Breast Cancer-Derived Exosomes Alters Human Salivary Gland-Derived Exosomes In Vitro

Objective: Saliva is a useful bio-fluid for the early detection of systemic diseases, but how distal tumors communicate with the oral cavity leading to disease specific biomarkers remains unclear. We hypothesized that tumor-derived exosomes interact with salivary gland cells altering its secreted exosomes. An in vitro breast cancer model was used to examine whether tumor-derived exosomes communicated with the salivary gland cells, altering the contents its secreted exosomes. Methods: Exosomes were isolated from breast cancer (MDA-MB-231; 231) and human salivary gland (HSG) cells by ultracentrifugation. To identify exosomes, electron microscopy and immunoblots were used. SDS-PAGE and Bio-Analyzer (Agilent) were conducted to identify exosomal protein and RNA. PKH26 kit (Sigma) was used to demonstrate the transfer of the fluorescent compound from 231-derived exosomes to HSG cells. Bio-Analyzer was used to determine the changes in HSG-RNA levels post-treatment with 231-derived exosomes. 2D-DIGE and microarray analysis were used to identify changes to HSG-derived exosomes proteomically and transcriptomically post-treatment with 231-derived exosomes. Results: We isolated exosomes from 231 and HSG cells. The isolates were validated as exosomes by morphology and the identification of CD63. Both 231 and HSG exosomes contained proteins and mRNA. We observed that PKH26 tagged 231-derived exosomes labeled HSG cells and activated transcription. Lastly, 231-derived exosomes altered the HSG-derived exosomes both transcriptomically and proteomically. Conclusion: We showed that 231 and HSG cells secreted exosomes and 231-derived exosomes are capable of communicating with HSG. Moreover, interplay between 231-derived exosomes and HSG cells altered HSG-derived exosomes. These findings suggest exosomes as a candidate vehicle for the connection between distal diseases and the oral cavity. Furthermore, these results allow us to speculate that exosomes provide the mechanistic underpinning for which the communication between the salivary glands and breast tumor in vivo.