Early diagnostic value of survivin and its alternative splice variants in breast cancer
1 Department of Biochemistry, Loma Linda University School of Medicine, Loma Linda, CA, USA
2 Center for Health Disparities & Molecular Medicine, Loma Linda University School of Medicine, 11085 Campus Street, Mortensen Hall Room 160, Loma Linda, CA 92350, USA
3 Department of Pathology & Laboratory Medicine, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA
4 Department of Medicine and LLU Cancer Center & San Manuel Band of Mission Indians Biospecimen Laboratory, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA
5 Division of Medical Oncology & Therapeutics, City of Hope Medical Center, Duarte, CA 91010, USA
BMC Cancer 2014, 14:176 doi:10.1186/1471-2407-14-176Published: 12 March 2014
The inhibitor of apoptosis (IAP) protein Survivin and its splice variants are differentially expressed in breast cancer tissues. Our previous work showed Survivin is released from tumor cells via small membrane-bound vesicles called exosomes. We, therefore, hypothesize that analysis of serum exosomal Survivin and its splice variants may provide a novel biomarker for early diagnosis of breast cancer.
We collected sera from forty breast cancer patients and ten control patients who were disease free for 5 years after treatment. In addition, twenty-three paired breast cancer tumor tissues from those same 40 patients were analyzed for splice variants. Serum levels of Survivin were analyzed using ELISA and exosomes were isolated from this serum using the commercially available ExoQuick kit, with subsequent Western blots and immunohistochemistry performed.
Survivin levels were significantly higher in all the breast cancer samples compared to controls (p < 0.05) with exosome amounts significantly higher in cancer patient sera compared to controls (p < 0.01). While Survivin and Survivin-∆Ex3 splice variant expression and localization was identical in serum exosomes, differential expression of Survivin-2B protein existed in the exosomes. Similarly, Survivin and Survivin-∆Ex3 proteins were the predominant forms detected in all of the breast cancer tissues evaluated in this study, whereas a more variable expression of Survivin-2B level was found at different cancer stages.
In this study we show for the first time that like Survivin, the Survivin splice variants are also exosomally packaged in the breast cancer patients’ sera, mimicking the survivin splice variant pattern that we also report in breast cancer tissues. Differential expression of exosomal-Survivin, particularly Survivin-2B, may serve as a diagnostic and/or prognostic marker, a “liquid biopsy” if you will, in early breast cancer patients. Furthermore, a more thorough understanding of the role of this prominent antiapoptotic pathway could lead to the development of potential therapeutics for breast cancer patients.