THE C-TERMINAL DOMAIN OF GLUTAMATE-RECEPTOR SUBUNIT-1 IS A TARGET FORCALPAIN-MEDIATED PROTEOLYSIS

The AMPA receptors are glutamate-gated ion channels mediating synaptic transmission at the majority of excitatory synapses in the mammalian CNS. They are composed of four subunits (GluR1-4) which exist in two a lternatively spliced variants (flip and flop) and are generally consid ered to form pentameric receptors.(7,15) The transmembrane structure o f the receptors remains a matter of controversy as some data suggest a transmembrane topology consisting of five,(15) four,(7) or three(3,8) membrane spanning regions. Some receptor properties have been shown t o be regulated by phosphorylation processes as well as by the phosphol ipid environment.(2,10,13) More recently, we have shown that calcium t reatment of thin (10 mu m) frozen-thawed brain sections resulted in pr ofound modifications of the immunochemical properties of the AMPA rece ptors.(5) More specifically, immunolabelling of the AMPA receptors wit h antibodies directed against the C-terminal domain of GluR1 and GluR2 /3 was markedly decreased in dendritic fields following such treatment at 35 degrees C. This effect was temperature-dependent and completely blocked by inhibitors of the calcium-dependent proteases calpains, an d we suggested that calpains are involved in the regulation of AMPA re ceptor properties, The results of the present study demonstrate that c alpain activation produces a partial proteolysis in the C-terminal dom ain of the receptors and generates a new receptor species with an appa rent molecular weight of 103,000 mol. wt. Sequence analysis of the Glu R1 C-terminal domain suggests a couple of cleavage sites for calpains, These results are of particular interest considering the body of evid ence implicating calpains and changes in excitatory amino acid recepto rs in mechanisms of synaptic plasticity as well as in neurodegenerativ e processes.(1,2,4,12) Copyright (C) 1996 IBRO.