Fucoidan downregulates insulin-like growth factor-I receptor levels in HT-29 human colon cancer cells.

Abstract

Fucoidan, a sulfated polysaccharide present in brown seaweed, has demonstrated anticancer activity in lung, breast, liver and colon cells. The insulin-like growth factor(IGF) signaling pathway regulates growth in HT-29 cells through the insulin receptor substrate-1 (IRS-1)/phosphatidylinositol3-kinase (PI3K)/protein kinaseB (AKT) and Ras/Raf/extracellular signal-regulated kinase (ERK) pathways. The aim of the present study was to investigate whether fucoidan downregulates the IGF-IR signaling pathway in HT-29human colon cancer cells. Fucoidan treatment (0-1,000µg/ml) was administered for 24h in HT-29cells. First, we investigated IRS-1/PI3K/AKT pathway-related protein expression levels following treatment with fucoidan (0-500µg/ml) using western blot analysis. Fucoidan significantly inhibited the expression of IGF-IR, PTEN, PI3K andAKT as well as their phosphorylated forms (p-IRS-1, p-PI3K and p-AKT). Next, we investigated the effects of fucoidan on Ras/Raf/ERK pathway‑related protein expression levels in HT-29cells. Fucoidan significantly inhibited the expression of IGF-IR, Shc, Ras, SOS, Raf andMEK. HT-29cells were then incubated in the presence of fucoidan (0 or250µg/ml), and IGF-I (10nM) was added for 0to60min. Immunoprecipitation (IP) experiments showed that fucoidan inhibited IGF-I-induced phosphorylation of IGF-IR, PI3K, Shc (IP,IGF-IR), and phosphorylated IRS-1 and PI3K (IP,IRS-1) compared to the control group. Western blot analysis showed that fucoidan inhibited the expression of IGF-I-induced p-IGF-IR/IGF-IR and p-AKT/AKT, but not p-ERK/ERK. In conclusion, the inhibition of cell viability by fucoidan in HT-29cells may be due to the downregulation of IGF-IR signaling through the main IRS-1/PI3K/AKTpathway. Fucoidan also partially impacted Ras/Raf signaling in the Ras/Raf/ERK pathway. Therefore, we suggest that fucoidan may be a suitable candidate chemopreventive agent in HT-29colon cancer cells.