Structural basis of DNA-dependent coactivator recruitment by the tuft cell master regulator POU2F3

Abstract

The transcription factor POU2F3 defines the identity of tuft cells and underlies a distinct molecular subtype of small cell lung cancer (SCLC). Although POU2F3 is considered undruggable, its activity critically depends on the coactivators OCA-T1 and OCA-T2. Here, we demonstrate that acute suppression of either POU2F3 or OCA-T1 induces regression of tuft cell-like SCLC xenografts in vivo. To explore the structural basis and druggability of this dependency, we determine crystal structures of POU2F3 bound to OCA-T1 or OCA-T2 in complex with DNA, revealing a tripartite, DNA-dependent interface. We further employ deep mutational scanning to assess the functional impact of 4,218 missense variants in POU2F3 and OCA-T1, uncovering both mutation-sensitive hotspots and structurally constrained regions critical for tumor cell fitness. These findings define a transcriptional complex that integrates DNA recognition with coactivator recruitment and nominate POU2F3-OCA-T as a structurally tractable vulnerability in tuft cell-like carcinomas.

Keywords: CP: cancer; CP: molecular biology; OCA-T1; OCA-T2; POU2AF2; POU2AF3; POU2F3; X-ray crystallography; deep mutational scanning; small cell lung cancer; tuft cell.