DIFFERENTIAL UTILIZATION OF SHCA TYROSINE RESIDUES AND FUNCTIONAL DOMAINS IN THE TRANSDUCTION OF EPIDERMAL GROWTH FACTOR-INDUCED MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION IN 293T CELLS AND NERVE GROWTH FACTOR-INDUCED NEURITE OUTGROWTH IN PC12 CELLS - IDENTIFICATION OF A NEW GRB2-CENTER-DOT-SOS1 BINDING-SITE

By transient expression of both truncated forms of p52(SHCA) and those with point mutations in 293T cells, it has been shown that, in additi on to Tyr-317, Tyr-239/240 is a major site of phosphorylation that ser ves as a docking site for Grb2.Sos1 complexes, In addition, analysis o f epidermal growth factor (EGF)-induced activation of mitogen-activate d protein kinase in 293T cells showed that the overexpression Shc SH2 or phosphotyrosine binding (PTB) domains of ShcA alone has a more pote nt negative effect than the overexpression of the forms of ShcA lackin g Tyr-317 or Tyr 239/240 or both. In transiently transfected PC12 cell s, the ShcA PTB domain and tyrosine phosphorylation in the CH1 domain, especially on Tyr-239/240, are crucial for mediating nerve growth fac tor (NGF)-induced neurite outgrowth, These findings suggest that the E GF and NGF (TrkA) receptor can utilize Shc in different ways to promot e their activity, For EGF-induced mitogen-activated protein kinase act ivation in 293T cells, both Shc PTB and SH2 domains are essential for optimal activation, indicating that a mechanism independent of Grb2 en gagement with Shc may exist, For NGF-induced neurite outgrowth in PC12 cells, Shc PTB plays an essential role, and phosphorylation on Tyr-23 9/240, but not on Tyr-317, is required.