VAMP8 stabilization by DRAM1 enables autophagosome-lysosome fusion and promotes metastatic extravasation.

Autophagosome-lysosome fusion, essential for macroautophagy/autophagy completion, requires the STX17-SNAP29-VAMP8 SNARE complex. While VAMP8 is crucial, its regulatory mechanisms remain incompletely understood. Here, we identify DRAM1 (DNA damage regulated autophagy modulator 1) as a key interactor and stabilizer of VAMP8 on lysosomes. In this study, we demonstrated that DRAM1 directly binds VAMP8, and this interaction is enhanced during autophagy induction. Mechanistically, DRAM1 inhibits ubiquitin-mediated degradation of lysosomal VAMP8 by the E3 ligase STUB1/CHIP to enhance autolysosome formation. DRAM1 competitively binds VAMP8 within residues 66-100 aa, shielding lysines 68, 72, and 75 from STUB1-mediated ubiquitination. This stabilization promotes assembly of the STX17-SNAP29-VAMP8 complex, enhancing autophagosome-lysosome fusion. Functionally, DRAM1-mediated VAMP8 stabilization and autophagic flux promote the extravasation and metastasis of hepatocellular carcinoma (HCC) cells in vitro and in vivo (mouse and zebrafish models). Depletion of core autophagy genes (ATG5 or ATG7) abolishes DRAM1's pro-metastatic effects. Our findings reveal a novel DRAM1-VAMP8 axis that regulates autophagic flux and identify DRAM1 as a potential therapeutic target for inhibiting autophagy-dependent HCC metastasis. Here, we summarize our findings and discuss their implications for our understanding of autophagy regulation.