Cancer Testis Antigen Promotes Triple Negative Breast Cancer Metastasis and is Traceable in the Circulating Extracellular Vesicles

Abstract

Triple negative breast cancer (TNBC) has poor survival, exhibits rapid metastases, lacks targeted therapies and reliable prognostic markers. Here, we examined metastasis promoting role of cancer testis antigen SPANXB1 in TNBC and its utility as a therapeutic target and prognostic biomarker. Expression pattern of SPANXB1 was determined using matched primary cancer, lymph node metastatic tissues and circulating small extracellular vesicles (sEVs). cDNA microarray analysis of TNBC cells stably integrated with a metastasis suppressor SH3GL2 identified SPANXB1 as a potential target gene. TNBC cells overexpressing SH3GL2 exhibited decreased levels of both SPANXB1 mRNA and protein. Silencing of SPANXB1 reduced migration, invasion and reactive oxygen species production of TNBC cells. S PANXB1 depletion augmented SH3GL2 expression and decreased RAC-1, FAK, A-Actinin and Vinculin expression. Phenotypic and molecular changes were reversed upon SPANXB1 re-expression. SPANXB1 overexpressing breast cancer cells with an enhanced SPANXB1:SH3GL2 ratio achieved pulmonary metastasis within 5 weeks, whereas controls cells failed to do so. Altered expression of SPANXB1 was detected in the sEVs of SPANXB1 transduced cells. Exclusive expression of SPANXB1 was traceable in circulating sEVs, which was associated with TNBC progression. SPANXB1 represents a novel and ideal therapeutic target for blocking TNBC metastases due to its unique expression pattern and may function as an EV based prognostic marker to improve TNBC survival. Uniquely restricted expression of SPANXB1 in TNBCs, makes it an ideal candidate for targeted therapeutics and prognostication.

Role of the V1G1 subunit of V-ATPase in breast cancer cell migration

“…RAC1 regulates the activation of vinculin, a well-characterized focal adhesion protein involved in many steps of cell migration 46,48 . In triple negative breast cancer cells reduction of tumorigenic phenotypes is accompanied by reduced expression of RAC1, alpha-actinin, vinculin and FAK 65 and silencing of vinculin reduces cell viability www.nature.com/scientificreports/ and decreases tumor volume in animal models 66 . The decrease in vinculin assembly observed in MDA-MB-231 cells overexpressing V1G1 is associated to a decrease in RAC1 protein amount (Fig.…”

Crosstalk between Stress Granules, Exosomes, Tumour Antigens, and Immune Cells: Significance for Cancer Immunity

“…Testis-specific lactate dehydrogenase C4 was upregulated in serumal exosomes from breast cancer patients [130]. CT antigen SPANXB1 was exclusively expressed in circulating small EVs and promoted the metastasis of triple-negative breast cancer [131]. In other words, expression of CT antigens correlates with tumour progression, and tumour-expressed CT antigens can be combined with exosomes for antigenic presentation.…”

Epigenetic Regulation of Immunotherapy Response in Triple-Negative Breast Cancer

“…For example, SPANXB1 expression was associated with increased migration and invasion abilities. In addition, its mRNA and protein levels were negatively correlated with the metastasis suppressor gene SH3GL2 [31].…”

“…Similarly, gene promoter hypermethylation has been proposed as a mechanism able to silence neo-antigen expression [27]. In TNBC, specifically, different studies have identified the upregulation of NY-ESO-1, MAGE-1, WT1, and SPANXB1 [29][30][31]. Thus, aberrant CTA expression in TNBC has become a therapeutic opportunity.…”