Epidermal growth factor induces an increase in cell adhesion and an arrangement of actin skeleton in stress fibres in pituitary cultured cells from infantile rats but not adult rats

Abstract

The rat anterior pituitary gland undergoes changes in its cyto-architecture during the second and third weeks of postnatal life. However, little is known about the factors that regulate these tissue conformational changes. The epidermal growth factor (EGF) is one of the growth factors that are synthesized by the pituitary gland, and almost all of the pituitary cells have EGF receptors (EGFR). In addition to the effects of the EGF on mitosis and differentiation, this growth factor can modulate cell adhesion, cell migration, and cytoskeletal organization. In this study we focussed our attention in examining the effects of EGF on the adhesion of cells to the extracellular matrix and on the actin cytoskeletal arrangement of pituitary cells from infantile and adult rats. Our results show that in infantile cells the EGF induces cell adhesion with increase in cell surface area. The arrangement of actin-F in infantile EGF-treated cells was in stress fibers and vinculin acquired a striped shape at the membrane border, suggesting the assembly of focal adhesion contacts. In contrast, in adult pituitary cells EGF does not induce any change in cell adhesion, and the cells maintain a rounded shape with an arrangement of actin-F in thin cortical bands even though, immuno-localization of the EGFR was observed in adult cells cultured in defined medium. We also looked for the EGFR in membrane preparations from infantile and adult pituitaries, and a marked difference in membrane EGFR was observed between them, the infantile pituitaries showing a significantly higher amount. Our results suggest that in infantile cells EGF induces the assembly of focal adhesion contacts, and that in adult cells the receptor of this growth factor is uncoupled of the signaling pathway by which a rearrangement of actin cytoskeleton occurs.