The RNA secondary structure of androgen receptor-FL and V7 transcripts reveals novel regulatory regions.

The androgen receptor (AR) is a ligand-dependent nuclear transcription factor belonging to the steroid hormone nuclear receptor family. Due to its roles in regulating cell proliferation and differentiation, AR is tightly regulated to maintain proper levels of itself and the many genes it controls. AR dysregulation is a driver of many human diseases including prostate cancer. Though this dysregulation often occurs at the RNA level, there are many unknowns surrounding post-transcriptional regulation of AR mRNA, particularly the role that RNA secondary structure plays. Thus, a comprehensive analysis of AR transcript secondary structure is needed. We address this through the computational and experimental analyses of two key isoforms, full length (AR-FL) and truncated (AR-V7). Here, a combination of in-cell RNA secondary structure probing experiments (targeted DMS-MaPseq) and computational predictions were used to characterize the static structural landscape and conformational dynamics of both isoforms. Additionally, in-cell assays were used to identify functionally relevant structures in the 5' and 3' UTRs of AR-FL. A notable example is a conserved stem loop structure in the 5'UTR of AR-FL that can bind to Poly(RC) Binding Protein 2 (PCBP2). Taken together, our results reveal novel features that regulate AR expression.

Identification of MYC intron 2 regions that modulate expression.

MYC pre-mRNA is spliced with high fidelity to produce the transcription factor known to regulate cellular differentiation, proliferation, apoptosis, and alternative splicing. The mechanisms underpinning the pre-mRNA splicing of MYC, however, remain mostly unexplored. In this study, we examined the interaction of heterogeneous nuclear ribonucleoprotein C (HNRNPC) with MYC intron 2. Building off published eCLIP studies, we confirmed this interaction with poly(U) regions in intron 2 of MYC and found that full binding is correlated with optimal protein production. The interaction appears to be compensatory, as mutational disruption of all three poly(U) regions was required to reduce both HNRNPC binding capacity and fidelity of either splicing or translation. Poly(U) sequences in MYC intron 2 were relatively conserved across sequences from several different species. Lastly, we identified a short sequence just upstream of an HNRNPC binding region that when removed enhances MYC translation.

Discovery of RNA secondary structural motifs using sequence-ordered thermodynamic stability and comparative sequence analysis.

Major advances in RNA secondary structural motif prediction have been achieved in the last few years; however, few methods harness the predictive power of multiple approaches to deliver in-depth characterizations of local RNA motifs and their potential functionality. Additionally, most available methods do not predict RNA pseudoknots. This work combines complementary bioinformatic systems into one robust discovery pipeline where: •RNA sequences are folded to search for thermodynamically favorable motifs utilizing ScanFold.•Motifs are expanded and refolded into alternate pseudoknot conformations by Knotty/Iterative HFold.•All conformations are evaluated for covariance via the cm-builder pipeline (Infernal and R-scape).

Analyses of human cancer driver genes uncovers evolutionarily conserved RNA structural elements involved in posttranscriptional control.

Experimental breakthroughs have provided unprecedented insights into the genes involved in cancer. The identification of such cancer driver genes is a major step in gaining a fuller understanding of oncogenesis and provides novel lists of potential therapeutic targets. A key area that requires additional study is the posttranscriptional control mechanisms at work in cancer driver genes. This is important not only for basic insights into the biology of cancer, but also to advance new therapeutic modalities that target RNA-an emerging field with great promise toward the treatment of various cancers. In the current study we performed an in silico analysis on the transcripts associated with 800 cancer driver genes (10,390 unique transcripts) that identified 179,190 secondary structural motifs with evidence of evolutionarily ordered structures with unusual thermodynamic stability. Narrowing to one transcript per gene, 35,426 predicted structures were subjected to phylogenetic comparisons of sequence and structural conservation. This identified 7,001 RNA secondary structures embedded in transcripts with evidence of covariation between paired sites, supporting structure models and suggesting functional significance. A select set of seven structures were tested in vitro for their ability to regulate gene expression; all were found to have significant effects. These results indicate potentially widespread roles for RNA structure in posttranscriptional control of human cancer driver genes.

A map of the SARS-CoV-2 RNA structurome.

SARS-CoV-2 has exploded throughout the human population. To facilitate efforts to gain insights into SARS-CoV-2 biology and to target the virus therapeutically, it is essential to have a roadmap of likely functional regions embedded in its RNA genome. In this report, we used a bioinformatics approach, ScanFold, to deduce the local RNA structural landscape of the SARS-CoV-2 genome with the highest likelihood of being functional. We recapitulate previously-known elements of RNA structure and provide a model for the folding of an essential frameshift signal. Our results find that SARS-CoV-2 is greatly enriched in unusually stable and likely evolutionarily ordered RNA structure, which provides a large reservoir of potential drug targets for RNA-binding small molecules. Results are enhanced via the re-analyses of publicly-available genome-wide biochemical structure probing datasets that are broadly in agreement with our models. Additionally, ScanFold was updated to incorporate experimental data as constraints in the analysis to facilitate comparisons between ScanFold and other RNA modelling approaches. Ultimately, ScanFold was able to identify eight highly structured/conserved motifs in SARS-CoV-2 that agree with experimental data, without explicitly using these data. All results are made available via a public database (the RNAStructuromeDB: https://structurome.bb.iastate.edu/sars-cov-2) and model comparisons are readily viewable at https://structurome.bb.iastate.edu/sars-cov-2-global-model-comparisons.

Differential expression analysis comparing EBV uninfected to infected human cell lines identifies induced non-micro small non-coding RNAs.

Epstein-Barr virus (EBV) is a ubiquitous human herpes virus, which is implicated in cancer and various autoimmune diseases. This study profiles non-micro small non-coding RNA expression changes induced by latent EBV infection. Using small RNA-Seq, 346 non-micro small RNAs were identified as being significantly differentially expressed between EBV(+) BJAB-B1 and EBV(-) BJAB cell lines. Select small RNA expression changes were experimentally validated in the BJAB-B1 cell line as well as the EBV-infected Raji and Jijoye cell lines. This latter analysis recapitulated the previously identified induction of vault RNA1, while also finding novel evidence for the deregulation of several tRNAs and a snoRNA.

RNA structural analysis of the MYC mRNA reveals conserved motifs that affect gene expression.

The MYC gene encodes a human transcription factor and proto-oncogene that is dysregulated in over half of all known cancers. To better understand potential post-transcriptional regulatory features affecting MYC expression, we analyzed secondary structures in the MYC mRNA using a program that is optimized for finding small locally-folded motifs with a high propensity for function. This was accomplished by calculating folding metrics across the MYC sequence using a sliding analysis window and generating unique consensus base pairing models weighted by their lower-than-random predicted folding energy. A series of 30 motifs were identified, primarily in the 5' and 3' untranslated regions, which show evidence of structural conservation and compensating mutations across vertebrate MYC homologs. This analysis was able to recapitulate known elements found within an internal ribosomal entry site, as well as discover a novel element in the 3' UTR that is unusually stable and conserved. This novel motif was shown to affect MYC expression, potentially via the modulation of miRNA target accessibility or other trans-regulatory factors. In addition to providing basic insights into mechanisms that regulate MYC expression, this study provides numerous, potentially druggable RNA targets for the MYC gene, which is considered "undruggable" at the protein level.

Preclinical activity of DCZ3301, a novel aryl-guanidino compound in the therapy of multiple myeloma.

We synthesized a novel aryl-guanidino compound, DCZ3301, and found that it has potent cytotoxicity against multiple human cancer cell lines. The anticancer activity was most potent against multiple myeloma (MM). DCZ3301 induced cytotoxicity in MM cell lines, as well as patient myeloma cells, in part by decreasing mitochondrial membrane potential to induce apoptosis. In contrast, DCZ3301 had no cytotoxic effect on normal cells. DCZ3301 also inhibited cell cycling and caused a G2/M accumulation that corresponded with downregulation of Cdc25C, CDK1, and Cyclin B1. DCZ3301 retained its activity against MM cells in the presence of exogenous cytokines (IL-6 or VEGF) or bone marrow stromal cells (BMSCs) and reduced activity of multiple signaling pathways (STAT3, NFκB, AKT, ERK1/2) in MM but not normal cells. The STAT3 pathway played an important role in modulating DCZ3301-mediated cytotoxicity. Knockdown of STAT3 using siRNA in MM cells enhanced DCZ3301-induced cytotoxicity, whereas overexpression of STAT3 in MM cells partially protected them from apoptosis. In addition, DCZ3301 inhibited VEGF and IL-6 secretion in a dose-dependent fashion in a co-culture of MM cells and BMSCs. Combining DCZ3301 with bortezomib induced synergistic cytotoxicity in MM cell lines and primary MM cells. Finally, in vivo efficacy of DCZ3301 was confirmed in an MM xenograft mouse model. Together, these results provide a rationale for translation of this small-molecule inhibitor, either alone or in combination, to the clinic against MM.

PIAS1 Promotes Lymphomagenesis through MYC Upregulation.

The MYC proto-oncogene is a transcription factor implicated in a broad range of cancers. MYC is regulated by several post-translational modifications including SUMOylation, but the functional impact of this post-translational modification is still unclear. Here, we report that the SUMO E3 ligase PIAS1 SUMOylates MYC. We demonstrate that PIAS1 promotes, in a SUMOylation-dependent manner, MYC phosphorylation at serine 62 and dephosphorylation at threonine 58. These events reduce the MYC turnover, leading to increased transcriptional activity. Furthermore, we find that MYC is SUMOylated in primary B cell lymphomas and that PIAS1 is required for the viability of MYC-dependent B cell lymphoma cells as well as several cancer cell lines of epithelial origin. Finally, Pias1-null mice display endothelial defects reminiscent of Myc-null mice. Taken together, these results indicate that PIAS1 is a positive regulator of MYC.

CDKN1A and FANCD2 are potential oncotargets in Burkitt lymphoma and multiple myeloma.

BACKGROUND: Comparative genetic and biological studies on malignant tumor counterparts in human beings and laboratory mice may be powerful gene discovery tools for blood cancers, including neoplasms of mature B-lymphocytes and plasma cells such as Burkitt lymphoma (BL) and multiple myeloma (MM). METHODS: We used EMSA to detect constitutive NF-κB/STAT3 activity in BL- and MM-like neoplasms that spontaneously developed in single-transgenic IL6 (interleukin-6) or MYC (c-Myc) mice, or in double-transgenic IL6MYC mice. qPCR measurements and analysis of clinical BL and MM datasets were employed to validate candidate NF-κB/STAT3 target genes. RESULTS: qPCR demonstrated that IL6- and/or MYC-dependent neoplasms in mice invariably contain elevated mRNA levels of the NF-κB target genes, Cdkn1a and Fancd2. Clinical studies on human CDKN1A, which encodes the cell cycle inhibitor and tumor suppressor p21, revealed that high p21 message predicts poor therapy response and survival in BL patients. Similarly, up-regulation of FANCD2, which encodes a key member of the Fanconi anemia and breast cancer pathway of DNA repair, was associated with poor outcome of patients with MM, particularly those with high-risk disease. CONCLUSIONS: Our findings suggest that CDKN1A and FANCD2 are potential oncotargets in BL and MM, respectively. Additionally, the IL-6- and/or MYC-driven mouse models of human BL and MM used in this study may lend themselves to the biological validation of CDKN1A and FANCD2 as molecular targets for new approaches to cancer therapy and prevention.

NIAM-deficient mice are predisposed to the development of proliferative lesions including B-cell lymphomas.

Nuclear Interactor of ARF and Mdm2 (NIAM, gene designation Tbrg1) is a largely unstudied inhibitor of cell proliferation that helps maintain chromosomal stability. It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance. To examine its predicted role as a tumor suppressor, we generated NIAM mutant (NIAM(m/m)) mice homozygous for a ß-galactosidase expressing gene-trap cassette in the endogenous gene. The mutant mice expressed significantly lower levels of NIAM protein in tissues compared to wild-type animals. Fifty percent of aged NIAM deficient mice (14 to 21 months) developed proliferative lesions, including a uterine hemangioma, pulmonary papillary adenoma, and a Harderian gland adenoma. No age-matched wild-type or NIAM(+/m) heterozygous animals developed lesions. In the spleen, NIAM(m/m) mice had prominent white pulp expansion which correlated with enhanced increased reactive lymphoid hyperplasia and evidence of systemic inflammation. Notably, 17% of NIAM mutant mice had splenic white pulp features indicating early B-cell lymphoma. This correlated with selective expansion of marginal zone B cells in the spleens of younger, tumor-free NIAM-deficient mice. Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells. In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers. These mice represent an outstanding platform for dissecting NIAM's role in tumorigenesis and various anti-cancer pathways, including p53 signaling.

Early versus deferred treatment for smoldering multiple myeloma: a meta-analysis of randomized, controlled trials.

PURPOSE: Whether patients with smoldering multiple myeloma (SMM) needed to receive early interventional treatment remains controversial. Herein, we conducted a meta-analysis comparing the efficacy and safety of early treatment over deferred treatment for patients with SMM. METHODS: MEDLINE and Cochrane Library were searched to May 2014 for randomized controlled trials (RCTs) that assessed the effect of early treatment over deferred treatment. Primary outcome measure was mortality, and secondary outcome measures were progression, response rate, and adverse events. RESULTS: Overall, 5 trials including 449 patients were identified. There was a markedly reduced risk of disease progression with early treatment (Odds Ratio [OR] = 0.13, 95% confidence interval [CI] = 0.07 to 0.24). There were no significant differences in mortality and response rate (OR = 0.85, 95% CI = 0.45 to 1.60, and OR = 0.63, 95% CI = 0.32 to 1.23, respectively). More patients in the early treatment arm experienced gastrointestinal toxicities (OR = 10.02, 95%CI = 4.32 to 23.23), constipation (OR = 8.58, 95%CI = 3.20 to 23.00) and fatigue or asthenia (OR = 2.72, 95%CI = 1.30 to 5.67). No significant differences were seen with the development of acute leukemia (OR = 2.80, 95%CI = 0.42 to 18.81), hematologic cancer (OR = 2.07, 95%CI = 0.43 to 10.01), second primary tumors (OR = 3.45, 95%CI = 0.81 to 14.68), nor vertebral compression (OR = 0.18, 95%CI = 0.02 to 1.59). CONCLUSIONS: Early treatment delayed disease progression but increased the risk of gastrointestinal toxicities, constipation and fatigue or asthenia. The differences on vertebral compression, acute leukemia, hematological cancer and second primary tumors were not statistically significant. Based on the current evidence, early treatment didn't significantly affect mortality and response rate. However, further much larger trials were needed to provide more evidence.

Forkhead box M1 regulates quiescence-associated radioresistance of human head and neck squamous carcinoma cells.

Cellular quiescence is a reversible growth arrest in which cells retain their ability to enter into and exit from the proliferative cycle. This study investigates the hypothesis that cell growth-state specific oxidative stress response regulates radiosensitivity of cancer cells. Results showed that quiescent (low proliferative index; >75% G1 phase and lower RNA content) Cal27 and FaDu human head and neck squamous cell carcinoma (HNSCC) are radioresistant compared to proliferating cells. Quiescent cells exhibited a three to tenfold increase in mRNA levels of Mn-superoxide dismutase (MnSOD), dual oxidase 2 (DUOX2) and dual-specificity phosphatase 1 (DUSP1), while mRNA levels of catalase (CAT), peroxiredoxin 3 (PRDX3) and C-C motif ligand 5 (CCL5) were approximately two to threefold lower compared to proliferating cells. mRNA levels of forkhead box M1 (FOXM1) showed the largest decrease in quiescent cells at approximately 18-fold. Surprisingly, radiation treatment resulted in a distinct gene expression pattern that is specific to proliferating and quiescent cells. Specifically, FOXM1 expression increased two to threefold in irradiated quiescent cells, while the same treatment had no net effect on FOXM1 mRNA expression in proliferating cells. RNA interference and pharmacological-based downregulation of FOXM1 abrogated radioresistance of quiescent cells. Furthermore, radioresistance of quiescent cells was associated with an increase in glucose consumption and expression of glucose-6-phosphate dehydrogenase (G6PD). Knockdown of FOXM1 resulted in a significant decrease in G6PD expression, and pharmacological-inhibition of G6PD sensitized quiescent cells to radiation. Taken together, these results suggest that targeting FOXM1 may overcome radioresistance of quiescent HNSCC.

Lenalidomide after stem-cell transplantation for multiple myeloma: a meta-analysis of randomized controlled trials.

The efficacy and safety of lenalidomide maintenance therapy after ASCT in patients with MM has been in question. In order to address the issue, we conducted a meta-analysis of two randomized double-blind placebo-controlled studies encompassing 1074 patients treated with lenalidomide or placebo maintenance therapy after ASCT. The predominant clinical outcomes of interest were overall survival (OS), progression-free survival (PFS), and adverse events. There was a marked benefit in PFS with lenalidomide (Odds Ratio [OR] = 2.5, 95% confidence interval [CI] = 1.93 to 3.24). There was statistically non-significant tendency toward benefit in OS with lenalidomide (OR = 1.21, 95% CI = 0.65 to 2.24). For adverse events, more patients in lenalidomide treatment arm experienced neutropenia (OR = 4.88, 95% CI = 3.67 to 6.50), infection (OR = 2.82, 95% CI = 1.67 to 4.73), hematologic cancers (OR = 3.31, 95% CI = 1.30 to 8.41), and solid tumors (OR = 2.24, 95% CI = 1.01 to 4.98). No significant differences were seen with deep vein thrombosis (OR = 2.15, 95% CI = 0.92 to 5.06), peripheral neuropathy (OR = 1.50, 95% CI = 0.53 to 4.25), thrombocytopenia (OR = 1.05, 95% CI = 0.12 to 9.54), and anemia (OR = 1.36, 95% CI = 0.02 to 83.86). Based on these results, we conclude that lenalidomide maintenance therapy for patients with MM after ASCT was effective in the improvement of PFS. However, treatment-related adverse events must be close monitored. Although there was a trend for increased OS with lenalidomide, there was no statistically significant difference in OS between lenalidomide maintenance therapy arm and placebo maintenance therapy arm. Therefore, longer follow-up and additional high quality RCTs were needed to evaluate the effects of lenalidomide maintenance on OS.

Proteasome inhibitor carfilzomib interacts synergistically with histone deacetylase inhibitor vorinostat in Jurkat T-leukemia cells.

In the present study, we investigated the interactions between proteasome inhibitor carfilzomib (CFZ) and histone deacetylase inhibitor vorinostat in Jurkat T-leukemia cells. Coexposure of cells to minimally lethal concentrations of CFZ with very low concentration of vorinostat resulted in synergistic antiproliferative effects and enhanced apoptosis in Jurkat T-leukemia cells, accompanied with the sharply increased reactive oxygen species (ROS), the striking decrease in the mitochondrial membrane potential (MMP), the increased release of cytochrome c, the enhanced activation of caspase-9 and -3, and the cleavage of PARP. The combined treatment of Jurkat cells pre-treated with ROS scavengers N-acetylcysteine (NAC) significantly blocked the loss of mitochondrial membrane potential, suggesting that ROS generation was a former event of the loss of mitochondrial membrane potential. Furthermore, NAC also resulted in a marked reduction in apoptotic cells, indicating a critical role for increased ROS generation by combined treatment. In addition, combined treatment arrested the cell cycle in G2-M phase. These results imply that CFZ interacted synergistically with vorinostat in Jurkat T-leukemia cells, which raised the possibility that the combination of carfilzomib with vorinostat may represent a novel strategy in treating T-cell Leukemia.

Preclinical validation of interleukin 6 as a therapeutic target in multiple myeloma.

Studies on the biologic and molecular genetic underpinnings of multiple myeloma (MM) have identified the pleiotropic, pro-inflammatory cytokine, interleukin-6 (IL-6), as a factor crucial to the growth, proliferation and survival of myeloma cells. IL-6 is also a potent stimulator of osteoclastogenesis and a sculptor of the tumor microenvironment in the bone marrow of patients with myeloma. This knowledge has engendered considerable interest in targeting IL-6 for therapeutic purposes, using a variety of antibody- and small-molecule-based therapies. However, despite the early recognition of the importance of IL-6 for myeloma and the steady progress in our knowledge of IL-6 in normal and malignant development of plasma cells, additional efforts will be required to translate the promise of IL-6 as a target for new myeloma therapies into significant clinical benefits for patients with myeloma. This review summarizes published research on the role of IL-6 in myeloma development and describes ongoing efforts by the University of Iowa Myeloma Multidisciplinary Oncology Group to develop new approaches to the design and testing of IL-6-targeted therapies and preventions of MM.

Nuclear interactor of ARF and Mdm2 regulates multiple pathways to activate p53.

The p53 tumor suppressor is controlled by an interactive network of factors that stimulate or inhibit its transcriptional activity. Within that network, Mdm2 functions as the major antagonist of p53 by promoting its ubiquitylation and degradation. Conversely, Tip60 activates p53 through direct association on target promoters as well as acetylation of p53 at lysine 120 (K120). This study examines the functional relationship between Mdm2 and Tip60 with a novel p53 regulator, NIAM (nuclear interactor of ARF and Mdm2). Previous work showed NIAM can suppress proliferation and activate p53 independently of ARF, indicating that other factors mediate those activities. Here, we demonstrate that NIAM is a chromatin-associated protein that binds Tip60. NIAM can promote p53 K120 acetylation, although that modification is not required for NIAM to inhibit proliferation or induce p53 transactivation of the p21 promoter. Notably, Tip60 silencing showed it contributes to but is not sufficient for NIAM-mediated p53 activation, suggesting other mechanisms are involved. Indeed, growth-inhibitory forms of NIAM also bind to Mdm2, and increased NIAM expression levels disrupt p53-Mdm2 association, inhibit p53 polyubiquitylation, and prevent Mdm2-mediated inhibition of p53 transcriptional activity. Importantly, loss of NIAM significantly impairs p53 activation. Together, these results show that NIAM activates p53 through multiple mechanisms involving Tip60 association and Mdm2 inhibition. Thus, NIAM regulates 2 critical pathways that control p53 function and are altered in human cancers, implying an important role for NIAM in tumorigenesis.

RABL6A, a novel RAB-like protein, controls centrosome amplification and chromosome instability in primary fibroblasts.

RABL6A (RAB-like 6 isoform A) is a novel protein that was originally identified based on its association with the Alternative Reading Frame (ARF) tumor suppressor. ARF acts through multiple p53-dependent and p53-independent pathways to prevent cancer. How RABL6A functions, to what extent it depends on ARF and p53 activity, and its importance in normal cell biology are entirely unknown. We examined the biological consequences of RABL6A silencing in primary mouse embryo fibroblasts (MEFs) that express or lack ARF, p53 or both proteins. We found that RABL6A depletion caused centrosome amplification, aneuploidy and multinucleation in MEFs regardless of ARF and p53 status. The centrosome amplification in RABL6A depleted p53-/- MEFs resulted from centrosome reduplication via Cdk2-mediated hyperphosphorylation of nucleophosmin (NPM) at threonine-199. Thus, RABL6A prevents centrosome amplification through an ARF/p53-independent mechanism that restricts NPM-T199 phosphorylation. These findings demonstrate an essential role for RABL6A in centrosome regulation and maintenance of chromosome stability in non-transformed cells, key processes that ensure genomic integrity and prevent tumorigenesis.

Identification of candidate B-lymphoma genes by cross-species gene expression profiling.

Comparative genome-wide expression profiling of malignant tumor counterparts across the human-mouse species barrier has a successful track record as a gene discovery tool in liver, breast, lung, prostate and other cancers, but has been largely neglected in studies on neoplasms of mature B-lymphocytes such as diffuse large B cell lymphoma (DLBCL) and Burkitt lymphoma (BL). We used global gene expression profiles of DLBCL-like tumors that arose spontaneously in Myc-transgenic C57BL/6 mice as a phylogenetically conserved filter for analyzing the human DLBCL transcriptome. The human and mouse lymphomas were found to have 60 concordantly deregulated genes in common, including 8 genes that Cox hazard regression analysis associated with overall survival in a published landmark dataset of DLBCL. Genetic network analysis of the 60 genes followed by biological validation studies indicate FOXM1 as a candidate DLBCL and BL gene, supporting a number of studies contending that FOXM1 is a therapeutic target in mature B cell tumors. Our findings demonstrate the value of the "mouse filter" for genomic studies of human B-lineage neoplasms for which a vast knowledge base already exists.

RABL6A Promotes Oxaliplatin Resistance in Tumor Cells and Is a New Marker of Survival for Resected Pancreatic Ductal Adenocarcinoma Patients.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by early recurrence following pancreatectomy, rapid progression, and chemoresistance. Novel prognostic and predictive biomarkers are urgently needed to both stratify patients for clinical trials and select patients for adjuvant therapy regimens. This study sought to determine the biological significance of RABL6A (RAB, member RAS oncogene family-like protein 6 isoform A), a novel pancreatic protein, in PDAC. Analyses of RABL6A protein expression in PDAC specimens from 73 patients who underwent pancreatic resection showed that RABL6A levels are altered in 74% of tumors relative to adjacent benign ductal epithelium. Undetectable RABL6A expression, found in 7% (5/73) of patients, correlated with improved overall survival (range 41 to 118 months with 3/5 patients still living), while patients with RABL6A expression had a worse outcome (range 3.3 to 100 months, median survival 20.3 months) (P = 0.0134). In agreement with those findings, RABL6A expression was increased in pancreatic cancer cell lines compared to normal pancreatic epithelial cells, and its knockdown inhibited pancreatic cancer cell proliferation and induced apoptosis. Moreover, RABL6A depletion selectively sensitized cells to oxaliplatin-induced arrest and death. This work reveals that RABL6A promotes the proliferation, survival, and oxaliplatin resistance of PDAC cells, whereas its loss is associated with extended survival in patients with resected PDAC. Such data suggest RABL6A is a novel biomarker of PDAC and potential target for anticancer therapy.