Recently, our group has shed the light onto the indisputable role of Hydrogen Sulphide (H2S) in BC. In parallel, immunotherapy has emerged a novel therapeutic approach acting by altering the immunogenic profile of BC tumors. Overexpression of Programmed death -ligand 1 (PD-L1) has become one of the most acceptable tactics for tumor cells to escape the immune surveillance phenomena. PD-L1 is highly expressed in BC tumors and correlated with its aggressiveness. Thus immune checkpoint blockades (ICBs) such as PD-L1 antibodies had reached the clinics, yet patients response is variable and resistance cases started to appear. So, the molecular engines regulating PD-L1 are needed to be investigated. Recently, our group showed that H2S postulates a powerful immunomodulatory role through tuning non-coding RNAs (ncRNAs). CCAT1 is an oncogenic long ncRNA which can act as a sponge for the direct regulator of PD-L1. Let-7a. The aim of this study is to investigate the impact of H2S on a novel ceRNA circuit and to probe ncRNAs linking H2S with PD-L1 in BC cells.
Thirty BC patients were recruited. Bioinformatics analysis was performed. MDA-MB-231 cells were cultured, transfected with CSE siRNAs using HiPerFect Transfection Reagent. H2S levels were measured using H2S detection plates. Total RNA was extracted using Biozol reagent, reverse transcribed and quantified using qRT-PCR.
Screening revealed an apparent paradoxical expression between CCAT1 and let-7a in PD-L1+ tumor tissues. Bioinformatics analysis showed that Let-7a has a high binding score targeting PD-L1 and CCAT1. Repression of H2S levels in MDA-MB-231 cells following CSE siRNA was confirmed. Knocking down of CSE-induced H2S production resulted in a marked induction of CCAT1 (>4000 folds), Let-7a (>4 folds) and an elevation of PD-L1 expression.
This study highlights a novel ceRNA circuit responsible for evading immune surveillance in BC patients. It showed that CCAT1 oncogenic lncRNA overrides the tumor suppressor activity of let-7a in regulating PD-L1 expression. Nonetheless, this study shows that targeting CSE-induced H2S production has a detrimental effect on the CD8+ T cells.
Legal entity responsible for the study
German University in Cairo.
Has not received any funding.
All authors have declared no conflicts of interest.