Negative regulation of PI 3-kinase by Ruk, a novel adaptor protein.
Class I(A) phosphatidylinositol 3-kinase (PI 3-kinase) is a key component of important intracellular signalling cascades. We have identified an adaptor protein, Ruk(l), which forms complexes with the PI 3-kinase holoenzyme in vitro and in vivo. This interaction involves the proline-rich region of Ruk and the SH3 domain of the p85 alpha regulatory subunit of the class I(A) PI 3-kinase. In contrast to many other adaptor proteins that activate PI 3-kinase, interaction with Ruk(l) substantially inhibits the lipid kinase activity of the enzyme. Overexpression of Ruk(l) in cultured primary neurons induces apoptosis, an effect that could be reversed by co-expression of constitutively activated forms of the p110 alpha catalytic subunit of PI 3-kinase or its downstream effector PKB/Akt. Our data provide evidence for the existence of a negative regulator of the PI 3-kinase signalling pathway that is essential for maintaining cellular homeostasis. Structural similarities between Ruk, CIN85 and CD2AP/CMS suggest that these proteins form a novel family of adaptor molecules that are involved in various intracellular signalling pathways.
Ludwig Institute for Cancer Research, Courtauld Building, 91 Riding House Street, London W1P 8BT, UK.
I
I
Gout
G
G
Middleton
J
J
Adu
N N
NN
Ninkina
L B
LB
Drobot
V
V
Filonenko
G
G
Matsuka
A M
AM
Davies
M
M
Waterfield
V L
VL
Buchman
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009475:Neurons, Afferent / Q000166:cytology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020298:U937 Cells; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D018076:DNA, Complementary; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; D011994:Recombinant Proteins; C498782:Sh3kbp1 protein, mouse