Fibroblast growth factor receptors (fgfrs) (fgfrs) are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. the extracellular domains of fgfr fgfr proteins bind specifically to signaling molecules called fibroblast growth factors. the intracellular domains of fgfr fgfr proteins function as protein kinases, enzymes that transfer phosphate groups from atp atp to protein substrates. fgfr fgfr activation occurs when binding by fibroblast growth factors causes fgfr fgfr proteins in the plasma membrane to become closely associated with each other. the association of two fgfr fgfr proteins stimulates protein kinase activity, which triggers the activation of intracellular signaling pathways. a simplified model of fgfr fgfr activation is represented in figure 1. figure 1. a simplified model of fgfr fgfr activation which of the following changes in the fgfr fgfr signaling pathway is most likely to result in uncontrolled cell proliferation?