Visit our Expo - Redox and Inflammation signaling 2012

Session III : Protein kinase cascades as therapeutic targets Poster III, 3
Grb2 associated binder 1 (Gab1) adaptor/scaffolding protein regulates Erk signal in
human B cells
Adrienn Angyal1, David Medgyesi2, Gabriella Sarmay1
1Department of Immunology, Lorand Eotvos University, Budapest 1117, Hungary, email:
a1117@freemail.hu, 2Research Group of the Hungarian Academy of Sciences at
the Department of Immunology, Lorand Eotvos University, Budapest 1117, Hungary
Grb2-associated binder 1 (Gab1) is a member of the Gab/dos family of adapter molecules
involved in the signal transduction pathways of a variety of growth factors, cytokines, and
antigen receptors. In contrast to its positive role upon cytokine and growth factor receptor
signaling, Gab1 was shown to be a negative regulator of T independent 2 response of
marginal zone B cells in the spleen and to participate in a negative feedback loop of T cell
activation. Gab adaptor proteins have several tyrosine residues that are phosphorylated upon
activation of tyrosine kinases and consequently bind signaling molecules with SH2 domains,
such as SHP-2 tyrosine phosphatase and phosphatidyl inositol 3-kinase (PI3-K); and also
have pleckstrin homologue (PH) domain, that binds to PIP3 in the cell membrane. Gab1 was
shown to participate in activating ras/MAPK pathway upon EGFR signaling that was
mediated by the SHP-2 tyrosine phosphatase and the ras regulating protein, rasGAP.
Furthermore, via positive feed back regulation, Gab1 enhances PI3-K activity, resulting in a
high level of phosphatidyl inositol 3,4,5 trisphosphate (PIP3) in the plasma membrane.
The function of Gab1 in B cell signaling has not been clarified yet. We explored this question
by using siRNA to temporarily knock down Gab1 in BL41 Burkitt lymphoma cell line. The
transfer of siRNA to the cells was carried out by nucleofector technology (Amaxa). 24 h after
the transfection with Gab1 siRNA the efficiency of silencing and its functional consequences
were tested by Western blot analysis. Activation of Erk and Akt was followed by using
antibodies specific for the phosphorylated forms of the kinases. Erk activation was almost
completely blocked while Akt phosphorylation was partially reduced in the Gab1 knocked
down samples. These results suggest that in human B cells Gab1 is a major regulator of Erk,
and a less potent regulator of Akt/PKB.
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