MicroRNAs (miRNA) are small endogenous non-coding RNAs that negatively regulate protein expression and biological processes such as proliferation, differentiation and apoptosis. The miRNA biogenesis consists of multistep events of RNA synthesis and processing that begin within the nucleus and end in the cytoplasm. Some miRNAs, called oncomiRs, participate in the tumorigenesis by inhibiting the expression of a tumor suppressor gene or activating an oncogene. Studies have demonstrated a decrease in the expression of let-7 family miRNAs in cancer, including thyroid cancer, acting as a tumor suppressor miRNA. Recent findings have shown that the RNA-binding proteins LIN28A and LIN28B inhibit the expression of let-7. These proteins act by binding on the let-7 primary and precursor transcripts, inhibiting their processing by the miRNA machinery. Interestingly in different cancer types, tumors showing a poor prognosis presented concomitant increased LIN28 expression and decreased let-7. In this work, we aim to evaluate the role of LIN28 regulatory proteins in thyroid cancer and its influence on let-7 miRNA expression. In fact, our preliminary results show that cell lines derived from poorly differentiated and undifferentiated thyroid carcinoma (more aggressive histopathological types) express high levels of LIN28B, suggesting a possible role of this protein in the progression of thyroid cancer. The results obtained in this study will contribute to the understanding of thyroid tumor progression and generate perspectives for the development of new therapeutic strategies.
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