Although recent studies have shown that adenosine-to-inosine (A-to-I) RNA editing occurs in microRNAs, its effects on tumor growth and metastasis are not well understood. We present evidence of CREB-mediated low expression of ADAR1 in metastatic melanoma cell lines and tumor specimens. Re-expression of ADAR1 resulted in the suppression of melanoma growth and metastasis in vivo. Consequently, we identified 3 miRs undergoing A-to-I editing in the low-metastatic melanoma but not in highly metastatic cell lines. One of these miRs, miR-455-5p has two A-to-I RNA editing sites. The biological function of edited miR-455-5p is different from the unedited form as it recognizes different set of genes. Indeed, w.t. miR-455-5p promotes melanoma metastasis via inhibition of the tumor suppressor gene CPEB1. Moreover, w.t. miR-455 enhances melanoma growth and metastasis in vivo while the edited form inhibits these features. These results demonstrate a previously unrecognized role of RNA editing in melanoma progression.

Prostate cancer antigen 3 (PCA3) is the most specific prostate cancer biomarker but its function remains unknown. Here we identify PRUNE2, a target protein-coding gene variant, which harbors the PCA3 locus, thereby classifying PCA3 as an antisense intronic long noncoding (lnc)RNA. We show that PCA3 controls PRUNE2 levels via a unique regulatory mechanism involving formation of a PRUNE2/PCA3 double-stranded RNA that undergoes adenosine deaminase acting on RNA (ADAR)-dependent adenosine-to-inosine RNA editing. PRUNE2 expression or silencing in prostate cancer cells decreased and increased cell proliferation, respectively. Moreover, PRUNE2 and PCA3 elicited opposite effects on tumor growth in immunodeficient tumor-bearing mice. Coregulation and RNA editing of PRUNE2 and PCA3 were confirmed in human prostate cancer specimens, supporting the medical relevance of our findings. These results establish PCA3 as a dominant-negative oncogene and PRUNE2 as an unrecognized tumor suppressor gene in human prostate cancer, and their regulatory axis represents a unique molecular target for diagnostic and therapeutic intervention.S everal lines of evidence demonstrate that long noncoding RNAs (lncRNAs) are functional in carcinogenesis through regulatory mechanisms such as promoter looping, alternative splicing, antisense gene silencing, transcriptional regulation, and DNA repair, thus potentially serving as tumor markers. A few lncRNA species have emerged as potential prostate cancer biomarkers such as prostate cancer gene expression marker-1 (PCGEM1) and prostate cancer noncoding RNA1 (PRNCR1), which enhance androgen receptor (AR)-dependent gene activation, and prostate cancer-associated ncRNA transcript-1 (PCAT1), which silences BRCA2 via posttranscriptional homologous recombination (1). Notably, the most specific biomarker in human prostate cancer identified to date is an lncRNA, prostate cancer antigen 3 (PCA3, also known as PCA3 DD3 or DD3 PCA3 ), which is up-regulated in human prostate cancer (2). Since its discovery more than 15 y ago, PCA3 has been extensively investigated (3) and has been approved for clinical applications to aid the diagnosis of prostate cancer in both the European Union and the United States. Paradoxically-despite its striking clinical specificity-the inherent cellular role of the lncRNA PCA3 in human prostate cancer, if any, remains completely unknown (1). Here we report a unique biological function for PCA3. Within a single functional genetic unit, we show that PCA3 is an antisense intronic lncRNA that down-regulates an as yet unrecognized tumor suppressor gene, a human homolog of the Drosophila prune gene, PRUNE2, through a process that involves RNA editing mediated by a supramolecular complex containing adenosine deaminase acting on RNA (ADAR) family members. We propose a working model in which PCA3 acts as a dominant-negative oncogene in prostate cancer and show consistent results in therapeutic preclinical models and in patient-derived human samples. Therefore, the molecular interaction of PRUNE2...

Vascular endothelial growth factor receptor-3 (VEGFR-3) plays a key role for the remodeling of the primary capillary plexus in the embryo and contributes to angiogenesis and lymphangiogenesis in the adult. However, VEGFR-3 signal transduction pathways remain to be elucidated. Here we investigated VEGFR-3 signaling in primary human umbilical vein endothelial cells (HUVECs) by the systematic mutation of the tyrosine residues potentially involved in VEGFR-3 signaling and identified the tyrosines critical for its function. Y1068 was shown to be essential for the kinase activity of the receptor. Y1063 signals the receptor-mediated survival by recruiting CRKI/II to the activated receptor, inducing a signaling cascade that, via mitogen-activated protein kinase kinase-4 (MKK4), activates c-Jun N-terminal kinase-1/2 (JNK1/2). Inhibition of JNK1/2 function either by specific peptide inhibitor JNKI1 or by RNA interference (RNAi) demonstrated that activation of JNK1/2 is required for a VEGFR-3-dependent prosurvival signaling. Y1230/Y1231 contributes, together with Y1337, to proliferation, migration, and survival of endothelial cells.Phospho-Y1230/Y1231 directly recruits growth factor receptor-bonus protein (GRB2) to the receptor, inducing the activation of both AKT and extracellular signal-related kinase 1/2 (ERK1/2) signaling. IntroductionVascular endothelial growth factor receptor-1 (VEGFR-1) (also known as Flt-1), VEGFR-2 (also known as KDR/Flk-1), and VEGFR-3 (also known as Flt-4) play a central role in vasculogenesis and angiogenesis. 1,2 They are activated by the family of angiogenic factors that is composed of several members with partially overlapping function due to the promiscuity of receptor recognition. Placental growth factor (PlGF) and vascular endothelial growth factor-B (VEGF-B) recognize VEGFR-1, VEGF is the ligand of both VEGFR-1 and VEGFR-2, while VEGF-C and VEGF-D each recognize and activate VEGFR-2 and VEGFR-3. These receptors are highly related, with an extracellular ligand binding site containing 7 immunoglobulin-homology segments, a single polypeptide chain transmembrane sequence, and an interrupted intracellular tyrosine kinase domain. Gene disruption experiments demonstrated that each of these receptors is essential for vascular development and angiogenesis. 2 Both VEGFR-1 and VEGFR-2 act early during endothelial differentiation although with different functions: while Vegfr-1 Ϫ/Ϫ embryos die for excessive endothelial proliferation, Vegfr-2 Ϫ/Ϫ die with no endothelial or hematopoietic cells. 3,4 The absence of Vegfr-3 does not impair the differentiation of endothelial cells or the formation of the primary vascular plexus; rather, it affects the remodeling of the primary vascular network. 5 In adults, VEGFR-3 is expressed mainly in lymphatic endothelial cells. 6,7 VEGFR-3 is also expressed in quiescent endothelial cells of fenestrated capillaries and microvessels of several tissues. [8][9][10] It is transiently induced in vessels undergoing active angiogenesis during wound healing and in tumors. [1...

Processes that promote cancer progression such as angiogenesis require a functional interplay between malignant and nonmalignant cells in the tumor microenvironment. The metalloprotease aminopeptidase N (APN; CD13) is often overexpressed in tumor cells and has been implicated in angiogenesis and cancer progression. Our previous studies of APN-null mice revealed impaired neoangiogenesis in model systems without cancer cells and suggested the hypothesis that APN expressed by nonmalignant cells might promote tumor growth. We tested this hypothesis by comparing the effects of APN deficiency in allografted malignant (tumor) and nonmalignant (host) cells on tumor growth and metastasis in APNnull mice. In two independent tumor graft models, APN activity in both the tumors and the host cells cooperate to promote tumor vascularization and growth. Loss of APN expression by the host and/ or the malignant cells also impaired lung metastasis in experimental mouse models. Thus, cooperation in APN expression by both cancer cells and nonmalignant stromal cells within the tumor microenvironment promotes angiogenesis, tumor growth, and metastasis.lung cancer | melanoma | proteolytic activity | shRNA | tumorigenesis A minopeptidase N (APN, CD13; EC 3.4.11.2) is a widely expressed type II membrane-bound metalloprotease (1, 2). It functions in the enzymatic cleavage of peptides, in endocytosis, and as a signaling molecule and has been implicated in the regulation of complex and diverse processes, including cell migration, cell survival, viral uptake, and angiogenesis (3). APN has also been linked specifically to cancer, having been identified as a cellsurface marker for malignant myeloid cells (4-7) and reaching high levels of expression in association with the progression of tumors, including breast, ovarian, and prostate cancer (8-14). Indeed, vascular endothelial growth factor (VEGF), a key angiogenesis regulator, induces the expression of APN at an early stage of tumor growth (15), again highlighting the role of this enzyme in angiogenesis, a process crucial for sustained growth of most solid tumors (16). Studies of bestatin, a CD13 inhibitor and antiangiogenic agent, also suggest that APN enzymatic activity is relevant for tumorigenesis (17,18). Nevertheless, the substrates of APN in the context of angiogenesis are still unknown. The only well-defined substrate is angiotensin III in the renin-angiotensin pathway, in which APN cleaves the NH 2 -terminal arginine residue of angiotensin III to form angiotensin IV. Consistent with several lines of evidence, we have previously identified APN as a target for inhibition of tumor vascularization and growth (18)(19)(20).Tumor growth relies on a complex microenvironment in which malignant cells cooperate with various other cell types: endothelial cells of the blood and lymphatic circulation, mesenchymal stromal cells/cancer-associated fibroblasts, and a variety of bone marrow-derived cells such as myeloid-derived suppressor cells and lymphocytes (21, 22). Some of these cell populations c...