J Biol Chem. 2020 Jan 30. pii: jbc.RA119.011930. [Epub ahead of print]
In human cancer cells that harbor mutant KRAS and WT P53 (P53), KRAS contributes to the maintenance of low P53 levels. Moreover, KRAS depletion stabilizes and reactivates P53 and thereby inhibits malignant transformation. However, the mechanism by which KRAS regulates P53 is largely unknown. Recently, we showed that KRAS depletion leads to P53 Ser-15 phosphorylation (P-P53) and increases the levels of P53 and its target P21/wild-type P53-activated fragment 1 (WAF1)/CIP1. Here, using several human lung cancer cell lines, siRNA-mediated gene silencing, immunoblotting, quantitative RT-PCR, promoter-reporter assays and reactive oxygen species (ROS) assays, we demonstrate that KRAS maintains low P53 levels by activating the NFE2-related factor 2 (NRF2)-regulated antioxidant defense system. We found that KRAS depletion led to down-regulation of NRF2 and its targets NAD(P)H quinone dehydrogenase 1 (NQO1) and solute carrier family 7 member 11 (SLC7A11), decreased reduced/oxidized glutathione (GSH/GSSG) ratio, and increased ROS levels. We noted that the increase in ROS is required for increased P-P53, P53, and P21/WAF1/CIP1 levels following KRAS depletion. Downstream of KRAS, depletion of RAS-like proto-oncogene B (RALB) and IκB kinase (IKK)-related TANK-binding kinase 1 (TBK1) activated P53 in a ROS- and NRF2-dependent manner. Consistent with this, the IKK inhibitor BAY11-7085 and dominant-negative mutant IκBαM inhibited NFκB activity and increased P-P53, P53, and P21/WAF1/CIP1 levels in a ROS-dependent manner. In conclusion, our findings uncover an important role for the NRF2-regulated antioxidant system in KRAS-mediated P53 suppression.
Keywords: GTPase Kras (KRAS); Nuclear factor 2 (erythroid-derived 2-like factor) (NFE2L2) (Nrf2); RalB; TBK1; p53; reactive oxygen species (ROS); redox signaling