Reprogrammed transsulfuration promotes basal-like breast tumor progression via realigning cellular cysteine persulfidation

Abstract

Basal-like breast cancer (BLBC) is the most aggressive subtype of breast tumors with poor prognosis and limited molecular-targeted therapy options. We show that BLBC cells have a high Cys demand and reprogrammed Cys metabolism. Patient-derived BLBC tumors from four different cohorts exhibited elevated expression of the transsulfuration enzyme cystathione β-synthetase (CBS). CBS silencing (shCBS) made BLBC cells less invasive, proliferate slower, more vulnerable to oxidative stress and cystine (CySSCy) deprivation, prone to ferroptosis, and less responsive to HIF1-α activation under hypoxia. shCBS xenograft tumors grew slower than controls and exhibited impaired angiogenesis and larger necrotic areas. Sulfur metabolite profiling suggested that realigned sulfide/persulfide-inducing functions of CBS are important in BLBC tumor progression. Supporting this, the exclusion of serine, a substrate of CBS for producing Cys but not for producing sulfide/persulfide, did not exacerbate CySSCy deprivation–induced ferroptosis in shCBS BLBC cells. Impaired Tyr phosphorylation was detected in shCBS cells and xenografts, likely due to persulfidation-inhibited phosphatase functions. Overexpression of cystathione γ-lyase (CSE), which can also contribute to cellular sulfide/persulfide production, compensated for the loss of CBS activities, and treatment of shCBS xenografts with a CSE inhibitor further blocked tumor growth. Glutathione and protein-Cys levels were not diminished in shCBS cells or xenografts, but levels of Cys persulfidation and the persulfide-catabolizing enzyme ETHE1 were suppressed. Finally, expression of enzymes of the oxidizing Cys catabolism pathway was diminished, but expression of the persulfide-producing CARS2 was elevated in human BLBC tumors. Hence, the persulfide-producing pathways are major targetable determinants of BLBC pathology that could be therapeutically exploited.

Emerging roles of cystathionine β-synthase in various forms of cancer

“…5 C): in fact, cystathionine was designated as an “oncometabolite” by the authors [ 63 ]. Analysis of in-depth quantitative proteomics data of 45 human breast cancer tumors from the Oslo 2 study cohort was subsequently conducted by the group of Nagy in 2021 [ 64 ]. Elevated CBS protein levels were reported in the luminal, HER2-negative and “normal-like” breast cancer subtypes, with a relatively rare subgroup of breast cancer, the basal-like cancer showing the highest CBS expression levels ( Fig.…”

“…5 D). CBS expression positively correlated with proliferation-related gene sets and negatively correlated with estrogen response–related genes [ 64 ].

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“…The panel was redrawn from data presented in Ref. [ 64 ]. E) Survival curve showing the impact of CBS expression on overall survival in invasive breast carcinoma from the BRCA dataset showing a trend for better survival in low-CBS-expressing patients.…”

“…The degree of CBS mRNA upregulation was comparable in the various subtypes of breast cancer (Luminal A, luminal B, HER2 enriched and TNBC) ( Fig. 5 D) [ 64 ]. Serum H 2 S levels – detected by a microplate based colorimetric method – were approximately 45% higher in breast cancer patients than in healthy gender and age matched controls [ 65 ].…”

“…When stratified by tumor proliferation index (ki-67), rapidly proliferating tumors expressed approximately 40-times higher CBS mRNA levels than slow-proliferating ones [ 65 ]. The study conducted by the group of Nagy – which has already demonstrated high CBS protein expression in breast cancer clinical specimens (see prior paragraph) – has also found a significant upregulation of CBS mRNA in several breast cancer clinical databases (Oslo 2, TCGA, NeoAva), with particularly high CBS mRNA levels in basal like breast cancer [ 64 ]. There was a good correlation between CBS mRNA and CBS protein expression in human breast cancer tissues [ 65 ], suggesting that the mechanism of CBS upregulation has a substantial transcriptional component in breast cancer cells.…”