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Iron-bound lipocalin-2 protects renal cell carcinoma from ferroptosis

ABSTRACT: While the importance of the iron-load of lipocalin-2 (Lcn-2) in promoting tumor progression is widely appreciated, underlying molecular mechanisms largely remain elusive. Considering its role as an iron-transporter, we aimed at clarifying iron-loaded, holo-Lcn-2 (hLcn-2)-dependent signaling pathways in affecting renal cancer cell viability. Applying RNA sequencing analysis in renal CAKI1 tumor cells to explore highly upregulated molecular signatures in response to hLcn-2, we identified a cluster of genes (SLC7A11, GCLM, GLS), which are implicated in regulating ferroptosis. Indeed, hLcn-2-stimulated cells are protected from erastin-induced ferroptosis. We also noticed a rapid increase in reactive oxygen species (ROS) with subsequent activation of the antioxidant Nrf2 pathway. However, knocking down Nrf2 by siRNA was not sufficient to induce erastin-dependent ferroptotic cell death in hLcn-2-stimulated tumor cells. In contrast, preventing oxidative stress through N-acetyl-L-cysteine (NAC) supple-mentation was still able to induce erastin-dependent ferroptotic cell death in hLcn-2-stimulated tumor cells. Besides an oxidative stress response, we noticed activation of the integrated stress response (ISR), shown by enhanced phosphorylation of eIF-2α and induction of ATF4 after hLcn-2 addition. ATF4 knockdown as well as inhibition of the ISR sensitized hLcn-2-treated renal tumor cells to ferroptosis, thus linking the ISR to pro-tumor characteristics of hLcn-2. Our study provides mechanistic details to better understand tumor pro-survival pathways initi-ated by iron-loaded Lcn-2.

ORGANISM(S): Homo sapiens

PROVIDER: GSE171939 | GEO | 2021/06/02

REPOSITORIES: GEO

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Project description:Ferroptosis is a form of regulated cell death characterized by iron-dependent lipid peroxidation. While ferroptosis has been identified as a mechanism for suppressing cancer, its overall physiological significance remains poorly understood. Recent studies have revealed that labile iron and lipid peroxides are released from ferroptotic cells, leading to the propagation of ferroptosis through lipid peroxidation. However, other specific effects of secreted factors derived from ferroptotic cells remain unclear. We constructed a model cell system capable of inducing ferroptosis by re-expressing the transcription factor BACH1, a potent inducer of ferroptosis, in immortalized mouse embryonic fibroblasts (iMEFs). We investigated the impact of the secreted factors from ferroptotic cells with the iMEFs. As a result, we observed that the administration of supernatant media from ferroptotic iMEFs activated proliferation of hepatoma cells and suppressed cellular senescence-like features. This suggested that ferroptotic MEFs secrete anti-senescent substances. Transcriptome analysis of ferroptotic MEFs revealed an increase in the secretion of longevity factor FGF21 in a BACH1-dependent manner. Furthermore, the anti-senescent effects of the supernatant media from these ferroptotic cells were canceled by the knockout of Fgf21. Totally, it is suggested that BACH1 promotes ferroptosis in fibroblasts and contributes to the suppression of cellular senescence in neighboring cells by inducing FGF21 secretion from fibroblasts. It was also discovered that BACH1 not only activates indirectly the transcription of FGF21 by enhancing ferroptotic stress but also increases FGF21 protein level by suppressing the selective autophagic degradation of FGF21 through the transcriptional repression for Sqstm1 and Lamp2a. This represents a dual mechanism of FGF21 upregulation mediated by BACH1, suggesting that BACH1 is a potent inducer of FGF21 expression. It was also found that the BACH1-ferroptosis-FGF21 axis can suppress obesity of mice under high fat diet or short lifespan of progeria mice, closely associated phenotypes with aging. The inhibition of these aging-related phenotypes is considered to be a novel physiological significance of ferroptosis, and BACH1 is considered to function as a longevity gene by promoting ferroptotsis and subsequent FGF21 expression.

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Iron-bound lipocalin-2 protects renal cell carcinoma from ferroptosis

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