Interleukin-7 induces the association of phosphatidylinositol 3-kinase with the alpha chain of the interleukin-7 receptor.
The recently characterized receptor for interleukin (IL)-7 (IL-7R) includes a unique alpha chain as well as a common gamma chain shared with the receptors for IL-2 and IL-4. Engagement of the IL-7R activates the intracellular enzyme phosphatidylinositol (PtdIns) 3-kinase but the mechanism of PtdIns 3-kinase activation and the molecular basis of its interaction with IL-7R are not known. Here we show that IL-7 causes the 85-kDa regulatory subunit of PtdIns 3-kinase (p85), and PtdIns 3-kinase activity, to associate with the IL-7R. This interaction can be ascribed to ligand-induced phosphorylation of a single Tyr residue in the receptor's unique alpha chain. Herbimycin A, a specific protein tyrosine kinase inhibitor, suppresses not only tyrosine phosphorylation of the IL-7R but also its association with p85. A phosphopeptide corresponding to the sequence surrounding Tyr449 in the cytoplasmic tail of the IL-7R alpha chain, but not its non-phosphorylated analogue or phosphopeptides coincident with the sequences surrounding other alpha chain Tyr residues, efficiently competes out p85 binding. Replacement of Tyr449 with Phe results in a loss of p85 binding. Finally, soluble forms of the src homology 2 domains of p85, which bind directly to phosphotyrosyl peptides, specifically inhibit the association of p85 with the IL-7R. Thus, PtdIns 3-kinase recruitment occurs through a single, phosphotyrosine dependent recognition motif surrounding Tyr449 in the IL-7R alpha chain. This motif corresponds to a canonical sequence for p85 binding, Tyr(P)-X-X-Met. Since the closely related IL-2R and IL-4R also activate PtdIns 3-kinase but are devoid of such canonical motifs, our results suggest that the mechanism by which IL-7R recruits and activates PtdIns 3-kinase differs fundamentally from that used by the other receptors. PtdIns 3-kinase may, therefore, play a unique and important role in the biological response to IL-7.
Venkitaraman
A R
AR
Medical Research Council, Laboratory of Molecular Biology, Cambridge, GB.
Cowling
R J
RJ
D000595:Amino Acid Sequence; D000818:Animals; D004789:Enzyme Activation / Q000276:immunology; D005982:Glutathione Transferase; D006801:Humans; D015151:Immunoblotting; D015851:Interleukin-7 / Q000502:physiology*; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D019000:Phosphotyrosine; D011233:Precipitin Tests; D011485:Protein Binding / Q000276:immunology; D018123:Receptors, Interleukin / Q000737:chemistry / Q000378:metabolism*; D020395:Receptors, Interleukin-7; D011993:Recombinant Fusion Proteins; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D015851:Interleukin-7; D018123:Receptors, Interleukin; D020395:Receptors, Interleukin-7; D011993:Recombinant Fusion Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D005982:Glutathione Transferase; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)