Identification of a Novel Gammaretrovirus in Prostate Tumors of Patients Homozygous for R462Q RNASEL Variant

Anatoly Urisman,Eric A Klein,Joseph L Derisi,Nicole Fischer,Graham Casey,Krishnamurthy Malathi,Don Ganem,Cristina Magi-Galluzzi,Raymond R Tubbs,Ross J Molinaro,Sarah J Plummer,Robert H Silverman,Susan Ross

doi:10.1371/journal.ppat.0020025

Abstract

Ribonuclease L (RNase L) is an important effector of the innate antiviral response. Mutations or variants that impair function of RNase L, particularly R462Q, have been proposed as susceptibility factors for prostate cancer. Given the role of this gene in viral defense, we sought to explore the possibility that a viral infection might contribute to prostate cancer in individuals harboring the R462Q variant. A viral detection DNA microarray composed of oligonucleotides corresponding to the most conserved sequences of all known viruses identified the presence of gammaretroviral sequences in cDNA samples from seven of 11 R462Q-homozygous (QQ) cases, and in one of eight heterozygous (RQ) and homozygous wild-type (RR) cases. An expanded survey of 86 tumors by specific RT-PCR detected the virus in eight of 20 QQ cases (40%), compared with only one sample (1.5%) among 66 RQ and RR cases. The full-length viral genome was cloned and sequenced independently from three positive QQ cases. The virus, named XMRV, is closely related to xenotropic murine leukemia viruses (MuLVs), but its sequence is clearly distinct from all known members of this group. Comparison of gag and pol sequences from different tumor isolates suggested infection with the same virus in all cases, yet sequence variation was consistent with the infections being independently acquired. Analysis of prostate tissues from XMRV-positive cases by in situ hybridization and immunohistochemistry showed that XMRV nucleic acid and protein can be detected in about 1% of stromal cells, predominantly fibroblasts and hematopoietic elements in regions adjacent to the carcinoma. These data provide to our knowledge the first demonstration that xenotropic MuLV-related viruses can produce an authentic human infection, and strongly implicate RNase L activity in the prevention or clearance of infection in vivo. These findings also raise questions about the possible relationship between exogenous infection and cancer development in genetically susceptible individuals.

Highlights

Type I interferons (IFNs) are rapidly mobilized in response to viral infection and trigger potent antiviral responses
Detection of Xenotropic murine leukemia viruses (MuLVs)-related virus (XMRV) by Microarray-Based Screening To search for potential viruses in prostate cancer tumors, we employed a DNA microarray-based strategy designed to screen for viruses from all known viral families [20,21]
The results presented here identify XMRV infection in prostate tissue from approximately 40% of patients with prostate cancer who are homozygous for the R462Q variant (QQ) of ribonuclease L (RNase L), as judged by both hybridization to the Virochip microarray and by RT-polymerase chain reaction (PCR) with XMRV-specific primers

Summary

Introduction

Type I interferons (IFNs) are rapidly mobilized in response to viral infection and trigger potent antiviral responses. One such response is the induction by IFN of a family of 2959 oligoadenylate synthetases (OAS); upon activation by virally encoded dsRNA, these enzymes produce 59-phosphorylated 29-59 linked oligoadenylates (2–5A) from ATP [1]. 2–5A, in turn, is an activator of ribonuclease L (RNase L) [2], which degrades viral (and cellular) single stranded RNAs [3]. Sustained activation of RNase L triggers a mitochondrial pathway of apoptosis that eliminates virusinfected cells [4,6,7,8]. Genetic lesions in RNase L impair this apoptotic response, which has raised interest in the possibility that such mutations might contribute to malignancy [9].

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Results

Conclusion