Histone chaperone Nucleophosmin regulates transcription of key genes involved in oral tumorigenesis.

Nucleophosmin (NPM1) is a multifunctional histone chaperone that can activate acetylation-dependent transcription from chromatin templates in vitro. Acetylation of NPM1 by p300 has been shown to further enhance its transcription activation potential. Moreover, its total and acetylated pools are increased in oral squamous cell carcinoma. However, the role of NPM1 or its acetylated form (AcNPM1) in transcriptional regulation in cells and oral tumorigenesis is not fully elucidated. Using ChIP-seq analyses, we provide the first genome-wide profile of AcNPM1 and show that AcNPM1 is enriched at transcriptional regulatory elements. AcNPM1 co-occupies marks of active transcription at promoters and DNase I hypersensitive sites at enhancers. In addition, using a high-throughput protein interaction profiling approach, we show that NPM1 interacts with RNA Pol II, general transcription factors, mediator subunits, histone acetyltransferase complexes, and chromatin remodelers. NPM1 histone chaperone activity also contributes to its transcription activation potential. Further, NPM1 depletion leads to decreased AcNPM1 occupancy and reduced expression of genes required for proliferative, migratory and invasive potential of oral cancer cells. NPM1 depletion also abrogates the growth of orthotopic tumors in mice. Collectively, these results establish that AcNPM1 functions as a coactivator during during RNA polymerase II-driven transcription and regulates the expression of genes that promote oral tumorigenesis.