FAM172A controls the nuclear import and alternative splicing function of AGO2

Abstract

The poorly characterized protein FAM172A is mutated in some individuals affected by a disorder of neural crest development called CHARGE syndrome. We also know that FAM172A can interact with the main CHARGE syndrome-associated protein CHD7 and the small RNA-binding protein AGO2 at the chromatin-spliceosome interface. Focusing on this intriguing FAM172A-AGO2 interaction, we now report that FAM172A is one of the long sought-after regulator of AGO2 nuclear import. This FAM172A function relies on its nuclear localization signal, being enhanced by CK2-mediated phosphorylation and abrogated by a CHARGE syndrome-associated missense mutation. Accordingly, Fam172a and Ago2 genetically interact in mice, and neural crest-specific depletion of Ago2 is sufficient to phenocopy CHARGE syndrome without impacting post-transcriptional gene silencing. Rapamycin-mediated rescue suggests that observed morphological anomalies are instead due to alternative splicing defects. This work thus demonstrates that non-canonical nuclear functions of AGO2 and associated regulatory mechanisms may be clinically relevant.

A C-terminal HaloTag Impairs AGO2 Function

“…Impaired nuclear localisation could arise for many reasons, most obviously perhaps due to the addition of the large (33 kDa) HaloTag preventing binding of mediators of nuclear import. 70,71 It may also be the case that loss of the carboxylate group of A859 specifically disrupts the structure of AGO2 in a way that impairs binding to nuclear import factors. Factors that regulate nuclear import of AGO2 continue to be revealed 72,73 and it may be that the PIWI domain and/or the C-terminal region are more critical in these interactions than is currently understood.…”