miRNA-34a underexpressed in Merkel cell polyomavirus-negative Merkel cell carcinoma.

Merkel cell polyomavirus (MCV) is frequently detectable in Merkel cell carcinoma (MCC) tumors, but the significance of MCV infection is not yet totally understood. Thus far, no key regulatory miRNA has been identified for MCC tumorigenesis. However, distinct miRNA expression profiles have been suggested for MCV-positive and MCV-negative tumors. We used microarray hybridization to identify miRNA expression differences in MCC tumor samples according to MCV status and further validated these results by quantitative reverse transcription polymerase chain reaction (qRT-PCR). When compared with MCV-negative tumors, we detected overexpression of miR-34a, miR-30a, miR-142-3p, and miR-1539 in those MCV positives. In addition, slight underexpression was detectable in MCV-positive tumors of miR-181d. We confirmed the distinct expression of miRNAs in MCV-positive and MCV-negative tumors and confirmed statistically significant underexpression of miR-34a in MCV-negative tumors by both array analysis and qRT-PCR. Neither tumor location nor development of metastases affected miRNA expression.