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Cancer-associated fibroblasts (CAFs) are an essential component in the tumor microenvironment and have been reported to contribute to tumor progression through many mechanisms; however, the detailed mechanism underlying the immune-suppression effect of CAFs is not clearly defined. In this study, human breast cancer-derived CAFs were cultured, and CAF-derived exosomes in a culture medium were isolated. Using a miRNA profiles assay, we identify a significantly higher level of microRNA-92 isolated in CAFs exosomes. After treatment by CAF-derived exosomes, breast cancer cells express higher programmed cell death receptor ligand 1 (PD-L1), accompanied with increased miR-92 expression. Increased PD-L1 expression, which was induced by CAF-derived exosomes, significantly promotes apoptosis and impaired proliferation of T cells. The underlying mechanism of this effect was studied, proliferation and migration of breast cancer cells were increased after the transfection of miR-92, LATS2 was recognized as a target gene of miR-92, and further confirmed by a luciferase assay. Immunoprecipitation showed that LATS2 can interact with YAP1, chromatin immunoprecipitation confirmed that after nuclear translocation YAP1 could bind to the enhancer region of PD-L1 to promotes transcription activity. Furthermore, the animal study confirmed that CAFs significantly promoted tumor progression and impaired the function of tumor-infiltrated immune cells in vivo . Our data revealed a novel mechanism that can induce immune suppression in the tumor microenvironment.

Background: Although trastuzumab provides significant clinical benefit for HER2-positive breast cancers, responses are limited by the emergence of resistance. Recent evidence suggests that long noncoding RNAs (lncRNAs) play important roles in tumorigenesis and chemoresistance. However, the regulatory mechanism of lncRNAs in trastuzumab resistance is not well established to date. In this research, we identified the differentially expressed lncRNA and investigated its regulatory role in trastuzumab resistance of breast cancer.Methods: LncRNA microarray and qRT-PCR were performed to identify the dysregulated lncRNAs. Transmission electron microscopy, differential ultracentrifugation and qRT-PCR were used to verify the existence of exosomal AFAP1-AS1 (actin filament associated protein 1 antisense RNA 1). Bioinformatics prediction, RNA fluorescence in situ hybridization (RNA-FISH) and immunoprecipitation assays were performed to identify the direct interactions between AFAP1-AS1 and other associated targets, such as AU-binding factor 1 (AUF1) and ERBB2. Finally, a series gain-or loss-functional assays were done to prove the precise role of AFAP1-AS1 in trastuzumab resistance.Results: AFAP1-AS1 was screened out due to its higher expression in trastuzumab-resistant cells compared to sensitive cells. Increased expression of AFAP1-AS1was associate with poorer response and shorter survival time of breast cancer patients. AFAP1-AS1 was upregulated by H3K27ac modification at promoter region, and knockdown of AFAP1-AS1 reversed trastuzumab resistance. Moreover, extracellular AFAP1-AS1 secreted from trastuzumab resistant cells was packaged into exosomes and then disseminated trastuzumab resistance of receipt cells. Mechanically, AFAP1-AS1 was associated with AUF1 protein, which further promoted the translation of ERBB2 without influencing the mRNA level.Conclusion: Exosomal AFAP1-AS1 could induce trastuzumab resistance through associating with AUF1 and promoting ERBB2 translation. Therefore, AFAP1-AS1 level may be useful for prediction of trastuzumab resistance and breast cancer treatment.

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