PLK1 and cancer: Since ALKBH4 knockdown downregulated the expression of PLK1 and PLK4 (Supplementary Table S2), ALKBH4 may function as a tumour promoter by accelerating cancer cell proliferation via upregulation of E2F1 signalling in early stage, and by promoting metastasis via upregulation of PLK signalling in late-stage NSCLC.