Gab2 is involved in differential phosphoinositide 3-kinase signaling by two splice forms of c-Kit

Area of Science:

• Molecular Biology
• Cell Signaling
• Cancer Biology

Background:

• The stem cell factor receptor, c-Kit, is vital for normal cell development and implicated in various cancers.
• Signal transduction pathways, particularly phosphoinositide 3-kinase (PI3K)/Akt, are critical for c-Kit-driven cellular transformation.
• Alternative splicing of c-Kit generates GNNK(-) and GNNK(+) variants, which exhibit distinct signaling properties.

Purpose of the Study:

• To investigate the differential activation of the PI3K/Akt pathway by GNNK(-) and GNNK(+) c-Kit splice variants.
• To elucidate the roles of Gab2 scaffolding protein and direct PI3K binding in c-Kit-mediated PI3K/Akt activation.
• To explore the implications of these findings in the context of human malignancies like acute myeloid leukemia.

Main Methods:

• Utilized the hematopoietic cell line Ba/F3 for experiments.
• Employed small interfering RNA (siRNA) technology to assess the role of Gab2.
• Analyzed c-Kit splice variant-specific signaling, Gab2 association, and PI3K/Akt activation.

Main Results:

• GNNK(-) c-Kit demonstrated significantly stronger PI3K/Akt activation compared to GNNK(+) c-Kit in Ba/F3 cells.
• Gab2 association with c-Kit and Src-mediated phosphorylation of Gab2 were key to this differential signaling.
• Direct PI3K binding to c-Kit also contributed to proliferation and survival, though Gab2's role was independently verified.
• PI3K activation by c-Kit was confirmed to be splice form-dependent, cell type-specific, and reliant on both direct binding and Gab2 phosphorylation.

Conclusions:

• c-Kit-mediated PI3K/Akt activation is complex, depending on c-Kit splice variants, Gab2, and direct PI3K binding.
• The findings highlight a potential mechanism involving Gab2-mediated PI3K activation in c-Kit-driven malignancies, especially given Gab2 overexpression in acute myeloid leukemia.