BTB_BCL6 dimers as building blocks for reversible drug-induced protein oligomerization

Here, we characterize the BTB domain of the transcription factor BCL6 (BTB_BCL6) as a small-molecule-controlled, reversible oligomerization switch, which oligomerizes upon BI-3802 treatment and de-oligomerizes upon addition of BI-3812. We show that the magnitude of oligomerization can be controlled in vitro by BI-3802 concentration and exposure time. In cellular models, exposure to BI-3802/BI-3812 can drive multiple cycles of foci formation consisting of BTB_BCL6 fused to EGFP, which are not degraded due to the lack of a degron. We generated an epidermal growth factor receptor (EGFR)-BTB_BCL6 fusion. Treatment with BI-3802, as an ON switch, induced EGFR-BTB_BCL6 phosphorylation and activation of downstream effectors, which could in part be reversed by the addition of BI-3812, as an OFF switch. Finally, BI-3802-induced oligomerization of the EGFR-BTB_BCL6 fusion enhanced proliferation of an EGF-dependent cell line in absence of EGF. These results demonstrate the successful application of small-molecule-induced, reversible oligomerization as a switch for synthetic biology.