title: Insulin-like growth factor-1 promotes G(1)/S cell cycle progression through bidirectional regulation of cyclins and cyclin-dependent kinase inhibitors via the phosphatidylinositol 3-kinase/Akt pathway in developing rat cerebral cortex.
abstract: Although survival-promoting effects of insulin-like growth factor-1 (IGF-1) during neurogenesis are well characterized, mitogenic effects remain less well substantiated. Here, we characterize cell cycle regulators and signaling pathways underlying IGF-1 effects on embryonic cortical precursor proliferation in vitro and in vivo. In vitro, IGF-1 stimulated cell cycle progression and increased cell number without promoting cell survival. IGF-1 induced rapid increases in cyclin D1 and D3 protein levels at 4 h and cyclin E at 8 h. Moreover, p27(KIP1) and p57(KIP2) expression were reduced, suggesting downregulation of negative regulators contributes to mitogenesis. Furthermore, the phosphatidylinositol 3-kinase (PI3K)/Akt pathway specifically underlies IGF-1 activity, because blocking this pathway, but not MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal-regulated kinase), prevented mitogenesis. To determine whether mechanisms defined in culture relate to corticogenesis in vivo, we performed transuterine intracerebroventricular injections. Whereas blockade of endogenous factor with anti-IGF-1 antibody decreased DNA synthesis, IGF-1 injection stimulated DNA synthesis and increased the number of S-phase cells in the ventricular zone. IGF-1 treatment increased phospho-Akt fourfold at 30 min, cyclins D1 and E by 6 h, and decreased p27(KIP1) and p57(KIP2) expression. Moreover, blockade of the PI3K/Akt pathway in vivo decreased DNA synthesis and cyclin E, increased p27(KIP1) and p57(KIP2) expression, and prevented IGF-1-induced cyclin E mRNA upregulation. Finally, IGF-1 injection in embryos increased postnatal day 10 brain DNA content by 28%, suggesting a role for IGF-1 in brain growth control. These results demonstrate a mitogenic role for IGF-1 that tightly controls both positive and negative cell cycle regulators, and indicate that the PI3K/Akt pathway mediates IGF-1 mitogenic signaling during corticogenesis.
authors.affiliation: Department of Neuroscience and Cell Biology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
authors.forename: Georges
authors.initials: G
authors.lastname: Mairet-Coello
authors.forename: Anna
authors.initials: A
authors.lastname: Tury
authors.forename: Emanuel
authors.initials: E
authors.lastname: DiCicco-Bloom
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001973:Bromodeoxyuridine / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002540:Cerebral Cortex / Q000166:cytology* / Q000196:embryology*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000494:pharmacology; D016213:Cyclins / Q000378:metabolism*; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007276:Injections, Intraventricular / Q000379:methods; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011247:Pregnancy; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors
chemical_list: D018797:Cell Cycle Proteins; D016213:Cyclins; D004791:Enzyme Inhibitors; D050760:Cyclin-Dependent Kinase Inhibitor p27; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; C111490:Akt3 protein, rat; D051057:Proto-Oncogene Proteins c-akt; D001973:Bromodeoxyuridine; D013936:Thymidine