Functional interaction of ubiquitin ligase RNF167 with UBE2D1 and UBE2N promotes ubiquitination of AMPA receptor.

Protein ubiquitination has been historically associated with protein degradation, but recent studies have demonstrated other cellular functions associated with substrate ubiquitination. Among the RING-type ubiquitin E3 ligase enzymes present in the human genome, RNF167 is a transmembrane protein located in endosomes and lysosomes and is implicated in controlling the endolysosomal pathway. Substrates of RNF167 have been identified, but the ubiquitin-conjugating E2 enzymes involved in the mechanism remain unknown. In this study, we describe the interaction between RNF167 and conjugating E2 enzymes. By means of in vitro autoubiquitination and binding assays, we show that RNF167 functionally interacts with many conjugating E2s, while fluorescence microscopy illustrates that these interactions occur in endosomes and lysosomes. Kinetic analyses of the interaction between RNF167 and selected conjugating E2 enzymes reveal submicromolar dissociation constants. The computed model of interaction between the RING domain of RNF167 and conjugating enzymes gives us insights on how RNF167 could interact with conjugating E2 enzymes. Furthermore, the results reveal that in vitro polyubiquitination of the AMPA-type glutamate receptor subunit GluA2, one of the RNF167's known substrates, is possible by the conjugating E2 enzyme UBE2N only after GluA2 has been primed by ubiquitin subsequent to the action of an initiating conjugating E2 enzyme functionally binding RNF167. Pharmacological inhibition of UBE2N in cultured hippocampal neurons diminishes AMPA-induced GluA2 ubiquitination. This study characterizes interacting partners of RNF167 and constitutes an initial step toward the identification of functional pairs assembled from RNF167 and ubiquitin-conjugating E2 enzymes involved in the ubiquitination of RNF167's substrate.