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 <i>in vitro</i> and <i>in vivo</i> (mouse and zebrafish models). Depletion of core autophagy genes (<i>ATG5</i> or <i>ATG7</i>) 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.