The clustering of NMDA receptor NR1 subunit is regulated by the interaction between the C-terminal exon cassettes and the cytoskeleton

The clustering of neurotransmitter receptors at postsynaptic sites is consi dered to play an important role in modulating synaptic efficacy. To investi gate the mechanisms underlying neurotransmitter receptor clustering, we exp ressed the NMDA (N-methyl-D-aspartate) receptor NR1A subunit in human embry onic kidney (HEK) 293 cells. As previously shown, the cells exhibited subce llular clusters of the receptor protein with a mean diameter of approximate ly 0.7 mu m. To examine the involvement of cytoskeletal structures on this clustering, we disrupted actin filaments or microtubules by treating the ce lls with alkaloids. In the actin filament-disrupted cells. the receptor pro tein shifted from the cellular membrane to the cytoplasm where it formed ma croclusters (approximate diameter 3 mu m). In the microtubule-disrupted cel ls, the subcellular clusters of NR1A could not be detected and the protein was diffusely distributed throughout the cytoplasm. Similar results were ob tained by coexpression of the receptor protein with fusion proteins harbori ng various C-terminal exon cassettes. These results suggest that subcellula r clustering of the NR1 subunit of the NMDA receptors is regulated by the i nteraction of its C-terminus with cytoskeletal components, where differenti ally spliced cassettes interact separately with actin filaments or microtub ules. Modulation of the interaction between the neurotransmitter receptors and the cytoskeleton leads to the rearrangement of the receptor clusters an d may contribute to certain types of synaptic plasticity. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.