The RNA helicase DHX34 functions as a scaffold for SMG1-mediated UPF1 phosphorylation

Area of Science:

• Molecular Biology
• RNA Biology
• Cellular Quality Control

Background:

• Nonsense-mediated decay (NMD) is a critical RNA quality-control pathway.
• SMG1-mediated phosphorylation of UPF1 initiates the NMD pathway.
• DHX34, an RNA helicase, was previously shown to activate NMD through mRNP remodeling.

Purpose of the Study:

• To elucidate the mechanism by which DHX34 collaborates with the SMG1 kinase in NMD.
• To define the structural basis for the interaction between DHX34, SMG1, and UPF1.

Main Methods:

• Utilized truncated forms of DHX34 to map protein-binding domains.
• Employed electron microscopy to visualize the SMG1-DHX34 complex.
• Assessed the impact of DHX34 structural modifications on UPF1 phosphorylation and NMD activity.

Main Results:

• DHX34 possesses distinct structural units: a core for UPF1 binding and a carboxy-terminal domain (CTD) for SMG1 binding.
• Truncation of the DHX34 CTD impaired SMG1 binding and UPF1 phosphorylation, abrogating NMD.
• Demonstrated that DHX34 functions as a scaffold, assembling SMG1 and UPF1.

Conclusions:

• DHX34 acts as a crucial scaffold protein, facilitating the formation of a functional SMG1-UPF1 complex.
• This DHX34-mediated scaffolding is essential for SMG1-dependent UPF1 phosphorylation and subsequent NMD activation.
• The findings reveal a key mechanistic step in the regulation of the nonsense-mediated decay pathway.