Covalent N-arylation by the pollutant 1,2-naphthoquinone activates the EGF receptor

Methyl vinyl ketone and its analogs covalently modify PI3K and alter physiological functions by inhibiting PI3K signaling

Reactive carbonyl species (RCS), which are abundant in the environment and are produced in vivo under stress, covalently bind to nucleophilic residues such as Cys in proteins. Disruption of protein function by RCS exposure is predicted to play a role in the development of various diseases such as cancer and metabolic disorders, but most studies on RCS have been limited to simple cytotoxicity validation, leaving their target proteins and resulting physiological changes unknown. In this study, we focused on methyl vinyl ketone (MVK), which is one of the main RCS found in cigarette smoke and exhaust gas. We found that MVK suppressed PI3K-Akt signaling, which regulates processes involved in cellular homeostasis, including cell proliferation, autophagy, and glucose metabolism. Interestingly, MVK inhibits the interaction between the epidermal growth factor receptor and PI3K. Cys656 in the SH2 domain of the PI3K p85 subunit, which is the covalently binding site of MVK, is important for this interaction. Suppression of PI3K-Akt signaling by MVK reversed epidermal growth factor-induced negative regulation of autophagy and attenuated glucose uptake. Furthermore, we analyzed the effects of the 23 RCS compounds with structures similar to MVK and showed that their analogs also suppressed PI3K-Akt signaling in a manner that correlated with their similarities to MVK. Our study demonstrates the mechanism of MVK and its analogs in suppressing PI3K-Akt signaling and modulating physiological functions, providing a model for future studies analyzing environmental reactive species.

[Molecular mechanism of EGFR signaling evoked by environmental pollutant 1,2-naphthoquinone]

The epidermal growth factor receptor (EGFR) is the most extensively examined receptor tyrosine kinase. Several EGFR mutations and modifications have been shown to induce self-activation, which plays a central role in carcinogenesis. Recently, environmental chemicals such as PM2.5 can also activate EGFR and become risk factors for cancer. Although, the detailed mechanism remains unknown. In this study, we focused on 1,2-naphthoquinone (1,2-NQ) which is a secondary metabolite of naphthalene. Humans are exposed to 1,2-NQ through the combustion of fossil and diesel fuel and from tobacco smoke and PM2.5. Here, we demonstrate that 1,2-NQ is a novel EGFR-specific activator. We found that 1,2-NQ forms a covalent bond called N-arylation with EGFR Lys80 which is in the extracellular domain by LC-MS/MS. This modification activates the EGFR-Akt signaling pathway, which inhibits serum deprivation-induced apoptosis in A549 cells. Our study reveals an original mode of EGFR activation via covalent binding. We propose the correlation between EGFR activation without ligands and environmental pollutant-associated diseases such as cancer.