Testican in human blood

Testican is a highly conserved, differentially expressed gene product of un known function. Since testican is expressed by human endothelial cells and includes a signal sequence, it was our hypothesis that testican protein wou ld be present in blood. We have developed chicken antibodies specific for t estican sequence near the N-terminal and identified a 130-kDa form of testi can in human plasma. This is much larger than the calculated molecular weig ht of the encoded polypeptide, suggesting glycosylation of this plasma prot ein, and large forms of recombinant testican produced in culture were found to include chondroitin sulfate. The 130-kDa form of testican is unstable i n plasma. It is converted to smaller stable forms by separable plasma facto rs that can be blocked by certain serine protease inhibitors, Testican size conversion may be important in its functional activation or decay. One tes tican domain has strong homology to thyropin-type cysteine protease-inhibit ors. Thus, testican may have a function related to protease inhibition in t he blood. (C) 2001 Academic Press.