receptor recycling

“…Importantly, CCR2B and β2AR signaling induces the phosphorylation of FLNa that promotes receptor recycling [70]. Several other actin regulators play a role in the biogenesis of tubular membrane carriers by regulating actin assembly, disassembly and/or bundling; these include the Cdc42-guanine nucleotide exchange factor FGD6 [74], the regulator of endocytic recycling EHBP-1 [75], and formins [76,77].…”