Short form of α9 promotes α9β1 integrin-dependent cell adhesion by modulating the function of the full-length α9 subunit

The alpha 9 beta 1 integrin is a multifunctional receptor that interacts with a variety of ligands including vascular cell adhesion molecule 1, tenascin-C, and osteopontin. A 2.3-kb truncated form of alpha 9 integrin subunit cDNA was identified by searching the Medline database. This splice variant, which we called the short form of alpha 9 integrin (SF alpha 9), encodes a 632-aa isoform lacking transmembrane and cytoplasmic domains, and its authentic expression was verified by PCR and Western blotting. SF alpha 9 is expressed on the cell surface but cannot bind ligand in the absence of the full-length alpha 9 subunit. Over-expression of SF alpha 9 in cells expressing full-length alpha 9 promotes alpha 9-dependent cell adhesion. This promoting effect of SF alpha 9 requires the authentic cytoplasmic domain of the co-expressed full-length alpha 9 subunit. Thus, SF alpha 9 is a novel functional modulator of alpha 9 beta 1 integrin by inside-out signaling. (c) 2011 Elsevier Inc. All rights reserved.