Pre-miR146a expression in follicular carcinomas of the thyroid

INTRODUCTION: Micro-RNA, a new class of small, non-coding RNAs, have been shown to be deregulated in several human carcinomas. In particular, SNP rs2910164 in pre-miR146a appears to be correlated with papillary thyroid carcinoma and may be involved in its genetic predisposition. Since data on follicular thyroid carcinomas (FTC) are lacking, we evaluated the involvement of SNP rs2910164 in FTC. METHODS: Thirty-nine cases of FTC and 20 follicular adenomas, defined according to WHO criteria, were selected. DNA and RNA were extracted from formalin-fixed paraffin-embedded blocks of both neoplastic and non-neoplastic areas. The DNA region of pre-miR146a, containing SNP rs2910164, was sequenced. Total RNA including miRNAs was used for stem-loop RT reactions, and applying a standard TaqMan PCR kit protocol for real-time PCR. Wilcoxon signed-rank test and Friedman test were used for statistical analyses. RESULTS: In 31% of FTC, the G allele was observed in neoplastic tissues, compared with the non-neoplastic areas (p < 0.05), whereas the CC phenotype was completely absent in tumours. Moreover, the expression of pre-miR146a was found to be significantly down-regulated in neoplastic tissues from FTC cases (p = 0.043), although no significant differences were seen in follicular thyroid adenomas. DISCUSSION: The expression profile of pre-miR146a can be correlated with FTC tumourigenesis. The G allele in SNP rs2910164 appears to be correlated with the transition from normal to neoplastic tissue. The GG and GC alleles appear to be associated with an increased risk for FTC, while the CC allele seems to play a protective role.