Early diagnostic value of survivin and its alternative splice variants in breast cancer

Abstract

BackgroundThe 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.MethodsWe 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.ResultsSurvivin 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.ConclusionIn 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.

The Role of Exosomes in Breast Cancer

“…Specifically, low expression of survivin-2B was found in the most aggressive breast cancer stages and corresponding exosomes. Overall, these studies support a role for exosomal (as well as tissuebased) survivin and its splice variants as diagnostic and prognostic biomarkers with potential for their exploitation in a therapeutic setting (43 ).…”

“…More recently, the use of serum-based exosomal survivin splice variants as early diagnostic biomarkers has shown promise in breast cancer. With the use of acetylcholinesterase activity assays, the amount of cancer exosomes was found to be significantly higher in breast cancer patient serum (n ϭ 40) than in control serum from female patients who had undergone neoadjuvant treatment followed by surgery with no recurrence (n ϭ 10) (43 ). Considering the roles of survivin and its splice variants in cancer (44 ), for which survivin is an inhibitor of apoptosis and survivin-⌬Ex3 and survivin-2B have apparently retained and lost antiapoptotic potential, respectively, Western blot analysis revealed an increase in antiapoptotic survivin and survivin-⌬Ex3 protein in breast cancer patient serumderived exosomes.…”

Expression of p16 and Survivin in gliomas and their correlation with cell proliferation

“…At present, Survivin has gained marked interest in the field of tumor research. The protein is tumor specific, which means that it is only expressed in tumor and embryonic tissues, and is closely associated with tumor differentiation, proliferation, invasion and metastasis (20,21). The expression of the Survivin gene has been identified to be upregulated in nasal type natural killer (NK)/T cell lymphoma cells and has been found to be significantly correlated with the expression of p53 and B cell lymphoma 2 proteins.…”

Exosomes Derived from Breast Cancer Cells, Small Trojan Horses?

“…There appears to be expression of survivin-2B in primary tumors at early stage of development but low or no expression in high-grade and metastatic tumors. [95]. Hence, survivin-2B may be useful as a biomarker for the early diagnosis of cancer.…”