Cysteine restriction induces ferroptosis depending on the polyamine biosynthetic pathway in hepatic cancer cells

Abstract

Background and Aims: Metabolic activities are also known to affect responses and disease processes of the liver which is a central organ for organismal metabolism. Liver diseases like intestinal failure associated liver disease (IFALD) and hepatocellular carcinoma are known to be affected by nutrition contents but the mechanisms behind remain unclear. In this study, we aimed to investigate the relationship between the concentration of sulfur-containing amino acids and hepatocellular response, and further investigated the mechanism focusing on methionine adenosyltransferase (MAT), which plays a central role in methionine metabolism by synthesizing S-adenosylmethionine (SAM). Methods: Mouse hepatoma Hepa1 cells were cultured in media with reduced amounts of cysteine, methionine, or both. Cell death was monitored using propidium iodide (PI) and annexin V staining followed by flow cytometry. Inhibitors of ferroptosis (Fer-1), autophagy (GSK872), SAM synthesis (cycloleucine), or polyamine synthesis (sardomozide and DFMO) were used. Results: Cysteine restriction induced marked cell death, whereas simultaneous restriction of cysteine and methionine fully suppressed the cell death. Cysteine restriction-induced cell death was suppressed with Fer-1 and GSK872, suggesting the involvement of ferroptosis in this process. Cysteine restriction-induced cell death was also suppressed with knockdown of MAT2A or its inhibitor cycloleucine. Furthermore, inhibitors of several enzymes in the polyamine biosynthetic pathway also suppressed the cell death. In contrast, primary culture of mouse hepatocytes did not show cell death upon cysteine restriction. Conclusions: These results suggest that SAM-polyamine metabolism is a critical modulator of ferroptosis of hepatic cancer cells. Since normal liver cells were more resistant to ferroptosis than cancer cells, cysteine restriction may be exploited in treating hepatic cancer by inducing ferroptosis specifically among cancer cells.