2280P - MiR-193a-3p: A pan-repressor of H2S synthesizing enzymes regulates tumorigenesis and immunosurveillance in breast cancer

Background

Hydrogen sulfide (H₂S) is an endogenous gaseous mediator implicated in breast cancer (BC) progression. The 3 principle enzymes responsible for H₂S production in mammals are cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3MST), whose overexpression was correlated with poor prognosis in BC patients. Besides, H₂Swas linked to the suppression of tumor immune microenvironment in BC. Our group recently reported that upon single or dual inhibition of any of H₂S-synthesizing enzymes, the other untargeted enzyme(s) is/are upregulated/activated as a compensatory mechanism for maintaining the level of H₂Sin cancer cells. Thus, the aim of this work is to find a pan-repressor of all 3 enzymes to skip the above compensatory/escape mechanism and to investigate its impact on oncogenic and immunogenic profiles of BC cells.

Methods

BC female patients (n=20) were recruited. In-silico analysis was used to identify microRNAs (miRNAs) that target CBS, CSE, and 3MST. MDA-MB-231 TNBC cells were cultured and transfected by oligonucleotides. Total RNA was extracted using Biazol, reverse transcribed and quantified using qRT-PCR. Western blot analysis was performed. H₂S levels were measured by AzMc. BC hallmarks were assessed by MTT, transwell migration, and clonogenic assays.

Results

MiRNA-193a was validated to regulate the expression of H₂S enzymes by 8 different bioinformatics software, and was found to be significantly downregulated in BC tissues. Further, miR-193a was negatively correlated with CBS, CSE and 3MST levels in BC patients. Ectopic expression of miR-193a resulted in a marked repression of CBS, CSE, and 3MST expression, inducing a significant decrease in cellular H₂S production. in TNBC cells overexpressing miRNA-193a, not only the cancer hallmarks were markedly suppressed but also the immune-suppressor proteins Galectin (GAL) 3 and GAL 9 were decreased significantly.

Conclusions

This study identifies miRNA-193a as a pan-repressor of the 3 principle H₂S-synthesizing enzymes in BC, bypassing the compensatory behavior observed at single or dual inhibition of H₂S enzymes. Thus, miR-193a emerges as a novel tumor suppressor and immunomodulatory miRNA in TNBC.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Swiss National Science Foundation (SNSF) grant SNF IZSTZ0_198887.

Disclosure

All authors have declared no conflicts of interest.