SUMMARY A high-throughput RNA interference (RNAi) screen targeting 542 genes of the human kinome was used to discover regulators of RNAi. Here we report that the proto-oncogene Akt-3/PKBγ (Akt3) phosphorylates Argonaute 2 (Ago2) at Ser387 which down-regulates cleavage and up-regulates translational repression of endogenous microRNA (miRNA)-targeted mRNAs. We further demonstrate that Akt3 co-immunoprecipitates with Ago2 and that phosphorylation of Ago2 at Ser387 facilitates its interaction with GW182 and localization to cytoplasmic P-bodies, where miRNA-targeted mRNAs are thought to be stored and degraded. Therefore, Akt3-mediated phosphorylation of Ago2 is a molecular switch between target mRNA cleavage and translational repression activities of Ago2.

Loss of the NF1 tumor suppressor gene causes the autosomal dominant condition, neurofibromatosis type 1 (NF1). Children and adults with NF1 suffer from pathologies including benign and malignant tumors to cognitive deficits, seizures, growth abnormalities, and peripheral neuropathies. NF1 encodes neurofibromin, a Ras-GTPase activating protein, and NF1 mutations result in hyperactivated Ras signaling in patients. Existing NF1 mutant mice mimic individual aspects of NF1, but none comprehensively models the disease. We describe a potentially novel Yucatan miniswine model bearing a heterozygotic mutation in NF1 (exon 42 deletion) orthologous to a mutation found in NF1 patients. NF1+/ex42del miniswine phenocopy the wide range of manifestations seen in NF1 patients, including café au lait spots, neurofibromas, axillary freckling, and neurological defects in learning and memory. Molecular analyses verified reduced neurofibromin expression in swine NF1+/ex42del fibroblasts, as well as hyperactivation of Ras, as measured by increased expression of its downstream effectors, phosphorylated ERK1/2, SIAH, and the checkpoint regulators p53 and p21. Consistent with altered pain signaling in NF1, dysregulation of calcium and sodium channels was observed in dorsal root ganglia expressing mutant NF1. Thus, these NF1+/ex42del miniswine recapitulate the disease and provide a unique, much-needed tool to advance the study and treatment of NF1.

Histone demethylase PHF8 is upregulated and plays oncogenic roles in various cancers; however, the mechanisms underlying its dysregulation and functions in carcinogenesis remain obscure. Here, we report the novel functions of PHF8 in EMT (epithelial to mesenchymal transition) and breast cancer development. Genome-wide gene expression analysis revealed that PHF8 overexpression induces an EMT-like process, including the upregulation of SNAI1 and ZEB1. PHF8 demethylates H3K9me1, H3K9me2 and sustains H3K4me3 to prime the transcriptional activation of SNAI1 by TGF-β signaling. We show that PHF8 is upregulated and positively correlated with MYC at protein levels in breast cancer. MYC post-transcriptionally regulates the expression of PHF8 via the repression of microRNAs. Specifically, miR-22 directly targets and inhibits PHF8 expression, and mediates the regulation of PHF8 by MYC and TGF-β signaling. This novel MYC/microRNAs/PHF8 regulatory axis thus places PHF8 as an important downstream effector of MYC. Indeed, PHF8 contributes to MYC-induced cell proliferation and the expression of EMT-related genes. We also report that PHF8 plays important roles in breast cancer cell migration and tumor growth. These oncogenic functions of PHF8 in breast cancer confer its candidacy as a promising therapeutic target for this disease.

Conflict of interest: The Icahn School of Medicine has filed patents covering composition of matter on the small molecules disclosed herein for the treatment of human cancer and other diseases and for methods of use for using these small-molecule PP2A activators (patent no. 9,937,186 B2). RAPPTA Therapeutics LLC has optioned this intellectual property for the clinical and commercial development of this series of small-molecule PP2A activators. GN has an ownership interest in RAPPTA Therapeutics LLC.

◥Purpose: Pancreatic neuroendocrine tumors (pNETs) are uncommon malignancies noted for their propensity to metastasize and comparatively favorable prognosis. Although both the treatment options and clinical outcomes have improved in the past decades, most patients will die of metastatic disease. New systemic therapies are needed.Experimental Design: Tissues were obtained from 43 patients with well-differentiated pNETs undergoing surgery. Gene expression was compared between primary tumors versus liver and lymph node metastases using RNA-Seq. Genes that were selectively elevated at only one metastatic site were filtered out to reduce tissue-specific effects. Ingenuity pathway analysis (IPA) and the Connectivity Map (CMap) identified drugs likely to antagonize metastasis-specific targets. The biological activity of top identified agents was tested in vitro using two pNET cell lines (BON-1 and QGP-1).Results: A total of 902 genes were differentially expressed in pNET metastases compared with primary tumors, 626 of which remained in the common metastatic profile after filtering. Analysis with IPA and CMap revealed altered activity of factors involved in survival and proliferation, and identified drugs targeting those pathways, including inhibitors of mTOR, PI3K, MEK, TOP2A, protein kinase C, NF-kB, cyclin-dependent kinase, and histone deacetylase. Inhibitors of MEK and TOP2A were consistently the most active compounds.Conclusions: We employed a complementary bioinformatics approach to identify novel therapeutics for pNETs by analyzing gene expression in metastatic tumors. The potential utility of these drugs was confirmed by in vitro cytotoxicity assays, suggesting drugs targeting MEK and TOP2A may be highly efficacious against metastatic pNETs. This is a promising strategy for discovering more effective treatments for patients with pNETs.