Cdk5 Regulation of the GRAB-Mediated Rab8-Rab11 Cascade in Axon Outgrowth

Abstract

Neurons communicate with each other through their axons and dendrites. However, a full characterization of the molecular mechanisms involved in axon and dendrite formation is still incomplete. Neurite outgrowth requires the supply of membrane components for surface expansion. Two membrane sources for axon outgrowth are suggested: Golgi secretary vesicles and endocytic recycling endosomes. In non-neuronal cells, trafficking of secretary vesicles from Golgi is regulated by Rab8, a member of Rab small GTPases, and that of recycling endosomes is by Rab11, another member of Rabs. However, whether these vesicles are coordinately or independently transported in growing axons is unknown. Herein, we find that GRAB, a guanine nucleotide exchange factor for Rab8, is a novel regulator of axon outgrowth. Knockdown of GRAB suppressed axon outgrowth of cultured mouse brain cortical neurons. GRAB mediates the interaction between Rab11A and Rab8A, and this activity is regulated by phosphorylation at Ser169 and Ser180 by Cdk5-p35. The nonphosphorylatable GRAB mutant S169/180A promoted axonal outgrowth to a greater extent than did the phosphomimetic GRAB mutant S169/180D. Phosphorylation of GRAB suppressed its guanine nucleotide exchange factor activity and its ability to recruit Rab8A-to Rab11A-positive endosomes. In vivo function of GRAB and its Cdk5-phophorylation were shown in migration and process formation of developing neurons in embryonic mouse brains. These results indicate that GRAB regulates axonal outgrowth via activation and recruitment of Rab8A-to Rab11A-positive endosomes in a Cdk5-dependent manner.

Inhibition of Cyclin‐Dependent Kinase 5: A Strategy to Improve Sorafenib Response in Hepatocellular Carcinoma Therapy

“…Moreover, during axon outgrowth, Cdk5 was shown to regulate Rab proteins, which coordinate vesicle trafficking, fusion, and maturation. (42) During recent years, endocytosis has emerged as a central process in cancer. Endocytic circuitries are deeply interconnected with the activation and execution of various pathways that regulate cancer growth, progression, and metastasis, including small GTPases, integrin, epithelial-mesenchymal transition, and growth factor receptor signaling.…”

Rab22A recruits BLOC ‐1 and BLOC ‐2 to promote the biogenesis of recycling endosomes

“…Although Rab11A has been implicated in the maturation of REs [31], we hypothesize that Rab22A possibly functions downstream of Rab11 or Rab11-tubular structures morphed into a different set of REs. In the latter case, we predict that Rab11 possibly interacts with either GRAB-Rab8A [32] or Rabin8-Rab8A [33,34] proteins that were observed during the neurite outgrowth of PC12 cells. We favour the earlier model, since the overexpression of Rab11A could not rescue the KIF13A-positive tubules either in Rab22A-or BLOC-1-knockdown cells (Fig EV1G).…”

Rab11a-Rab8a cascade regulate the formation of tunneling nanotubes through vesicle recycling

“…It has been reported that GRAB (a guanine nucleotide exchange factor for Rab8a) mediates the Rab11a-Rab8a cascade mechanism and facilitates axonal growth (Furusawa et al, 2017). Therefore, we tested the effect of GRAB on TNT formation.…”

“…The mouse catecholaminergic neuronal CAD cell line (mouse catecholaminergic neuronal cell line, Cath.aDifferentiated) (Gousset et al, 2013) was grown in Gibco OptiMEM supplemented with 10% fetal bovine serum (FBS) and 1% penicillin-streptomycin. pEGFP-C1-Rab plasmids library, pEGFP-C1-Rab8a(Q67L), pEGFP-C1-Rab8a(T22N), pEGFP-C1-Rab11a(Q70L), pEGFP-C1-Rab11a(S25N) and pEGFP-C1-Rabin8, and pEGFP-C1-GRAB were prepared as described previously (Furusawa et al, 2017;Ishida et al, 2012;Matsui and Fukuda, 2011;Tsuboi and Fukuda, 2006). GFP-VAMP3 was a kind gift from Thierry Galli (Center of Psychiatry and Neuroscience, INSERM U894, Paris France).…”