IGFBP-2 Stimulates Proliferation And Promotes Phosphorylation And Nuclear Translocation Of ERK1/2 In U251 Cells

IntroductionInsulin-like growth factor binding protein-2(IGFBP-2),a member of insulin-like growth factor(IGF)system,is dramatically over-expressed in a variety of carcinomas, so that it has recently gained attention.That IGFBP-2 is a separate growth regulator has been recognized.IGFBP-2 can modulate cell proliferation,apoptosis and survival independently.It was recently discovered.that IGFBP-2 is over-expressed in the most advanced stage of human glioma,glioblastoma multiforme(GBM).But the exact role of IGFBP-2 in neural carcinogenesis remains unknown.Extracellular signal regulated kinases(ERK1/2)are serine/threonine kinases that can be activated in response to a variety of extracellular stimuli and mediate signal transduction from the cell surface to the nucleus to control cell growth and differentiation.The ERK pathway is predominantly activated by various receptors including receptor tyrosine kinases (RTKs),integrins and ion channels.This pathway has been known to be activated in normal and malignant cells by external stimuli such as growth factors.Using U251 human glioblastoma cells,the effects of exogenous IGFBP-2 on cell proliferation and activation of ERK1/2 signaling pathway were detected.ObjectiveTo investigate the effects of exogenous IGFBP-2 on U251 human glioblastoma cells proliferation and activation of ERK1/2 signaling pathway.Methods1.MTT assay was used to examine the influence of IGFBP-2 on U251cells proliferation. 2.The phosphorylation level and intracellulat localization of ERK1/2 in cells treated with IGFBP-2 were tested by western blotting analysis and immunofluorescence staining respectively.Results1.Various concentration of exogenous IGFBP-2(125,250,500ng/ml)dramatically stimulates U251 cells growth(p<0.01),500ng/ml IGFBP-2 most significantly promoted U251 cell proliferation by 2.6-fold(P<0.01),while 125ng/ml IGFBP-2 and 250ng/ml IGFBP-2 had similar effects that they both enhanced U251 cell proliferation by 1.8-fold(P<0.05).2.In U251 cells treated by 500ng/ml IGFBP-2 for 5min,phosphorylated ERK1/2 increasted by nearly one-fold(P<0.05),In U251 cells treated by 500ng/ml IGFBP-2 for 30min,phosphorylated ERK1/2 increasted by over two-fold(P<0.05)3.Immunofluorescence staining showed that stimulation of U251 cells with 500ng/ml IGFBP-2 for 30min resulted in nuclear translocation of phosphorylated ERK1/2(P<0.01).ConclusionIGFBP-2 induced U251 cell proliferation may be mediated by activation of the ERK1/2 pathway.These novel findings may give rise to development of innovative strategies for the treatment and management of glioblastoma.