Double vulnerability of active-NRF2 Lung Squamous cell carcinoma to NRF2 and TRIM24
Lung squamous cell cancer (LUSC) is associated with very poor survival due to the lack of specific treatments. A common genetic alteration in LUSC involves mutations in NFE2L2 (also named NRF2) or its regulator, KEAP1, resulting in increased activity of the NRF2 transcription factor (TF). This study compares the requirement for active-NRF2 in LUSC cell lines. Although normal-NRF2 cells are more sensitive to oxidative stress, they do not require NRF2 for survival under non-stress conditions, while LUSC cells with active-NRF2 mutations depend on NRF2 for viability. NRF2 depletion in patient-derived organoid cultures with active-NRF2 as well as in xenografts with active-NRF2 triggers cell death. A CRISPRa/dCas9 screening for gene targets capable of rescuing cell survival in these cells identified TRIM24 as a gene whose expression rescues cell survival in NRF2-depleted active-NRF2 LUSC cells. Alongside oxidative stress, the lack of TRIM24 selectively contributed to the induction of cell death (apoptosis and ferroptosis) in active-NRF2 LUSC cells. Cells with a high NFE2L2/KEAP1 copy number ratio also undergo cell death. The increase in cell death observed upon TRIM24 depletion involves a reduction in AKT activity resulting from destabilization of the PI3Ka catalytic subunit. Notably, overexpression of PI3Ka rescues cell survival in TRIM24-depleted active-NRF2 cells. These findings point to novel therapeutic approaches in LUSC. Overall design: The authors have investigated the relevance of the NRF2 (NFE2L2) pathway in lung squamous cell carcinoma (LUSC) with the aim to identify novel therapeutic strategies. They report frequent activation of the NRF2/KEAP1 axis in LUSC and suggest impact on resistance to stress conditions (in particular ROS-induced oxidative stress) and dependency of LUSC cells on active NRF2 signaling. Depletion of NRF2 using shRNA results in loss of cell viability in LUSC cells and patient-derived organoids which also translates in reduced in vivo growth in a cell line xenograft model. Using CRIPRa/dCas9 screening they subsequently identify potential mediators of NRF2 dependency and further investigate the role of TRIM24. In cells with activated NRF2 signaling the reduction of TRIM24 induces cell death through apoptosis and ferroptosis. The mechanism underlying cell death mediated by TRIM24 depletion involves reduction of AKT activity through post-translational regulation of PI3Ka levels. The authors suggest that these findings could have therapeutic implications in LUSC.