Non denatured gel sample loading buffer

Total protein was isolated from TNBC samples (tumour tissues, paired normal adjacent tissues and cell lines) using RIPA lysis buffer (Beyotime Institute of Biotechnology). Total protein was separated by 10% SDS‐PAGE (25 μg protein per lane), and the protein was transferred with PVDF membrane (MilliporeSigma). Blocking of PVDF membrane was performed with 5% nonfat milk powder (Beyotime). To detect the expression of PKM2 protein in different conformations, the total protein extracted from the sample was not thermal denatured and was denatured using a non‐denatured gel sample loading buffer (Beyotime). Next, protein electrophoresis was performed using native PAGE running buffer (Beyotime). The PVDF membranes were probed at 4°C overnight with antibodies against METTL14 (1:1000; Abcam), PKM2 (ProteinTech Group, Inc.), DGCR8 (1:1000; Abcam), TRIM9 (1:1000; Abcam) and β‐actin (1:5000; Abcam). Finally, protein expression was analysed by chemiluminescence reagents (Hyperfilm ECL).