The role of the insulin receptor substrate-1 in the differentiation of rat hippocampal neuronal cells.
H19-7/IGF-IR cells are rat hippocampal cells expressing a human IGF-I receptor, which differentiate to a neuronal phenotype when stimulated by IGF-I at 39 degrees C. H19-7/IGF-IR cells have low levels of expression of insulin receptor substrate-l (IRS-1), a major substrate of the IGF-IR. IGF-I induces serine-phosphorylation and down-regulation of the endogenous IRS-1 upon differentiation of H19-7/IGF-IR cells. The profound influence of IRS-1 on differentiation of H19-7/IGF-IR cells was confirmed by transfecting these cells with a plasmid expressing mouse IRS-1. Over-expression of wild type IRS-1 in H19-7/IGF-IR cells abolishes IGF-I-induced differentiation at 39 degrees C. A mutant of IRS-1 lacking the PTB domain loses the ability to inhibit the differentiation program. H19-7/IGF-IR/IRS-1 cells at 39 degrees C show a stronger and prolonged activation of Akt, when compared to H19-7/IGF-IR cells. The role of Akt in the inhibition of the differentiation program was confirmed by using the inhibitor of Class I PI3 kinases LY29400, which restores IGF-I-induced differentiation of H19-7/IGF-IR/IRS-1 cells. H19-7/IGF-IR/IRS-1 cells show a strong reduction in MAP kinases signaling, which is related to the superactivation of Akt. This was confirmed by expressing in H19-7/IGF-IR cells a constitutively active Akt, which inhibited MAP kinases activation in these cells. These experiments confirm the importance of MAPK in the mechanism of IGF-I-mediated differentiation of H19-7/IGF-IR cells
Morrione
A
A
Kimmel Cancer Center, Thomas Jefferson University, 233 S 10th Street, 624 BLSB, Philadelphia, Pennsylvania, PA 19107, USA.
Navarro
M
M
Romano
G
G
Dews
M
M
Reiss
K
K
Valentinis
B
B
Belletti
B
B
Baserga
R
R
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D006624:Hippocampus / Q000166:cytology*; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D010750:Phosphoproteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000032:analysis; D019893:Ribosomal Protein S6 Kinases / Q000502:physiology
D002867:Chromones; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C526296:Irs1 protein, rat; D009025:Morpholines; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D020928:Mitogen-Activated Protein Kinases