7-Dehydrocholesterol is an endogenous suppressor of ferroptosis.

Ferroptosis is a form of cell death that has received considerable attention not only as a means to eradicate defined tumour entities but also because it provides unforeseen insights into the metabolic adaptation that tumours exploit to counteract phospholipid oxidation1,2. Here, we identify proferroptotic activity of 7-dehydrocholesterol reductase (DHCR7) and an unexpected prosurvival function of its substrate, 7-dehydrocholesterol (7-DHC). Although previous studies suggested that high concentrations of 7-DHC are cytotoxic to developing neurons by favouring lipid peroxidation3, we now show that 7-DHC accumulation confers a robust prosurvival function in cancer cells. Because of its far superior reactivity towards peroxyl radicals, 7-DHC effectively shields (phospho)lipids from autoxidation and subsequent fragmentation. We provide validation in neuroblastoma and Burkitt's lymphoma xenografts where we demonstrate that the accumulation of 7-DHC is capable of inducing a shift towards a ferroptosis-resistant state in these tumours ultimately resulting in a more aggressive phenotype. Conclusively, our findings provide compelling evidence of a yet-unrecognized antiferroptotic activity of 7-DHC as a cell-intrinsic mechanism that could be exploited by cancer cells to escape ferroptosis.

Enhancing cellular sulfane sulfur through ß-glycosidase-activated persulfide donors: mechanistic insights and oxidative stress mitigation.

Sulfane sulfur species such as persulfides and polysulfides along with hydrogen sulfide protect cells from oxidative stress and are key members of the cellular antioxidant pool. Here, we report perthiocarbamate-based prodrugs that are cleaved by ß-glycosidases to produce persulfide and relatively innocuous byproducts. The ß-glucosidase-activated persulfide donor enhances cellular sulfane sulfur and protects cells against lethality induced by elevated reactive oxygen species (ROS).

CobT and BzaC catalyze the regiospecific activation and methylation of the 5-hydroxybenzimidazole lower ligand in anaerobic cobamide biosynthesis.

Vitamin B12 and other cobamides are essential cofactors required by many organisms and are synthesized by a subset of prokaryotes via distinct aerobic and anaerobic routes. The anaerobic biosynthesis of 5,6-dimethylbenzimidazole (DMB), the lower ligand of vitamin B12, involves five reactions catalyzed by the bza operon gene products, namely the hydroxybenzimidazole synthase BzaAB/BzaF, phosphoribosyltransferase CobT, and three methyltransferases, BzaC, BzaD, and BzaE, that conduct three distinct methylation steps. Of these, the methyltransferases that contribute to benzimidazole lower ligand diversity in cobamides remain to be characterized, and the precise role of the bza operon protein CobT is unclear. In this study, we used the bza operon from the anaerobic bacterium Moorella thermoacetica (comprising bzaA-bzaB-cobT-bzaC) to examine the role of CobT and investigate the activity of the first methyltransferase, BzaC. We studied the phosphoribosylation catalyzed by MtCobT and found that it regiospecifically activates 5-hydroxybenzimidazole (5-OHBza) to form the 5-OHBza-ribotide (5-OHBza-RP) isomer as the sole product. Next, we characterized the domains of MtBzaC and reconstituted its methyltransferase activity with the predicted substrate 5-OHBza and with two alternative substrates, the MtCobT product 5-OHBza-RP and its riboside derivative 5-OHBza-R. Unexpectedly, we found that 5-OHBza-R is the most favored MtBzaC substrate. Our results collectively explain the long-standing observation that the attachment of the lower ligand in anaerobic cobamide biosynthesis is regiospecific. In conclusion, we validate MtBzaC as a SAM:hydroxybenzimidazole-riboside methyltransferase (HBIR-OMT). Finally, we propose a new pathway for the synthesis and activation of the benzimidazolyl lower ligand in anaerobic cobamide biosynthesis.