Regulation of AMPA-type glutamate receptor homolog GLR-1 by ERAD ubiquitin ligases in C. elegans

Endoplasmic reticulum-associated degradation (ERAD) maintains cellular health by removing misfolded proteins from the endoplasmic reticulum (ER). ERAD is ubiquitin-dependent, and ubiquitination of target proteins can be catalyzed by ER-resident E3 ubiquitin ligases. In C. elegans, genes for three putative ERAD E3 ubiquitin ligases have been identified: hrd-1, hrdl-1, and marc-6 (HRD-1, GP78/AMFR, and MARCH-6 in mammalian systems). In C. elegans, these three genes cooperate to maintain the overall health of animals during ER stress. We are testing the roles of hrd-1, hrdl-1, and marc-6 in the neurons of C. elegans. GLR-1 is a glutamate receptor that is expressed in a subset of interneurons in C. elegans. It is homologous to human AMPA-type glutamate receptors, which are central for the processes of learning and memory. GLR-1 that is tagged with GFP (GLR-1::GFP) recapitulates normal biochemical GLR-1 function and allows observation of its abundance and localization in live animals. Animals harboring mutations in the ERAD E3 ligases hrd-1 and hrdl-1 have increased GLR-1::GFP abundance compared to wild-type animals. hrd-1 and hrdl-1 mutants also show defects in GLR-1::GFP localization. Double mutant analysis suggests that hrdl-1 and hrd-1 do not act redundantly, but could act in the same pathway. We are currently testing how a mutation in marc-6 affects GLR-1::GFP. Future experiments will focus on determining the mechanism(s) by which GLR-1 is selected as a substrate by the ERAD E3 ligases and their associated E2 ligases.