Blebs regulate phosphoinositides distribution and promote cell survival through the Septin-SH3KBP1-PI3K axis.

Abstract

Cells rely on substrate adhesion to activate diverse signaling pathways essential for proliferation and survival. In the absence of proper adhesion to extracellular matrix, cells undergo anoikis, a form of programmed cell death. Poorly attached cells often exhibit rounded morphology and form dynamic protrusions called blebs. While the role of blebs in amoeboid migration is well-documented, recent studies have highlighted their role in anoikis resistance. However, little is known about whether the most abundant membrane components-phospholipids- function in blebs-facilitated anoikis resistance. Here, we report an enrichment of PI(3,4,5)P₃ and a depletion of PI(4,5)P₂ at bleb membrane, compared to non-bleb regions of the plasma membrane. Our results have shown that both PI(3,4,5)P₃ and PI(4,5)P₂ have restricted diffusion pattern between the bleb and non-bleb membrane regions. Subsequently, we reveal that PI3K is recruited by SH3KBP1 via liquid-liquid phase separation (LLPS) and interacted with Septin at the bleb necks. This Septin-SH3KBP1-PI3K axis then contributes to differential phosphoinositides (PIs) distribution and anoikis resistance. These novel insights into PIs dynamics and the associated molecular scaffolding not only elucidate the mechanisms of blebs formation and anoikis resistance, but also highlight potential targets for therapeutic interventions in anchorage-independent cancers.