DGCR8 microprocessor defect and deregulation of its expression in thyroid cancer

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Abstract Background The alteration of microRNA (miRNA) processing is a driver event in several tumors including thyroid cancer (TC). Upon the discovery of DICER mutations affecting the miRNA biogenesis in TC, other genes encoding proteins with similar functions have been studied. The DiGeorge Critical Region 8 (DGCR8) gene holds a critical role in miRNA biogenesis as a microprocessor complex component. Previous studies identified a hotspot DGCR8 mutation - the variant c.1552G > A (p.E518K) that alters canonical miRNA production. As miRNAs are necessary to accurately establish thyroid follicles and hormone synthesis, the deregulation of their expression are common in TC. The goal of this study was to characterize the variant p.E518K of DGCR8 in thyroid lesions and evaluate its expression. Methods 242 samples of 214 patients with tumor or tumor-like lesions of thyroid were evaluated by direct sequencing for the presence of c.1552 G > A (p.E518K). Formalin-fixed paraffin embedded (FFPE) sections of these lesions were studied for DGCR8 immunoexpression. When frozen tissue was available, DGCR8 mRNA expression was analyzed by quantitative PCR (qPCR). Results The presence of the variant c.1552G > A (p.E518K) was a rare event in our series. Only 1 case was found mutated, and it corresponded to a poorly differentiated thyroid carcinoma (PDTC). Unexpectedly, mRNA DGCR8 expression and DGCR8 expression shown an aberrant expression in PDTC cases which could lead to a miRNA downregulation. Conclusions The results obtained so far point that DGCR8 may have a role in thyroid carcinogenesis. Although mutations are rare, aberrant expression affecting miRNA expression seems to be a common event.

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