Abstract
We have used two experimental approaches to examine the possible role of phosphatidylinositol 3-kinase (PI 3-kinase) in the regulation of glucose transport in oocytes isolated from Xenopus laevis. Incubation of oocytes with the PI 3-kinase inhibitor wortmannin inhibited insulin-like growth factor-1-stimulated deoxyglucose uptake. Half-maximal inhibition was observed at concentrations approximately 20 nM. Conversely, we also examined the effects of microinjection of synthetic peptides designed to interact with Src homology 2 domains of the regulatory subunit of PI 3-kinase on deoxyglucose transport in oocytes. We show that a bifunctional synthetic peptide containing two YMXM consensus sequences for binding to SH2 domains stimulated both PI 3-kinase activity and deoxyglucose transport when both tyrosine residues were phosphorylated. However, non-phosphorylated or bisphosphonotyrosine peptides with the identical amino acid sequence failed to stimulate transport or PI 3-kinase activity. Taken together, these data argue strongly for a role for PI 3-kinase in the regulation of glucose transport in oocytes.
Highlights
Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom, Wfizer Central Research, Groton, Connecticut 06340, and the Department of Physiology and Pharmacology, University of Strathclyde, Glasgow GI lxW,Scotland, United Kingdom transport incells, we have utilized oocytes isolated from Xenop u s laeuis as a model system
Half-maximal inhibition was observed at concentrations 20 we examined the effects of microinjection of synthetic peptides designed to interact with Src homology 2 domains of the regulatory subunitof PI S-kinaseon deoxyglucosetransport in oocytes
We show that a bifunctional synthetic peptide containing two Y” consensus sequences for binding to SH2 domains stimulatedboth PI 3-kinaseacmaturation have been proposed on the basis of inhibitory effects of antibodies microinjected into the oocyte cytosol
Summary
Incubation of oo- potential roles for Ras (Korn et al, 1987) and tyrosine phoscytes with the PI 3-kinase inhibitor wortmannin inhib- phorylation (Janicot and Lane, 1989)in IGF-1-induced oocyte ited insulin-like growth factor-1-stimulated deoxyglu- Kletzien and Perdue,1974; Rollins et al, 1988; Kitagawa et al, prepared a range of synthetic phosphono- and phosphotyrosine1989; Hiraki et al, 1989).Chronicexposure to a variety of containing peptidesdesigned to interact with the SH2 domain polypeptide growth factors stimulates glucose transport by ac- of the regulatory subuniotf PI 3-kinase (Shoelson et al, 19921, tivation of glucose transporter (GLUTl)’ gene transcription inand we have evaluated the effects of microinjection of these peptides on deoxyglucose transport in oocytes.
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