Exosomal circular RNAs derived from serum: Promising biomarkers for therapeutic targets and prognosis of triple-negative breast cancer (TNBC).

Abstract

3528 Background: Exosomes are well known by the "exosomal shuttle" that delivers oncogenic microRNAs (miRNAs), mRNAs, circular RNAs (circRNAs) and proteins to the recipient cells and tumor microenvironment, and may be used as promising biomarkers for disease diagnosis. This study aims to provide a theoretical basis to use stable exosomal circRNAs as new biomarkers for predicting the development, metastasis and therapeutic targets of TNBC. Methods: A strategy combining RNA-sequencing technique, bioinformatic analysis and RT-qPCR was used to determine the level of differential expressed circRNAs in serum exosomes samples (n = 43) from TNBC patients compared with non-TNBC patients. The expression of circHSDL2 were also detected in tumor tissues (n = 20) from TNBC patients and breast cancer cell lines by qRT-PCR. Cell cycle analysis, the wound healing assays and transwell assays were used to investigate the function of circHSDL2 in proliferation, invasion and metastasis of TNBC cells. FISH, dual-luciferase reporter and functional assays were performed to confirm the interaction between circHSDL2 and let-7a-2-3p in TNBC cells. Results: We profiled the circRNAs in the serum exosomes samples from TNBC patients and non-TNBC patients by RNA sequencing and detected 803 significantly differentially-expressed circRNAs. After bioinformatic analysis, circHSDL2 was chose to further study. RT-qPCR results showed that higher expression of circHSDL2 in TNBC cell lines and tumor tissues from TNBC patients. Moreover, overexpression of circHSDL2 promoted TNBC cells proliferation and invasion, while knockdown of circHSDL2 inhibited TNBC cells proliferation and invasion. Mechanistically, circHSDL2 acted as a "miRNAs sponge" to absorb let-7a-2-3p; let-7a-2-3p inhibited TNBC cell invasion and metastasis. Kaplan-Meier plots showed lower expression of let-7a-2-3p was connected to poor prognosis in TNBC metastasis patients from TCGA database. Conclusions: The expression of circHSDL2 was found significantly upregulated in serum exosomes and tumor tissues from TNBC patients. Moreover, circHSDL2 could promote cell proliferation, invasion and metastasis in TNBC cells. CircHSDL2 might be function as competing endogenous RNAs (ceRNAs) by targeting let-7a-2-3p in the progression of TNBC. Therefore, this study provides a fresh perspective on novel therapeutic targets and potential biomarkers for TNBC from exosomal circRNAs.