Regulation of microRNA expression by HMGA1 proteins

Abstract

The High Mobility Group proteins HMGA1 are nuclear architectural factors that play a critical role in a wide range of biological processes. Since recent studies have identified the microRNAs (miRNAs) as important regulators of gene expression, modulating critical cellular functions such as proliferation, apoptosis and differentiation, the aim of our work was to identify the miRNAs that are physiologically regulated by HMGA1 proteins. To this purpose, we have analysed the miRNA expression profile of mouse embryonic fibroblasts (MEFs) carrying two, one or no Hmga1 functional alleles using a microarray (miRNA microarray). By this approach, we found a miRNA expression profile that differentiates Hmga1-null MEFs from the wild-type ones. In particular, a significant decrease in miR-196a-2, miR-101b, miR-331 and miR-29a was detected in homozygous Hmga1-knockout MEFs in comparison with wild-type cells. Consistently, these miRNAs are downregulated in most of the analysed tissues of Hmga1-null mice in comparison with the wild-type mice. ChIP assay shows that HMGA1 is able to bind regions upstream of these miRNAs. Moreover, we identified the HMGA2 gene product as a putative target of miR-196a-2, suggesting that HMGA1 proteins are able to downregulate the expression of the other member of the HMGA family through the regulation of the miR-196a-2 expression. Finally, ATXN1 and STC1 gene products have been identified as targets of miR-101b. Therefore, it is reasonable to hypothesize that HMGA1 proteins are involved in several functions by regulating miRNA expression.

Epidrug mediated re-expression of miRNA targeting the HMGA transcripts in pituitary cells

“…However, and in common with protein-coding genes, miRNAs can be silenced through aberrant hypermethylation of CpG islands and/or by histone modifications. [18] Irrespective of pituitary adenoma subtype a significant proportion overexpress HMGA1 and HMGA2 [33,10,34,35], indeed, in the cohort we now describe, similar conclusions are apparent (data not shown). Convincing evidence for the role of these genes, and their protein products, in tumour evolution are provided through studies in transgenic mice, where, enforced expression of either hmga1 or hmga2 leads to the development of pituitary adenomas.…”

Downregulation of HMGA-targeting microRNAs has a critical role in human pituitary tumorigenesis

“…Moreover, it is noteworthy that these five miRNAs were associated by the web system to 57 cellular processes, including those in which HMGA proteins have been previously demonstrated to be involved, such as cell proliferation, differentiation, DNA-repair, chromatin modification and regulation of transcription (Fusco and Fedele, 2007;. The direct targeting of HMGA1 by miR-16 (Kaddar et al, 2009), and of HMGA2 by Let-7a (Lee and Dutta, 2007) and miR196ab (De Martino et al, 2009a) was previously reported. Moreover, previous studies showed that miR-26a regulates HMGA2 expression (Lee et al, 2011).…”

“…The 3 0 -UTR region of HMGA2 gene, including binding sites for miR-15, miR16, miR26ab, miR-196a and let-7a was previously described (De Martino et al, 2009a). The 3 0 -UTR region of the HMGA1 gene, including binding sites miR-15, miR16, miR26ab, miR-196a and let-7a was amplified by PCR from human genomic DNA by using the following primers:…”

“…HMGAs are a family of small nonhistone chromatin proteins that include four members, HMGA1a, HMGA1b, HMGA1c (encoded by the HMGA1 gene through alternative splicings) and HMGA2 (encoded by the homonymous gene) (Johnson et al, 1989). HMGA proteins do not have transcriptional activity per se, however by interacting with the transcriptional machinery they alter the chromatin structure and, thereby, regulate, negatively or positively, the transcriptional activity of several genes and micro RNAs (miRNAs) (Thanos and Maniatis, 1992;Thanos et al, 1993;De Martino et al, 2009a).…”

“…Recent studies have shown that HMGA protein levels are regulated by miRNAs (Lee and Dutta, 2007;De Martino et al, 2009a), a class of small (19-25 nucleotides) noncoding RNAs involved in temporal and tissuespecific eukaryotic gene regulation (Lagos-Quintana et al, 2002) by binding the 3 0 -untranslated region (UTR) of target messenger RNAs (mRNAs) and inducing mRNA degradation or inhibition of its translation (Bartel, 2004;Calin and Croce, 2006). Indeed, the loss of HMGA2 3 0 -UTR, frequently detected in benign tumors of mesenchymal origin, results in the lack of inhibitory control of HMGA2 expression by different miRNAs (Hebert et al, 2007;Lee and Dutta, 2007), thereby leading to HMGA2 protein overexpression that accounts for cell transformation.…”