Effect of RIF1 on response of non-small-cell lung cancer patients to platinum-based chemotherapy by regulating MYC signaling pathway.

Platinum-based chemotherapy is used as first-line therapy for advanced non-small-cell lung cancer (NSCLC). However, there is no effective indicator to predict whether the patient would be chemo-resistant or sensitive to the therapy. In addition, it is urgent to elucidate the mechanisms of cisplatin resistance. RIF1 plays important roles in DNA replication regulation and DNA repair pathway. However, the role of RIF1 in NSCLC progression and chemotherapy response is still unknown. In this study, we found that RIF1 expression was correlated with the response of NSCLC patients to platinum-based chemotherapy (n=89, P=0.002). Among patients who have been treated with platinum chemo-therapy, those with high levels of RIF1 expression had significantly shorter survival than those with low RIF1 expression (P<0.05). RIF1 knockdown increased sensitivity to cisplatin in NSCLC patients both in vitro and in vivo . Moreover, RIF1 knockdown induced G0/G1 phase arrest and increased cisplatin-induced apoptosis and DNA damage. Further investigation showed that RIF1 regulated the expression of MYC and MYC downstream targets, including the cell cycle and double-stranded break (DSB) repair genes which might mediate the effect of RIF1 on cellular response to cisplatin. Overexpression of MYC could reverse the inhibition of MYC targets by RIF1 knockdown. Taken together, these data revealed that RIF1 played an important role in regulating MYC and MYC-activated genes, which in turn contributes to cellular response to cisplatin and NSCLC patients' response to platinum-based chemotherapy. RIF1 might serve as a novel biomarker for predicting platinum-based chemo-sensitivity and the prognosis of NSCLC patients, so as to guide the chemotherapy regimen adjustment for individual patient with NSCLC and improve their clinical outcomes.