SPLICE VARIANTS OF THE DROSOPHILA PS2 INTEGRINS DIFFERENTIALLY INTERACT WITH RGD-CONTAINING FRAGMENTS OF THE EXTRACELLULAR PROTEINS TIGGRIN, 10-M, AND D-LAMININ ALPHA-2

Two new potential ligands of the Drosophila PS2 integrins have been ch aracterized by functional interaction in cell culture. These potential ligands are a new Drosophila laminin alpha 2 chain encoded by the win g blister locus and Ten-m, an extracellular protein known to be involv ed in embryonic pattern formation. As with previously identified PS2 l igands, both contain RGD sequences, and RGD-containing fragments of th ese two proteins (DLAM-RGD and TENM-RGD) can support PS2 integrin-medi ated cell spreading. In all cases, this spreading is inhibited specifi cally by short RGD-containing peptides. As previously found for the PS 2 ligand tiggrin (and the tiggrin fragment TIG-RGD), TENM-RGD induces maximal spreading of cells expressing integrin containing the alpha(PS 2C) splice variant. This is in contrast to DLAM-RGD, which is the firs t Drosophila polypeptide shown to interact preferentially with cells e xpressing the alpha(PS2m8) splice variant. The beta(PS) integrin subun it also varies in the presumed ligand binding region as a result of al ternative splicing. For TIG-RGD and TENM-RGD, the beta splice variant has little effect, but for DLAM-RGD, maximal cell spreading is support ed only by the beta(PS4A) form of the protein. Thus, the diversity in PS2 integrins due to splicing variations, in combination with diversit y of matrix ligands, can greatly enhance the functional complexity of PS2-ligand interactions in the developing animal. The data also sugges t that the splice variants may alter regions of the subunits that are directly involved in ligand interactions, and this is discussed with r espect to models of integrin structure.