We established an APEX proximity labeling strategy in coupled with mass spectrometry to identify interacting proteins of RNF214. In this approach, we first fused an engineered ascorbate peroxidase (APEX2) to either N-terminus or C-terminus of RNF214, expressed these two fusion proteins in HLF, an HCC cell line, near the endogenous level, and generated short-lived radicals around the APEX2-RNF214 fusion proteins to label biotin on nearby interactive proteins by adding hydrogen peroxide (H2O2) and biotin-phenol (also called biotin-tyramide) transiently. Biotinylated proteins were then isolated using Streptavidin resin for protein identification by mass spectrometry.