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.