DIFFERENTIAL REGULATION OF INSULIN-RECEPTOR SUBSTRATE-2 AND MITOGEN-ACTIVATED PROTEIN-KINASE TYROSINE PHOSPHORYLATION BY PHOSPHATIDYLINOSITOL 3-KINASE INHIBITORS IN SH-SY5Y HUMAN NEUROBLASTOMA-CELLS
B. Kim et al., DIFFERENTIAL REGULATION OF INSULIN-RECEPTOR SUBSTRATE-2 AND MITOGEN-ACTIVATED PROTEIN-KINASE TYROSINE PHOSPHORYLATION BY PHOSPHATIDYLINOSITOL 3-KINASE INHIBITORS IN SH-SY5Y HUMAN NEUROBLASTOMA-CELLS, Endocrinology, 139(12), 1998, pp. 4881-4889
Insulin-like growth factor I (IGF-I) is a potent neurotropic factor pr
omoting the differentiation and survival of neuronal cells. SH-SY5Y hu
man neuroblastoma cells are a well characterized in vitro model of ner
vous system growth. We report here that IGF-I stimulated the tyrosine
phosphorylation of the type I IGF receptor (IGF-IR) and insulin recept
or substrate-2 (IRS-2) in a time- and concentration-dependent manner.
These cells lacked IRS-1. After being tyrosine phosphorylated, IRS-2 a
ssociated transiently with downstream signaling molecules, including p
hosphatidylinositol 3-kinase (PI 3-K) and Grb2. Treatment of the cells
with PI 3-K inhibitors (wortmannin and LY294002) increased IGF-I-indu
ced tyrosine phosphorylation of IRS-2. We also observed a concomitant
increase in the mobility of IRS-2, suggesting that PI 3-K mediates or
is required for IRS-2 serine/threonine phosphorylation, and that this
phosphorylation inhibits IRS-2 tyrosine phosphorylation. Treatment wit
h PI 3-K inhibitors induced an increased association of IRS-2 with Grb
2, probably as a result of the increased IRS-2 tyrosine phosphorylatio
n. However, even though the PI 3-K inhibitors enhanced the association
of Grb2 with IRS-2, these compounds suppressed IGF-I-induced mitogen-
activated protein kinase activation and neurite outgrowth. Together, t
hese results indicate that although PI 3-K participates in a negative
regulation of IRS-2 tyrosine phosphorylation, its activity is required
for IGF-IR-mediated mitogen-activated protein kinase activation and n
eurite outgrowth.