A mitochondria-driven quality control mechanism for peroxisomal membrane proteins

Area of Science:

• Cell Biology
• Organelle Biology
• Proteostasis

Background:

• Peroxisomes are vital organelles for metabolism, requiring correct targeting of peroxisomal membrane proteins (PMPs).
• Peroxisome biogenesis disorders lead to reduced PMP levels, but the mechanisms are poorly understood.

Purpose of the Study:

• To elucidate the mechanisms behind PMP downregulation in peroxisome-deficient cells.
• To identify the quality control pathways involved in managing mislocalized PMPs.

Main Methods:

• Quantitative proteomics and transcriptomics in peroxisome-deficient cells.
• CRISPR screening to identify genetic modifiers.
• Analysis of protein turnover, ubiquitination, and degradation pathways.

Main Results:

• Post-transcriptional downregulation of PMPs occurs due to increased protein turnover via ubiquitination and proteasomal degradation.
• A novel mitochondrial quality control axis was discovered where misrouted PMPs are degraded.
• Mitochondrial outer membrane E3 ligases MUL1 and MARCH5 redundantly target PMPs for degradation.
• The transmembrane domain of PMPs is sufficient for mitochondrial targeting and turnover.

Conclusions:

• Mitochondria act as a surveillance hub to clear PMPs when peroxisomes are absent, maintaining cellular proteostasis.
• This inter-organelle quality control pathway is essential for cell proliferation, particularly under conditions of peroxisome dysfunction.