The Two Stem Cell MicroRNA Gene Clusters C19MC and miR-371-3 Are Activated by Specific Chromosomal Rearrangements in a Subgroup of Thyroid Adenomas

Abstract

Thyroid adenomas are common benign human tumors with a high prevalence of about 5% of the adult population even in iodine sufficient areas. Rearrangements of chromosomal band 19q13.4 represent a frequent clonal cytogenetic deviation in these tumors making them the most frequent non-random chromosomal translocations in human epithelial tumors at all. Two microRNA (miRNA) gene clusters i.e. C19MC and miR-371-3 are located in close proximity to the breakpoint region of these chromosomal rearrangements and have been checked for a possible up-regulation due to the genomic alteration. In 4/5 cell lines established from thyroid adenomas with 19q13.4 rearrangements and 5/5 primary adenomas with that type of rearrangement both the C19MC and miR-371-3 cluster were found to be significantly overexpressed compared to controls lacking that particular chromosome abnormality. In the remaining cell line qRT-PCR revealed overexpression of members of the miR-371-3 cluster only which might be due to a deletion accompanying the chromosomal rearrangement in that case. In depth molecular characterization of the breakpoint in a cell line from one adenoma of this type reveals the existence of large Pol-II mRNA fragments as the most likely source of up-regulation of the C19MC cluster. The up-regulation of the clusters is likely to be causally associated with the pathogenesis of the corresponding tumors. Of note, the expression of miRNAs miR-520c and miR-373 is known to characterize stem cells and in terms of molecular oncology has been implicated in invasive growth of epithelial cells in vitro and in vivo thus allowing to delineate a distinct molecular subtype of thyroid adenomas. Besides thyroid adenomas rearrangements of 19q13.4 are frequently found in other human neoplasias as well, suggesting that activation of both clusters might be a more general phenomenon in human neoplasias.

Epigenetic silencing of microRNA-373 plays an important role in regulating cell proliferation in colon cancer

“…On the other hand, it has been reported that some miRNAs are located in miRNA clusters (17). Six miRNAs which we investigated were also located in two miRNA clusters, respectively.…”

The microRNA cluster C19MC is deregulated in parathyroid tumours

“…1) and their biological importance, as described previously (Toffanin et al 2011, Augello et al 2012. Furthermore, to get insight into deregulation of chr.19 miRNA clusters, allelic CNV of 19q13.41-42 locus (Rakheja et al 2004, Li et al 2009a, Rippe et al 2010) and the epigenetic status of C19MC promoter (Tsai et al 2009) were investigated. Importantly, our cohort comprised five matched metastatic lesions of four primitive parathyroid Ca.…”

“…Reports recently described that members of the C19MC or MIR371-3 clusters are expressed by human embryonic stem cells (hESCs; Laurent et al 2008, Li et al 2009b, Ren et al 2009) and over-expressed by human cancers (Toffanin et al 2011). Activation of both clusters might be a general phenomenon in human tumourigenesis, as rearrangements of 19q13.4, genomic amplification and methylation abnormalities including the C19MC locus have been frequently found in several human neoplasias (Li et al 2009a, Rippe et al 2010, Toffanin et al 2011. Finally, two members of the C19MC cluster, namely MIR517C and 520G, were shown to act as oncogenes, by promoting disease development in animal models (Li et al 2009a).…”

Reactivation of epigenetically silenced miR-512 and miR-373 sensitizes lung cancer cells to cisplatin and restricts tumor growth

“…Although the C19MC is silenced by promoter methylation in many cell lines, 19 it is activated together with the miR-371-373 cluster in a subgroup of thyroid adenomas, owing to chromosomal rearrangements. 48 miR-373 was identified by Agami and coworkers 28 as a potential oncogene in testicular germ-cell tumors, partly by targeting the Lats2 tumor suppressor. Later, the same group showed that it promotes breast cancer cell invasion and metastasis by targeting CD44.…”