FTO-mediated m6A modification of QPCT promotes tumorigenesis in lung adenocarcinoma by inducing macrophage chemotaxis and M2 polarization.

Abstract

Lung adenocarcinoma (LUAD), the most common histologic subtype of lung cancer, is characterized by malignant and high infiltrating. Glutaminyl-peptide cyclotransferase (QPCT) promotes cancer progression by modifying the N-terminus of chemokine C-C motif ligand 2 (CCL2) to a pyroglutamate residue and stabilizing the protein. The role of QPCT in LUAD is still unknown. QPCT mRNA and protein expression were up-regulated in clinical LUAD specimens. By generating stable HCC44 cells with QPCT overexpression and stable A549 cells with QPCT knockdown, we found that QPCT knockdown notably inhibited LUAD cell proliferation. Additionally, QPCT deletion reduced the CCL2 contents in LUAD cell supernatants and inhibited phorbol 12-myristate 13-acetate-induced THP-1 macrophage chemotaxis toward tumor cells or tumor cell conditioned medium. The CD68⁺/CD206⁺ cell ratio was reduced by QPCT deletion in vitro. Nude mice inoculated with parental A549 or cells with stable QPCT knockdown were used to explore QPCT functions. The results were consistent with in vitro experiments. QPCT is predicted to be modified by N6-methyladenosine (m6A), and we performed methylated RNA immunoprecipitation PCR to confirm this result in A549 cells. The m6A demethylase fat mass and obesity-associated protein (FTO) mRNA expression positively correlated with QPCT mRNA in LUAD samples. FTO bound to QPCT mRNA and FTO knockdown affected QPCT mRNA stability. FTO deletion in HCC44 cells abrogated the macrophage recruitment and macrophage M2 polarization induced by QPCT overexpression. In conclusion, QPCT promotes tumorigenesis in LUAD by increasing macrophage recruitment and M2 macrophage proportion. This may be due to FTO-mediated demethylation increasing the QPCT mRNA stability.