MEX3C interacts with adaptor-related protein complex 2 and involves in miR-451a exosomal sorting

Area of Science:

• Molecular Biology
• Cell Biology
• Exosome Biology

Background:

• Exosomes are key mediators of intercellular communication, selectively packaging RNA species like microRNAs.
• The precise mechanisms governing the selective sorting of RNA into exosomes remain largely unknown.
• RNA-binding proteins are implicated in RNA localization, but their direct role in exosome sorting is under investigation.

Purpose of the Study:

• To elucidate the mechanism by which specific microRNAs are sorted into exosomes.
• To identify the protein machinery involved in the selective exosomal sorting of microRNA miR-451a.
• To investigate the role of RNA-binding ubiquitin E3 ligase (MEX3C) in microRNA exosomal export.

Main Methods:

• Investigated interactions between RNA-binding ubiquitin E3 ligase (MEX3C) variants and adaptor-related protein complex 2 (AP-2).
• Utilized siRNA-mediated inhibition to assess the impact of MEX3C and AP-2 on microRNA expression.
• Examined the role of ceramide and ESCRT pathways in microRNA exosomal sorting.

Main Results:

• All three MEX3C variants interact with AP-2, a clathrin-mediated endocytosis adaptor.
• MEX3C association with the endolysosomal compartment occurs via an endocytosis-like process.
• Inhibition of MEX3C or AP-2 significantly reduced exosomal miR-451a levels, but not cellular levels.
• Exosomal sorting of miR-451a was found to be ceramide-dependent and ESCRT-independent.

Conclusions:

• RNA-binding proteins associate with membrane trafficking machinery to regulate exosome cargo.
• MEX3C and AP-2 play a crucial role in the selective recruitment of microRNA miR-451a to endosomes for exosomal sorting.
• This study suggests a novel mechanism for specific RNA recruitment into exosomes, highlighting the importance of ceramide.