An EMT-driven Exoc7 splicing switch controls the PRPF19-GATA3 axis to destabilize the hybrid E/M state

The epithelial-mesenchymal transition (EMT) is a dynamic process that cancer cells exploit to gain metastatic competence, with the hybrid E/M state-co-expressing both epithelial and mesenchymal markers-being particularly critical due to its heightened plasticity and association with aggressive disease. However, the molecular mechanisms that stabilize this hybrid phenotype and govern its reversible transition to a full mesenchymal state remain a central unanswered question. Our research identified the transcription factor GATA3 as a key stabilizer of the hybrid E/M state in head and neck squamous cell carcinoma (HNSCC). Surprisingly, we found that induction of core EMT transcription factors leads to a reduction in GATA3 protein levels but does not alter its mRNA levels. This led us to explore the possibility that a post-translational mechanism drives this regulation. We analyzed the GATA3-interactome and identified PRPF19, a dual splicing factor and E3 ubiquitin ligase, as the enzyme responsible for GATA3 ubiquitination. Notably, while PRPF19 expression remains constant during EMT, its ligase activity is precisely regulated by alternative splicing. The EMT-driven loss of epithelial spliceosome switches the Exoc7 gene product from the epithelial isoform 5 (Exoc7-iso5) to the mesenchymal isoform 2 (Exoc7-iso2). Mechanistically, PRPF19 preferentially binds to Exoc7-iso5, and this interaction acts as a molecular brake by inhibiting the full cofactor assembly essential for the E3 ligase activity of PRPF19. Consequently, the EMT-associated loss of Exoc7-iso5 unleashes PRPF19, leading to unrestrained GATA3 ubiquitination and degradation. Crucially, restoring Exoc7-iso5 expression successfully rescued GATA3 protein levels and epithelial markers, formally confirming a splicing-dependent regulatory mechanism. Collectively, we propose an integrated model in which EMT-driven alternative splicing of Exoc7 serves as a functional switch to control PRPF19 E3 ligase activity, thereby targeting GATA3 for degradation to dismantle the hybrid E/M state and drive mesenchymal commitment in HNSCC, revealing this axis as a possible regulatory mechanism that controls the stability and reversibility of the hybrid E/M state.