The roles of RNA modification during organ metastasis of cancer cells are not known. Here we established breast cancer lung metastasis cells by three rounds of selection of lung metastatic subpopulations in vivo and designated them as BCLMF3 cells. In these cells, mRNA N6-methyladenosine (m6A) and methyltransferase METTL3 were increased, while the demethylase FTO was decreased. Epi-transcriptome and transcriptome analyses together with functional studies identified keratin 7 (KRT7) as a key effector for m6A-induced breast cancer lung metastasis. Specifically, increased METTL3 methylated KRT7-AS at A877 to increase the stability of a KRT7-AS/KRT7 mRNA duplex via IGF2BP1/HuR complexes. Furthermore, YTHDF1/eEF-1 was involved in FTO-regulated translational elongation of KRT7 mRNA, with methylated A950 in KRT7 exon 6 as the key site for methylation. In vivo and clinical studies confirmed the essential roles of KRT7, KRT7-AS, and METTL3 for lung metastasis and clinical progression of breast cancer. Collectively, m6A promotes breast cancer lung metastasis by increasing the stability of a KRT7-AS/KRT7 mRNA duplex and translation of KRT7. Significance: This study suggests that N6-methyladenosine is a key driver and potential therapeutic target in breast cancer metastasis.

Background Dysregulation of N6-methyladenosine (m6A) is associated with various human diseases including cancer. This study aimed to evaluate the level of m6A as a biomarker for gastric cancer (GC) diagnosis. Methods Peripheral blood samples were collected from 100 GC patients, 30 benign gastric disease (BGD) patients, and 75 healthy controls (HCs). Levels of m6A in total RNA and expression of m6A-related proteins were analyzed. Results The m6A levels in peripheral blood RNA were significantly increased in the GC group compared with those in the BGD or HC groups; moreover, levels increased with the progression and metastasis of GC and decreased in GC patients after surgery. The area under the curve (AUC) for m6A in the GC group was 0.929 (95% CI, 0.88–0.96), which is markedly greater than the AUCs for carcinoembryonic antigen (CEA; 0.694) and carbohydrate antigen 199 (CA199; 0.603). The combination of CEA and CA199 with m6A improved the AUC to 0.955 (95% CI, 0.91–0.98). The expressions of m6A demethylases ALKBH5 and FTO were significantly downregulated in the GC group compared with the HC group. Coculture with GC cells increased the m6A of RNA in promyelocytic (HL-60) and monocytic (THP-1) leukemia cells and nontumorigenic human peripheral blood B lymphocyte cells (PENG-EBV). Furthermore, a xenograft model enhanced the m6A in peripheral blood RNA of mice. Accordingly, expressions of ALKBH5 and FTO were decreased both in vitro and in vivo. Conclusions Level of m6A in peripheral blood RNA is a promising noninvasive diagnostic biomarker for GC patients.

Background tRNA-derived small RNAs (tDRs), which are widely distributed in human tissues including blood and urine, play an important role in the progression of cancer. However, the expression of tDRs in colorectal cancer (CRC) plasma and their potential diagnostic values have not been systematically explored. Methods The expression profiles of tDRs in plasma of CRC and health controls (HCs) are investigated by small RNA sequencing. The level and diagnostic value of 5′-tRF-GlyGCC are evaluated by quantitative PCR in plasma samples from 105 CRC patients and 90 HCs. The mechanisms responsible for biogenesis of 5′-tRF-GlyGCC are checked by in vitro and in vivo models. Results 5′-tRF-GlyGCC is dramatically increased in plasma of CRC patients compared to that of HCs. The area under curve (AUC) for 5′-tRF-GlyGCC in CRC group is 0.882. The combination of carcinoembryonic antigen (CEA) and carbohydrate antigen 199 (CA199) with 5′-tRF-GlyGCC improves the AUC to 0.926. Consistently, the expression levels of 5′-tRF-GlyGCC in CRC cells and xenograft tissues are significantly greater than that in their corresponding controls. Blood cells co-cultured with CRC cells or mice xenografted with CRC tumors show increased levels of 5′-tRF-GlyGCC. In addition, we find that the increased expression of 5′-tRF-GlyGCC is dependent on the upregulation of AlkB homolog 3 (ALKBH3), a tRNA demethylase which can promote tRNA cleaving to generate tDRs. Conclusions The level of 5′-tRF-GlyGCC in plasma is a promising diagnostic biomarker for CRC diagnosis.