Biological activity of rainbow trout Ea4‐peptide of the pro‐insulin‐like growth factor (pro‐IGF)‐I on promoting attachment of breast cancer cells (MDA‐MB‐231) via α2‐ and β1‐integrin

E‐peptide of pro‐IGF‐I was considered as biologically inactive. We have demonstrated that rainbow trout (rt) Ea4‐peptide exerted biological activities in several established tumor cell lines [Chen et al., 2002; Kuo and Chen, 2002]. Here we report the activity of rtEa4‐peptide in promoting attachment of human breast cancer cells (MDA‐MB‐231). While rtEa2‐, rtEa3‐, and rtEa4‐peptides enhanced the attachment of MDA‐MB‐231 cells in a dose dependent manner, rtEa4‐peptide possessed the highest activity. Antibodies specific to α2 and β1 integrins significantly inhibited the attachment of cells to rtEa4‐peptide coated‐plates by 40%. In addition, rtEa4‐peptide induced the expression of fibronectin 1 and laminin receptor genes in MDA‐MB‐231 cells. Blocking new protein synthesis by cycloheximide significantly reduced the attachment of MDA‐MB‐231 cells to rtEa4‐peptide coated wells by 50%. These results suggest that rtEa4‐peptide may promote cell attachment by interacting with α2/β1 integrin receptors at the cell surface and by inducing the expression of fibronectin 1 and laminin receptor genes. Expression of fibronectin 1 gene induced by rtEa4‐peptide in MDA‐MB‐231 cells was abolished by inhibitors of PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signaling transduction molecules. These results suggested that induction of fibronectin 1 gene expression in MDA‐MB‐231 cells by rtEa4‐peptide may be mediated via PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signal transduction molecules. J. Cell. Biochem. 99: 1524–1535, 2006. © 2006 Wiley‐Liss, Inc.