Role of ubiquitination in IGPR-1 regulation
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Immunoglobulin-containing and proline-rich receptor-1 (IGPR-1), is a newly identified cell adhesion molecule and is expressed in various cell types including, epithelial and endothelial cell origin. IGPR-1 regulates cell-cell adhesion and promotes angiogenesis, activated by shear stress and mediates endothelial cells response to shear stress. Moreover, IGPR-1 expression is upregulated in colon cancer and supports colon tumor growth. IGPR-1 contains a single extracellular immunoglobulin domain, a transmembrane domain and followed by a cytoplasmic proline-rich C-terminus. We demonstrate that ubiquitin E3 protein ligase neural precursor cell expressed developmentally down regulated 4 (NEDD4) binds to and ubiquitinates IGPR-1. Furthermore, among the four WW domains, the C-terminus WW domain#4 selectively mediates the binding of NEDD4 with IGPR-1. We used in vitro ubiquitination assay and identified UbcH6, as an E2 conjugating enzyme required for NEDD4-mediated ubiquitination of IGPR-1. Taken together, our data identifies NEDD4/Ubc6H ubiquitination system as a major pathway involved in the ubiquitination of IGPR-1.