Acta Pharmacologica Sinica 2008 February; 29 (2): 204-210; doi: 10.1111/j.1745-7254.2008.00723.x

Aim: The molecular mechanisms of the affinity regulation of αvβ3 integrin are important in tumor development, wound repairing, and angiogenesis. It has been established that the cytoplasmic domains of αvβ3 integrin play an important role in integrin-ligand affinity regulation. However, the relationship of structure-function within these domains remains unclear.

Methods: The extracellular and transmembrane domain of αIIb was fused to the αv integrin cytoplasmic domain, and the chimeric α subunit was coexpressed in Chinese hamster ovary (CHO) cells with the wild-type β3 subunit or with 3 mutant β3 sequences bearing truncations at the positions of T741, Y747, and F754, respectively. The CHO cells expressing these recombinant integrins were tested for soluble fibrinogen binding and the cell adhesion and spreading on immobilized fibrinogen.

Results: All 4 types of integrins bound soluble fibrinogen in the absence of agonist stimulation, and only the cells expressing the chimeric α subunit with the wild-type β3 subunit, but not those with truncated β3, could adhere to and spread on immobilized fibrinogen.

Conclusion: The substitution aIIb at the cytoplasmic domain with the av cytoplasmic sequence rendered the extracellular αIIbβ3 a constitutively activated conformation for ligands without the need of "inside-out" signals. Our results also indicated that the COOH-terminal sequence of b3 might play a key role in integrin aIIb/αvβ3-mediated cell adhesion and spreading on immobilized fibrinogen. The cells expressing aIIb/αvβ3 have enormous potential for facilitating drug screening for antagonists either to αvβ3 intracellular interactions or to αIIbβ3 receptor functions.

Keywords: integrin; cell adhesion; fibrinogen; signal transduction