Simple retroviruses induce tumors by integrating into the host genome, activating cellular oncogenes and microRNAs, or inactivating tumor suppressor genes. The identification of these genes elucidates molecular mechanisms of tumorigenesis. In this study, we identified avian leukosis virus (ALV) proviral integration sites in rapid-onset B cell lymphomas arising <12 weeks after infection of chicken embryos. By using inverse PCR, 28 unique viral integration sites were identified in rapid-onset tumors. Integrations in the telomerase reverse transcriptase (TERT) promoter/enhancer region were observed in four different tumors, suggesting that this is a common integration site. These provirus integrations ranged from 217 to 2,584 bp upstream of the TERT transcription initiation site and were all in the opposite transcriptional orientation to TERT. Southern blots of tumor samples demonstrated that these integrations are clonal and therefore occurred early in the process of tumorigenesis. Real-time RT-PCR showed overexpression of TERT mRNA in tumors harboring viral integrations in the TERT promoter. Telomerase activity was also up-regulated in these tumors; however, telomere-length alterations were not detected. Furthermore, viral LTR sequences directly enhanced the expression of luciferase reporters containing the TERT promoter sequences. This study documents retroviral up-regulation of cellular TERT by insertional activation to initiate or enhance tumor progression. retroviral tagging ͉ chicken tumors ͉ chicken telomerase

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Background Mesothelin, previously shown to be expressed in triple negative breast cancer (TNBC), is a potential therapeutic target and prognostic marker in breast cancer. Methods We analyzed clinical data from two cohorts comprising of 141 patients treated between 2009 and 2011 at our institution (discovery cohort) and 844 patients from The Cancer Genome Atlas (TCGA) (validation cohort). Mesothelin expression was quantified by immunohistochemistry (IHC) or by RNA transcript levels as measured by whole-transcriptome sequencing in the discovery and validation cohorts respectively. Results In the discovery cohort, the median follow up was 3.55 years. Univariate analyses demonstrated that tumor size (hazard ratio (HR) =1.30, 95% confidence interval (CI) 1.11–1.51), positive (+) axillary lymph nodes (HR=3.34; 95% CI 1.51–7.39), and mesothelin expression (HR = 2.03; 95% CI 1.10–3.74) were associated with overall and disease-specific survival. We used a Cox-proportional hazard (Cox-PH) model to adjust for the two independent predictors of survival, namely (+) axilla lymph nodes and tumor size, and we found a significant association between mesothelin expression and overall and disease-specific survival in the discovery cohort (HR = 3.06, 95% CI 1.40–6.68). Using the TCGA dataset, we confirmed that, over a median follow-up of 16.0 months, patients with mesothelin-expressing tumors had poorer overall survival (HR=1.46; 95% CI 1.05–2.03). On Cox-PH multivariate analysis, mesothelin-positivity was an independent predictor of worse survival, after adjusting for (+) axillary lymph nodes and tumor size (HR = 1.69; 95%CI 1.17–2.42). Conclusions Our results suggest that mesothelin is a prognostic breast tumor marker whose expression is highly enriched in TNBC tumors, especially in African American women. As there is no existing targeted therapy for TNBC, mesothelin may be a promising drug target for TNBC. Future work is needed to evaluate the efficacy of mesothelin directed targeted therapy in the treatment of breast cancer.