Dissecting the Role of TNFSF13 in Regulating the Metastatic Potential and Investigating the Prognostic Significance of MTORC1 Gene Set in Triple-Negative Breast Cancer

Background: Triple-negative breast cancer (TNBC) represents a subtype of breast cancer characterized by the lack of expression the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). The lack of reliable predictive biomarkers is a challenge to the application of targeted therapies in TNBC. Aim: Here we aimed to explore the role of TNFSF13 in regulating the metastatic potential and investigate the prognostic significance of the MTORC1 gene set in TNBC. Methods: The mRNA expression profiles of TNFSF13 in normal tissues and primary tumors from TNBC patients as well as non-TNBC were collected from The Cancer Genome Atlas (TCGA) database. The endogenous gene expression levels in normal mammary and TNBC cell lines were detected in RT-PCR. Transwell migration assay was used to detect the migration abilities of TNBC cell variants. In vitro studies were conducted to investigate the mechanism of TNFSF13 in regulating the metastatic potential of TNBC. Moreover, we used the Chi-square test of independence to assess the prognostic significance of TNFSF13 in TNBC. We executed a bioinformatics analysis to identify differentially expressed genes (DEGs) of the mammalian target of rapamycin complex 1 (MTORC1) gene set comparing normal tissues with primary tumors samples from patients with TNBC using The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Cox proportional hazard regression analysis was conducted to determine independent prognostic factors. The validation of prognostic gene expression at the protein level was performed in TNBC models and clinical specimens using western blot and IHC approaches. Results: Here we report that TNFSF13 is downregulated in TNBC. In vitro
experiments show that TNFSF13 downregulation promotes the metastatic potential of TNBC by regulating the STAT1 activity. On the other hand, our results present FADS2 and TOMM40 as prognostic biomarkers for TNBC. TOMM40 (HR= 2.243) is a risk factor and FADS2 is a protective factor (HR= 0.652). An elevated TOMM40/FADS2 ratio is correlated with unfavorable prognosis in TNBC patients. The TOMM40/FADS2 ratio was significantly associated (p < 0.05) with clinicopathological characteristics of TNBC patients, including, age, tumor size, lymph node metastasis, pathologic stage, and overall survival of patients with TNBC. Notably, MTT cytotoxicity assay demonstrated that TNBC cell lines with a higher TOMM40/FADS2 ratio are more sensitive to mammalian target of rapamycin (mTOR) inhibitor treatment than cell lines exhibiting lower TOMM40/FADS2 ratio.
Conclusion: Our findings support a potential therapeutic strategy for TNBC by highlighting the TNFSF13–STAT1 axis as a promising therapeutic target and identifying the TOMM40/FADS2 expression ratio as a predictive biomarker of cellular response to mTOR inhibitor treatment