The mechanism of METTL6/DALRD3 regulating cell cycle-mediated chemoresistance in hepatocellular carcinoma

Chemoresistance worsens the prognosis of hepatocellular carcinoma (HCC). This study focuses on how methyltransferase-like protein 6 (METTL6)/DALR anticodon binding domain containing 3 (DALRD3) regulates cell cycle progression and impacts HCC chemoresistance. HCC cell lines with relatively low or high METTL6 expression were intervened with cisplatin (DDP) to construct DDP-resistant cell models, and later transfected with overexpression (oe)-METTL6 plasmid, oe-DALRD3 plasmid, small interfering RNA (si)-METTL6, and/or si-DALRD3. A battery of cellular biological functional experiments and DDP drug sensitivity tests were performed to characterize the modulatory effects of METTL6 or DALRD3 on HCC chemoresistance. The interaction between METTL6 and DALRD3 was validated using coimmunoprecipitation. 3-methylcytosine (m 3 C) modification and expression were further detected using dot blot and Northern blot assays. A subcutaneous xenograft mouse model was established with METTL6- or DALRD3-deficient HCC cells, which were exposed to DDP for experimental validation of in vitro findings. METTL6 and DALRD3 were upregulated in DDP-resistant HCC cells, and their upregulation in HCC tissues correlated with poor prognosis. Re-expression of METTL6 or DALRD3 led to strengthened cell proliferation, aggravated cell cycle progression, and augmented DDP chemoresistance. The validated METTL6-DALRD3 interaction increased m 3 C modification. Northern blot further validated serine transfer RNA-m 3 C at position 32 (tRNA Ser -m 3 C32) modification mediated by the METTL6-DALRD3 complex. Rescue experiments unveiled that DALRD3 overexpression reversed METTL6 knockdown-mediated HCC phenotypes. Either METTL6 or DALRD3 knockdown potentiated DDP chemosensitivity in HCC xenograft mice. METTL6/DALRD3 mediated tRNA Ser -m 3 C32 modification may participate in DDP resistance in HCC cells by regulating cell cycle progression.