HUMAN AMNION CONTAINS A NOVEL LAMININ VARIANT, LAMININ-7, WHICH LIKE LAMININ-6, COVALENTLY ASSOCIATES WITH LAMININ-5 TO PROMOTE STABLE EPITHELIAL-STROMAL ATTACHMENT

Stable attachment of external epithelia to the basement membrane and u nderlying stroma is mediated by transmembrane proteins such as the int egrin alpha 6 beta 4 and bullous pemphigoid antigen 2 within the hemid esmosomes along the basolateral surface of the epithelial cell and the ir ligands that include a specialized subfamily of laminins. The lamin in 5 molecule (previously termed kalinin/nicein/epiligrin) is a member of this epithelial-specific subfamily. Laminin 5 chains are not only considerably truncated within domains III-VI, but are also extensively proteolytically processed in vitro and in vivo. As a result, the doma ins expected to be required for the association of laminins with other basement membrane components are lacking in the mature laminin 5 mole cule, Therefore, the tight binding of laminin to the basement membrane may occur by a unique mechanism. To examine laminin 5 in tissue, we c hose human amnion as the source, because of Its availability and the s imilarity of the amni otic epithelial basement membrane with that of s kin. We isolated the laminin 5 contained within the basement membrane of human amnion. In addition to monomeric laminin 5, we find that much of the laminin 5 isolated is covalently adducted with laminin 6 (alph a 3 beta 1 gamma 1) and a novel laminin isotype we have termed laminin 7 (alpha 3 beta 2 gamma 1), We propose that the association between l aminin 5 and laminins 6 and 7 is a mechanism used in amnion to allow s table association of laminin 5 with the basement membrane. The beta 2 chain is seen at the human amniotic epithelial-stromal interface and a t the dermal-epidermal junction of fetal and adult bovine skin by immu nofluorescence, but is not present, or only weakly present, in neonata l human skin.