Intra-cellular signals generated by integrin-based adhesion contribute to the proper regulation of immune function. Failure to regulate of these processes has been linked to chronic inflammatory diseases such as inflammatory bowel disease and atherosclerosis. This grant focuses on elucidating the role of the adapter molecule Skap-hom in transmitting integrin-stimulated responses in macrophages and neutrophils. We have previously demonstrated that Skap-hom's activity is controlled downstream of phosphoinositide 3- kinase (PI3K) signaling following integrin engagement. Our data now shows that Skap-hom is essential for migration and chemotaxis in macrophages. Furthermore, Skap-hom is required for adhesion-induced Src family kinase (SFK) activation and optimal tyrosyl-phosphorylation of selected molecules involved in cytoskeletal rearrangement in macrophages. Skap-hom deficiency exclusively affects adhesion-induced responses, as Skap-hom-deficient macrophages respond normally to cytokines and phagocytic stimuli. Skap- hom constitutively binds to the transmembrane receptor, Sirp1, (a.k.a SHPS-1). Our preliminary studies reveal that neutrophils expressing a variant of Sirp1 (SHPS1?/?), where the cytoplasmic domain that normally binds Skap-hom has been deleted exhibit similar defects in adhesion-mediated responses as their Skap-hom-/- counterparts. These data strongly suggests that Sirp1 and Skap-hom function as an integrin-mediated signaling complex.
In Aim 1, we will characterize the signaling pathway defects that lead to the cellular phenotypes of Skap-hom-/- myeloid cells and test this potential relationship between Skap-hom and Sirp1.
In Aim 2, we will perform structure/function analysis of Skap-hom to determine the domains and residues that are crucial for its function. Using mass spectrometry, we also seek to identify novel protein binding partners that may explain how Skap-hom propagates signals downstream.
In Aim 3, we will test the role of Skap-hom in controlling inflammatory diseases in macrophage- and integrin-dependent disease models of colitis and atherosclerosis. These studies suggest a new means of controlling signaling pathways that are activated in response to integrin stimulation and thus may lead to the identification of novel therapeutics in the treatment of inflammatory disorders.
The proposed studies will provide significant insights into how inflammatory processes are regulated by the adaptor protein, Skap-hom. Thus, our findings will have implications for the treatment of chronic inflammatory diseases, including colitis and atherosclerosis.
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