Histone H3 E50K mutation confers oncogenic activity and supports an EMT phenotype.

Sequencing of human patient tumors has identified recurrent missense mutations in genes encoding core histones. We report that mutations that convert histone H3 amino acid 50 from a glutamate to a lysine (H3E50K) support an oncogenic phenotype in human cells. Expression of H3E50K is sufficient to transform human cells as evidenced by a dramatic increase in cell migration and invasion, and a statistically significant increase in proliferation and clonogenicity. H3E50K also increases the invasive phenotype in the context of co-occurring BRAF mutations, which are present in patient tumors characterized by H3E50K. H3E50 lies on the globular domain surface in a region that contacts H4 within the nucleosome. We find that H3E50K perturbs proximal H3 post-translational modifications globally and dysregulates gene expression, activating the epithelial to mesenchymal transition. Functional studies using S. cerevisiae reveal that, while yeast cells that express H3E50K as the sole copy of histone H3 show sensitivity to cellular stressors, including caffeine, H3E50K cells display some genetic interactions that are distinct from the characterized H3K36M oncohistone yeast model. Taken together, these data suggest that additional histone H3 mutations have the potential to be oncogenic drivers and function through distinct mechanisms that dysregulate gene expression.

A leptomycin B-sensitive homologue of human CRM1 promotes nuclear export of nuclear export sequence-containing proteins in Drosophila cells.

The Rev protein of human immunodeficiency virus is a nuclear shuttling protein that promotes nuclear export of mRNAs that encode the viral structural proteins Gag, Pol, and Env. Rev binds to a highly structured RNA motif, the Rev-responsive element (RRE), that is present in all Rev-responsive viral transcripts and facilitates their entry into a nuclear export pathway by recruiting cellular export factors. In mammalian and yeast cells, the principal export receptor engaged by Rev has been identified as the importin/transportin family member CRM1/exportin 1. CRM1 binds directly to a leucine-rich nuclear export sequence (NES) present in Rev, and similar motifs have been identified in a variety of cellular nuclear shuttling proteins. We and our colleagues previously demonstrated that, in transfected Drosophila cells, HIV-1 Rev is fully functional and promotes expression of the viral envelope glycoprotein. We now demonstrate that the fundamental mechanism of Rev action in insect cells is identical to that observed in the mammalian systems. In particular, we show that Drosophila cells express a leptomycin B-sensitive homologue of human CRM1 that supports Rev-dependent gene expression and is required for nuclear export of NES-containing proteins in insect cells.