Annexin V inhibits the 12-O-tetradecanoylphorbol-13-acetate-induced activation of Ras/extracellular signal-regulated kinase (ERK) signaling pathway upstream of Shc in MCF-7 cells

Annexin V is a Ca2+-dependent phospholipid binding protein. Although it has been shown to inhibit protein kinase C (PKC) in cell-free systems, its role in the intact cell is unclear, A stable,MCF-7 human breast cancer cell overexpression system was established to investigate the function of annexin V, In these cells, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced phosphorylation and kinase activity of ERK1/2 were suppressed. Morphological changes induced by TPA were reduced by annexin V overexpression as well as by the pan-PKC inhibitor, bisindolylmaleimide I, and by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor, PD98059, TPA-induced MEK1/2 and Raf-l phosphorylation were reduced in these cells, The TP,S-enhanced active Ras, and its association with Raf-1, were reduced. TPA treatment of MCF-7 cells caused an increased association of She with Grb2, However, this increased association was prevented in the annexin V-overexpressors. p21(WAF/CIPI) is responsible for inhibition of cell cycle progression in MICF-7 cells. TPA induced the expression of p21(WAF/CIPI) to a greater extent in MCF-7 parent and control plasmid cells than in annexin V overexpressors, PD98059 inhibited this increase, suggesting that TPA upregulation of p21(WAF/CIPI) occurs via the MEK pathway, and that annexin V overexpression blunts it, This work shows that annexin V overexpression suppresses the TPA-induced Ras/ERK; signaling by inhibiting at/or upstream of She, possibly through the inhibition of PkCs.