T. Karlsson et al., THE SRC HOMOLOGY 2 DOMAIN PROTEIN SHB TRANSMITS BASIC FIBROBLAST GROWTH FACTOR-DEPENDENT AND NERVE GROWTH FACTOR-DEPENDENT DIFFERENTIATION SIGNALS IN PC12 CELLS, Cell growth & differentiation, 9(9), 1998, pp. 757-766
To assess a possible role for the Src homology 2 (SH2) domain adaptor
protein Shb in PC12 cell signal transduction and differentiation, we h
ave investigated the expression of Shb in PC12 cells and found that th
e differentiation factors nerve growth factor (NGF) and basic fibrobla
st growth factor (bFGF), as well as the PC12 cell mitogen epidermal gr
owth factor, increased Shb protein expression and Shb mRNA steady-stat
e levels, Two PC12 cell clones stably overexpressing the Shb cDNA exhi
bited enhanced NGF- or bFGF-induced differentiation, assessed as neuri
te outgrowth, This effect showed no direct correlation to mitogen-acti
vated protein kinase activation, although the mitogen-activated protei
n kinase/kinase inhibitor PD-98059 caused a partial inhibition of neur
ite outgrowth, Furthermore, it was found that the Shb-overexpressing c
ells extended neurites in response to epidermal growth factor, The eff
ects of Shb overexpression on neurite outgrowth required a functional
SH2 domain because PC12 cells expressing Shb with an inactivated SH2 d
omain did not differentiate more readily in response to NGF, Tyrosine
phosphorylation of the p13 Suc1-associated neurotrophic factor-induced
tyrosine-phosphorylated target protein in response to bFGF was strong
ly inhibited by Shb overexpression, without correlating with the corre
sponding rate of neurite outgrowth, NGF-induced tyrosine phosphorylati
on of phospholipase C gamma, TrkA, and Shc was unaltered in the Shb-ov
erexpressing cells, whereas that of Shb was greatly enhanced in these
cells compared with control PC12-neo cells. In addition, an NGF-activa
ted M-r 140,000 phosphotyrosine protein was found to be associated wit
h Shb in immunoprecipitation experiments. The data in this study sugge
st that Shb is involved in transmission of NGF- and bFGF-dependent dif
ferentiation signals in PC12 cells.