Abstract
The term “PI 3-kinase” is now applied to a growing family of proteins that are able to convert phosphatidylinositol (PtdIns), PtdIns(4)P and PtdIns(4,5)P2 into PtdIns(3)P, PtdIns(3,4)P2 and PtdIns(3,4,5)P3 respectively, by phosphorylating the D-3 position of the inositol head groups of phosphoinositide lipids (collectively known as D-3 phosphoinositide lipids shown in Fig. 1) (1,2). PtdIns(3)P is constitutively present in eukaryotic cells and its levels are largely unaltered upon cellular stimulation. In contrast, PtdIns(3,4)P2 and PtdIns(3,4,5)P3 are generally absent from resting cells, but their intracellular concentration rises markedly upon stimulation via a variety of receptors suggesting a likely function as a second messenger (1,2). PI 3-kinases can be divided into three main classes on the basis of their in vitro lipid substrate specificity, structure and likely mode of regulation. Class I PI 3-kinases phos-phorylate PtdIns, PtdIns(4)P and PtdIns(4,5)P2, interact with Ras and form heterodimeric complexes with adaptor proteins that link them to different upstream signaling events (1). The prototypical class IA PI 3-kinase is a heterodimer consisting of the 85 kDa regulatory subunit (responsible for protein-protein interactions either via protein tyrosine phosphate-binding SH2 domains or SH3 domains and/or proline rich regions) and a catalytic 110 kDa subunit. The class IB PI 3-kinases are stimulated by G protein αγ subunits and do not interact with the SH2-containing adaptors that bind class IA PI 3-kinases. Instead, the first identified member of this family p1 10γ, associates with a unique p101 adaptor molecule (1). The class II PI 3-kinases are characterized by the presence of a C-2 domain at the carboxy terminus and utilize predominantly PtdIns and PtdIns(4)P as substrates (e.g., PI3K-C2α), whereas the class III PI 3-kinases utilize only PtdIns as a substrate (e.g., mammalian PtdIns 3-kinase and yeast Vps34p) (1). Generally, PI 3 kinases are now regarded as an important intracellular signal upstream of a variety of biochemical (e.g., activation of Akt/protein kinase B and/or p70 S6 kinase and inhibition of glycogen synthase kinase-3) and functional responses (membrane trafficking of proteins such as the glucose transporter GLUT4, postendocytic sorting of ligand-stimulated receptors such as the Platelet-derived growth factor (PDGF) receptor, membrane ruffling, superoxide production, and chemotaxis) (1,2).
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Ward, S.G. (2000). Measurement of Phosphoinositide 3-Kinase Activity. In: Proudfoot, A.E.I., Wells, T.N.C., Power, C.A. (eds) Chemokine Protocols. Methods in Molecular Biology, vol 138. Humana Press. https://doi.org/10.1385/1-59259-058-6:163
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DOI: https://doi.org/10.1385/1-59259-058-6:163
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