Endoplasmic reticulum tubule junctions are sites of autophagy.

Selective endoplasmic reticulum (ER) macroautophagy/autophagy, also called reticulophagy, is a disposal pathway that degrades ER domains. A major role of reticulophagy is the removal of ER domains that contain misfolded proteins resistant to ER-associated degradation (ERAD). Our studies have shown that RTN3L, the SEC24C-SEC23 COPII coat subcomplex, and the CUL3KLHL12 E3 ligase that ubiquitinates RTN3L targets ERAD-resistant misfolded protein condensates for degradation at ER-reticulophagy sites (ERPHS), autophagic sites that form at tubule junctions. Unexpectedly, we found that the Parkinson disease protein PINK1 regulates ER tubulation. Loss of PINK1 disrupts the formation of peripheral tubule junctions, and, as a consequence, reticulophagy is blocked and misfolded proteins accumulate in the ER. Overexpression of the ER tubulating domain of DNM1L/DRP1, a multifunctional PINK1 kinase substrate that localizes to ER-mitochondria contact sites, increases junctions and restores reticulophagy. Our findings show that PINK1 shapes the ER to target misfolded proteins for RTN3L-SEC24C-mediated macroreticulophagy at defined ER sites, peripheral tubule junctions.