In the hematopoietic compartment, the CD13/APN metalloprotease is one of the earliest markers of cells committed to the myeloid lineage where it is expressed exclusively on the surface of myeloid progenitors and their differentiated progeny. CD13/APN is also found in nonhematopoietic tissues, and its novel expression on the endothelial cells of angiogenic, but not normal, vasculature was recently IntroductionAngiogenesis refers to the formation of new blood vessels from the existing vasculature and occurs at extremely low levels in the adult organism. One notable exception to this paradigm occurs in tumors that have undergone the "angiogenic switch" from a benign to a metastatic phenotype, in which new vessels are actively assembled and directly responsible for the sustained growth and dissemination of the tumor. 1 It is clear that the modulation of blood vessel growth is a remarkably effective means to limit or control tumor growth and spread, and therefore, the search for unique targets modulating angiogenesis is of significant importance.Recent studies designed to identify unique peptides that home specifically to solid tumors in murine breast carcinoma models revealed that the NGR motif binds strictly to the endothelium of angiogenic blood vessels. 2 Further investigation identified the CD13/APN cell-surface antigen as the principal receptor for this peptide motif and demonstrated that this protein is expressed exclusively on the endothelial cells of angiogenic but not normal vasculature, 3 thereby explaining the tumorspecific destination of the NGR peptide. CD13/APN was originally described in studies seeking to identify lineage-specific markers that would facilitate the classification of human leukemias. 4 In this regard, the appearance of CD13 coincides with commitment to the myeloid lineage and is exclusively expressed on the normal and leukemic progeny of myeloid cells within the hematopoietic compartment. The subsequent molecular cloning of the gene encoding this cell surface glycoprotein identified it as the membrane-bound metalloprotease, aminopeptidase N (APN, EC 3.4.11.2), thus extending its known range of expression beyond the hematopoietic system to include fibroblasts and epithelial cells in the liver, intestine, brain, and lung. 5 CD13/APN cleaves amino terminal residues from short peptides, and consequently, its specific function in individual tissues (primarily the activation or inactivation of small bioactive molecules) is mandated by available substrates (reviewed in Shipp and Look 6 ). Insights into the function of this unique vascular marker in angiogenesis were gained through experiments in which treatment of animals with CD13/APN functional inhibitors significantly arrested retinal neovascularization, chorioallantoic membrane angiogenesis, and xenograft tumor growth, indicating that CD13/ APN plays an important role in the progression of tumor vasculogenesis and identifying it as a critical regulator of angiogenesis. 3 Therefore, understanding the mechanisms regulating the expression o...

Cytochrome P4501A1 is a hepatic, microsomal membrane–bound enzyme that is highly induced by various xenobiotic agents. Two NH2-terminal truncated forms of this P450, termed P450MT2a and MT2b, are also found localized in mitochondria from β-naphthoflavone–induced livers. In this paper, we demonstrate that P4501A1 has a chimeric NH2-terminal signal that facilitates the targeting of the protein to both the ER and mitochondria. The NH2-terminal 30–amino acid stretch of P4501A1 is thought to provide signals for ER membrane insertion and also stop transfer. The present study provides evidence that a sequence motif immediately COOH-terminal (residues 33–44) to the transmembrane domain functions as a mitochondrial targeting signal under both in vivo and in vitro conditions, and that the positively charged residues at positions 34 and 39 are critical for mitochondrial targeting. Results suggest that 25% of P4501A1 nascent chains, which escape ER membrane insertion, are processed by a liver cytosolic endoprotease. We postulate that the NH2-terminal proteolytic cleavage activates a cryptic mitochondrial targeting signal. Immunofluorescence microscopy showed that a portion of transiently expressed P4501A1 is colocalized with the mitochondrial-specific marker protein cytochrome oxidase subunit I. The mitochondrial-associated MT2a and MT2b are localized within the inner membrane compartment, as tested by resistance to limited proteolysis in both intact mitochondria and mitoplasts. Our results therefore describe a novel mechanism whereby proteins with chimeric signal sequence are targeted to the ER as well as to the mitochondria.

The phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway is frequently activated in human cancers, and mTOR is a clinically validated target. mTOR forms two distinct multiprotein complexes, mTORC1 and mTORC2, which regulate cell growth, metabolism, proliferation, and survival. Rapamycin and its analogues partially inhibit mTOR through allosteric binding to mTORC1, but not mTORC2, and have shown clinical utility in certain cancers. Here, we report the preclinical characterization of OSI-027, a selective and potent dual inhibitor of mTORC1 and mTORC2 with biochemical IC 50 values of 22 nmol/L and 65 nmol/L, respectively. OSI-027 shows more than 100-fold selectivity for mTOR relative to PI3Ka, PI3Kb, PI3Kg, and DNA-PK. OSI-027 inhibits phosphorylation of the mTORC1 substrates 4E-BP1 and S6K1 as well as the mTORC2 substrate AKT in diverse cancer models in vitro and in vivo. OSI-027 and OXA-01 (close analogue of OSI-027) potently inhibit proliferation of several rapamycin-sensitive and -insensitive nonengineered and engineered cancer cell lines and also, induce cell death in tumor cell lines with activated PI3K-AKT signaling.

The Cancer Genome Atlas (TCGA) projects have advanced our understanding of the driver mutations, genetic backgrounds, and key pathways activated across cancer types. Analysis of TCGA datasets have mostly focused on somatic mutations and translocations, with less emphasis placed on gene amplifications. Here we describe a bioinformatics screening strategy to identify putative cancer driver genes amplified across TCGA datasets. We carried out GISTIC2 analysis of TCGA datasets spanning 14 cancer subtypes and identified 461 genes that were amplified in two or more datasets. The list was narrowed to 73 cancer-associated genes with potential “druggable” properties. The majority of the genes were localized to 14 amplicons spread across the genome. To identify potential cancer driver genes, we analyzed gene copy number and mRNA expression data from individual patient samples and identified 40 putative cancer driver genes linked to diverse oncogenic processes. Oncogenic activity was further validated by siRNA/shRNA knockdown and by referencing the Project Achilles datasets. The amplified genes represented a number of gene families, including epigenetic regulators, cell cycle-associated genes, DNA damage response/repair genes, metabolic regulators, and genes linked to the Wnt, Notch, Hedgehog, JAK/STAT, NF-KB and MAPK signaling pathways. Among the 40 putative driver genes were known driver genes, such as EGFR, ERBB2 and PIK3CA. Wild-type KRAS was amplified in several cancer types, and KRAS-amplified cancer cell lines were most sensitive to KRAS shRNA, suggesting that KRAS amplification was an independent oncogenic event. A number of MAP kinase adapters were co-amplified with their receptor tyrosine kinases, such as the FGFR adapter FRS2 and the EGFR family adapter GRB7. The ubiquitin-like ligase DCUN1D1 and the histone methyltransferase NSD3 were also identified as novel putative cancer driver genes. We discuss the patient tailoring implications for existing cancer drug targets and we further discuss potential novel opportunities for drug discovery efforts.

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IntroductionAngiogenesis is functionally defined as the sprouting of new vessels from pre-existing vasculature and consists of several distinct stages including endothelial cell proliferation, migration, invasion, differentiation into capillaries, and eventual maturation into blood vessels 1,2 This process is initiated and maintained in part by interactions of specific angiogenic growth factors with their receptors and the subsequent triggering of signaling pathways and gene expression programs essential for angiogenic progression. The activation of fundamentally dormant vascular endothelium is a sequentially regulated process activated by a shift in equilibrium between proand antiangiogenic mediators. 2,3 A change in the balance of angiogenic inducers to angiogenic inhibitors is capable of initiating an intracellular sequence culminating in new vessel formation. For endothelial cell activation, the Ras pathway is pivotal for coordinating and transducing multiple angiogenic signals. [4][5][6][7][8][9][10] Accordingly, the downstream targets of Ras inevitably assume major roles in the induction and maintenance of the angiogenic phenotype.CD13/aminopeptidase N (CD13/APN) is a type II membranebound metalloprotease that is expressed on the endothelial cells of angiogenic, but not normal, vasculature. 11 Importantly, treatment of animals bearing breast carcinoma xenografts with CD13/APN functional inhibitors significantly impaired tumor growth, indicating that CD13/APN plays a functional role in tumorigenesis. 11 Further investigation into the mechanisms regulating the activated endothelial cell-specific expression of CD13/APN showed that hypoxia, angiogenic growth factors, and signals mediating capillary network formation potently induce CD13/APN transcription in primary endothelial cells and tumor xenografts. 12 Finally, capillary network formation is significantly inhibited by treatment of endothelial cells with inhibitory anti-CD13/APN monoclonal antibodies or functional inhibitors of CD13/APN, thus identifying this metallopeptidase as essential for later stages of neovascular formation and as an important angiogenic activator. 12 The aim of the present study was to investigate the signaling pathways that regulate CD13/APN expression in response to angiogenic stimulation. In this report we provide evidence that CD13/APN is a transcriptional target of 2 Ras-mediated signaling pathways that have been implicated in the switch from quiescent to activated endothelium: Ras/mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI-3K). 13 Importantly, addition of functional CD13/APN is sufficient to restore arrested endothelial migration and morphogenesis in vitro and cell migration and angiogenesis in vivo resulting from inhibition of Ras/ MAPK or PI-3K mediated signaling. Our data indicate that The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 U.S.C. s...

SUMMARY We address whether combinations with a pan-RAF inhibitor (RAFi) would be effective in KRAS mutant pancreatic ductal adenocarcinoma (PDAC). Chemical library and CRISPR genetic screens identify combinations causing apoptotic anti-tumor activity. The most potent combination, concurrent inhibition of RAF (RAFi) and ERK (ERKi), is highly synergistic at low doses in cell line, organoid, and rat models of PDAC, whereas each inhibitor alone is only cytostatic. Comprehensive mechanistic signaling studies using reverse phase protein array (RPPA) pathway mapping and RNA sequencing (RNA-seq) show that RAFi/ERKi induced insensitivity to loss of negative feedback and system failures including loss of ERK signaling, FOSL1 , and MYC; shutdown of the MYC transcriptome; and induction of mesenchymal-to-epithelial transition. We conclude that low-dose vertical inhibition of the RAF-MEK-ERK cascade is an effective therapeutic strategy for KRAS mutant PDAC.

The biochemical and molecular characteristics of cytochrome P4501A1 targeted to rat brain mitochondria was studied to determine the generality of the targeting mechanism previously described for mitochondrial cytochrome P450MT2 (P450MT2) from rat liver. In rat brain and C6 glioma cells chronically exposed to ␤-naphoflavone (BNF), P450MT2 content reached 50 and 95% of the total cellular pool, respectively. P450MT2 from 10 days of BNF-treated rat brain was purified to over 85% purity using hydrophobic chromatography followed by adrenodoxin affinity binding. Purified brain P450MT2 consisted of two distinct molecular species with NH 2 termini identical to liver mitochondrial forms. These results confirm the specificity of endoprotease-processing sites. The purified P450MT2 showed a preference for adrenodoxin ؉ adrenodoxin reductase electron donor system and exhibited high erythromycin N-demethylation activity. Brain mitoplasts from 10-day BNF-treated rats and also purified P450MT2 exhibited high N-demethylation activities for a number of neuroactive drugs, including trycyclic anti-depressants, anti-convulsants, and opiates. At 10 days of BNF treatment, the mitochondrial metabolism of these neuroactive drugs represented about 85% of the total tissue activity. These results provide new insights on the role of P450MT2 in modulating the pharmacological potencies of different neuroactive drugs in chronically exposed individuals.Cytochrome P450 (P450) 1 enzymes play a critical role in the metabolism of an array of endogenous as well as exogenous substrates (1-3). The xenobiotic inducible forms with roles in the metabolism of carcinogens, pollutants, and drugs were thought to be exclusively associated with the endoplasmic reticulum (hereafter referred to as microsomes) of liver, brain, and other tissues. In contrast to this general belief, recent reports from our laboratory showed that the BNF-inducible P4501A1 and phenobarbital-inducible P4502B1 are also targeted to mitochondria under both in vitro and in vivo cell transfection conditions. These results are consistent with previous studies from our, as well as, other laboratories showing the presence of P450 proteins cross-reacting with antibodies to the major microsomal forms, in liver and brain mitochondria from inducer treated and untreated rats, and also insects (4 -10). Direct sequencing of hepatic mitochondrial P450 proteins purified from BNF-treated rats suggested the occurrence of two forms of P450MT2, both of which were NH 2 -terminal cleaved versions of P4501A1 (11). The molecular form cleaved past the 4th amino acid residue (ϩ5/1A1) represents a minor component while that cleaved past residue 32 (ϩ33/1A1) represents the major component in mitochondria from BNF-treated rat liver. This major form will be routinely referred to as P450MT2 throughout this paper.The mitochondrial targeted P450MT2 exhibited many molecular and biochemical properties distinct from the parent microsomal P4501A1 (12): 1) P450MT2 interacted with Adx with an affinity of 0.6 M K d , 2) funct...