Epidermal growth factor negatively regulates chondrogenesis of mesenchymalcells by modulating the protein kinase C-alpha, Erk-1, and p38 MAPK signaling pathways

During limb development, epithelial cells in the apical ectodermal ridge ke ep the underlying mesenchymal cells in a proliferative state preventing dif ferentiation by secreting signaling molecules such as epidermal growth fact or (EGF). We investigated the molecular mechanism of the EGF effect on the regulation of micromass culture-induced chondrogenesis of chick limb bud me senchymal cells as a model system. We found that expression and tyrosine ph osphorylation of the EGF receptor was increased transiently during chondrog enesis, Exogenous EGF inhibited chondrogenic differentiation of mesenchymal cells, and this effect was reversed by the EGF receptor inhibitor AG1478, EGF treatment also inhibited the expression and activation of protein kinas e C-alpha, whereas it activated Erk-1 and inhibited p38 mitogen-activated p rotein kinase, all of which appeared to be involved in the EGF-induced inhi bition of chondrogenesis. Stimulation of the EGF receptor blocked precartil age condensation and altered the expression of cell adhesion molecules such as N-cadherin and integrins alpha(5) and beta(1), All these EGF effects we re reversible by AG1478, The data indicate that EGF negatively regulate cho ndrogenesis of chick limb bud mesenchymal cells by inhibiting precartilage condensation and by modulating signaling pathways including those of protei n kinase C-alpha, Erk-1, and p38 mitogen-activated protein kinase.