ABSTRACT
The αVß6 integrin, an epithelial-specific cell surface receptor absent in normal prostate and expressed during prostate cancer (PrCa) progression, is a therapeutic target in many cancers. Here, we report that transcript levels of ITGB6 (encoding the ß6 integrin subunit) are significantly increased in metastatic castrate-resistant androgen receptor-negative prostate tumors compared to androgen receptor-positive prostate tumors. In addition, the αVß6 integrin protein levels are significantly elevated in androgen receptor-negative PrCa patient derived xenografts (PDXs) compared to androgen receptor-positive PDXs. In vitro, the androgen receptor-negative PrCa cells express high levels of the αVß6 integrin compared to androgen receptor-positive PrCa cells. Additionally, expression of androgen receptor (wild type or variant 7) in androgen receptor-negative PrCa cells downregulates the expression of the ß6 but not αV subunit compared to control cells. We demonstrate an efficient strategy to therapeutically target the αVß6 integrin during PrCa progression by using short interfering RNA (siRNA) loaded into PrCa cell-derived small extracellular vesicles (sEVs). We first demonstrate that fluorescently-labeled siRNAs can be efficiently loaded into PrCa cell-derived sEVs by electroporation. By confocal microscopy, we show efficient internalization of these siRNA-loaded sEVs into PrCa cells. We show that sEV-mediated delivery of ITGB6-targeting siRNAs into PC3 cells specifically downregulates expression of the ß6 subunit. Furthermore, treatment with sEVs encapsulating ITGB6 siRNA significantly reduces cell adhesion and migration of PrCa cells on an αVß6-specific substrate, LAP-TGFß1. Our results demonstrate an approach for specific targeting of the αVß6 integrin in PrCa cells using sEVs encapsulating ITGB6-specific siRNAs.
Subject(s)
Extracellular Vesicles , Prostatic Neoplasms , Animals , Antigens, Neoplasm/genetics , Antigens, Neoplasm/metabolism , Disease Models, Animal , Extracellular Vesicles/metabolism , Humans , Integrin beta Chains , Integrins , Male , Prostate , Prostatic Neoplasms/genetics , Prostatic Neoplasms/metabolism , RNA, Small Interfering/genetics , Receptors, AndrogenABSTRACT
The ß1 integrins, known to promote cancer progression, are abundant in extracellular vesicles (EVs). We investigated whether prostate cancer (PrCa) EVs affect anchorage-independent growth and whether ß1 integrins are required for this effect. Specifically using a cell-line-based genetic rescue and an in vivo PrCa model, we show that gradient-purified small EVs (sEVs) from either cancer cells or blood from tumor-bearing TRAMP (transgenic adenocarcinoma of the mouse prostate) mice promote anchorage-independent growth of PrCa cells. In contrast, sEVs from cultured PrCa cells harboring a short hairpin RNA to ß1, from wild-type mice or from TRAMP mice carrying a ß1 conditional ablation in the prostatic epithelium (ß1pc-/-), do not. We find that sEVs, from cancer cells or TRAMP blood, are functional and co-express ß1 and sEV markers; in contrast, sEVs from ß1pc-/-/TRAMP or wild-type mice lack ß1 and sEV markers. Our results demonstrate that ß1 integrins in tumor-cell-derived sEVs are required for stimulation of anchorage-independent growth.
