Avian integrin alpha v subunit associates with multiple beta subunits and shows tissue-specific variation in its association.

Integrins are heterodimeric cell surface receptors involved in cell adhesion to extracellular matrix proteins and in cell-cell interactions. RGD peptide-specific integrin subunit alpha v and its associated beta subunits were isolated by GRGDSPK-Sepharose affinity chromatography. Using Western blot and immunoprecipitation techniques, the nature of this integrin complexity in the avian system was studied in comparison with that of the human system. As found in human cell systems, in chicken embryo fibroblasts the integrin alpha v subunit is associated with both the 90-kDa beta 3 and the 110-kDa beta 1-like subunits with high specific binding to RGD peptides. Furthermore, immunoprecipitation studies revealed the presence of an unidentified 120-kDa subunit and an 85-kDa beta 5 subunit associated with the alpha v subunit in these cells. No qualitative differences were observed in the beta subunit profile associated with alpha v, as a function of the proliferating nonconfluent or nonproliferating confluent states of the embryonic fibroblast cultures. In adult chicken gizzard, a 110-kDa beta 1-like subunit and a 90-kDa subunit that does not cross-react with anti-H-beta 3 and anti-H-beta 5 are associated with the alpha v subunit. The structure of the novel 120-kDa subunit found in the embryonic fibroblasts and the 90-kDa subunit found in adult chicken gizzard and the ligand specificities of these novel combinations of alpha v are not known at present, but these integrins are RGD specific. It is hypothesized that embryonic fibroblasts, being the primordial proliferating cells, display a wider spectrum of alpha v-associated beta subunits, whose expression may progressively be restricted or highly reduced in favor of one or more beta subunits in subsequent progenies as differentiation progresses.