NIT2 epigenetically restrains oxidative phosphorylation to overcome fluorouracil resistance in gastric cancer

Fluorouracil (5-FU) chemoresistance is an important reason for the postoperative recurrence and poor prognosis of gastric cancer, but there is still no effective way to overcome chemoresistance. Here, by using the CRISPR/Cas9 system, we identify nitrilase family member 2 (NIT2) reverses chemoresistance, regardless of its metabolic function. NIT2 depletion causes H3K14 acetylation (H3K14ac) increase and NF-?B signalling activation, in turn upregulating oxidative phosphorylation (OXPHOS) and promoting chemoresistance. Mechanistically, NIT2 prevents BRD1 from binding histones and releases ING4 to degrade the transcription factor RELA. Upon 5-FU stimulation, the E3 ligase CCNB1IP1 interacts with NIT2 to cause autophagic degradation of NIT2. In addition, NIT2 downregulation correlates with poor prognosis in gastric cancer patients, and this is probably related to the promotion of OXPHOS. Our finding highlights the nonenzymatic function of NIT2 in chemoresistance and show that the blockade of OXPHOS by metformin can enhance chemosensitivity to 5-FU upon loss of NIT2. Overall design: Control and shNIT2 MKN45 cells were crosslinked with formaldehyde and quenched with 125 mM glycine. The fragmented chromatin fragments were pre-cleared and then immunoprecipitated with Protein A + G Magnetic beads coupled with anti-H3K14ac antibodies. After reverse crosslinking, ChIP and input DNA fragments were end-repaired and A-tailed followed by adaptor ligation. The DNA libraries were amplified for 15 cycles and sequenced.