Functional properties of alternatively spliced forms of the Drosophila PS2 integrin alpha subunit.

The Drosophila alpha PS2 protein is encoded by two alternatively spliced transcripts. The respective alpha PS2 proteins differ by the presence of 25 amino acids in the alpha PS2(C) protein, not found in the alpha PS2(m8) subunit, in a region thought to be important for ligand binding. We examined the functional properties of Drosophila S2 cells transformed with genes expressing either of these proteins, in association with a beta PS subunit. Both PS2 integrins support cell spreading on vertebrate vitronectin or, to a lesser extent, on fibronectin. Interestingly, the PS2(C) form promotes spreading more efficiently on vitronectin than does the PS2(m8) form, with an opposite relative efficiency seen for fibronectin. Also, the two forms of PS2 show different requirements for divalent cations in order to mediate efficient cell spreading. These divalent cations are not required to maintain the association of alpha and beta subunits. Spreading of both cell types is similarly RGD sensitive, and both PS2 integrins appear to associate with the actin cytoskeleton. To our knowledge, this represents the first demonstration of functional differences in integrin subunits resulting from splicing variation to generate different extracellular, ligand binding domains.