Hillis, A. | bioRxiv Science

bioRxiv2026

MAPK signaling links BRD2 chromatin occupancy to PI3K/AKT inhibitor sensitivity

Bromodomain and extra-terminal (BET) proteins, BRD2, BRD3, BRD4, and BRDT, couple histone acetylation to transcription by recruiting elongation and transcription factor complexes to chromatin. Although BET proteins are promising therapeutic targets, the functions of individual family members remain incompletely understood. We identify BRD2 as a co-targetable vulnerability with PI3K/AKT inhibition in breast cancer. Pan-BET inhibition and BRD2 knockout synergized with PI3K pathway inhibitors in breast cancer cell lines, patient-derived organoids, and in vivo models. BRD2 knockout impaired proliferation of triple-negative breast cancer cells and upregulated signaling and stress-response pathways, including the DNA damage response. Mechanistically, BRD2 is phosphorylated at Ser37 by the mitogen- and stress-activated kinases MSK and RSK, and Ser37 phosphorylation is required for chromatin binding and reader function. Finally, mechanistic digital twin modeling identified BETi-PI3Ki regimens that maintained efficacy while reducing drug exposure. Together, these findings identify BRD2 as a phosphorylation-dependent, co-targetable vulnerability in PI3K-inhibited breast cancer.

cancer biology↗

bioRxiv2024

Parallel phosphoproteomics and metabolomics map the global metabolic tyrosine phosphoproteome

Tyrosine phosphorylation of metabolic enzymes is an evolutionarily conserved post-translational modification that facilitates rapid and reversible modulation of enzyme activity, localization or function. Despite the high abundance of tyrosine phosphorylation events detected on metabolic enzymes in high-throughput mass spectrometry-based studies, functional characterization of tyrosine phosphorylation sites has been limited to a subset of enzymes. Since tyrosine phosphorylation is dysregulated across human diseases, including cancer, understanding the consequences of metabolic enzyme tyrosine phosphorylation events is critical for informing disease biology and therapeutic interventions. To globally identify metabolic enzyme tyrosine phosphorylation events and simultaneously assign functional significance to these sites, we performed parallel phosphoproteomics and polar metabolomics in non-tumorigenic mammary epithelial cells (MCF10A) stimulated with epidermal growth factor (EGF) in the absence or presence of the epidermal growth factor receptor (EGFR) inhibitor erlotinib. We performed an integrated analysis of the phosphoproteomic and metabolomic datasets to identify tyrosine phosphorylation sites on metabolic enzymes with functional consequences. We identified two previously characterized (PKM, PGAM1) and two novel (GSTP1, GLUD1) tyrosine phosphorylation sites on metabolic enzymes with purported functions based on metabolomic analyses. We validated these hits using a doxycycline-inducible CRISPR interference (CRISPRi) system in MCF10A cells, in which target metabolic enzymes were depleted with simultaneous re-expression of wild-type, phosphomutant or phosphomimetic isoforms. Together, these data provide a framework for identification, prioritization and characterization of tyrosine phosphorylation sites on metabolic enzymes with functional significance.

biochemistry↗