ENDOTHELIAL AND SERUM FACTORS WHICH INCLUDE APOLIPOPROTEIN A1 TETHER ELASTIN TO SMOOTH-MUSCLE CELLS INDUCING SERINE ELASTASE ACTIVITY VIA TYROSINE KINASE-MEDIATED TRANSCRIPTION AND TRANSLATION

We previously reported that serine elastase activity is induced in cul tured porcine pulmonary artery (PA) smooth muscle cells (SMC) followin g serum stimulation by a mechanism involving adhesion of elastin to an elastin binding protein and tyrosine kinase activity. The present stu dy demonstrates that a PA endothelial cell factor also promotes a four fold increase in elastin adhesion to PA SMC and a twofold increase in serine elastase activity. The mechanism involves tethering of the fact or to SMC, since [H-3]-elastin pre-incubated with serum or endothelial cell (EC)-conditioned medium or SMC pre-treated with serum accelerate s binding of elastin and tyrosine-kinase related elastase activity. Th e serum factor appears to interact with integrins as elastase inductio n is partially inhibited by RGD peptides. The elastase-inducing proper ties of serum could not, however, be attributed to several RGD-contain ing proteins. While a 120 kD fibronectin fragment partially reproduced the effect, it was not found in the serum fraction containing elastas e-inducing activity. Instead, a 27 kD serum protein was enriched by el astin affinity chromatography, identified as apolipoprotein (Apo) A1 b y microsequence analysis, and found to have about 50% of the elastase- inducing activity of serum. Elastase induction is inhibited by actinom ycin and cycloheximide, suggesting a requirement for mRNA transcriptio n and protein synthesis. Our results suggest a novel cell-extracellula r matrix interaction whereby a soluble factor, in this case a lipoprot ein, binds and tethers a matrix component to the cell surface and indu ces tyrosine kinase-dependent transcription of mRNA culminating in sub strate proteolysis. (C) 1998 Wiley-Liss, Inc.