EXPRESSION OF THE MURINE PLASMA-CELL NUCLEOTIDE PYROPHOSPHOHYDROLASE PC-1 IS SHARED BY HUMAN LIVER, BONE, AND CARTILAGE CELLS - REGULATION OF PC-1 EXPRESSION IN OSTEOSARCOMA CELLS BY TRANSFORMING GROWTH-FACTOR-BETA

A bone and cartilage enzyme with both 5'-nucleotide phosphodiesterase I and nucleotide pyrophosphohydrolase (NTPPPH) activity modulates phys iologic mineralization and pathologic chondrocalcinosis by generating inorganic pyrophosphate. We hypothesized that, as for alkaline phospha tase, expression of an NTPPPH gene can be shared by cells from bone, c artilage, and liver and by certain leukocytes. Recently, we demonstrat ed the hepatocyte and murine plasma cell membrane glycoprotein PC-1 to have both 5'-nucleotide phosphodiesterase I and NTPPPH activity. We d etected polypeptides cross-reactive with PC-1 in human U20S osteosarco ma cells, articular chondrocytes, homogenized human knee cartilages, h uman knee synovial fluids, hepatoma cells, and murine plasmacytoma cel ls. Constitutive low abundance PC-1 mRNA expression was detected in U2 0S cells and chondrocytes by a nested RNA-PCR assay and by Northern bl otting. TGF beta is known to substantially increase NTPPPH activity in primary osteoblast cultures. We demonstrated that TGF beta 1 increase d NTPPPH activity and the level of PC-1 mRNA and imnunoprecipitable [S -35]-methionine-labeled PC-1 polypeptides in U20S cells. The identific ation of PC-1 as an NTPPPH expressed in cells derived from bone and ca rtilage may prove useful in furthering the understanding of the role o f NTPPPH in physiologic and pathologic mineralization.