NINJ1 mediated plasma membrane rupture is a two-step process requiring cell swelling

Ninjurin-1 (NINJ1) executes cell lysis by polymerizing into filaments, yet how these form membrane lesions is unknown. Integrating cell-based assays with molecular dynamics simulations, we demonstrate that NINJ1-driven membrane rupture starts with the lateral association of NINJ1 dimers into double filaments. Subsequently, swelling of necrotic cells increases plasma membrane tension, leading to separation of the filament interface and NINJ1 lesion opening. Inhibiting cell swelling prevents this increase in tension, blocking NINJ1-mediated plasma membrane rupture without disrupting NINJ1 oligomerization, implicating membrane tension as key for opening NINJ1 lesions. The NINJ1 homolog NINJ2 oligomerizes but fails to form membrane lesions during cell death due to the greater stability of its dimer. Finally, using atomic force microscopy of NINJ1-containing proteoliposomes, we show that NINJ1 forms large pores by stabilizing membrane edges. In summary, our findings support a model whereby membrane tension drives a zipper-like opening of NINJ1 double filaments, initiating necrotic cell lysis.