Activation of the two microRNA clusters C19MC and miR-371-3 does not play prominent role in thyroid cancer

Abstract

Chromosomal rearrangements of band 19q13.4 are frequent cytogenetic alterations in benign thyroid adenomas. Apparently, these alterations lead to the upregulation of genes encoding microRNAs of two clusters mapping to the breakpoint region, i.e. miR-371-3 and C19MC. Since members of both clusters have been associated with neoplastic growth in other tumor entities the question arises whether or not their upregulation predisposes to malignant transformation of follicular cells of the thyroid. To address this question we have quantified the expression of miR-372 and miR-520c-3p in samples of 114 thyroid cancers including eight anaplastic thyroid carcinomas, 25 follicular thyroid carcinomas, 78 papillary thyroid carcinomas (including 13 follicular variants thereof), two medullary thyroid carcinomas and one oncocytic thyroid carcinoma. Additionally, we quantified miR-371a-3p and miR-519a-3p in selected samples. While in neither of the cases miR-520c-3p and miR-519a-3p were found to be upregulated, one papillary and one anaplastic thyroid carcinoma, respectively, showed upregulation of miR-372 and miR-371a-3p. However, in these cases fluorescence in situ hybridization did not reveal rearrangements of the common breakpoint region as affected in adenomas. Thus, these rearrangements do apparently not play a major role as first steps in malignant transformation of the thyroid epithelium. Moreover, there is no evidence that 19q13.4 rearrangements characterize a subgroup of thyroid adenomas associated with a higher risk to undergo malignant transformation. Vice versa, the mechanisms by which 19q13.4 rearrangements contribute to benign tumorigenesis in the thyroid remain to be elucidated.

Figure 1

miR-372 was upregulated in 2 of 114 thyroid carcinomas. (A) Relative expression of miR-372 was quantified in 114 thyroid carcinoma samples of different types (PTC: papillary thyroid carcinoma, FTC: follicular thyroid carcinoma, ATC: anaplastic thyroid carcinoma, MTC: medullary thyroid carcinoma, OTC: oncocytic thyroid carcinoma). Expression is compared to three different normal thyroid tissues. The thyroid tissue showing the highest expression of miR-372 was used as calibrator. A thyroid adenoma with 19q13.4 rearrangement (S1016) served as a positive control of abundant miR-372 expression. The arrows indicate the samples that also appear in Figure 3 (from left to right: normal thyroid tissue, S1016, KS 99, KS 97, KS 61, KS 41, KS 82, KS 106, KS 100, KS 13). RQ: relative quantity (logarithmic scale). The lower panel shows histological sections of (B) case KS 13, a follicular variant of papillary thyroid carcinoma (PTC) and (C) case KS 100, an anaplastic thyroid carcinoma (ATC).

Figure 2

Relative expression of miR-372 in case KS 13 and surrounding normal tissue. Surrounding normal tissue (ST) was obtained from another FFPE block of the same sample. Expression is compared to normal thyroid tissue and a thyroid adenoma with 19q13.4 rearrangement (S1016) as positive control.

Figure 3

Relative expression of miR-371a-3p, miR-520c-3p, and miR-519a-3p in thyroid carcinoma samples. (A) Relative expression of miR-371a-3p was quantified in five thyroid carcinoma samples of different histological subgroups. (B) Relative expression of miR-520c-3p was quantified in 114 thyroid carcinoma samples of different types (as no upregulation was observed in any of the samples only a selection of samples is shown including the three cases with the highest expression of miR-520c-3p. (C) Relative expression of miR-519a-3p in five thyroid carcinoma samples of different types. In A,B and C the expression is compared to normal thyroid tissue and a thyroid adenoma with 19q13.4 rearrangement (S1016) as positive control. RQ: relative quantity (logarithmic scale). PTC: papillary thyroid carcinoma, FTC: follicular thyroid carcinoma, ATC: anaplastic thyroid carcinoma.

Figure 4

Fluorescence in situ hybridization for the detection of 19q13.4 rearrangements. Interphase fluorescence in situ hybridization (FISH) was carried out with a dual-color break-apart rearrangement probe (TBPC19; thyroid adenoma breakpoint cluster 19q13.4) for nuclei of cases KS 13 (A), KS 100 (B), and the positive control S1016 (C), respectively. In addition, a partial karyotype of the latter case with an apparently balanced translocation t(2;19)(p13;q13.4) is shown (D).