A Rho-related GTPase Is Involved in Ca2+-dependent Neurotransmitter Exocytosis

Abstract

Rho, Rac, and Cdc42 monomeric GTPases are well known regulators of the actin cytoskeleton and phosphoinositide metabolism and have been implicated in hormone secretion in endocrine cells. Here, we examine their possible implication in Ca 2؉ -dependent exocytosis of neurotransmitters. Using subcellular fractionation procedures, we found that RhoA, RhoB, Rac1, and Cdc42 are present in rat brain synaptosomes; however, only Rac1 was associated with highly purified synaptic vesicles. To determine the synaptic function of these GTPases, toxins that impair Rho-related proteins were microinjected into Aplysia neurons. We used lethal toxin from Clostridium sordellii, which inactivates Rac; toxin B from Clostridium difficile, which inactivates Rho, Rac, and Cdc42; and C3 exoenzyme from Clostridium botulinum and cytotoxic necrotizing factor 1 from Escherichia coli, which mainly affect Rho. Analysis of the toxin effects on evoked acetylcholine release revealed that a member of the Rho family, most likely Rac1, was implicated in the control of neurotransmitter release. Strikingly, blockage of acetylcholine release by lethal toxin and toxin B could be completely removed in <1 s by high frequency stimulation of nerve terminals. Further characterization of the inhibitory action produced by lethal toxin suggests that Rac1 protein regulates a late step in Ca 2؉ -dependent neuroexocytosis.

βPIX-activated Rac1 stimulates the activation of phospholipase D, which is associated with exocytosis in neuroendocrine cells

“…Among them, Rac isoforms have been involved in various processes of exocytosis, including mast cell and neutrophil degranulation (Abdel-Latif et al, 2004;Hong-Geller and Cerione, 2000), endocrine and neuroendocrine secretion (Amin et al, 2003;Bi and Williams, 2005;Frantz et al, 2002;Li et al, 2003), and neurotransmitter release (Doussau et al, 2000;Humeau et al, 2007;Humeau et al, 2002). However, most of these studies rely on the use of dominant-negative and constitutively active versions of Rac proteins and do not directly address the participation of endogenous Rac1 in the basic exocytotic machinery.…”

α-Tocopherol Protects Against Oxidative Stress in the Fragile X Knockout Mouse: an Experimental Therapeutic Approach for the Fmr1 Deficiency

“…Additionally, Rac1-GTPase (a protein interacting with FMR1P trough the CIFYP protein) is involved in controlling the formation of fine dendritic branches (Lee et al, 2003), and this protein is known to regulate vesicle neurosecretion (Doussau et al, 2000;Li et al, 2003), and free radical production (Sundaresan et al, 1996). Rac1-GTPase has two distinct roles at different stages of neuronal development.…”

Bacterial protein toxins and lipids: role in toxin targeting and activity

“…LTs block evoked acetylcholine release in Aplysia, probably through Rac inactivation (Dousseau et al, 2000;Humeau et al, 2002). Two mechanisms may Review be involved.…”

“…Second, PLD1, which is regulated by Rac, may generate PtdAc from membrane PC (Figure 3). PtdAc inserts into lipid bilayer, promoting negative curvature and the formation of hemifusion intermediates during membrane fusion (Dousseau et al, 2000;Vitale et al, 2001).…”