In a study published in EBioMedicine, the researchers from Shanghai Institute of Nutrition and Health of the Chinese Academy of Sciences and Zhongshan Hospital (Shanghai) uncovered that Scribble is critical to the efficacy of cisplatin-based chemotherapy, an effect mediated by LRR domain-dependent protection of Nox2 from degradation, thereby promoting Nox2/Ros signaling. Interestingly, they found that Scribble is responsible for elevated Nrf2/PD-L1 expression, which may separately contribute to cisplatin resistance in non-small cell lung cancer (NSCLC). 

Cisplatin (cis-diamminedichloro-platinum(II), CDDP) is one of the most commonly used chemotherapeutic agents in the treatment of cancer, in particular, in NSCLC. Platinum-containing drugs are used as first-line chemotherapeutic agents for the treatment of human NSCLC.

Scribble (Scrib) is one component of the Scribble/Discs large (Dlg) /Lethal giant larvae (Lgl) polarity complex, which localizes to the basolateral side of the epithelial cell membrane. Human Scribble (hScrib) is a functional homologue of Drosophila Scribble. Scribble acts via the MAPK-ERK pathway to decrease the tumor burden in the Kras^LSL-G12D lung cancer mouse model. However, the mechanism underlying the tumor suppressor function of Scribble and its potential relevance to the efficacy of chemotherapy in NSCLC are poorly understood. 

Therefore, the researchers collected tumor specimens from NSCLC patients who had not previously received chemotherapy, and then used standard cisplatin or carboplatin-based first-line chemotherapy to treat these NSCLC patients. The results revealed that Scribble protein level positively correlated with chemotherapeutic sensitivity in NSCLC, which was further confirmed by another cohort consisting of 72 NSCLC patients and xenograft experiment in vivo. 

Chemotherapeutic agents generate reactive oxygen species (ROS) in patients undergoing chemotherapy. The only enzyme family that produces ROS as its main product is the NADPH oxidase (Nox) family, among which Nox2 is robustly expressed in lung alveolar epithelial cells and is involved in the regulation of epithelial cell function, a pattern similar to that of Scribble. It has been reported that Scribble contributes to Nox complex activation and ROS generation in inflammation in primary myeloid cells. 

Using mass spectrometric, immunofluorescence and immunoprecipitation assays, the researchers identified Scribble interacted with Nox2 in LRR-domain dependent fashion. They also found that Scribble correlated with Nox2 accumulation, an effect mediated by decrease in proteasomal degradation of Nox2 protein. This stabilization was critical to cisplatin-induced ROS generation and apoptosis, which is closely related to cisplatin sensitivity during chemotherapy.  

Previous data have been reported that nuclear factor, erythroid 2 like 2 (Nrf2), an antioxidant proteins-associated transcription factor, directly induces PD-L1 expression in melanoma, an observation that is consistent with the researchers’ findings in NSCLC cells exposed to cisplatin. Notably, conventional chemotherapy-induced PD-L1 expression was demonstrated to promote chemoresistance in NSCLC. 

Performing dataset analysis, Kras^LSL-G12D genetically engineered lung cancer mouse model and assessing NSCLC cell lines and chemoresistance cell lines, the researchers revealed that a negative correlation between Nrf2/PD-L1 and Scribble levels was seen both in vitro and in vivo. They further showed that Scribble might suppress PD-L1 expression via inhibition of Nrf2’s transcriptional activity, which might depend (in part) on ROS level. 

This study revealed that loss of Scribble confers cisplatin resistance during NSCLC chemotherapy, an effect that is mediated via Nox2/ROS and Nrf2/PD-L1 signaling. Although it appears to lead to the development of cisplatin resistance (by imapring Nox2/ROS and Nrf2/PD-L1), Scribble deficiency is still possible that Scribble deficiency-elevated PD-L1 may offer benefits in immunotherapy. 

Schematic figure for the proposed model of regulation of Nox2/ROS and Nrf2/PD-L1 signaling and regulation of cisplatin resistance by Scribble in NSCLC. (Image by Prof. ZHAN's group)