Annexin A1 (ANXA1) is a multifunctional protein known to regulate the innate and adaptive immune responses. It has also been implicated in the progression of various cancers. In most types of breast cancer there is a significant loss of ANXA1 expression in the primary tumour. However, increased expression of ANXA1 in patients with invasive breast tumour correlates with poor outcomes and survival (Yom et al., 2011). Similarly, breast cancer cell lines with a more metastatic phenotype show higher levels of ANXA1. We therefore hypothesized that ANXA1 contributes to the metastatic processes of breast cancer.
Using the breast adenocarcinoma MDA-MB-231 cell line and a highly metastatic (MDA-MB-231HM) variant cell line derived from six cycles of pulmonary metastasis to the mammary fat pad (Li et al., 2006), we investigated the influence of ANXA1 on migration and proliferation.
MDA-MB-231HM.LNm5 cells were isolated from an axillary lymph node metastasis from Balb-SCID mice inoculated intramammary fat pad with MDA-MB-231 HM cells (Cancer Metastasis Laboratory, Peter MacCallum Cancer Centre). Compared to MDA-MB-231 cells, MDA-MB-231HM.LNm5 cell line have significantly higher levels of ANXA1 (P<0.05) and appear to have increased migratory response to FCS (1%v/v) in the modified Boyden Chamber (167±26% P<0.05). Stable knock-down of ANXA1 in the MDA-MB-231HM.LNm5 reduces cell migration to levels shown by the parent MDA-MB-231 cells. Proliferation after 48h was significantly lower in the MDA-MB-231HM.LNm5 cells compared with MDA-MB-231 cells (59±8% P<0.05). This slowly proliferating pheynotype was also reverted when ANXA1 level was stably decreased. In contrast, knocking down ANXA1 affected neither the migration nor the proliferation of the parent MDA-MB-231 cells.
Our results demonstrated that decreasing ANXA1 levels could reverse aspects of the phenotype MDA-MB-231 cells acquired after cycles of metastasis and re-implantation, suggesting a contribution of annexin A1 to metastasis of breast cancer.