Crocin induces ROS-mediated papillary thyroid cancer cell apoptosis by modulating the miR-34a-5p/PTPN4 axis in vitro

miR-34a-5p has been reported to be upregulated and function as an oncogene in papillary thyroid cancer (PTC). Crocin, the major chemical constituent of saffron, has been demonstrated to possess anti-tumorigenic activity and decrease miR-34a-5p expression. Thus we hypothesized that crocin exerted anti-PCT effect by downregulating miR-34a-5p. Herein, the hypothetical mechanism underlying the anti-PCT effect of crocin was explored. Cell viability and apoptosis were assessed by CCK-8 and TUNEL assays, respectively. Reactive oxygen species (ROS) level, caspase-3 activity, and LDH release were measured using corresponding commercially available assay kits. Expression of miR-34a-5p and protein tyrosine phosphatase nonreceptor type 4 (PTPN4) was analyzed using qRT-PCR and western blot analyses. Interaction between miR-34a-5p and targets were predicted by Targetscan, starbase, miRDB, microT-CDS, and miRWalk and validated using luciferase reporter assay. Results showed that crocin inhibited the viability and miR-34a-5p expression in papillary thyroid cancer (PTC) cells in a dose-dependent manner. The Venn diagram showed that 10 overlapped targets of miR-34a-5p were identified, among which PTPN4 was the most significantly downregulated target gene in thyroid cancer tissues based on the heat map and bar plot from GSE33630 analysis. Luciferase reporter assay validated the direct interaction between miR-34a-5p and PTPN4. Crocin upregulated PTPN4 by decreasing miR-34a-5p expression in PTC cells. Crocin promoted apoptosis and increased caspase-3 activity and LDH release, which were reversed by ROS scavenger N-acetyl-L-cysteine (NAC), miR-34a overexpression, and PTPN4 silencing. To conclude, crocin promoted ROS-mediated apoptosis of PTC cells by modulating the miR-34a-5p/PTPN4 axis.