Analysis of microRNA Patterns in Hodgkin's Lymphoma (HL).

Abstract

Mature microRNAs (miRNA) are recently discovered small RNA molecules of 21–25 nucleotides in length. They act as negative regulators of expression of important genes like those participating in cellular proliferation or apoptosis. There is evidence that miRNA play an important role in carcinogenesis. The objective of this study was to compare the miRNA expression patterns in normal lymph nodes and in lymph nodes from patients with HL. Moreover, we investigated the miRNA pattern of HL depending on Epstein-Barr Virus (EBV) expression. We assessed 156 mature miRNAs by Stem-loop RT-PCR and Real time PCR in ABI PRISM 7500 in 9 normal lymph nodes and 39 patients diagnosed with HL nodular sclerosis subtype (15 EBV+ and 24 EBV-)at a single institution. Patients median age was 27 years (range, 15–52), and clinical stage was I (n=1); II (n=22); III (n=8) and IV (n=8); 41% of the patients reported B symptoms. RNA was obtained in all cases from formalin fixed paraffin embedded tissues. miRNA expression data was normalized to let-7a miRNA and to global median. Relative quantification of miRNA expression was calculated with the 2−ΔΔCt method. The data were presented as log10 of relative quantity of target miRNA. Normal human lymph node tissue was used as calibrator for all samples. Data were analyzed by means of Significant Analysis of Microarrays (SAM), Student's t-test (with random variance model) and Class prediction methods using BRB Array Tools version 3.4.0 and TIGR Multiexperiment Viewer version 3.1. Of the 156 miRNAs analyzed, 35 were differentially expressed between normal lymph nodes and HL (12 miRNAs were upregulated and 23 downregulated). The most differentially overexpressed miRNAs was miR-216, which inhibits apoptosis pathway. Other differentially expressed miRNAs were miR-140, 204, 19a, 20, 191 and 142-3p, which have been associated to the genesis of hematological and non-hematological malignances. With respect to EBV+ vs. EBV− cases, we found that miR-96 and miR-335 were underexpressed in the EBV+ cases as compared to EBV− (p=0.001). These miRNAs have RNF34 and BIRC2 genes as targets, which have an antiapoptotic function. We also found that miR-138 was more frequently overexpressed in clinical stages I–II versus clinical stages III–IV (p=0.004), and that miR-328 was more frequently overexpressed in stages III–IV (p=0.004). In conclusion, miRNAs might have a role in the pathogenesis of HL. The miRNA pattern is different between the EBV+ and EBV− cases, and the differentially expressed miRNAs seems to be related to the apoptotic pathway.