Tumor-derived IFN triggers chronic pathway agonism and sensitivity to ADAR loss.

Interferons (IFNs) are cytokines that play a critical role in limiting infectious and malignant diseases . Emerging data suggest that the strength and duration of IFN signaling can differentially impact cancer therapies, including immune checkpoint blockade . Here, we characterize the output of IFN signaling, specifically IFN-stimulated gene (ISG) signatures, in primary tumors from The Cancer Genome Atlas.

Project DRIVE: A Compendium of Cancer Dependencies and Synthetic Lethal Relationships Uncovered by Large-Scale, Deep RNAi Screening.

Elucidation of the mutational landscape of human cancer has progressed rapidly and been accompanied by the development of therapeutics targeting mutant oncogenes. However, a comprehensive mapping of cancer dependencies has lagged behind and the discovery of therapeutic targets for counteracting tumor suppressor gene loss is needed. To identify vulnerabilities relevant to specific cancer subtypes, we conducted a large-scale RNAi screen in which viability effects of mRNA knockdown were assessed for 7,837 genes using an average of 20 shRNAs per gene in 398 cancer cell lines.

Disordered methionine metabolism in MTAP/CDKN2A-deleted cancers leads to dependence on PRMT5.

5-Methylthioadenosine phosphorylase (MTAP) is a key enzyme in the methionine salvage pathway. The MTAP gene is frequently deleted in human cancers because of its chromosomal proximity to the tumor suppressor gene CDKN2A. By interrogating data from a large-scale short hairpin RNA-mediated screen across 390 cancer cell line models, we found that the viability of MTAP-deficient cancer cells is impaired by depletion of the protein arginine methyltransferase PRMT5.

PTEN-deficient cancers depend on PIK3CB.

Deregulation of the PI3K signaling pathway is observed in many human cancers and occurs most frequently through loss of PTEN phosphatase tumor suppressor function or through somatic activating mutations in the Class IA PI3K, PIK3CA. Tumors harboring activated p110alpha, the protein product of PIK3CA, require p110alpha activity for growth and survival and hence are expected to be responsive to inhibitors of its lipid kinase activity. Whether PTEN-deficient cancers similarly depend on p110alpha activity to sustain activation of the PI3K pathway has been unclear.

An ARC/Mediator subunit required for SREBP control of cholesterol and lipid homeostasis.

The sterol regulatory element binding protein (SREBP) family of transcription activators are critical regulators of cholesterol and fatty acid homeostasis. We previously demonstrated that human SREBPs bind the CREB-binding protein (CBP)/p300 acetyltransferase KIX domain and recruit activator-recruited co-factor (ARC)/Mediator co-activator complexes through unknown mechanisms. Here we show that SREBPs use the evolutionarily conserved ARC105 (also called MED15) subunit to activate target genes.

The activator-recruited cofactor/Mediator coactivator subunit ARC92 is a functionally important target of the VP16 transcriptional activator.

The human activator-recruited cofactor (ARC), a family of large transcriptional coactivator complexes related to the yeast Mediator, was recently identified based on functional association with the activation domains of multiple cellular and viral transcriptional activators, including the herpes simplex viral activator VP16, sterol regulatory element binding protein, and NF-kappaB. Here we describe the biochemical purification and cloning of the 92-kDa ARC/Mediator subunit, ARC92, that is specifically targeted by the activation domain of the VP16 transactivator. Affinity chromatography using the VP16 activation domain followed by peptide microsequencing led to the identification of ARC92 as a specific cellular interaction partner of the VP16 activation domain.