Iron-Bound Lipocalin-2 Protects Renal Cell Carcinoma from Ferroptosis

oleh: Julia K. Meier, Matthias Schnetz, Susanne Beck, Tobias Schmid, Monica Dominguez, Sanela Kalinovic, Andreas Daiber, Bernhard Brüne, Michaela Jung

Format: Article
Diterbitkan: MDPI AG 2021-05-01

Deskripsi

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 (<i>SLC7A11, GCLM, GLS</i>), 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 <i>Nrf2</i> pathway. However, knocking down <i>Nrf2</i> by siRNA was not sufficient to induce erastin-dependent ferroptotic cell death in hLcn-2-stimulated tumor cells. In contrast, preventing oxidative stress through <i>N</i>-acetyl-<span style="font-variant: small-caps;">l</span>-cysteine (NAC) supplementation 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 <i>ATF4</i> after hLcn-2 addition. <i>ATF4</i> 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 initiated by iron-loaded Lcn-2.