Annexin A6 contributes to the invasiveness of breast carcinoma cells by influencing the organization and localization of functional focal adhesions

Abstract

The interaction of annexin A6 (AnxA6) with membrane phospholipids and either specific extracellular matrix (ECM) components or F-actin suggests that it may influence cellular processes associated with rapid plasma membrane reorganization such as cell adhesion and motility. Here, we examined the putative roles of AnxA6 in adhesion-related cellular processes that contribute to breast cancer progression. We show that breast cancer cells secrete annexins via the exosomal pathway and that the secreted annexins are predominantly cell surface-associated. Depletion of AnxA6 in the invasive BT-549 breast cancer cells is accompanied by enhanced anchorage-independent cell growth but cell-cell cohesion, cell adhesion/spreading onto collagen type IV or fetuin-A, cell motility and invasiveness were strongly inhibited. To explain the loss in adhesion/motility, we show that vinculin-based focal adhesions in the AnxA6-depleted BT-549 cells are elongated and randomly distributed. These focal contacts are also functionally defective because the activation of focal adhesion kinase and the phosphoinositide-3 kinase/Akt pathway were strongly inhibited while the MAP kinase pathway remained constitutively active. Compared with normal human breast tissues, reduced AnxA6 expression in breast carcinoma tissues correlates with enhanced cell proliferation. Together this suggests that reduced AnxA6 expression contributes to breast cancer progression by promoting the loss of functional cell-cell and/or cell-ECM contacts and anchorage-independent cell proliferation.

Role of annexin A6 in cancer

“…The protein expression levels of AnxA6 may also be associated with BC invasiveness: Sakwe et al (34) demonstrated that AnxA6 was secreted via a Ca 2+ -dependent exosomal pathway, and the cell surface-associated AnxA6 was observed to be concentrated in the membrane protrusions of BC cells. Other studies indicated that AnxA6 acted as an adhesion receptor to fetuin-A (α2 HS-glycoprotein), a major serum adhesive protein on the surface of BC cells, by mediating growth signaling (43,44).…”

“…Other studies indicated that AnxA6 acted as an adhesion receptor to fetuin-A (α2 HS-glycoprotein), a major serum adhesive protein on the surface of BC cells, by mediating growth signaling (43,44). AnxA6 has been observed to promote the invasiveness of BT-549 BC cells, which express higher levels of AnxA6 than MCF-10A cells, since the depletion of AnxA6 in BT-549 cells reduced their motility and abolished invasiveness (34,35). AnxA6 knockdown in BT-549 BC cells (BT-A6A cells) altered their cell morphology in a dose-dependent manner, compared with parental BT-549 cells (34).…”

“…AnxA6 has been observed to promote the invasiveness of BT-549 BC cells, which express higher levels of AnxA6 than MCF-10A cells, since the depletion of AnxA6 in BT-549 cells reduced their motility and abolished invasiveness (34,35). AnxA6 knockdown in BT-549 BC cells (BT-A6A cells) altered their cell morphology in a dose-dependent manner, compared with parental BT-549 cells (34). When cultured, the parental BT-549 cells developed as cell masses, and were confluent by day 4, while the BT-A6A cells proliferated as single cells in an anchorage-independent mode, and continued to proliferate without attaining confluence (34).…”

“…AnxA6 knockdown in BT-549 BC cells (BT-A6A cells) altered their cell morphology in a dose-dependent manner, compared with parental BT-549 cells (34). When cultured, the parental BT-549 cells developed as cell masses, and were confluent by day 4, while the BT-A6A cells proliferated as single cells in an anchorage-independent mode, and continued to proliferate without attaining confluence (34). These observations suggest that the loss of AnxA6 abolished contact inhibition and enhanced anchorage-independent cell proliferation in BC cells.…”

“…It has been implicated as a potential marker for cervical cancer (CC) (25), and as a tumor suppressor in melanoma (26), epithelial carcinoma (23,(27)(28)(29), breast cancer (BC) (23,28), gastric cancer (GC) (30), prostate cancer (PCa) (31,32) and chronic myeloid leukemia (CML) (33). Furthermore, AnxA6 is considered to act as a promoting factor in the cellular adhesion, motility and invasiveness of BC (34,35), the progression of acute lymphoblastic leukemia (ALL) (36), the adhesion of lymphoma (37), and the secretory processes in myeloma cells (21).…”