CPA4 and non-small cell lung carcinoma: Next, based on the previous studies [29, 34], we also uncovered the regulating mechanisms of circ-CPA4, let-7 miRNA and PD-L1 in NSCLC cells, and found that circ-CPA4 overexpression promoted PD-L1 expressions by acting as RNA sponges for let-7 miRNA.