LINC00894 expression was primarily localized in the cytoplasm as revealed by the analysis using the lncLocator website, suggesting that LINC00894 primarily functions by adsorbing miRNA. StarBase 3.0, RNAInter, and oncomiR analysis revealed three potential miRNAs (miR-424-5p, miR-15a-5p, and let-7e-5p) sponged by LINC00894 (Fig.
3A). As LINC00894 was found to be expressed at a low level, miRNAs that were expressed at high levels may be potential target genes of LINC00894 in thyroid cancer. Among the three miRNAs, let-7e-5p was significantly upregulated in thyroid cancer. In addition, a high level of let-7e-5p was correlated with poor prognosis in thyroid cancer according to starBase 3.0 and Kaplan–Meier survival analyses (Fig.
3B, C), suggesting that let-7e-5p is the main miRNA adsorbed by LINC00894 in thyroid cancer. Therefore, let-7e-5p was chosen as the potential target gene of LINC00894. The binding and mutational sites of LINC00894 which bound with let-7e-5p are shown in Fig.
3D. Ago-RIP analysis showed that LINC00894 and let-7e-5p expression was more abundant in the anti-AGO2 antibodies group than in the anti-IgG group, suggesting that LINC00894 binds to let-7e-5p via AGO2 (Fig.
3E). Compared to that in the WT-LINC00894 + NC mimic group, the
Renilla-to-firefly luciferase activity in the WT-LINC00894 + let-7e-5p mimic group was reduced but was not significantly different between the Mut-LINC00894 + NC and Mut-LINC00894 + let-7e-5p mimic groups, indicating that LINC00894 can bind to let-7e-5p (Fig.
3F). Moreover, let-7e-5p was highly expressed in thyroid cancer cells, which is consistent with its expression in thyroid cancer tissues (Fig.
3G). Additionally, it was demonstrated that LINC00894 overexpression did not affect let-7e-5p expression (Fig.
3H). These results show that LINC00894 only adsorbs let-7e-5p without affecting its expression.
Additional potential target genes regulated by let-7e-5p were investigated using starBase 3.0, TargetScan 8.0, and RNAInter, and those which had a significantly positive correlation with LINC00894 expression in thyroid cancer were analyzed using GEPIA2. TIA-1 was identified at the intersection of the four groups (Fig.
4A). TIA-1 was significantly downregulated in thyroid cancer include follicular thyroid cancer and papillary thyroid cancer and this low TIA1expression was related to poor prognosis according to GEPIA2 and Kaplan–Meier survival analyses (Fig.
4B, C). TIA-1 expression had no significantly changed between follicular thyroid cancer, papillary thyroid cancer, and other thyroid cancer (Fig.
4B). These results indicate that TIA-1 and LINC00894 expressions are significantly related and that TIA-1 is a potential target gene for let-7e-5p in thyroid cancer. The binding sites of let-7e-5p and TIA-1 are shown in Fig.
4D. The luciferase assay showed that luciferase activity was significantly decreased in the WT-TIA-1 + let-7e-5p mimic group compared with that in the WT-TIA-1 + NC mimic group but was not significantly different between the Mut-TIA-1 + NC mimic and Mut-TIA-1 + let-7e-5p mimic groups, indicating that the 3′-UTR of TIA-1 can bind to let-7e-5p (Fig.
4E). Moreover, overexpression of LINC00894 promoted TIA-1 expression (Fig.
4F). These results indicate that LINC00894 and TIA-1 3-UTR have a ceRNA regulatory relationship by binding the same let-7e-5p and that LINC00894 increases TIA-1 protein expression by sponging let-7e-5p in thyroid cancer cells.