Fumarate Mediates a Chronic Proliferative Signal in Fumarate Hydratase-Inactivated Cancer Cells by Increasing Transcription and Translation of Ferritin Genes

Abstract

Germ line mutations of the gene encoding the tricarboxylic acid (TCA) cycle enzyme fumarate hydratase (FH) cause a hereditary cancer syndrome known as hereditary leiomyomatosis and renal cell cancer (HLRCC). HLRCC-associated tumors harbor biallelic FH inactivation that results in the accumulation of the TCA cycle metabolite fumarate. Although it is known that fumarate accumulation can alter cellular signaling, if and how fumarate confers a growth advantage remain unclear. Here we show that fumarate accumulation confers a chronic proliferative signal by disrupting cellular iron signaling. Specifically, fumarate covalently modifies cysteine residues on iron regulatory protein 2 (IRP2), rendering it unable to repress ferritin mRNA translation. Simultaneously, fumarate increases ferritin gene transcription by activating the NRF2 (nuclear factor [erythroid-derived 2]-like 2) transcription factor. In turn, in- creased ferritin protein levels promote the expression of the promitotic transcription factor FOXM1 (Forkhead box protein M1). Consistently, clinical HLRCC tissues showed increased expression levels of both FOXM1 and its proliferation-associated target genes. This finding demonstrates how FH inactivation can endow cells with a growth advantage. Specific Aims 1. Show biallelic fumarate hydratase (FH) inactivation results in fumarate accumulation. We currently hypothesize FH inactivation will result in an inactive enzyme that cannot process fumarate. 2. Determine if and how fumarate accumulation endows cells with a chronic proliferative signal. We hypothesize that fumarate accumulation disrupts cellular iron signaling resulting in a chronic proliferative signal. Main Result - Fumarate accumulation confers a chronic proliferative signal in HLRCC cells. Conclusion - FH inactivation disrupts cellular iron signaling and induces a chronic proliferative phenotype, providing a mechanistic explanation for how the inactivation of FH can give rise to a fundamental cancer hallmark.