Abstract 5098: <i>In silico</i> analysis of the membrane targeting mechanism of the pleckstrin homology domains within the oncogenic Grb2-associated-binding protein family
Authors: Antonio Lopez, Ezza Awan, Areeba Zaheer, Shaneen Singh
Journal: Cancer Research (2019)

Abstract Members of the metazoan Grb2-associated-binding (GAB) family of proteins are crucial regulatory elements of receptor tyrosine kinase (RTK) signaling pathways. These scaffold proteins link and amplify plasma membrane receptor signaling to downstream targets by staging protein-protein interactions. Aberrant GAB expression is associated with improper growth and development, and several members of the GAB family have been implicated as oncogenes. GAB1, GAB2, and GAB3 are overexpressed in various cancers including lung, breast, colorectal, nervous system, and ovarian cancers, along with certain leukemias and melanomas. Recent studies suggest a direct relationship between GAB expression levels and tumorigenesis, where induced or silenced expression respectively accelerated or inhibited tumor proliferation. Silencing of GAB1 in colorectal cancers and GAB2 in glioblastoma via miRNA, and GAB3 in gliomas via siRNA inhibits tumor proliferation indicating that GAB proteins can be potentially effective targets in cancer therapy. The most conserved structural moiety in all members of the GAB family is an N-terminally located pleckstrin homology (PH domain) that directs subcellular localization and is crucial for effective protein function. Given the challenges facing RNA-based cancer therapies, more practical therapeutic avenues may be found in disrupting or inhibiting proper PH domain function; however, the mechanism of membrane targeting of all GABs remains to be elucidated. To this end, we have performed a comprehensive computational analysis of the six known GAB family members - chordate GAB1, GAB2, GAB3, and GAB4; Caenorhabditis elegans Suppressor of Clear (SOC1); Drosophila melanogaster Daughter of Sevenless (DOS) and their respective homologs to establish intra-familiar relationships via sequence analysis. Furthermore, in silico homology-based and ab initio modeling techniques were employed to propose suitable structural models of the PH domains and confirm the structural conservation of the fold. The refined theoretical models were docked against phosphoinositide head-groups to establish binding affinities and the mechanism of GAB PH domain localization. Our results suggest that non-specific electrostatics may be a key component for membrane targeting of GAB PH domains acting in concert with interaction through specific conserved residues and reveal an alternative binding pocket in addition to the canonical binding site. Our study is the first step in rational design of potential therapies based on targeting GAB function via the PH domain. Citation Format: Antonio Lopez, Ezza Awan, Areeba Zaheer, Shaneen Singh. In silico analysis of the membrane targeting mechanism of the pleckstrin homology domains within the oncogenic Grb2-associated-binding protein family [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5098.