RSL1D1 knockdown induces ferroptosis and mediates ferrous iron accumulation in senescent cells by inhibiting FTH1 mRNA stability.

Iron metabolism plays an important role in maintaining cellular multiple biological functions. Dysfunction of iron homeostasis-maintaining systems was observed in many diseases, including cancer. RSL1D1 is an RNA-binding protein involved in multiple cellular processes, including cellular senescence, proliferation and apoptosis. However, the regulatory mechanism of RSL1D1 underlying cellular senescence and its biological process in colorectal cancer (CRC) is not clearly understood. Here, we report that RSL1D1 expression is downregulated by ubiquitin-mediated proteolysis in senescence-like CRC cells. RSL1D1, as an anti-senescence factor, is frequently up-regulated in CRC, and elevated RSL1D1 prevents CRC cells from senescence-like phenotype, and correlated with poor prognosis of CRC patients. Knockdown of RSL1D1 inhibited cell proliferation, and induced cell cycle arrest and apoptosis. Notably, RSL1D1 plays important roles in regulating iron metabolism of cancer cells. In RSL1D1 knockdown cells, FTH1 expression was significantly decreased, while TFRC expression was increased, leading to intra-cellular ferrous iron accumulation, which subsequently promoted ferroptosis, indicated by the increased malondialdehyde (MDA) and decreased GPX4 levels. Mechanically, RSL1D1 directly bound with 3' untranslated region (3'UTR) of FTH1 and subsequently promoted the mRNA stability. Moreover, RSL1D1 mediated downregulation of FTH1 was also observed in H2O2-induced senescence-like cancer cells. Taken together, these findings support RSL1D1 plays an important role in regulating intra-cellular iron homeostasis in CRC, and suggest that RSL1D1 could be a potential therapeutic target for cancer treatment.