Epidermal growth factor-mediated Rab25 pathway regulates integrin beta 1 trafficking in colon cancer

Abstract

Background: Integrins play a critical role in carcinogenesis. Integrin beta 1 localization is regulated by the guanosine5'- triphosphate hydrolase Rab25 and integrin beta 1 levels are elevated in the serum of colon cancer patients; thus, the present study examined the effects of epidermal growth factor (EGF) and Rab25 on integrin beta 1 localization in colon cancer cells. Methods: HCT116 human colon cancer cells were treated with increasing concentrations of EGF, and cell proliferation and protein expression were monitored by MTT and western blot analyses, respectively. Cell fractionation was performed to determine integrin beta 1 localization in the membrane and cytosol. Integrin beta 1 extracellular shedding was monitored by enzyme-linked immunosorbent assays (ELISAs) with culture supernatants from stimulated cells. HCT116 cells were transfected with Rab25-specific siRNA to determine the significance of Rab25 in integrin beta 1 trafficking in the presence of EGF. Results: Total integrin beta 1 expression increased in response to EGF and subsequently decreased at 24 h post-stimulation. A similar decrease was observed in purified membrane fractions, whereas no changes were observed in cytosolic levels. ELISAs using media from stimulated cell cultures demonstrated increased integrin beta 1 levels corresponding to the decrease observed in membrane fractions, suggesting that EGF induces integrin receptor shedding. EGF stimulation in Rab25-knockdown cells resulted in integrin beta 1 accumulation in the membrane, suggesting that Rab25 promotes integrin endocytosis. Conclusions: Integrin beta 1 is shed from colon cancer cells in response to EGF stimulation in a Rab25-dependent manner. These results further the present understanding of the role of integrin beta 1 in colon cancer progression.