Purpose: The purpose of this study is to establish Annexin A2, a known calcium-dependent phospholipid binding protein as a biomarker in TNBC and to delineate the mechanism of cancer recurrence after Herceptin therapy in breast cancer patients.
Methods: Annexin A2 and ErbB2 expression in 12 different breast cancer cell lines were analyzed by Western, qPCR and Immunohistochemistry. Dharmacon smart pool siRNA was used to knockdown Annexin A2 and HER2 in different cell lines and the expression of respective proteins and downstream signaling molecules was studied by Western analysis. AccuMax tissue micro-array was used to study the expression of these proteins in different breast cancer cases.
Results: : In this study, we show that Annexin A2 is over expressed in different TNBC cell lines, where there is a basal or very low level of HER2 expression or vice-versa. Here we demonstrate for the first time that blocking HER2 expression in SK-BR-3 cells, lead to increased levels of Annexin A2. In addition, we found that inhibition of both Annexin A2 and HER2 in cells over expressing HER2 blocked all the downstream signaling mechanism that helps in cancer cell growth. Conversly, in TNBC cell lines that lack HER2 expression, we could successfully block the metastatic function of cancer cells (AKT downstream signaling) by down regulating only Annexin A2. Although the Annexin A2 is not a secretory protein, we noticed that large amounts of Annexin A2 is secreted from these cancer cells. This unique property could help us in developing tools using Annexin A2 as a marker to identify TNBC cases.
Conclusions: This current observation addresses the concern about the low response of TNBC to Herceptin therapy in treatment of basal carcinoma and the recurrence of cancer after HER2 blocking. This particular study, HER2/Annexin A2 cross talk opens up a new horizon in this area and we are in the process of establishing Annexin A2 involved therapeutic intervention of TNBC.