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

Cells rely on substrate adhesion to activate diverse signaling pathways essential for survival. In the absence of proper adhesion, cells undergo anoikis, a form of programmed cell death. Poorly attached cells often exhibit rounded morphologies and form small round protrusions called blebs. While the role of blebs in amoeboid migration is well-documented, recent studies have highlighted their function in anoikis resistance with the help of curvature-recognized proteins. However, little is known about whether the most abundant membrane components-phospholipids function in blebs-facilitated cell survival. Here, we found enriched PI(3,4,5)P3 and diluted PI(4,5)P2 at the bleb membrane, compared to non-bleb plasma membrane regions. Our experimental results showed that both phosphoinositides (PIs) have restricted diffusion pattern between the bleb and non-bleb membranes. Subsequently, we reveal SH3KBP1 to play a crucial role in recruiting PI3K and organizing the Septin-SH3KBP1-PI3K complex at the bleb necks. This process then contributes to differential PIs distribution and anoikis resistance. These novel insights into PIs dynamics elucidate their role in cell blebbing, cancer cell behavior and metastasis, presenting potential targets for new therapeutic interventions.