Disease-associated polyalanine expansion mutations impair UBA6-dependent ubiquitination

• Published in: The EMBO journal Vol. 43; no. 2; pp. 250 - 276
• Main Authors: Amer-Sarsour, Fatima, Falik, Daniel, Berdichevsky, Yevgeny, Kordonsky, Alina, Eid, Sharbel, Rabinski, Tatiana, Ishtayeh, Hasan, Cohen-Adiv, Stav, Braverman, Itzhak, Blumen, Sergiu C, Laviv, Tal, Prag, Gali, Vatine, Gad D, Ashkenazi, Avraham
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 16-01-2024
• Subjects: Animals; Biomedical and Life Sciences; EMBO24; EMBO27; EMBO31; Humans; Life Sciences; Mice; Mutation; Peptides; Ubiquitin - genetics; Ubiquitin - metabolism; Ubiquitin-Activating Enzymes - genetics; Ubiquitin-Activating Enzymes - metabolism; Ubiquitination; Congenital Central Hypoventilation Syndrome; Trinucleotide Repeats; Autonomic Nervous System; Ubiquitin Transfer System; Ubiquitin-Activating Enzyme
• ISSN: 1460-2075; 0261-4189; 1460-2075
• DOI: 10.1038/s44318-023-00018-9

Expansion mutations in polyalanine stretches are associated with a growing number of diseases sharing a high degree of genotypic and phenotypic commonality. These similarities prompted us to query the normal function of physiological polyalanine stretches and to investigate whether a common molecular mechanism is involved in these diseases. Here, we show that UBA6, an E1 ubiquitin-activating enzyme, recognizes a polyalanine stretch within its cognate E2 ubiquitin-conjugating enzyme USE1. Aberrations in this polyalanine stretch reduce ubiquitin transfer to USE1 and, subsequently, polyubiquitination and degradation of its target, the ubiquitin ligase E6AP. Furthermore, we identify competition for the UBA6-USE1 interaction by various proteins with polyalanine expansion mutations in the disease state. The deleterious interactions of expanded polyalanine tract proteins with UBA6 in mouse primary neurons alter the levels and ubiquitination-dependent degradation of E6AP, which in turn affects the levels of the synaptic protein Arc. These effects are also observed in induced pluripotent stem cell-derived autonomic neurons from patients with polyalanine expansion mutations, where UBA6 overexpression increases neuronal resilience to cell death. Our results suggest a shared mechanism for such mutations that may contribute to the congenital malformations seen in polyalanine tract diseases.
Synopsis
Polyalanine tract mutations are associated with several diseases, but their exact role in disease development is unclear. This study demonstrates that disease-causing polyalanine expansions interfere with the UBA6-USE1 ubiquitin transfer system and proposes a common molecular mechanism shared by different polyalanine tract diseases.
A polyalanine stretch in the E2 ubiquitin-conjugating enzyme USE1 contributes to its recognition by the E1 ubiquitin-activating enzyme UBA6.
Mutations in this stretch affect polyubiquitination and degradation of the UBA6-USE1 target E6AP.
Various disease proteins with polyalanine expansion mutations interact with UBA6, compete for binding with USE1, and dysregulate E6AP.
Such interactions in mouse primary neurons affect the levels of the synaptic protein Arc.
UBA6 overexpression rescues cell death in autonomic neurons derived from congenital central hypoventilation syndrome (CCHS) patients.
Polyalanine tract mutations may contribute to the congenital malformations observed in polyalanine tract diseases by interfering with the ubiquitin transfer system.