7157 Unveiling PROP1 protein complex: NFIB as a key candidate in pituitary development

Abstract Disclosure: L.C. Iglesias García: None. M.F. Mercogliano: None. C. Schuster: None. L. Cheung: None. F. Brunello: None. V. Michan: None. M. Waldman: None. L. Defelipe: None. M. Martí: None. S.A. Camper: None. M.I. Perez-Millan: None. The transcription factor PROP1 is essential for pituitary development, and mutations in the gene are the most common cause of hypopituitarism in children. To understand PROP1 function, it is essential to identify the protein components of the PROP1 transcription complex. Rapid immunoprecipitation and mass spectrometry (RIME) experiments in GHFT1 cells, genetically engineered to express biotin-tagged PROP1, have revealed the association of PROP1 with 43 transcription factors (including β-CATENIN and the Nuclear Factor I/B). In silico analysis showed association between the armadillo domains of β-CATENIN and a predicted nuclear localization signal motif of PROP1. This interaction between PROP1 and β-CATENIN was confirmed in pituitary GHFT1 cells, where over-expression of PROP1 induces the translocation of β-CATENIN from the membrane and cytoplasm to the nucleus. Moreover, in pituitaries from Prop1df/df mutant embryos at e12.5, β-CATENIN was predominantly membrane-bound compared to wild-type embryos. These findings suggest that PROP1 is necessary for translocation of β-CATENIN to the nucleus during pituitary development.The association of PROP1 with NFIB is intriguing because PROP1 is necessary for the epithelial to mesenchymal-like transition of stem cells in pituitary development, and NFIB is associated with induction of EMT in several cancer models. We used immunohistochemistry to show that NFIB is expressed in embryonic pituitary glands from e12.5 to e16.5, and it co-localizes with the stem cell marker SOX2. To determine whether PROP1 and NFIB have common downstream targets, we performed CUT&RUN experiments for NFIB in GHFT-1 cells and compared the results with those from PROP1 ChIP-seq. Both PROP1 and NFIB bind to three sites in the NFIB gene, suggesting that NFIB is a downstream target of PROP1 and subject to autoregulation. Consistent with this idea, NFIB is reduced in pituitaries from Prop1df/df embryos at both e12.5 and e14.5 relative to normal littermates. Integration of the results from PROP1 ChIP-seq and RNA-seq (GHFT1 vs PROP1-GHFT1 cells) with NFIB CUT&RUN generated a list of 190 potential target genes. These genes are associated with cell migration, emphasizing their correlation with the EMT-like process orchestrated by PROP1 during pituitary development. In sum, we have identified an interesting set of PROP1 interacting proteins, including the transcription factor NFIB, which plays an important role in regulating stem cell differentiation in several organ systems. We have also cataloged the genome-wide set of binding sites for PROP1 and NFIB, which overlap at many genes regulating cell migration, a process that is important for pituitary stem cells to leave the niche and initiate differentiation. Presentation: 6/3/2024