Optogenetic control of a GEF of RhoA uncovers a signaling switch from retraction to protrusion

The ability of a single signaling protein to induce distinct cellular processes is a well-known feature of cell signaling networks. This assumes that proteins can switch their function depending on the cellular context. However, causally proving and understanding such a switch is an arduous task because of the multiple feedbacks and crosstalks. Here, using an optogenetic tool to control membrane localization of RhoA nucleotide exchange factors (GEFs), we show that a single protein can trigger either protrusion or retraction when recruited to the plasma membrane, polarizing the cell in two opposite directions. We found that the switch from retraction to protrusion is due to the increase of the basal concentration of the GEF prior to activation. The unexpected protruding behavior arises from the simultaneous activation of Cdc42 and inhibition of RhoA by the PH domain of the GEF at high concentrations. We propose a minimal model and use its predictions to control the two phenotypes within selected cells by adjusting the frequency of light pulses. Our work exemplifies a unique case of control of antagonist phenotypes by a single protein that switches its function based on its concentration or dynamics of activity. It raises numerous open questions about the link between signaling protein and function, particularly in contexts where proteins are highly overexpressed, as often observed in cancer. ### Competing Interest Statement The authors have declared no competing interest.