Blebs Promote Cell Survival by Assembling Oncogenic Signaling Hubs

For most human cells, anchorage is a key necessity for survival. Cell-substrate adhesion activates diverse signaling pathways, without which cells undergo anoikis - a form of programmed cell death1. Acquisition of anoikis resistance is a pivotal step in cancer disease progression, as metastasizing cancer cells often lose firm attachment to surrounding tissue2-5. In these poorly attached states, cells often adopt rounded morphologies and form small hemispherical plasma membrane protrusions called blebs6-13. Bleb function has long been investigated in the context of amoeboid migration but is far less deeply examined in other scenarios14-19. Here we show by quantitative subcellular 3D imaging and manipulation of cell morphological states that blebbing triggers the formation of membrane-proximal signaling hubs that initiate signaling cascades leading to anoikis resistance. Specifically, in melanoma cells we discovered that blebbing generates plasma membrane contours that recruit curvature sensing septin proteins, which scaffold constitutively active mutant NRAS and effectors, driving the upregulation of ERK and PI3K signaling. Inhibition of blebs or septins has little effect on the survival of well-adhered cells, but in detached cells causes NRAS mislocalization, reduced MAPK and PI3K signaling, and ultimately, death. These data unveil an unanticipated morphological requirement for mutant NRAS to operate as an effective oncoprotein, suggesting novel clinical targets for the treatment of NRAS-driven melanoma. Furthermore, they define an unforeseen role for blebs as potent signaling organelles capable of integrating myriad cellular information flows into concerted signaling responses, in this case granting robust anoikis resistance. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/441200v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@a00b78org.highwire.dtl.DTLVardef@15120bcorg.highwire.dtl.DTLVardef@13c51c9org.highwire.dtl.DTLVardef@11d8dd0_HPS_FORMAT_FIGEXP M_FIG C_FIG