Abstract
Many serine proteases play important regulatory roles incomplex biological systems, but only a few have been linkeddirectly with capillary morphogenesis and angiogenesis. Herewe provide evidence that serine protease activities, independentof the plasminogen activation cascade, are required formicrovascular endothelial cell reorganization and capillary morphogenesisin vitro. A homology cloning approach targeting conservedmotifs present in all serine proteases, was used to identifycandidate serine proteases involved in these processes, andrevealed 5 genes (acrosin, testisin, neurosin, PSP andneurotrypsin), none of which had been associated previouslywith expression in endothelial cells. A subsequent gene-specificRT-PCR screen for 22 serine proteases confirmed expression of these 5 genes and identified 7 additional serine proteasegenes expressed by human endothelial cells, urokinase-typeplasminogen activator, protein C, TMPRSS2, hepsin, matriptase/MT-SP1, dipeptidylpeptidase IV, and seprase. Differences in serineprotease gene expression between microvascular andhuman umbilical vein endothelial cells (HUVECs) were identifiedand several serine protease genes were found to be regulated bythe nature of the substratum, ie. Artificial basement membraneor fibrillar type I collagen. mRNA transcripts of several serineprotease genes were associated with blood vessels in vivo by insitu hybridization of human tissue specimens.These data suggesta potential role for serine proteases, not previously associatedwith endothelium, in vascular function and angiogenesis.
