CD46 (membrane cofactor protein) associates with multiple beta 1 integrinsand tetraspans

The tetraspans associate with a large number of surface molecules, includin g a subset of beta 1 integrins and, indirectly through CD19, with the compl ement receptor CD21. To further characterize the tetraspan complexes we hav e raised and selected monoclonal antibodies (mAb) for their ability to immu noprecipitate a molecule associated with CD9. A unique mAb was identified w hich recognizes the complement regulator CD46 (membrane cofactor protein). CD46 associated in part with several tetranspans and with all beta 1 integr ins that were tested (CD29/CD49a, CD29/CD49b, CD29/CD49c, CD29/CD49e, CD29/ CD49f) but not with beta 4 integrins. These data, together with cross-linki ng experiments showing the existence in living cells of CD46/integrin compl exes, suggest that CD46 associates directly with beta 1 integrins and indir ectly with tetraspans. CD46 also acts as a receptor for measles virus; howe ver, mAb to various integrins and tetraspans did not modify the virus fusio n entry step.