Drosophila Keap1 Proteins Assemble Nuclear Condensates in Response to Oxidative Stress

The Keap1-Nrf2 signaling pathway is a central regulator of transcriptional responses to oxidative stress and is strongly linked to diverse pathologies, particularly cancer. In the cytoplasm, Keap1 (Kelch-like ECH-associated protein 1) promotes proteasomal degradation of Nrf2 (NF-E2-related factor 2). Oxidative stimuli disrupt the Keap1-Nrf2 interaction, facilitating Nrf2 nuclear accumulation and activation of antioxidant and detoxifying genes. Recent evidence suggests that Keap1 family proteins also enter the nucleus, bind chromatin, and regulate transcription, but the underlying mechanisms remain less understood. Here, we show that the <i>Drosophila</i> Keap1 ortholog, dKeap1, accumulates in the nucleus and gradually assembles stable nuclear foci in cells following oxidative treatment. FRAP analyses revealed reduced mobility of dKeap1 within these foci. Both the N-terminal (NTD) and C-terminal (CTD) domains of dKeap1 were required for foci formation. Two intrinsically disordered regions (IDRs) were identified within the CTD, and CTD-YFP fusion proteins readily formed condensates in vitro. Conversely, deletion of the Kelch domain resulted in robust cytoplasmic foci even under basal conditions, and in vitro assays also indicated that the Kelch domain suppresses dKeap1 condensate formation. Together, these findings reveal a novel molecular mechanism for the nuclear function of dKeap1, providing new insight into the broader roles of Keap1 factors in oxidative response, development, and disease.