Objective: IGFBP-3 has been demonstrated to stimulate or inhibit cell proliferation independently of its ability to bind IGF and a specific IGFBP-3 receptor has been proposed. EGF has been implicated in the cancer development and carcinogenesis. Only limited data are available on the crosstalk between IGFBP-3 signaling and EGF induced cell survival and signal transduction. The current studies were undertaken to characterize IGFBP-3 binding to endometrial cancer cells (HHUA) and determine its biological effects, as well as whether IGFBP-3 exposure alters the cell proliferation stimulated by EGF.
Methods: Cell proliferation and apoptosis were analyzed by ELISA using specific antibodies. The interaction between HHUA cell and IGFBP-3 was analyzed using a biosensor. The phosphorylation abundance of specific proteins and their phosphorylation in response to EGF and IGFBP-3 was analyzed by immunoprecipitation followed by immunoblotting.
Results: Biosensor analysis showed that IGFBP-3 could bind to HHUA cell surface. IGFBP-3 inhibited BrdU uptake, potentiated ssDNA production and induced p53 in HHUA cells. Although EGF stimulated HHUA cell proliferation and Akt phosphorylation, IGFBP-3 inhibited cell proliferation and Akt phosphorylation that had been stimulated by EGF. However, EGF receptor phosphorylation and expression were not reduced by IGFBP-3. Since HHUA cells lack IGF receptors and do not show biological response to IGF these results suggest that IGFBP-3 can bind to HHUA cells, inhibit cell proliferation and induce apoptosis independently of its ability to bind to IGFs possibly by binding to an IGFBP-3 receptor.
Conclusions: Taken together these findings demonstrate that IGFBP-3 binds to HHUA cell surface, and inhibits cell division induced by EGF, possibly by modulating the EGF-mediated signal transduction system.