Gab2 is involved in differential phosphoinositide 3-kinase signaling by two splice forms of c-Kit.
The stem cell factor receptor/c-Kit plays an important physiological role in hematopoiesis, melanogenesis, and gametogenesis. It has also been implicated in numerous human malignancies. Signal transduction pathways shown to be of importance for c-Kit-mediated transformation include the phosphoinositide 3-kinase (PI3K)/Akt pathway. We have previously shown that two alternative splice forms of c-Kit, denoted GNNK(-) and GNNK(+), mediate distinctively different signals. In this study, we found that in the hematopoietic cell line Ba/F3, GNNK(-) c-Kit mediates a substantially stronger activation of PI3K/Akt than GNNK(+) c-Kit. This difference in signaling was shown to be dependent on the association of the scaffolding protein Gab2 with c-Kit, and Src-mediated phosphorylation of Gab2 was shown to be to be independent of the direct association of PI3K with c-Kit. Furthermore, proliferation and survival of Ba/F3 cells expressing a mutant of c-Kit that fails to bind to PI3K directly were slightly decreased compared with wild-type c-Kit-expressing cells. Using small interfering RNA technology, we further verified a role of Gab2 in inducing activation of PI3K/Akt downstream of c-Kit. To summarize, we show that PI3K activation by c-Kit is both splice form-dependent and cell type-specific. Furthermore, activation of PI3K by c-Kit is dependent both on the direct PI3K-binding site in c-Kit and on the phosphorylation of Gab2. The fact that c-Kit has been found mutated in numerous human malignancies, including acute myeloid leukemia, and that Gab2 is often overexpressed in acute myeloid leukemia suggests a potential role of Gab2-mediated PI3K activation in transformation.
Sun
Jianmin
J
Experimental Clinical Chemistry, Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden.
Pedersen
Malin
M
Experimental Clinical Chemistry, Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden.
Rönnstrand
Lars
L
Experimental Clinical Chemistry, Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden. Electronic address: Lars.Ronnstrand@med.lu.se.
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000235:genetics; D005718:Gametogenesis / Q000235:genetics; D006410:Hematopoiesis / Q000235:genetics; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D022821:RNA Splice Sites / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D019061:src-Family Kinases / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; C490895:GAB2 protein, human; C490894:Gab2 protein, mouse; D010750:Phosphoproteins; D022821:RNA Splice Sites; D019869:Phosphatidylinositol 3-Kinases; D019009:Proto-Oncogene Proteins c-kit; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt