Insulin-like growth factor-binding protein 1 stimulates human trophoblast migration by signaling through alpha 5 beta 1 integrin via mitogen-activated protein kinase pathway

A highly migratory subpopulation of the human placental trophoblast, known as the extravillous trophoblast (EVT), invades the uterus and its vasculatu re, to establish adequate exchange of key molecules between the maternal an d fetal circulations. During their formation, EVT cells selectively acquire alpha5 beta1 integrin. We had shown that alpha5 beta1 is required for thei r migratory function, and that EVT cell migration is stimulated by insulin- like growth factor-binding protein (IGFBP)-1 produced by the uterine decidu a. The present study examined whether this stimulation is dependent on bind ing of the Arg-Gly-Asp (RGD) domain of IGFBP-1 to an RGD binding site on th e alpha5 beta1 integrin, followed by activation of focal adhesion kinase (F AK) and stimulation of the mitogen-activated protein kinase (MAPK) pathway. IGFBP-1 treatment increased migration of EVT cells, whereas an anti-alpha5 beta1 integrin antibody blocked migration regardless of IGFBP-1 treatment. Migration stimulation by IGFBP-1 was abrogated by pretreatment with a Gly- Arg-Gly-Asp-Ser-Pro (GRGDSP), but not, a Gly-Arg-Gly-Glu-Ser-Pro (GRGESP) h exapeptide, and by mutation of the RGD domain of IGFBP-1 to Trp-Gly-Asp (WG D). IGFBP-1 treatment caused a rapid localization of immunoreactive FAK to cellular lamellipodia, a rapid increase in phosphorylation of FAK and extra cellular-signal regulated kinases 1 and 2. Preincubation of EVT cells with Herbimycin A, a tyrosine kinase inhibitor, abrogated IGFBP-1 effects; where as an MAPK kinase inhibitor, PD 98059, reduced migration regardless of IGFB P-1 treatment. These results indicate that IGFBP-1 stimulation of EVT cell migration occurs by binding of its RGD domain to the alpha5 beta1 integrin, leading to activation of FAK and stimulation of MAPK pathway.