KEL-8 is an E3 ubiquitin ligase substrate receptor required for GLR-1 regulation in Caenorhabditis elegans

The regulation of AMPA-type glutamate receptor trafficking and abundance is important for modulating synaptic strength. The insertion and removal of AMPA receptors at the postsynaptic membrane is dynamic, and mechanisms for both rapid and long-term changes are needed to maintain subtle control over synaptic signaling. The nematode Caenorhabditis elegans requires the BTB-Kelch protein KEL-8 to maintain normal levels of the AMPA-type glutamate receptor subunit GLR-1 at synapses that mediate mechanosensory and spontaneous behavior. KEL-8 is expressed in the same cells as GLR-1, where it localizes to GLR-1-containing postsynaptic specializations. KEL-8 functions as a substrate receptor for cullin-3-dependent ubiquitin ligases, and interacts with CUL-3 in a manner similar to other BTB-Cullin interactions. Consistent with this finding, an enzymatic pathway required for cullin function is also required for GLR-1 degradation, and a dominant negative truncated CUL-3 protein interferes with normal GLR-1 turnover. GLR-1 is ubiquitinated on cytosolic residues, leading to GLR-1 internalization and destruction. kel-8 mutants are resistant to the ubiquitin-mediated degradation of GLR-1; however, GLR-1 is able to be ubiquitinated in kel-8 mutants. The experiments in this thesis characterize KEL-8, a dedicated regulator of GLR-1 with a physiological role in synaptic strength modulation.