Elevated levels of annexin I protein in vitro and in vivo in rat and human mammary adenocarcinoma

Abstract

Annexin I is a phospholipid and actin binding protein which may play a role in signal transduction to the cytoskeleton. Previous work reported the differential expression of annexin I mRNA among rat adenocarcinoma cell lines of various metastatic potential (MTLn3, MTLn2, MTC.4: highest to lowest, respectively) (Pencil et al. 1993, Breast Cancer Res Treat, 25, 165-74). This relationship has been extended to the protein level in in vitro cultures using Western blotting and flow cytometry. Annexin I protein levels in MTLn3 cells are 3- to 5-fold higher than in MTC.4 cells. The weakly metastatic cell line MTLn2 shows levels 1.5- to 2.5-fold higher than MTC.4. In vivo tumors were produced by injecting 1 x 10(6) cells into mammary fat pads of syngeneic rats and necropsies were performed 40 days later. Semiquantitative immunohistochemical color image analysis was performed using a polyclonal rat annexin I specific antibody. Annexin I protein expression was highest in lung metastases of MTLn3, at 8-fold the levels observed in the MTC.4 primary tumors. MTLn3 cells in the primary tumor had an annexin I specific optical density 3-fold higher than that of cells in the MTC.4 primary tumor. MTLn2 primary tumors had an annexin I specific optical density 1.5-fold higher than MTC.4. A proportion of human mammary adenocarcinomas also have positive annexin I immunoreactivity, often with more uniform annexin I staining in the lymph node metastases. These results suggest that there may be survival advantages for nascent metastatic cells with high annexin I levels.