Fig. 1
circPLPP4 expression is increased in CDDP-resistant OC cells and tissues. A, B Unsupervised hierarchical clustering and volcano plot analysis of the circRNAs differentially expressed in Platinum resistant OC tissues and Platinum sensitive OC tissues. C qRT-PCR analysis of circPLPP4 expression in a 20-case cohort of freshly collected human OC samples with Platinum resistance and 20-case cohort of Platinum sensitive OC samples. The nonparametric Mann–Whitney U-test was used. D qRT-PCR analysis of circPLPP4 in two CDDP resistant OC cells and its corresponding parent cell. E Schematic illustration demonstrated the circularization of exons 2–4 of PLPP4 forms circPLPP4 by “head-to-tail” junction and the upper black arrow represents the splicing sites. F, G circPLPP4 expression in A2780-CDDP and SKOV3-CDDP cells examined by RT-PCR. Agarose gel electrophoresis demonstrated that divergent primers amplified circPLPP4 in cDNA rather than genomic DNA (gDNA). GAPDH acted as a negative control. H RT–qPCR analysis for the expression of circPLPP4 and PLPP4 mRNA after treatment with RNase R in A2780-CDDP and SKOV3-CDDP cells. Data represent mean ± S.D. from three independent experiments; The P value was determined by a two-tailed unpaired Student’s t test. I, J qRT–PCR analysis for the expression of circPLPP4 and PLPP4 mRNAs after Actinomycin D treatment at the indicated time in A2780-CDDP and SKOV3-CDDP cells. Data represent mean ± S.D. from three independent experiments; The P value was evaluated by a two-way ANOVA. K, L Cytoplasmic and Nuclear mRNA Fractionation experiment indicating that circPLPP4 mainly localized in the cytoplasm. β-actin and U3 were applied as positive controls in the cytoplasm and nucleus, respectively. Data represent mean ± S.D. from three independent experiments; The P value was evaluated by a two-tailed unpaired Student’s t test. M, N. FISH for circPLPP4. Nuclei were stained with DAPI. * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001, ns indicates no significance. Each error bar represents the mean ± SD of three independent experiments