Micro-RNA Target Identification, Expression and Immunophenotype Analysis: Possible Role for TRDMT1 in the Pathogenesis of Papillary Thyroid Carcinoma
Artur Rangel Filho, Vania Nose. University of Miami, Miami, FL
Background: Micro-RNA (miR) deregulation has emerged as an important mechanism in human cancers. Multiple studies have shown up-regulation of miR-221, miR-146a, miR-222 and miR-181b in papillary thyroid carcinoma (PTC). We hypothesized that gene targets simultaneously regulated by these four miRs may be involved in pathways important in PTC carcinogenesis. We aimed to identify predicted gene targets of these miRs potentially useful as novel diagnostic or prognostic biomarkers in PTC.
Design: Four miRs, consistently deregulated in PTC were selected. Genome-wide miR target prediction was performed using the mirDB algorithm. Pairwise comparisons of predicted genes identified a common target for all four miRs. In silico validation of the candidate gene was carried out by mining multiple available databases to determine: 1) If RNA and protein gene products are expressed in thyroid; 2) if there is evidence of altered expression in PTC vs. normal thyroid. Target gene product was assayed by IHC in 50 sections of normal and benign/malignant neoplastic thyroid including histological subtypes of PTC.
Results: The gene tRNA aspartic acid methyltransferase 1 (TRDMT1) was the only potential common target of all four miRs. Data mining indicated that: 1)TRDMT1 RNA and protein are expressed in thyroid; 2) Two microarray experiments suggested significant downregulation of TRMDT1 in PTC vs. thyroid (p <0.03 for both). IHC for TRDMT1 was positive in all cases. Combinations of complete nuclear, speckled nuclear, perinuclear, and cytoplasmic staining with variable intensities were observed in both normal and neoplastic cells. Follicular cells showed predominantly positive nuclear staining. Decreased nuclear and positive cytoplasmic staining was observed in PTCs. This pattern however, was not unique to PTC. Overall, no single combination of staining patterns was able to reliably distinguish among all tumors tested.
Conclusions: We presented an in silico approach to biomarker identification using publicly available experimental data and offered a rationale for prioritization for experimental validation. We identified TRDMT1 as a single common target of 4 miRs reproducibly overexpressed in PTC and documented the patterns of IHC staining in a variety of benign and malignant thyroid samples. In this preliminary study, the limited number of cases analyzed precludes correlation to specific pathologic entities. This limitation will be addressed by continued expansion of the number of cases.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 33, Tuesday Afternoon