The signal transduction pathways that mediate metabolic and mitogenic effects in primary rat hepatocytes were investigated. Transcriptional inhibition by insulin of the metabolic gene insulin-like growth factor binding protein-1 (IGFBP-1) was P13-kinase-dependent and sensitive to rapamycin, an Inhibitor of p7Os6k activation at the level of mTOR. In hepatocytes, P13-kinase contributes to p70s6k activation. Our results described the first example of an insulin-specific gene, whose regulation is both P13-kinase- and p70s6k-dependent. MAP kinases were not Involved in regulating this nuclear event. / DNA synthesis by insulin was not effected by to MAP kinase signalling pathway, but was p13-kinase-dependent and sensitive to rapamycin. Thus, p13-kinase and p70s6k determine metabolic and mitogenic signalling by insulin in kw cob. DNA synthesis by EGF was also mediated by the P13-kinase/p70 s6k pathway. Unlike insulin however, EGF augmented cymc mRNA levels and this response was effected by activation of the MAP kinase pathway. Of particular Interest, EGF was without effect on hepatic IGFBP-1 mRNA despite its ability to activate P13-kinase and p70s6k to levels comparable to those observed after insulin treatment. / We demonstrated that the protein tyrosine phosphatase (PTP) inhibitor, bpV(phen), triggers early signaling events identical to insulin by promoting insulin receptor kinase (IRK) autophosphorylation and activation, suggesting that bpV(phen) inhibits an IRK-associated PTP(s). Consistent with these data, bpV(phen) mimicked insulin effects on DNA synthesis and IGFBP-1 mRNA expression. In contrast to insulin however, bpV(phen) decreased IGFBP-4, as well as IGFBP-1 mRNA levels through an additional signaling pathway, unrelated to P13-kinase/p70 s6k, and it activated MAP kinases independently of their upstream activator, MEK. Thus, bpV(phen) may inhibit a PTP(s) involved in MAP kinase inactivation, and MAP kinases may mediate the inhibitory effect of bpV(phen) on IGFBP-1 and/or -4 mRNA expression. Together, these data reveal the complexity of metabolic and genetic regulation: (1) the P13-kinase/p70s6k pathway cannot, in itself, explain metabolism, and (2) multiple signaling pathways may converge to regulate a common gene.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35851 |
| Date | January 1998 |
| Creators | Band, Christian J. |
| Contributors | Posner, Barry (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001650433, proquestno: NQ50106, Theses scanned by UMI/ProQuest. |
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