Neurexins Are Functional α-Latrotoxin Receptors

receptor for ␣-latrotoxin and that neurexin 1␣ is not a functional receptor (Lelianova et al., 1997). However, the Southwestern Medical Center Dallas, Texas 75235 Ca 2ϩ independence of ␣-latrotoxin action is controversial , and the possible function of neurexins as ␣-latro-toxin receptors has not been tested directly. Studies of neurexin 1␣ knockout mice demonstrated that ␣-latro-Summary toxin can still trigger glutamate release in the absence of neurexin 1␣, although its potency is reduced (Geppert ␣-Latrotoxin is a potent neurotoxin that triggers syn-et al., 1998). These data suggested that neurexin 1␣ aptic exocytosis. Surprisingly, two distinct neuronal has a function related to ␣-latrotoxin without revealing receptors for ␣-latrotoxin have been described: CIRL/ whether or not it is a functional ␣-latrotoxin receptor. latrophilin 1 (CL1) and neurexin-1␣. ␣-Latrotoxin is Exocytosis from chromaffin cells or PC12 cells is stim-thought to trigger exocytosis by binding to CL1, while ulated by relatively high concentrations of ␣-latrotoxin the role of neurexin 1␣ is uncertain. Using PC12 cells, (Ͼ0.1 nM) in a Ca 2ϩ-dependent manner. Expression of we now demonstrate that neurexins indeed function CL1 in chromaffin cells or PC12 cells produces a major as ␣-latrotoxin receptors that are at least as potent shift in the ␣-latrotoxin concentration dependence of as CL1. Both ␣-and ␤-neurexins represent autono-these cells (Bittner et al., 1998; Sugita et al., 1998). Cells mous ␣-latrotoxin receptors that are regulated by al-containing CL1 are stimulated by picomolar instead of ternative splicing. Similar to CL1, truncated neurexins nanomolar concentrations of ␣-latrotoxin. This result without intracellular sequences are fully active; there-provided crucial evidence that CL1 is indeed a real fore, neurexins and CL1 recruit ␣-latrotoxin but are ␣-latrotoxin receptor. We have now used this assay to not themselves involved in exocytosis. Thus, ␣-latro-test if neurexins act as functional ␣-latrotoxin receptors. toxin is unique among neurotoxins, because it utilizes Our data demonstrate that multiple neurexins are ␣-latro-two unrelated receptors, probably to amplify recruit-toxin receptors that are regulated by alternative splicing. ment of ␣-latrotoxin to active sites. Direct comparisons show that neurexins are more potent in this assay than CL1 and that they do not cooper-Introduction ate with CL1 in triggering exocytosis. ␣-Latrotoxin is a potent excitatory neurotoxin that stimulates synaptic vesicle exocytosis and induces massive Results neurotransmitter release (reviewed by Rosenthal and Meldolesi, 1989). At the synapse, ␣-latrotoxin binds to Neurexin 1␣ Is a Functional ␣-Latrotoxin Receptor receptors close to the active zone to initiate exocytosis. We …