The antibiotic azatyrosine suppresses progesterone or [Val12]p21 Ha-ras/insulin-like growth factor I-induced germinal vesicle breakdown and tyrosine phosphorylation of Xenopus mitogen-activated protein kinase in oocytes

Selective cytotoxicity of azatyrosinamides against ras-transformed NIH 3T3 cells

This study aims to develop novel azatyrosinamide compounds structurally modified from ras-specific antioncogenic azatyrosine. Analogues 4-15 were prepared and their inhibition on the growth of wild-type and ras-transformed NIH 3T3 cell lines was compared. Compound 12 was found to be the most active with IC50 16.5+/-2.2 microM which is 458-fold more potent than that of azatyrosine. The selective toxicity, defined as IC(50 wild-type)/IC(50 ras-transformed) for this compound was 138.5.

Enantioselective synthesis of (2-pyridyl)alanines via catalytic hydrogenation and application to the synthesis of L-azatyrosine

[reaction: see text] A novel method for the synthesis of (2-pyridyl)alanines 2a-b was developed by converting (2-pyridyl)dehydroamino acid derivatives 1a-b to the corresponding N-oxides 3a-b followed by asymmetric hydrogenation using (R,R)-[Rh(Et-DUPHOS)(COD)]BF(4) [(R,R)-6] catalyst and subsequent N-oxide reduction in 80-83% ee. This methodology was applied to the total synthesis of L-azatyrosine [(+)-12], an antitumor antibiotic, starting from (5-benzyloxy)-2-pyridylmethanol (7), in >96% enantiomeric purity.

Micro-injection of recombinant lysyl oxidase blocks oncogenic p21-Ha-Ras and progesterone effects on Xenopus laevis oocyte maturation

Previous evidence suggested an anti-oncogenic role for lysyl oxidase, mainly in ras-transformed cells. Here we prove that recombinant lysyl oxidase is actually able to antagonize p21-Ha-Ras-induced Xenopus laevis oocyte maturation. Lysyl oxidase was also effective on progesterone-dependent maturation, indicating a block lying downstream of Ras. Maturation induced by activated 'maturation promoting factor', normally triggered by progesterone, was also inhibited by lysyl oxidase. Finally, lysyl oxidase did not abolish p42Erk2 phosphorylation upon maturation triggering, suggesting a block downstream of Erk2. Further investigation showed that lysyl oxidase action depends on protein synthesis and is therefore probably mediated by a newly synthesized protein.

A functional insulin-like growth factor I receptor is required for the mitogenic and transforming activities of the epidermal growth factor receptor

When wild-type mouse embryo cells are stably transfected with a plasmid constitutively overexpressing the epidermal growth factor (EGF) receptor (EGFR), the resulting cells can grow in serum-free medium supplemented solely with EGF. Supplementation with EGF also induces in these cells the transformed phenotype (growth in soft agar). However, when the same EGFR expression plasmid is introduced and overexpressed in cells derived from littermate embryos in which the insulin-like growth factor I (IGF-I) receptor genes have been disrupted by homologous recombination, the resulting cells are unable to grow or to be transformed by the addition of EGF. Reintroduction into these cells (null for the IGF-I receptor) of a wild-type (but not of a mutant) IGF-I receptor restores EGF-mediated growth and transformation. Our results indicate that at least in mouse embryo fibroblasts, the EGFR requires the presence of a functional IGF-I receptor for its mitogenic and transforming activities.

A functional insulin-like growth factor I receptor is required for the mitogenic and transforming activities of the epidermal growth factor receptor

When wild-type mouse embryo cells are stably transfected with a plasmid constitutively overexpressing the epidermal growth factor (EGF) receptor (EGFR), the resulting cells can grow in serum-free medium supplemented solely with EGF. Supplementation with EGF also induces in these cells the transformed phenotype (growth in soft agar). However, when the same EGFR expression plasmid is introduced and overexpressed in cells derived from littermate embryos in which the insulin-like growth factor I (IGF-I) receptor genes have been disrupted by homologous recombination, the resulting cells are unable to grow or to be transformed by the addition of EGF. Reintroduction into these cells (null for the IGF-I receptor) of a wild-type (but not of a mutant) IGF-I receptor restores EGF-mediated growth and transformation. Our results indicate that at least in mouse embryo fibroblasts, the EGFR requires the presence of a functional IGF-I receptor for its mitogenic and transforming activities.

Insulin-stimulated oocyte maturation requires insulin receptor substrate 1 and interaction with the SH2 domains of phosphatidylinositol 3-kinase

Xenopus oocytes from unprimed frogs possess insulin-like growth factor I (IGF-I) receptors but lack insulin and IGF-I receptor substrate 1 (IRS-1), the endogenous substrate of this kinase, and fail to show downstream responses to hormonal stimulation. Microinjection of recombinant IRS-1 protein enhances insulin-stimulated phosphatidylinositol (PtdIns) 3-kinase activity and restores the germinal vesicle breakdown response. Activation of PtdIns 3-kinase results from formation of a complex between phosphorylated IRS-1 and the p85 subunit of PtdIns 3-kinase. Microinjection of a phosphonopeptide containing a pYMXM motif with high affinity for the src homology 2 (SH2) domain of PtdIns 3-kinase p85 inhibits IRS-1 association with and activation of the PtdIns 3-kinase. Formation of the IRS-1-PtdIns 3-kinase complex and insulin-stimulated PtdIns 3-kinase activation are also inhibited by microinjection of a glutathione S-transferase fusion protein containing the SH2 domain of p85. This effect occurs in a concentration-dependent fashion and results in a parallel loss of hormone-stimulated oocyte maturation. These inhibitory effects are specific and are not mimicked by glutathione S-transferase fusion proteins expressing the SH2 domains of ras-GAP or phospholipase C gamma. Moreover, injection of the SH2 domains of p85, ras-GAP, and phospholipase C gamma do not interfere with progesterone-induced oocyte maturation. These data demonstrate that phosphorylation of IRS-1 plays an essential role in IGF-I and insulin signaling in oocyte maturation and that this effect occurs through interactions of the phosphorylated YMXM/YXXM motifs of IRS-1 with SH2 domains of PtdIns 3-kinase or some related molecules.

Insulin-stimulated oocyte maturation requires insulin receptor substrate 1 and interaction with the SH2 domains of phosphatidylinositol 3-kinase

Xenopus oocytes from unprimed frogs possess insulin-like growth factor I (IGF-I) receptors but lack insulin and IGF-I receptor substrate 1 (IRS-1), the endogenous substrate of this kinase, and fail to show downstream responses to hormonal stimulation. Microinjection of recombinant IRS-1 protein enhances insulin-stimulated phosphatidylinositol (PtdIns) 3-kinase activity and restores the germinal vesicle breakdown response. Activation of PtdIns 3-kinase results from formation of a complex between phosphorylated IRS-1 and the p85 subunit of PtdIns 3-kinase. Microinjection of a phosphonopeptide containing a pYMXM motif with high affinity for the src homology 2 (SH2) domain of PtdIns 3-kinase p85 inhibits IRS-1 association with and activation of the PtdIns 3-kinase. Formation of the IRS-1-PtdIns 3-kinase complex and insulin-stimulated PtdIns 3-kinase activation are also inhibited by microinjection of a glutathione S-transferase fusion protein containing the SH2 domain of p85. This effect occurs in a concentration-dependent fashion and results in a parallel loss of hormone-stimulated oocyte maturation. These inhibitory effects are specific and are not mimicked by glutathione S-transferase fusion proteins expressing the SH2 domains of ras-GAP or phospholipase C gamma. Moreover, injection of the SH2 domains of p85, ras-GAP, and phospholipase C gamma do not interfere with progesterone-induced oocyte maturation. These data demonstrate that phosphorylation of IRS-1 plays an essential role in IGF-I and insulin signaling in oocyte maturation and that this effect occurs through interactions of the phosphorylated YMXM/YXXM motifs of IRS-1 with SH2 domains of PtdIns 3-kinase or some related molecules.

Activation of the mitogen-activated protein kinase pathway in Triton X-100 disrupted NIH-3T3 cells by p21 ras and in vitro by plasma membranes from NIH 3T3 cells

We describe a novel Triton-disrupted mammalian cell system wherein the pathways for activation of mitogen-activated protein (MAP) kinases (MAPKs) are capable of direct biochemical manipulation in vitro. MAPKs p42mapk and p44mapk are activated in signal transduction cascade(s) initiated by occupancy of plasma membrane receptors for peptide growth factors, hormones, and neurotransmitters. One likely activation pathway for MAPKs consists of sequential activations of c-ras, c-raf-1, and a protein-tyrosine/threonine kinase, MAP kinase kinase. Triton-disrupted cells retained capacity for activation of the pathway by both peptide growth factors and by addition of GTP-loaded p21 rasVal12. Incubation of disrupted cells with an antibody that neutralized the function of c-ras (Y13-259) abolished receptor-mediated stimulation of MAPK as did acute addition of 200 microM azatyrosine. Activation of the pathway was reconstituted in a cell-free system using high-speed supernatants generated from Triton-disrupted cells together with purified plasma membranes from parental cells and as a heterogeneous system using purified plasma membranes from v-ras-transformed cells. These systems will allow biochemical dissection in vitro of the interaction(s) between c-ras and the MAPK pathway in mammalian cells.