THE 67-KDA ENZYMATICALLY INACTIVE ALTERNATIVELY SPLICED VARIANT OF BETA-GALACTOSIDASE IS IDENTICAL TO THE ELASTIN LAMININ-BINDING PROTEIN/

Our previous studies showed immunological and functional similarities, as well as partial sequence homology, between the enzymatically inact ive alternatively spliced variant of human beta-galactosidase (S-gal) and the 67-kDa elastin/laminin-binding protein (EBP) from sheep. To de fine the genetic origin of the EBP further, a full-length human S-gal cDNA clone was constructed and subjected to in vitro transcription/tra nslation. The cDNA was also transfected into COS-1 cells and into the EBP-deficient smooth muscle cells (SMC) from sheep ductus arteriosus ( DA). In vitro translation yielded an unglycosylated form of the S-gal protein, which immunoreacted with anti-beta-galactosidase antibodies a nd bound to elastin and laminin affinity columns. S-gal cDNA transfect ions into COS-1 and DA SMC increased expression of a 67-kDa protein th at immunolocalized intracellularly and to the cell surface and, when e xtracted from the cells, bound to elastin. The S-gal-transfected cells displayed increased adherence to elastin-covered dishes, consistent w ith the cell surface distribution of the newly produced S-gal-encoded protein. Transfection of DA SMC additionally corrected their impaired elastic fiber assembly. These results conclusively identify the 67-kDa splice variant of beta-galactosidase as EBP.