CDNA CLONING AND MESSENGER-RNA EXPRESSION OF A SERINE PROTEINASE-INHIBITOR SECRETED BY CANCER-CELLS - IDENTIFICATION AS PLACENTAL PROTEIN-5AND TISSUE FACTOR PATHWAY INHIBITOR-2

A serine proteinase inhibitor was purified from conditioned medium of the human glioblastoma cell line T98G. Analysis of its partial amino a cid sequences indicated that this protein was identical to placental p rotein 5 (PP5), a placenta-derived glycoprotein with serine proteinase inhibitor activity, the amino acid sequence of which had been partial ly determined. cDNA cloning of PP5 demonstrated that it belonged to th e Kunitz-type serine proteinase inhibitor family, having three putativ e Kunitz-type inhibitor domains, and that it was identical to a recent ly reported inhibitor, tissue factor pathway inhibitor-2 (TFPI-2) [Spr echer et al. (1994) Proc. Natl. Acad. Sci. USA 91, 3353-3357]. PPS/TFP I-2 transcripts were highly abundant in the full-term placenta and wid ely expressed in various adult human tissues, such as the liver, skele tal muscle, heart, kidney, and pancreas. Several ovarian carcinoma cel ls as well as T98G also contained significant amounts of the transcrip ts.