Molecular pathological findings of Merkel cell polyomavirus in lung cancer: A possible etiopathogenetic link?

Abstract

Dear Editor, The proportion of cancers caused by infectious agents, including bacteria, parasitic worms and viruses, was recently estimated to be more than 20%, while the contribution of several viruses is particularly high in certain types of cancer. Over 50 years of polyomavirus research has provided novel insights into not only the general biological functions in mammalian cells but has also provided a great deal of information as to how conditions can be altered and signaling systems tweaked to produce transformation phenotypes. Over the past few years, three new members (KIV, WUV and MCPyV) have joined the two previously known (JCV and BKV) human polyomaviruses. MCPyV was the third novel polyomavirus identified in a rare but aggressive skin cancer of neuroendocrine origin, termed Merkel cell carcinoma. We appreciate the comments of the Japanese research group (submitted letter IJC-13-0568), giving us the opportunity to further discuss the role of polyoma viruses, and particularly that of Merkel virus, in lung carcinogenesis, as a number of studies have recently been published in this interesting research field. Polyoma viruses, such as BK virus (BKV), JC virus (JCV) and MCPyV are typically non-oncogenic. The evidence for their role in human cancer remains controversial, although they have been detected in a variety of human neoplasms. The aforementioned viruses BKV, JCV and SV40, or their early proteins can induce tumors in animal models, and can immortalize or transform cultured cells, including human cells. However, similar studies on the newly discovered polyoma viruses are lacking. We have read with great interest the commentary by Hashida et al (submitted letter IJC-13-0568), as the authors have shown for the first time in their original study, a prevalence of 17.9% for MCPyV in non-small cell lung cancer (NSCLC) in an Asian population. The current literature in lung cancinogenesis and more specifically in NSCLC has detected a varying prevalence for MCPyV from 5% in Chile, 9.1% in Greece to 16.7% in North America. It should also be noted that both HPV and MCPyV are directly associated with 33% of NSCLC cases. Moreover, our preliminary data indicate that in the same set of samples, HPV DNA is detectable in 19% of the specimens (unpublished data). We are of the opinion that these variations in prevalence between studies from different geographical regions emphasize the complexity of regulation levels at different stages in carcinogenesis. Recently, the interplay of the microenvironment, pathogens, immunity, inflammation, cellular epigenetic alterations and various chronic diseases has attracted increasing attention. Previous studies thus far have shown that factors, such as disease stage, clinical parameters and methodological issues are rather minor issues. It is becoming more evident that further studies are required to determine whether polyomavirus may be placed among the determinants of risk. Smoking is a major risk factor for lung cancer and it is recognized as having a critical epigenetic effect. In the Japanese study, 68.8% (22 out of 32) of women and 6.3% (5 out of 80) of men with lung cancer were never-smokers. However, among the number of samples positive for the presence of MCPyV, only one had a negative smoking history, while the mean pack-year history was increased in our study. On the other hand, Hashida and coworkers showed a trend toward a higher detection rate of MCPyV in never-smokers (submitted letter IJC-13-0568). A similar trend has been also observed in studies on HPV in Asian cohorts (16). We fully agree with our Japanese colleagues that this discrepancy is due to the different epidemiology of lung cancer in Asia. As regards the possible oncogenic effect of Merkel cell polyomavirus, it is known that MCPyV large T antigen contains merkel cell carcinoma (MCC) tumor-specific mutations that ablate its replication capacity but preserve its oncogenic functions, and the small T antigen promotes an environment favorable for cap-dependent translation. In our study, we describe for the first time, a possible oncogenic mechanism for MCPyV, as we observed a downregulation of the Bcl-2 gene and an upregulation of the BRAF gene in MCPyVpositive patients. On the other hand, the results of the Japanese study show a non-statistical trend toward higher expression levels of the Bcl-2 gene in MCPyV-positive samples (submitted letter) and a statistical significant correlation occurring only in adenocarcinoma-positive samples. In our study, Bcl-2 expression was found to be downregulated in the NSCLC samples compared to the controls (p 5 0.047), Le tt er to th e E di to r