Mechanism of the N6-methyladenosine reader heterogeneous nuclear ribonucleoprotein C facilitating immune escape in thyroid cancer by stabilizing programmed death ligand 1.

Abstract

Thyroid cancer (TC) is a leading malignancy of the endocrine system. We investigated mechanism of the N6-methyladenosine (m6A) reader heterogeneous nuclear ribonucleoprotein C (HNRNPC) facilitating immune escape in TC by stabilizing programmed death ligand 1 (PD-L1). HNRNPC expression in TC tissues was analyzed using databases. Human TC cells (BHT-101, B-CPAP, SW579) and human thyroid follicular epithelial cells (Nthy-ori3-1) were cultured in vitro. SW579 cells were treated with pcDNA3.1-HNRNPC (oe-HNRNPC) and small interfering (si)-PD-L1, and B-CPAP cells were transfected with si-HNRNPC. HNRNPC and PD-L1 expression levels were assessed by RT-qPCR and Western blot. Cell proliferation, migration and invasion were evaluated by CCK-8, colony formation, and Transwell assays. Carboxyfluorescein diacetate succinimidyl ester-labelled CD8⁺ T cell proliferation and effector cytokine (interferon-γ, tumor necrosis factor-α) levels were measured by flow cytometry and ELISA. The correlation between HNRNPC and PD-L1 expression in TC tissues, m6A modification sites on PD-L1 messenger RNA (mRNA), and HNRNPC-PD-L1 interaction were analyzed by databases and RIP assay. PD-L1 m6A modification was determined by Me-RIP assay. PD-L1 mRNA stability was detected by treating cells with actinomycin D. HNRNPC was notably highly expressed in TC cells. HNRNPC promoted TC cell proliferation, migration and invasion, facilitating immune escape. Mechanistically, HNRNPC mediated m6A modification to strengthen PD-L1 mRNA stability and up-regulate PD-L1 expression. Moreover, knockdown of PD-L1 partially reversed the promotional effect of HNRNPC on immune escape in TC cells. HNRNPC bolstered PD-L1 stability and up-regulated PD-L1 expression through m6A modification, thus promoting immune escape in TC.