Circ_0001402 knockdown suppresses the chemoresistance and development of DDP‐resistant cutaneous squamous cell carcinoma cells by functioning as a ceRNA for miR‐625‐5p

Abstract Cutaneous squamous cell carcinoma (CSCC) is the most common metastatic skin cancer. Circular RNAs (circRNAs) are differentially expressed in CSCC and can sequester and sponge microRNAs. GSE74758 shows that hsa_circ_0001402 (circ_0001402) is the most overexpressed circRNA in CSCC. Expression of circ_0001402, microRNA(miR)‐625‐5p and karyopherin subunit alpha 4 (KPNA4) was detected by quantitative real‐time polymerase chain reaction and/or Western blot. Colon formation, flow cytometry, Transwell assays and xenograft tumour model confirmed the development of CSCC cells. The competing endogenous RNA (ceRNA) interaction was confirmed by dual‐luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Circ_0001402 was significantly upregulated in CSCC tissues and cells, and higher expression of circ_0001402 was found in DDP‐resistant samples. Functionally, circ_0001402 knockdown induced apoptosis and inhibited half maximal inhibitory concentration of DDP, colony formation, migration and invasion of DDP‐resistant CSCC cells, accompanied with the depressed multi‐drug resistance‐1 (MDR1) and MDR‐related protein‐1, while miR‐625‐5p inhibitor could counteract these effects. Mechanically, circ_0001402 mediated the expression regulation of KPNA4 via functioning as a ceRNA for miR‐625‐5p. KPNA4 re‐expression could abate the functions of miR‐625‐5p. Furthermore, circ_0001402 knockdown could hinder tumour growth of DDP‐resistant CSCC. Circ_0001402 knockdown can suppress the development and chemoresistance of DDP‐resistant CSCC cells at least partly through targeting miR‐625‐5p/KPNA4 axis.