Circulating microRNAs predict biochemical recurrence in prostate cancer patients.

BACKGROUND: Circulating microRNAs (miRNAs) are emerging as promising biomarkers for prostate cancer. Here, we investigated the potential of these molecules to assist in prognosis and treatment decision-making. METHODS: MicroRNAs in the serum of patients who had experienced rapid biochemical recurrence (BCR) (n=8) or no recurrence (n=8) following radical prostatectomy (RP) were profiled using high-throughput qRT-PCR. Recurrence-associated miRNAs were subsequently quantitated by qRT-PCR in a validation cohort comprised of 70 patients with Gleason 7 cancers treated by RP, 31 of whom had undergone disease progression following surgery. The expression of recurrence-associated miRNAs was also examined in tumour tissue cohorts. RESULTS: Three miRNAs - miR-141, miR-146b-3p and miR-194 - were elevated in patients who subsequently experienced BCR in the screening study. MiR-146b-3p and miR-194 were also associated with disease progression in the validation cohort, as determined by log-rank tests and Cox proportional hazards regression. Multivariate analysis revealed that miR-146b-3p possessed prognostic information beyond standard clinicopathological parameters. Analysis of tissue cohorts revealed that miR-194 was robustly expressed in the prostate, elevated in metastases, and its expression in primary tumours was associated with a poor prognosis. CONCLUSION: Our study suggests that circulating miRNAs, measured at the time of RP, could be combined with current prognostic tools to predict future disease progression in men with intermediate risk prostate cancers.

Anti-CD3 monoclonal antibody treatment in newly diagnosed Type 1 diabetes patients: a hypothetical modelling analysis.

AIMS: Although limited clinical data exist for anti-CD3 monoclonal antibody therapies, it is believed that they may influence glycaemic control, endogenous insulin secretion and hypoglycaemic event rates in individuals newly diagnosed with Type 1 diabetes. In the absence of suitable empirical evidence, the objective of this study was to estimate the potential long-term clinical outcomes associated with treatment via a hypothetical modelling analysis. METHODS: Analyses were performed using a published and validated computer simulation model of diabetes in a hypothetical US cohort based on published literature and expert opinion. The efficacy of anti-CD3 monoclonal antibody treatment was estimated from clinical data and expert opinion and simulations were performed over a 60-year time horizon. The impact on quality of life associated with treatment was also captured via published utility values. RESULTS: Assuming that a treatment course of an anti-CD3 monoclonal antibody produced an initial reduction in glycated haemoglobin of -0.8%, and that the effects persisted for up to 5 years, treatment was projected to lead to an increase in undiscounted life expectancy of 0.43 years and an increase in quality-adjusted life expectancy of 0.36 quality-adjusted life years compared with conventional exogenous insulin. CONCLUSIONS: A course of a hypothetical anti-CD3 monoclonal antibody treatment associated with improved glycaemic control and, potentially, the preservation of pancreatic beta-cell function was estimated to lead to improved life expectancy and quality-adjusted life expectancy compared with conventional treatment in patients with newly diagnosed Type 1 diabetes.

The role of microRNAs in metastasis and epithelial-mesenchymal transition.

For a tumour cell to metastasize it must successfully negotiate a number of events, requiring a series of coordinated changes in the expression of many genes. MicroRNAs are small non-coding RNA molecules that post-transcriptionally control gene expression. As microRNAs are now recognised as master regulators of gene networks and play important roles in tumourigenesis, it is no surprise that microRNAs have recently been demonstrated to have central roles during metastasis. Recent work has also demonstrated critical roles for microRNAs in epithelial-mesenchymal transition, a phenotypic change underlain by altered gene expression patterns that is believed to mirror events in metastatic progression. These findings offer new potential for improved prognostics through expression profiling and may represent novel molecular treatment targets for future therapy. In this review, we summarise the multistep processes of metastasis and epithelial-mesenchymal transition and describe the recent discoveries of microRNAs that participate in controlling these processes.

Evaluation of exenatide vs. insulin glargine in type 2 diabetes: cost-effectiveness analysis in the German setting.

OBJECTIVES: The objective of this analysis was to determine the cost-effectiveness of exenatide vs. insulin glargine in patients with type 2 diabetes failing to achieve glycaemic control with oral antidiabetic agents, in the German setting, from a third-party payer perspective. METHODS: Data from a published randomized controlled trial were used in combination with a published, validated computer simulation model of type 2 diabetes to project clinical and cost outcomes over a time horizon of 10 years. Cost data were obtained from published literature and expert opinion. Clinical and cost outcomes were discounted at 5% per annum. Sensitivity analyses were performed to establish key drivers and parameters. RESULTS: Treatment with exenatide compared with insulin glargine was projected to be associated with improvements in life expectancy of 0.016 years and quality-adjusted life expectancy of 0.280 quality-adjusted life years (QALYs), increased lifetime direct medical costs of euro 3854 (euro 22 095 vs. euro 18 242) and an incremental cost-effectiveness ratio (ICER) of euro 13 746 per QALY. If quality of life was not taken into account, exenatide was associated with an ICER of euro 238 201 per life year gained vs. insulin glargine. Sensitivity analyses revealed that outcomes were most sensitive to changes in assumptions for (dis)utility values relating to weight change and the rate of self-monitored blood glucose testing. CONCLUSIONS: Exenatide was projected to be associated with similar clinical outcomes and increased costs compared with insulin glargine. Analysis of cost-effectiveness from a third-party perspective suggests that exenatide is likely to represent good value for money in the German setting.

Cost-effectiveness of pioglitazone in patients with type 2 diabetes and a history of macrovascular disease in a Swiss setting.

OBJECTIVES: To evaluate the cost-effectiveness of pioglitazone versus placebo, given in addition to existing treatment regimens, in patients with type 2 diabetes and evidence of macrovascular disease in Switzerland. METHODS: Event rates corresponding to macrovascular outcomes from the PROactive (Prospective Pioglitazone Clinical Trial in Macrovascular Events) trial of pioglitazone were used to project long-term clinical outcomes as part of a modified version of the previously validated CORE Diabetes Model. Direct medical costs associated with treatment regimens, complications and patient management were accounted in 2005 values based on Swiss-specific unit costs. Time horizon was set to lifetime (35 years). Future costs and clinical benefits were discounted at 2.5% annually in line with Swiss recommendations. One-way sensitivity analyses were performed. RESULTS: Addition of pioglitazone was associated with a reduced incidence of most diabetes-related complications, improved life expectancy (0.258 years) and improved quality-adjusted life expectancy (0.180 QALYs) compared with placebo. Pioglitazone treatment increased direct costs by CHF 10,914 per patient over a lifetime horizon. The incremental cost-effectiveness ratio (ICER) of pioglitazone versus placebo was CHF 42,274 per life-year gained and CHF 60,596 per QALY gained. ICERs were sensitive to variation in time horizon and duration of pioglitazone treatment effects. With a willingness to pay of CHF 80,000 per QALY in the Swiss setting, there was a 62.5% chance that pioglitazone would be cost-effective. CONCLUSIONS: Addition of pioglitazone to existing therapy was projected to reduce the long-term cumulative incidence of most diabetes complications and improve quality-adjusted life expectancy. Evaluation of incremental direct medical costs associated with these clinical benefits indicated that pioglitazone is likely to be a cost-effective treatment option in the Swiss setting over patient lifetimes.

Exenatide versus insulin glargine: a cost-effectiveness evaluation in patients with Type 2 diabetes in Switzerland.

OBJECTIVES: To investigate the long-term clinical and economic outcomes associated with exenatide versus insulin glargine as "add-on" treatments to oral therapy in individuals with Type 2 diabetes inadequately controlled with combination oral agents in the Swiss setting. METHODS: A computer simulation model of diabetes was used to project complications, life expectancy, quality-adjusted life expectancy and direct medical costs over a 35-year time horizon. Cohort characteristics and treatment effect data were derived from a 26-week randomized clinical trial comparing exenatide and insulin glargine. Modeled treatment effects included reductions in glycosylated hemoglobin (HbA1c) by -0.99% and -1.07% and in body mass index (BMI) by -0.80 and +0.55 kg/m2 with exenatide and insulin glargine respectively. Changes in systolic blood pressure and serum lipid levels were also captured. Simulations incorporated published quality of life utilities and Swiss costs from 2006. Extensive sensitivity analyses were conducted to assess the robustness of projected outcomes. Future clinical and economic outcomes were discounted at 2.5% per annum. RESULTS: In the base-case analysis exenatide was associated with comparable life expectancy (11,549 years versus 11,468 years) and an improvement in quality-adjusted life expectancy of 0.43 quality-adjusted life years (QALYs) versus insulin glargine over a 35-year time horizon. Exenatide was associated with a reduced cumulative incidence of most diabetes-related complications including an absolute reduction in myocardial infarction by 0.28%. Assuming an annual treatment cost of CHF 2,797.74 for exenatide, direct costs increased by CHF 8,378 per patient over the 35-year time horizon compared to insulin glargine. The resultant incremental cost-effectiveness ratio was CHF 19,450 per QALY gained for exenatide versus insulin glargine. CONCLUSIONS: Exenatide was associated with comparable life expectancy and an improvement in quality-adjusted life expectancy versus insulin glargine over a 35-year time horizon. Based on current standards exenatide would be a cost-effective treatment alternative to insulin glargine in Switzerland for Type 2 diabetes patients inadequately controlled on oral therapy.

Author Correction: LSD1 activation promotes inducible EMT programs and modulates the tumour microenvironment in breast cancer.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Biphasic insulin aspart 70/30 vs. insulin glargine in insulin naïve type 2 diabetes patients: modelling the long-term health economic implications in a Swedish setting.

OBJECTIVES: To evaluate the long-term clinical and economic outcomes of biphasic insulin aspart 70/30 (BIAsp 70/30) treatment vs. insulin glargine in insulin naïve, type 2 diabetes patients failing oral antidiabetic drugs in a Swedish setting. METHODS: A published and validated computer simulation model (the CORE Diabetes Model) was used to project life expectancy, quality-adjusted life expectancy (QALE) and costs over patient lifetimes. Cohort characteristics [54.5% male, mean age 52.4 years, 9 years mean diabetes duration, mean glycosylated haemoglobin (HbA1c) 9.77%] and treatment effects were based on results from the Initiate Insulin by Aggressive Titration and Education (INITIATE) clinical trial. Direct medical costs were accounted in 2006 Swedish Kronor (SEK) and economic and clinical benefits were discounted at 3% per annum. RESULTS: Biphasic insulin aspart 70/30 treatment when compared with insulin glargine treatment was associated with improvements in discounted life expectancy of 0.21 years (13.10 vs. 12.89 years) and QALE of 0.21 quality-adjusted life years (QALYs) (9.16 vs. 8.96 QALYs). Reductions in the incidence of diabetes-related complications in the BIAsp 70/30 treatment arm led to reduced total costs of SEK 10,367 when compared with insulin glargine (SEK 396,475 vs. SEK 406,842) over patient lifetimes. BIAsp 70/30 treatment was projected to be dominant (cost and lifesaving) when compared with insulin glargine in the base case analysis. CONCLUSIONS: Biphasic insulin aspart 70/30 treatment was associated with improved clinical outcomes and reduced costs compared with insulin glargine treatment over patient lifetimes. These results were driven by improved HbA1c levels associated with BIAsp 70/30 compared with insulin glargine and the accompanying reduction in diabetes-related complications despite increases in body mass index.

LSD1 activation promotes inducible EMT programs and modulates the tumour microenvironment in breast cancer.

Complex regulatory networks control epithelial-to-mesenchymal transition (EMT) but the underlying epigenetic control is poorly understood. Lysine-specific demethylase 1 (LSD1) is a key histone demethylase that alters the epigenetic landscape. Here we explored the role of LSD1 in global epigenetic regulation of EMT, cancer stem cells (CSCs), the tumour microenvironment, and therapeutic resistance in breast cancer. LSD1 induced pan-genomic gene expression in networks implicated in EMT and selectively elicits gene expression programs in CSCs whilst repressing non-CSC programs. LSD1 phosphorylation at serine-111 (LSD1-s111p) by chromatin anchored protein kinase C-theta (PKC-θ), is critical for its demethylase and EMT promoting activity and LSD1-s111p is enriched in chemoresistant cells in vivo. LSD1 couples to PKC-θ on the mesenchymal gene epigenetic template promotes LSD1-mediated gene induction. In vivo, chemotherapy reduced tumour volume, and when combined with an LSD1 inhibitor, abrogated the mesenchymal signature and promoted an innate, M1 macrophage-like tumouricidal immune response. Circulating tumour cells (CTCs) from metastatic breast cancer (MBC) patients were enriched with LSD1 and pharmacological blockade of LSD1 suppressed the mesenchymal and stem-like signature in these patient-derived CTCs. Overall, LSD1 inhibition may serve as a promising epigenetic adjuvant therapy to subvert its pleiotropic roles in breast cancer progression and treatment resistance.

AUUUA is not sufficient to promote poly(A) shortening and degradation of an mRNA: the functional sequence within AU-rich elements may be UUAUUUA(U/A)(U/A).

AU-rich elements (AREs) in the 3' untranslated regions of several cytokine and oncogene mRNAs have been shown to function as signals for rapid mRNA degradation, and it is assumed that the many other cytokine and oncogene mRNAs that contain AU-rich sequences in the 3' untranslated region are similarly targeted for rapid turnover. We have used a chimeric gene composed mostly of growth hormone sequences with expression driven by the c-fos promoter to investigate the minimal sequence required to act as a functional destabilizing element and to monitor the effect of these sequences on early steps in the degradation pathway. We find that neither AUUUA, UAUUUA, nor AUUUAU can function as a destabilizing element. However, the sequence UAUUUAU, when present in three copies, is sufficient to destabilize a chimeric mRNA. We propose that this sequence functions by virtue of being a sufficient portion of the larger sequence, UUAUUUA(U/A)(U/A), that we propose forms the optimal binding site for a destabilizing factor. The destabilizing effect depends on the number of copies of this proposed binding site and their degree of mismatch in the first two and last two positions, with mismatches in the AUUUA sequence not being tolerated. We found a strict correlation between the effect of an ARE on degradation rate and the effect on the rate of poly(A) shortening, consistent with deadenylation being the first and rate-limiting step in degradation, and the step stimulated by destabilizing AREs. Deadenylation was observed to occur in at least two phases, with an oligo(A) intermediate transiently accumulating, consistent with the suggestion that the degradation processes may be similar in yeast and mammalian cells. AREs that are especially U rich and contain no UUAUUUA(U/A)(U/A) motifs failed to influence the degradation rate or the deadenylation rate, either when downstream of suboptimal destabilizing AREs or when alone.

RNA destabilization by the granulocyte colony-stimulating factor stem-loop destabilizing element involves a single stem-loop that promotes deadenylation.

Granulocyte colony-stimulating factor (G-CSF) mRNA contains two distinct types of cis-acting mRNA destabilizing elements in the 3'-untranslated region. In addition to several copies of the AU-rich element the G-CSF mRNA also contains a destabilizing region that includes several predicted stem-loop structures. We report here that the destabilizing activity resides in a single stem-loop structure within this region. A consensus sequence for the active structure has been derived by site-directed mutagenesis, revealing that a three-base loop of sequence YAU and unpaired bases either side of the stem contribute to the activity. The helical nature of the stem is essential and the stem must be less than 11 bp in length, but the destabilizing activity is relatively insensitive to the sequence within the helix. The stem-loop increases the rate of mRNA deadenylation, most likely by enhancing the processivity of the deadenylation reaction. A protein that binds the stem-loop, but not an inactive mutant form, has been detected in cytoplasmic lysates.

Human interleukin-3 (IL-3) induces disulfide-linked IL-3 receptor alpha- and beta-chain heterodimerization, which is required for receptor activation but not high-affinity binding.

The human interleukin-3 receptor (IL-3R) is a heterodimer that comprises an IL-3 specific alpha chain (IL-3R alpha) and a common beta chain (beta C) that is shared with the receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5. These receptors belong to the cytokine receptor superfamily, but they are structurally and functionally more related to each other and thus make up a distinct subfamily. Although activation of the normal receptor occurs only in the presence of ligand, the underlying mechanisms are not known. We show here that human IL-3 induces heterodimerization of IL-3R alpha and beta c and that disulfide linkage of these chains is involved in receptor activation but not high-affinity binding. Monoclonal antibodies (MAb) to IL-3R alpha and beta c were developed which immunoprecipitated, in the absence of IL-3, the respective chains from cells labelled with 125I on the cell surface. However, in the presence of IL-3, each MAb immunoprecipitated both IL-3R alpha and beta c. IL-3-induced receptor dimers were disulfide and nondisulfide linked and were dependent on IL-3 interacting with both IL-3R alpha and beta c. In the presence of IL-3 and under nonreducing conditions, MAb to either IL-3R alpha or beta c immunoprecipitated complexes with apparent molecular weights of 215,000 and 245,000 and IL-3R alpha and beta c monomers. Preincubation with iodoacetamide prevented the formation of the two high-molecular-weight complexes without affecting noncovalent dimer formation or high-affinity IL-3 binding. Two-dimensional gel electrophoresis and Western blotting (immunoblotting) demonstrated the presence of both IL-3R alpha and beta c in the disulfide-linked complexes. IL-3 could also be coimmunoprecipitated with anti-IL-3R alpha or anti-beta c MAB, but it was not covalently attached to the receptor. Following IL-3 stimulation, only the disulfide-linked heterodimers exhibited reactivity with antiphosphotyrosine antibodies, with beta c but not IL-3R alpha being the phosphorylated species. A model of IL-3R activation is proposed which may be also applicable to the related GM-CSF and IL-5 receptors.

Hypoxic regulation of vascular endothelial growth factor mRNA stability requires the cooperation of multiple RNA elements.

Vascular endothelial growth factor (VEGF) is a key regulator of developmental, physiological, and tumor angiogenesis. Upregulation of VEGF expression by hypoxia appears to be a critical step in the neovascularization of solid cancers. The VEGF mRNA is intrinsically labile, but in response to hypoxia the mRNA is stabilized. We have systematically analyzed the regions in the VEGF mRNA that are responsible for its lability under normoxic conditions and for stabilization in response to hypoxia. We find that the VEGF mRNA not only contains destabilizing elements in its 3' untranslated region (3'UTR), but also contains destabilizing elements in the 5'UTR and coding region. Each region can independently promote mRNA degradation, and together they act additively to effect rapid degradation under normoxic conditions. Stabilization of the mRNA in response to hypoxia is completely dependent on the cooperation of elements in each of the 5'UTR, coding region, and 3'UTR. Combinations of any of two of these three regions were completely ineffective in responding to hypoxia, whereas combining all three regions allowed recapitulation of the hypoxic stabilization seen with the endogenous VEGF mRNA. We conclude that multiple regions in the VEGF mRNA cooperate both to ensure the rapid degradation of the mRNA under normoxic conditions and to allow stabilization of the mRNA in response to hypoxia. Our findings highlight the complexity of VEGF gene expression and also reveal a mechanism of gene regulation that could become the target for strategies of therapeutic intervention.

Functionally distinct roles for different miR-155 expression levels through contrasting effects on gene expression, in acute myeloid leukaemia.

Enforced expression of microRNA-155 (miR-155) in myeloid cells has been shown to have both oncogenic or tumour-suppressor functions in acute myeloid leukaemia (AML). We sought to resolve these contrasting effects of miR-155 overexpression using murine models of AML and human paediatric AML data sets. We show that the highest miR-155 expression levels inhibited proliferation in murine AML models. Over time, enforced miR-155 expression in AML in vitro and in vivo, however, favours selection of intermediate miR-155 expression levels that results in increased tumour burden in mice, without accelerating the onset of disease. Strikingly, we show that intermediate and high miR-155 expression also regulate very different subsets of miR-155 targets and have contrasting downstream effects on the transcriptional environments of AML cells, including genes involved in haematopoiesis and leukaemia. Furthermore, we show that elevated miR-155 expression detected in paediatric AML correlates with intermediate and not high miR-155 expression identified in our experimental models. These findings collectively describe a novel dose-dependent role for miR-155 in the regulation of AML, which may have important therapeutic implications.

A ZEB1-miR-375-YAP1 pathway regulates epithelial plasticity in prostate cancer.

MicroRNA-375 (miR-375) is frequently elevated in prostate tumors and cell-free fractions of patient blood, but its role in genesis and progression of prostate cancer is poorly understood. In this study, we demonstrated that miR-375 is inversely correlated with epithelial-mesenchymal transition signatures (EMT) in clinical samples and can drive mesenchymal-epithelial transition (MET) in model systems. Indeed, miR-375 potently inhibited invasion and migration of multiple prostate cancer lines. The transcription factor YAP1 was found to be a direct target of miR-375 in prostate cancer. Knockdown of YAP1 phenocopied miR-375 overexpression, and overexpression of YAP1 rescued anti-invasive effects mediated by miR-375. Furthermore, transcription of the miR-375 gene was shown to be directly repressed by the EMT transcription factor, ZEB1. Analysis of multiple patient cohorts provided evidence for this ZEB1-miR-375-YAP1 regulatory circuit in clinical samples. Despite its anti-invasive and anti-EMT capacities, plasma miR-375 was found to be correlated with circulating tumor cells in men with metastatic disease. Collectively, this study provides new insight into the function of miR-375 in prostate cancer, and more broadly identifies a novel pathway controlling epithelial plasticity and tumor cell invasion in this disease.

Expression profiling reveals functionally important genes and coordinately regulated signaling pathway genes during in vitro angiogenesis.

Angiogenesis is a complex multicellular process requiring the orchestration of many events including migration, alignment, proliferation, lumen formation, remodeling, and maturation. Such complexity indicates that not only individual genes but also entire signaling pathways will be crucial in angiogenesis. To define an angiogenic blueprint of regulated genes, we utilized our well-characterized three-dimensional collagen gel model of in vitro angiogenesis, in which the majority of cells synchronously progress through defined morphological stages culminating in the formation of capillary tubes. We developed a comprehensive three-tiered approach using microarray analysis, which allowed us to identify genes known to be involved in angiogenesis and genes hitherto unlinked to angiogenesis as well as novel genes and has proven especially useful for genes where the magnitude of change is small. Of interest is the ability to recognize complete signaling pathways that are regulated and genes clustering into ontological groups implicating the functional importance of particular processes. We have shown that consecutive members of the mitogen-activated protein kinase and leukemia inhibitory factor signaling pathways are altered at the mRNA level during in vitro angiogenesis. Thus, at least for the mitogen-activated protein kinase pathway, mRNA changes as well as the phosphorylation changes of these gene products may be important in the control of blood vessel morphogenesis. Furthermore, in this study, we demonstrated the power of virtual Northern blot analysis, as an alternative to quantitative RT-PCR, for measuring the magnitudes of differential gene expression.

Nucleotide sequence of the mouse VEGF 3'UTR and quantitative analysis of sites of polyadenylation.

Sequencing of rat and human vascular endothelial growth factor (VEGF) cDNA clones has previously identified a 3' untranslated region of approximately 1.9 kb, although the apparent site of polyadenylation differed in the two species, despite a high degree of sequence conservation in the region. Neither site is preceded by a canonical AAUAAA polyadenylation signal, a situation frequently found in genes that are subject to alternative polyadenylation. We have sequenced 2.25 kb of the 3' region of the mouse VEGF gene and mapped the usage of potential polyadenylation sites in fibroblasts cultured under both normoxic and hypoxic conditions. We find that two sites for polyadenylation are present in the mouse VEGF gene but the majority of transcripts contain the longer form of the 3'UTR and that their usage is not effected by environmental oxygen tension.

A mechanism for the transfer of the carboxyl-group from 1'-N-carboxybiotin to acceptor substrates by biotin-containing enzymes.

Previous proposals for the mechanism by which biotin-dependent enzymes catalyse the transfer of the carboxyl group from 1'-N-carboxybiotin to acceptor molecules do not appear to be consistent with all of the experimental observations now available. We propose a multi-step mechanism in which (a) substrate and then carboxybiotin bind at the second partial reaction site, (b) a base positioned adjacent to the 3'-N of the carboxybiotin abstracts a proton from the 3'-N and (c) the resulting enolate ion and the acceptor substrate undergo a concerted reaction resulting in carboxyl-group transfer.

The vascular endothelial growth factor mRNA contains an internal ribosome entry site.

Vascular endothelial growth factor (VEGF), an essential regulator of angiogenesis during early development as well as during the growth of solid tumours, bears an unusually large 5' untranslated region (5'-UTR) in the mRNA of over 1000 nucleotides. We found that the VEGF 5'-UTR, despite being GC-rich and containing an upstream short open reading frame, promotes efficient translation of a luciferase reporter. The VEGF 5'-UTR also allowed translation of luciferase from a dicistronic mRNA when placed between the two cistrons, demonstrating that it contains an internal ribosome entry site. Deletion analysis indicated that the IRES resides towards the 3' end of the 5'-UTR.