β 1 integrins modulate p66 ShcA expression and EGF-induced MAP kinase activation in fetal lung cells

Abstract

ShcA proteins mediate Erk1/Erk2 activation by integrins and epidermal growth factor (EGF), and are expressed as p46 ShcA, p52 ShcA, and p66 ShcA. Although p52 ShcA and p46 ShcA mediate Erk1/Erk2 activation, p66 ShcA antagonizes Erk activation. p66 ShcA is spatially regulated during lung development, leading us to hypothesize that integrin signaling regulates p66 ShcA expression and, consequently, EGF signaling. Fetal lung mesenchymal cells were isolated from E16 Swiss–Webster mice, stimulated with oligopeptide extracellular matrix analogs or anti-integrin antibodies, and subjected to ShcA Western analyses and EGF-stimulated Erk1/Erk2 kinase assays. p66 ShcA expression was decreased by anti-α 1 integrin antibody and DGEA collagen analog, and increased by anti-β 1, anti-α 4, and anti-α 5 integrin antibodies and RGDS fibronectin analog. Paradoxically, β 1 integrin stimulation increased EGF-induced Erk activation while increasing expression of the inhibitory p66 ShcA isoform. This paradox was resolved by demonstrating that Erk inhibition attenuates integrin-mediated p66 ShcA induction. These results suggest that p66 ShcA is up-regulated as inhibitory feedback on integrin-mediated Erk activation.