RIM1 confers sustained activity and neurotransmitter vesicle anchoring to presynaptic Ca2+ channels

Abstract

The molecular organization of presynaptic active zones is important for the neurotransmitter release that is triggered by depolarization-induced Ca2+ influx. Here, we demonstrate a previously unknown interaction between two components of the presynaptic active zone, RIM1 and voltage-dependent Ca2+ channels (VDCCs), that controls neurotransmitter release in mammalian neurons. RIM1 associated with VDCC beta-subunits via its C terminus to markedly suppress voltage-dependent inactivation among different neuronal VDCCs. Consistently, in pheochromocytoma neuroendocrine PC12 cells, acetylcholine release was significantly potentiated by the full-length and C-terminal RIM1 constructs, but membrane docking of vesicles was enhanced only by the full-length RIM1. The beta construct beta-AID dominant negative, which disrupts the RIM1-beta association, accelerated the inactivation of native VDCC currents, suppressed vesicle docking and acetylcholine release in PC12 cells, and inhibited glutamate release in cultured cerebellar neurons. Thus, RIM1 association with beta in the presynaptic active zone supports release via two distinct mechanisms: sustaining Ca2+ influx through inhibition of channel inactivation, and anchoring neurotransmitter-containing vesicles in the vicinity of VDCCs.

cAMP/PKA signaling and RIM1α mediate presynaptic LTP in the lateral amygdala

“…RIM1␣, however, interacts directly with Ca 2ϩ -binding proteins such as Munc13-1 and synaptotagmin 1 (19, 20, 32). Moreover, RIM1␣ interacts directly or indirectly with presynaptic VDCCs, thereby regulating the function and/or the physical location of VDCCs in relation to the release site (20,21,33). Thus, RIM1␣ might orchestrate presynaptic signaling complexes and enable compartmentalized signal transduction within presynaptic scaffolds by bringing VDCCs, Ca 2ϩ sensors, and the vesicular fusion machinery into close proximity allowing for activity-dependent and persistent modifications in the vesicular release probability.…”

Old proteins, developing roles: The regulation of calcium channels by synaptic proteins

“…A recent study showed that RIM1 anchors SNAREs close to calcium channels by C-terminal binding to the channel β subunit, thereby prolonging calcium influx by inhibiting channel inactivation. 128 This effect was seen in P/Q-type channels as well as N-and R-type channels, and suggests that RIM may be an important regulator of synaptic calcium channel function.…”

RIM genes differentially contribute to organizing presynaptic release sites

“…Gene deletion experiments (Table S1) showed that RIMs are essential for multiple aspects of neurotransmitter release (4, 6-10) and for presynaptic short-and long-term plasticity (4, 6, 11-13). However, how different RIM isoforms contribute to neurotransmitter release is unclear.Recent studies revealed that RIMs regulate presynaptic Ca 2+ channels via two independent mechanisms, namely by recruiting Ca 2+ channels to active zones (14) and by modulating Ca 2+ -channel opening times (15,16). The first activity is mediated by a tripartite complex of RIMs, RIM-BPs, and Ca 2+ channels in which the RIM PDZ domains directly bind to the C-termini of N-and P/Q-type Ca 2+ channels, the RIM PxxP-sequences bind to RIM-BPs, and RIM-BPs, in turn, directly bind to the C-termini of Ca 2+ channels (14, 17, 18).…”

“…The first activity is mediated by a tripartite complex of RIMs, RIM-BPs, and Ca 2+ channels in which the RIM PDZ domains directly bind to the C-termini of N-and P/Q-type Ca 2+ channels, the RIM PxxP-sequences bind to RIM-BPs, and RIM-BPs, in turn, directly bind to the C-termini of Ca 2+ channels (14,17,18). The second activity is mediated by the RIM C 2 B-domain, possibly by binding to β4 subunits of Ca 2+ channels (15,16). However, the relative contributions of different RIM isoforms and of their interactions with Ca 2+ channels are unknown.…”