N 6 -methyladenosine (m 6 A) modification of mRNAs is a predominant epigenetic regulatory mechanism in tumor initiation and progression. Cancer stem cells (CSCs) are the key drivers of colorectal cancer (CRC) initiation and chemotherapy resistance. Here, we found that the m 6 A reader YT521-B homologous domain family, member 1 (YTHDF1), promotes CRC stemness, tumorigenesis, and chemotherapy resistance. YTHDF1 protein expression was positively correlated with CD133 and LGR5 expression in human CRC tissues (N = 184, P < 0.001 for both markers). YTHDF1 promoted m 6 A-dependent self-renewal in CSCs and patient-derived organoids and increased the tumor-initiating potential in vivo. Lgr5-specific Ythdf1 -KI mice presented accelerated Apc Min/+ ( P < 0.05) and AOM/DSS ( P < 0.05)-induced colorectal tumorigenesis, whereas Lgr5-specific Ythdf1 knockout in Apc Min/+ mice inhibited tumorigenesis ( P < 0.01). Integrative multiomic profiling revealed NOTCH1 as a downstream target. YTHDF1 binds m 6 A-modified NOTCH1 , promoting its translation and enhancing NOTCH signaling. NOTCH1 knockdown or blockade by the γ-secretase inhibitor DAPT abolished YTHDF1-mediated tumorigenesis in Ythdf1 knock-in mice ( P < 0.01). YTHDF1 promoted resistance to oxaliplatin and 5-fluorouracil in CSCs by inhibiting apoptosis and DNA damage. AOM/DSS-treated Ythdf1 knock-in mice presented increased resistance to oxaliplatin ( P < 0.001) and 5-fluorouracil ( P < 0.05). Translationally, in vivo targeting of YTHDF1 via VNP-encapsulated si YTHDF1 or salvianolic acid C inhibited tumor growth ( P < 0.05 for both treatments) and increased treatment efficacy when VNP was combined with oxaliplatin ( P < 0.05, SAC: P < 0.01) or 5-fluorouracil ( P < 0.05 for both treatments). In conclusion, YTHDF1 promotes stemness and chemoresistance in CRC via NOTCH1 activation. Targeting YTHDF1 is a promising strategy to improve the outcome of chemotherapy in CRC.
Cheung et al. (Mon,) studied this question.