Figure 2. The downstream consequences of activation of the epidermal growth factor receptor (EGFr) in intestinal epithelial cells differ depending on the way in which it is activated.

When EGFr is directly activated by EGF, it becomes phosphorylated at at least six cytoplasmic tyrosine residues that recruit distinct binding partners (left side of figure). When EGFr is transactivated secondary to the binding of carbachol (CCh) to the m₃ muscarinic receptor (m₃R), which occurs via the release of transforming growth factor‐α (TGF‐α), two cytoplasmic tyrosine residues (Y992 and Y1068) are simultaneously dephosphorylated by the ability of CCh also to activate protein tyrosine phosphatase 1B (PTP1B) (right side of figure). This alters the signalling intermediates and consequences of EGFr activation.