growth factor th factor Extracellular growth factors receptor stimulate cell growth Activation of cell-surface receptors Pl 3-kinas protein kinase activation Activation of pi 3-kinase active active phosphorylated S6 kinase Activation of elF4E (translation increased mRNA translation initiation factor)and s6 kinase(phosphorylates ribosomal STIMULATION OF CELL GROWTH protein S6) Figure 17-44 One way in which growth factors promote cell growt In this simplified scheme, activation of cell-surface receptors leads to the activation of Pl 3-kinase, which promotes Increasing protein synthesis and cell protein synthesis, at least partly through the activation of elF4E and S6 kinase growth Growth factors also inhibit protein breakdown(not shown) by poorly understood pathway.Extracellular growth factors stimulate cell growth Activation of cell-surface receptors Activation of PI 3-kinase Activation of elF4E (translation initiation factor) and S6 kinase(phosphorylates ribosomal protein S6) Increasing protein synthesis and cell growth