MicroRNA-21 (miR-21) post-transcriptionally downregulates tumor suppressor PDCD4 and promotes cell transformation, proliferation, and metastasis in renal cell carcinoma.

MiR-21 induces neoplastic transformation, cell proliferation, and metastasis and downregulates programmed cell death4 (PDCD4) in some cancers. The aim of this study was to investigate the roles and interactions of PDCD4 and miR-21 in human renal cell carcinoma (RCC). A total of 32 paired tumor and normal tissue specimens from RCC patients as well as three renal cancer cell lines (786-O, A498, caki-1) and one normal epithelial kidney cell line (HK-2) were studied. The expression levels of PDCD4 (protein and mRNA) and miR-21 were examined by Western blot analysis and by qRT-PCR and luciferase reporter assays. Furthermore, we transfected 786-O cells with pre-miR-21 (mimics) and anti-miR-21 (inhibitor) and then again analyzed the expression of PDCD4 protein and mRNA, and determined cell proliferation and transformation capabilities by EDU and soft agar colony formation assay. MiR-21 expression was significantly upregulated in RCC, metastatic RCC specimens and renal cancer cell lines (A498, 786-O, caki-1) compared to normal non-metastatic RCC specimens and HK-2 cells (P<0.05). In contrast, PDCD4 protein expression significantly decreased (P<0.05), whereas PDCD4 mRNA expression remained unaltered (P>0.05). Moreover, we observed a significant reduction in PDCD4 protein levels in miR-21mimic-transfected cells, but a significant increase in miR-21inhibitor-transfected cells (P<0.05), whereas PDCD4 mRNA was practically unaltered (P>0.05). Furthermore, miR-21mimic-transfected cells exhibited increased cell proliferation and transformation capacity according to EDU analysis and soft agar formation assay, whereas miR-21inhibitor-transfected cells exhibited the opposite phenomenon(P<0.05). MiR-21 not only promoted cancer cell hyperplasia and contributed to tumor cell transformation and metastasis, but also post-transcriptionally downregulated PDCD4 protein expression. PDCD4 and miR-21 expression levels potentially play an important role in renal cell cancer.