Iron is an essential element for normal cellular function, and many tumor cells satisfy their high iron requirement via altered expression of proteins that regulate iron metabolism. While iron fuels tumor growth, it presents a paradox: how to maintain redox homeostasis and resist ferroptosis, a ROS-reliant and iron-dependent form of regulated cell death. Many tumor types resist the ferroptotic cascade via increased expression/activity of antioxidant ferroptosis suppressor pathways (FSPs). To date, two complementary but non-redundant pathways have been identified: a canonical glutathione (GSH)-dependent pathway and, more recently, a novel FSP that relies on ubiquinol (the reduced form of CoQ) to prevent lethal lipid peroxidation. Our goal is to determine how the oncogenic Kaposi sarcoma herpesvirus (KSHV) manipulates host iron metabolism and antioxidant defense to promote Kaposi sarcoma (KS) tumorigenesis while resisting ferroptosis.
Lymphatic endothelial cells (LEC) de novo-infected with KSHV-BAC16 were used for this study. Expression of host genes involved in iron metabolism and ferroptosis resistance was evaluated by RNA-seq, qPCR, immunoblot, FACS and IFA. Cellular iron content was measured by ICP-MS. Markers of pro/antioxidant status (e.g., ROS, GSH) were measured via quantitative colorimetric assay. Susceptibility to ferroptosis was evaluated using selective inducers and inhibitors, and measured via cell viability and lipid peroxidation assays.
Our data indicate that KSHV manipulates the host iron regulon to promote iron acquisition and an iron-responsive growth phenotype. However, despite these changes, infected cells do not succumb to ferroptosis. Notably, KSHV significantly upregulates the expression of xCT, the small subunit of system xc– that functions as the upstream node of the GSH-dependent FSP. Chemical inhibition of xCT induces ferroptotic death only in KSHV-infected LEC, suggesting that enhanced xCT function is central to the ability of infected cells to resist ferroptosis. KSHV also upregulates the oxidoreductase FSP1 (formerly AIFM2), the key component of the novel CoQ-dependent FSP, identifying a second ferroptosis escape mechanism in infected cells.
We have identified unique vulnerabilities in KSHV-infected cells that reflect the delicate pro/antioxidant balance required to facilitate growth and survival. Our work suggests that selective induction of ferroptosis in KSHV-infected cells represents a promising anti-KS strategy.