An Autism-Linked Mutation Disables Phosphorylation Control of UBE3A

Abstract

Summary Deletion of UBE3A causes the neurodevelopmental disorder Angelman syndrome (AS) while duplication or triplication of UBE3A is linked to autism. These genetic findings suggest that the ubiquitin ligase activity of UBE3A must be tightly maintained to promote normal brain development. Here, we found that protein kinase A (PKA) phosphorylates UBE3A in a region outside the catalytic domain, at residue T485, and inhibits UBE3A activity towards itself and other substrates. A de novo autism-linked missense mutation disrupts this phosphorylation site, causing enhanced UBE3A activity in vitro, enhanced substrate turnover in patient-derived cells, and excessive dendritic spine development in the brain. Our study identifies PKA as an upstream regulator of UBE3A activity, and shows that an autism-linked mutation disrupts this phosphorylation control. Moreover, our findings implicate excessive UBE3A activity and the resulting synaptic dysfunction to autism pathogenesis.

Do Low Serum UCH-L1 and TDP-43 Levels Indicate Disturbed Ubiquitin- Proteosome System in Autism Spectrum Disorder?

“…As previously shown, molecules that are involved in ubiquitination play a significant role in brain development processes, such as synaptogenesis, as the balance between ubiquitination and deubiquitination is critical for synapse function (5,24). For example, regulation of ubiquitination via UBE3A with phoshorylation was impaired, and it led to increased synapsis and dendritic spine density in an autism proband with a mutant of T485 (4,5). To our knowledge, this is the first research investigating UCH-L1 and TDP-43 serum levels in ASD, in which both molecules are involved in protein formation.…”

Structural mechanisms of HECT-type ubiquitin ligases

“…More recently, a non-conservative amino acid substitution at the trimer interface, F727D, was found to decrease the size of recombinant, full-length E6AP, consistent with a trimer-to-monomer transition (Ronchi et al, 2014). Moreover, various studies have referenced the crystallographic trimer to rationalize mutational results (Chan et al, 2013;Ronchi et al, 2014;Mortensen et al, 2015;Yi et al, 2015). For instance, several mutations at the crystallographic trimer interface, including F727D, R626A, D543A, Y533A (a mutation site in Angelman syndrome), and Y636D (a variant mimicking phosphorylation of Y636 by the tyrosine kinase c-ABL) were found to reduce the activity of E6AP, nourishing the idea that the E6AP trimer represents an activated state (Chan et al, 2013;Ronchi et al, 2014).…”

“…Cell-based analyses have revealed yet another interesting facet in the oligomerization behavior of E6AP (Yi et al, 2015). Full-length E6AP was found to self-associate upon mutation of a physiological phosphorylation site for PKA in the α1′-helix region (T485A).…”

Subcellular organization of UBE3A in neurons

“…For example, UBE3A may act by ubiquitinating SOD1 (Superoxide dismutase 1), which can itself act as a nuclear transcription factor (Mishra et al, 2013;Tsang et al, 2014). SOD1 mutations have been linked to autism (Kovac et al, 2014), which in turn has been linked to maternal 15q11-13 copy number variation that may cause UBE3A overexpression, and to modified phosphorylation that can cause UBE3A hyperfunction (Cook et al, 1997;Christian et al, 2008;Glessner et al, 2009;Hogart et al, 2009;Hogart et al, 2010;Iossifov et al, 2014;Yi et al, 2015). UBE3A also exhibits transcriptional effects independent of its role as an E3 ligase (El Hokayem and Nawaz, 2014).…”