Correlation analysis of DLG5 and PD-L1 expression in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is among the most aggressive forms of breast cancer, characterized by a dismal prognosis. In the absence of drug-targetable receptors, chemotherapy remains the sole systemic treatment alternative. Recent advancements in immunotherapy, particularly immune checkpoint inhibitors (ICIs) that target programmed death 1/programmed death ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte associated antigen 4 (CTLA-4), have provided renewed optimism for the treatment of patients with TNBC. Prior research has indicated that the expression level of the cell polarity protein discs large homolog 5 (DLG5) correlates with the malignant progression and prognosis of breast cancer; nevertheless, its influence on PD-L1 expression and its function in immunotherapy for TNBC require further investigation.

This study provides new theoretical evidence and potential therapeutic targets for the immunotherapy strategies of TNBC, holding significant clinical application value.

The hypoxia cell model was established by simulating the cell hypoxic microenvironment in the human SUM159 and MDA-MB-231 cell lines using cobalt II chloride (CoCl2). A combination of PD-L1 inhibitors and DLG5 RNA interference techniques was used, along with various methods including cell counting kit-8 (CCK-8), colony formation, wound healing, transwell migration, reverse transcription-quantitative real-time PCR (RT-qPCR), immunofluorescence, immunohistochemical staining (IHC), expression analysis from datasets and western blotting. These methods were employed to evaluate changes in cell proliferation, migration, and the expression levels of PD-L1 and DLG5. Additionally, the correlation between the expression of PD-L1 and DLG5 in clinical samples was analyzed.

(1) In vitro experiments, a cellular hypoxia model was effectively established utilizing 150 µM CoCl&sub2;. Under these conditions, cell clone formation, invasiveness, and migration rate were all significantly inhibited. (2) The expression levels of DLG5 and PD-L1 were significantly increased in both MDA-MB-231 and SUM159 cells following treatment with 150 µM CoCl&sub2;. (3) Silencing DLG5 resulted in a considerable upregulation of PD-L1 expression in MDA-MB-231 and SUM159 cells under normoxic circumstances, but it was markedly downregulated under hypoxic settings. Inhibition of PD-L1 expression resulted in a considerable increase in DLG5 expression under normoxic conditions, but it decreased under hypoxic conditions. Correlation research demonstrated an inverse association between the expression of DLG5 and PD-L1 in TNBC tissues.