The RNA-binding E3 ubiquitin ligase MEX-3C links ubiquitination with MHC-I mRNA degradation

Area of Science:

• Immunology
• Molecular Biology
• RNA Biology

Background:

• Major histocompatibility complex class I (MHC-I) molecules are crucial for immune surveillance by T-cells and NK cells.
• Regulation of MHC-I cell-surface expression is vital for adaptive and innate immunity.
• The function of RNA-binding E3 ubiquitin ligases, including their role in mRNA regulation, is largely unknown.

Purpose of the Study:

• To investigate the function of RNA-binding E3 ubiquitin ligases in the context of MHC-I regulation.
• To identify novel mechanisms controlling post-transcriptional regulation of MHC-I.
• To explore the role of ubiquitination in mRNA degradation pathways.

Main Methods:

• Functional siRNA ubiquitome screen to identify relevant E3 ligases.
• Characterization of MEX-3C's interaction with HLA-A2 mRNA.
• Analysis of MEX-3C's RING domain in regulating mRNA degradation and protein expression.

Main Results:

• MEX-3C, a novel RNA-binding ubiquitin E3 ligase, was identified as a key regulator of MHC-I.
• MEX-3C binds the 3'UTR of HLA-A2 mRNA, leading to its degradation.
• The RING domain of MEX-3C is essential for mRNA degradation but not for cell-surface protein downregulation.

Conclusions:

• A novel post-transcriptional regulatory pathway involving ubiquitination and mRNA degradation for HLA-A allotypes has been uncovered.
• MEX-3C mediates allotype-specific regulation of MHC-I through targeted mRNA decay.
• This study establishes a direct link between ubiquitination machinery and mRNA degradation in immune regulation.