Clinical roles of miR-136-5p and its target metadherin in thyroid carcinoma

Thyroid carcinoma (TC) is a common malignancy of the endocrine system. This research aimed to examine the expression levels of miR-136-5p and metadherin (MTDH) in TC and unveil their potential targeting relationship.

TC microRNA (miRNA) microarray and miRNA-sequencing data were collected to evaluated miR-136-5p expression. We assessed the comprehensive expression of miR-136-5p by calculating the standard mean difference (SMD) and summary receiver operating characteristic curves (sROC). Subsequently, the miR-136-5p mimic and inhibitor were transfected into the TC B-CPAP cell, Thiazolyl Blue Tetrazolium Bromide (MTT) assay and cell apoptosis assay by FACS with Annexin V-/7-AAD double staining were performed to explore the biological role of miR-136-5p in the B-CPAP cell line. Prediction of target genes and potential biological function analysis of miR-136-5p were made using miRWalk2.0 and DAVID, respectively. Through target gene prediction, MTDH may be the candidate target gene of miR-136-5p. Subsequently, gene microarrays and RNA-sequencing data were also leveraged for MTDH expression. The meta-analysis method was conducted to evaluate the comprehensive expression level of MTDH. In addition, MTDH protein expression was identified using immunohistochemistry. The MTDH protein levels post-miR-136-5p transfection were verified by western blot, and the dual luciferase reporter assay was adapted to confirm the direct targeting relation between miR-136-5p and MTDH.

The miR-136-5p level was remarkably downregulated in TC, the pooled SMD was -0.47 (95% CI: -0.70 to -0.23, I²=36.6%, P=0.192) and the area under the curve (AUC) of the sROC was 0.67 based on 543 cases of TC. MTT indicated that the overexpression of miR-136-5p dramatically inhibited the proliferation of B-CPAP cells. The cell apoptosis increased in the miR-136-5p mimic group compared to the negative control group. In addition, both MTDH mRNA and protein levels were markedly overexpressed, with the pooled SMD being 0.94 (95% CI: -0.35 to 2.24, I²=98.8%, P<0.001), and the AUC of the sROC being 0.85 with 1054 cases of TC. The MTDH protein level was significantly up-regulated in TC than in the non-carcinomic tissues by immunohistochemistry (8.292±1.717 vs. 2.618±2.570, P<0.001). Western blot indicated that MTDH protein expression was suppressed by miR-136-5p mimic in the B-CPAP cell line, which was further supported by the dual luciferase reporter assay.

The miR-136-5p/MTDH axis may play a vital role in modulating TC tumorigenesis, providing new insight into possible molecular mechanisms of TC oncogenesis.