Nuclear Factor I Family Members are Key Transcription Factors Regulating Gene Expression.

The Nuclear Factor I (NFI) family of transcription factors (TFs) plays key roles in cellular differentiation, proliferation, and homeostasis. As such, NFI family members engage in a large number of interactions with other proteins and chromatin. However, despite their well-established significance, the NFIs' interactomes, their dynamics, and their functions have not been comprehensively examined. Here, we employed complementary omics-level techniques, i.e. interactomics (affinity purification mass spectrometry (AP-MS) and proximity-dependent biotinylation (BioID)), and chromatin immunoprecipitation sequencing (ChIP-Seq), to obtain a comprehensive view of the NFI proteins and their interactions in different cell lines. Our analyses included all four NFI family members, and a less-studied short isoform of NFIB (NFIB4), which lacks the DNA binding domain. We observed that, despite exhibiting redundancy, each family member had unique high-confidence interactors and target genes, suggesting distinct roles within the transcriptional regulatory networks. The study revealed that NFIs interact with other TFs to co-regulate a broad range of regulatory networks and cellular processes. Notably, time-dependent proximity-labeling unveiled a highly dynamic nature of NFI protein-protein interaction networks and hinted at the temporal modulation of NFI interactions. Furthermore, gene ontology (GO) enrichment analysis of NFI interactome and targetome revealed the involvement of NFIs in transcriptional regulation, chromatin organization, cellular signaling pathways, and pathways related to cancer. Additionally, we observed that NFIB4 engages with proteins associated with mRNA regulation, which suggests that NFIs have roles beyond traditional DNA binding and transcriptional modulation. We propose that NFIs may function as potential pioneering TFs, given their role in regulating the DNA binding ability of other TFs and their interactions with key chromatin remodeling complexes, thereby influencing a wide range of cellular processes. These insights into NFI protein-protein interactions and their dynamic, context-dependent nature provide a deeper understanding of gene regulation mechanisms and hint at the role of NFIs as master regulators.