cDNA cloning and mRNA expression of a serine proteinase inhibitor secreted by cancer cells: identification as placental protein 5 and 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 acid sequences indicated that this protein was identical to placental protein 5 (PP5), a placenta-derived glycoprotein with serine proteinase inhibitor activity, the amino acid sequence of which had been partially determined. cDNA cloning of PP5 demonstrated that it belonged to the Kunitz-type serine proteinase inhibitor family, having three putative Kunitz-type inhibitor domains, and that it was identical to a recently reported inhibitor, tissue factor pathway inhibitor-2 (TFPI-2) [Sprecher et al. (1994) Proc. Natl. Acad. Sci. USA 91, 3353-3357]. PP5/TFPI-2 transcripts were highly abundant in the full-term placenta and widely expressed in various adult human tissues, such as the liver, skeletal muscle, heart, kidney, and pancreas. Several ovarian carcinoma cells as well as T98G also contained significant amounts of the transcripts.