EMILIN, a component of the elastic fiber and a new member of the C1q/Tumornecrosis factor superfamily of proteins

EMILIN (elastin microfibril interface located protein) is an extracellular matrix glycoprotein abundantly expressed in elastin-rich tissues such as bl ood vessels, skin, heart, and lung. It occurs associated with elastic fiber s at the interface between amorphous elastin and microfibrils, Avian EMILIN was extracted from 19-day-old embryonic chick aortas and associated blood vessels and purified by ion-exchange chromatography and gel filtration. Try ptic peptides were generated from EMILIN and sequenced, and degenerate inos ine-containing oligonucleotide primers were designed from some peptides. A set of primers allowed the amplification of a 360-base pair reverse transcr iption polymerase chain reaction product from chick aorta mRNA, A probe bas ed on a human homologue selected by comparison of the chick sequence with E ST data base was used to select overlapping clones from both human aorta an d kidney cDNA libraries. Here we present the cDNA sequence of the entire co ding region of human EMILIN encompassing an open reading frame of 1016 amin o acid residues. There was a high degree of homology (76% identity and 88% similarity) between the chick C terminus and the human sequence as well as between the N terminus of the mature chick protein where 10 of 12 residues, as determined by N-terminal sequencing, were identical or similar to the d educed N terminus of human EMILIN. The domain organization of human EMILIN includes a Clq-like globular domain at the C terminus, a collagenous stalk, and a longer segment in which at least four heptad repeats and a leucine z ipper can be identified with a high potential for forming coiled-coil alpha helices, At the N terminus there is a cysteine-rich sequence stretch simil ar to a region of multimerin, a platelet and endothelial cell component, co ntaining a partial epidermal growth factor-like motif, The native state of the recombinantly expressed EMILIN C1q-like domain to be used in cell adhes ion was determined by CD spectra analysis, which indicated a high value of beta-sheet conformation. The EMILIN C1q-like domain promoted a high cell ad hesion of the leiomyosarcoma cell line SK-UT-1, whereas the fibrosarcoma ce ll line HT1080 was negative.