Endogenous bioluminescent reporters reveal a sustained increase in utrophin gene expression upon EZH2 and ERK1/2 inhibition.

Duchenne muscular dystrophy (DMD) is an X-linked disorder caused by loss of function mutations in the dystrophin gene (Dmd), resulting in progressive muscle weakening. Here we modelled the longitudinal expression of endogenous Dmd, and its paralogue Utrn, in mice and in myoblasts by generating bespoke bioluminescent gene reporters. As utrophin can partially compensate for Dmd-deficiency, these reporters were used as tools to ask whether chromatin-modifying drugs can enhance Utrn expression in developing muscle. Myoblasts treated with different PRC2 inhibitors showed significant increases in Utrn transcripts and bioluminescent signals, and these responses were independently verified by conditional Ezh2 deletion. Inhibition of ERK1/2 signalling provoked an additional increase in Utrn expression that was also seen in Dmd-mutant cells, and maintained as myoblasts differentiate. These data reveal PRC2 and ERK1/2 to be negative regulators of Utrn expression and provide specialised molecular imaging tools to monitor utrophin expression as a therapeutic strategy for DMD.

Oncogenic Rag GTPase signaling enhances B cell activation and drives follicular lymphoma sensitive to pharmacological inhibition of mTOR.

The humoral immune response demands that B cells undergo a sudden anabolic shift and high cellular nutrient levels which are required to sustain the subsequent proliferative burst. Follicular lymphoma (FL) originates from B cells that have participated in the humoral response, and 15% of FL samples harbor point, activating mutations in RRAGC, an essential activator of mTORC1 downstream of the sensing of cellular nutrients. The impact of recurrent RRAGC mutations in B cell function and lymphoma is unexplored. RRAGC mutations, targeted to the endogenous locus in mice, confer a partial insensitivity to nutrient deprivation, but strongly exacerbate B cell responses and accelerate lymphomagenesis, while creating a selective vulnerability to pharmacological inhibition of mTORC1. This moderate increase in nutrient signaling synergizes with paracrine cues from the supportive T cell microenvironment that activates B cells via the PI3K-Akt-mTORC1 axis. Hence, Rragc mutations sustain induced germinal centers and murine and human FL in the presence of decreased T cell help. Our results support a model in which activating mutations in the nutrient signaling pathway foster lymphomagenesis by corrupting a nutrient-dependent control over paracrine signals from the T cell microenvironment.