SIAH2-mediated and organ-specific restriction of HO-1 expression by a dual mechanism.

The intracellular levels of the cytoprotective enzyme heme oxygenase-1 (HO-1) are tightly controlled. Here, we reveal a novel mechanism preventing the exaggerated expression of HO-1. The analysis of mice with a knock-out in the ubiquitin E3 ligase seven in absentia homolog 2 (SIAH2) showed elevated HO-1 protein levels in specific organs such as heart, kidney and skeletal muscle. Increased HO-1 protein amounts were also seen in human cells deleted for the SIAH2 gene. The higher HO-1 levels are not only due to an increased protein stability but also to elevated expression of the HO-1 encoding HMOX1 gene, which depends on the transcription factor nuclear factor E2-related factor 2 (NRF2), a known SIAH2 target. Dependent on its RING (really interesting new gene) domain, expression of SIAH2 mediates proteasome-dependent degradation of its interaction partner HO-1. Additionally SIAH2-deficient cells are also characterized by reduced expression levels of glutathione peroxidase 4 (GPX4), rendering the knock-out cells more sensitive to ferroptosis.

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