The Role And Mechanism Of PRR15 Gene On The Malignant Progression And Drug Efficacy Of Triple-negative Breast Cancer

Background and aimsTriple-negative breast cancer(TNBC)is the most aggressive subtype of breast neoplasms with a higher risk of recurrence and metastasis than non-TNBC.Due to the lack of effective receptor targets,conventional chemotherapy still represents the mainstay of therapeutic strategics combating TNBC,which is prone to being resistant to chemotherapeutic agents,resulting in a dismal prognosis.Meanwhile,the factors responsible for the differences in the malignant behavior between TNBC and non-TNBC are not fully explored.Proline rich 15(PRR15)is a protein involved in the progression of several tumor types,but its specific functions and mechanisms are still controversial.Therefore,this study aimed to investigate the biological role and promise for clinical applications of PRR15 on TNBC.MethodsBioinformatic analyses were performed for the identification of differentially expressed genes(DEG),pan-cancer analysis,partial mechanistic exploration,and evaluation of the effect of PRR15 on the efficacy of anthracyclines in breast cancer patients.TNBC and nonTNBC cells with silencing or overexpressing PRR15 were constructed using lentivirus and applied to a vast array of in vitro assays and in vivo experiments on tumor-bearing mice to evaluate the biological function of PRR15,such as reverse transcription quantitative polymerase chain reaction,IncuCyte proliferation assay,wound healing assay,transwell migration assay,transwell invasion assay,tumor xenografts,and pulmonary metastasis models.Additionally,we screened antineoplastics with higher inhibitory efficiency against PRR15-deficient TNBC through high-throughput drug sensitivity testing(397 compounds)and validated the potential pathways involved via RNA sequencing,Western blot,immunohistochemistry,and pharmacological blockade in mice.Medical records and tumor tissues of TNBC patients were also collected and analyzed to determine the correlation of PRR15 expression with clinicopathological features and the prognostic value of PRR15.ResultsPRR15 gene was differentially expressed between TNBC and non-TNBC patients,previously described as an oncogenic factor in breast cancer.However,our results showed a decreased expression of PRR15 that portended a favorable prognosis in TNBC rather than non-TNBC.PRR15 knockdown facilitated the proliferation,migration,and invasive ability of TNBC cells in vitro,which was abolished by PRR15 restoration,without remarkable effects on non-TNBC.Moreover,PRR15 silencing conferred TNBC cells the potentiation of tumorigenesis as well as lung metastasis colonization in mice relative to control groups.Highthroughput drug sensitivity revealed that PI3K/Akt signaling was involved in the aggressive properties of PRR15 silencing.Subsequent validation of this mechanism demonstrated that DEG of PRR 15-knockdown and control TNBC cells clustered in the PI3K/Akt pathway after transcriptome sequencing,and Western blot suggested increased expression of key molecules representing the PI3K/Akt pathway in PRR15-silenced TNBC cells,which was actually the opposite in TNBC cells with ectopic PRR15.PI3K/Akt signaling was activated in the tumor tissues of PRR15Low TNBC patients,and PI3K inhibitors reversed the metastatic capacity of TNBC cells with knockdown of PRR 15 in mice.In addition,the impact of PRR15 low expression on invasion and metastasis of TNBC partly through the epithelial-mesenchymal transition mechanism.The reduced PRR15 expression in TNBC patients was positively correlated with more aggressive clinicopathological characteristics,enhanced metastasis,and poor disease-free survival.Breast cancer patients with high PRR 15 expression had higher response rates to anthracyclines,however,this trend was reversed in TNBC and anthracyclines were more potent inhibitors of PRR 15 knockdown TNBC cells.ConclusionsThis work explored the biological effect of PRR 15 on breast cancer using basic experiments,particularly TNBC.PRR 15 silencing promoted malignant progression in vitro and in vivo through the PI3K/Akt signaling in TNBC rather than in non-TNBC,affected the response of TNBC to antitumor agents.Low PRR15 expression was correlated with aggressive clinicopathological features and acted as a novel indicator to predict the efficacy of antineoplastics and clinical prognosis in TNBC.