Matrix vesicle plasma cell membrane glycoprotein-1 regulates mineralization by murine osteoblastic MC3T3 cells.
A naturally occurring nonsense truncation mutation of the inorganic pyrophosphate (PPi)-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH) PC-1 is associated with spinal and periarticular ligament hyperostosis and cartilage calcification in "tiptoe walking" (ttw) mice. Thus, we tested the hypothesis that PC-1 acts directly in the extracellular matrix to restrain mineralization. Cultured osteoblastic MC3T3 cells expressed PC-1 mRNA and produced hydroxyapatite deposits at 12-14 days. NTPPPH activity increased steadily over 14 days. Transforming growth factor-beta and 1,25-dihydroxyvitamin D3 increased PC-1 and NTPPPH in matrix vesicles (MVs). Because PC-1/NTPPPH was regulated in mineralizing MC3T3 cells, we stably transfected or infected cells with recombinant adenovirus, in order to express 2- to 6-fold more PC-1. PC-1/NTPPPH and PPi content increased severalfold in MVs derived from cells transfected with PC-1. Furthermore, MC3T3 cells transfected with PC-1 deposited approximately 80-90% less hydroxyapatite (by weight) than cells transfected with empty plasmid or enzymatically inactive PC-1. ATP-dependent 45Ca precipitation by MVs from cells overexpressing active PC-1 was comparably diminished. Thus, regulation of PC-1 controls the PPi content and function of osteoblast-derived MVs and matrix hydroxyapatite deposition. PC-1 may provide a novel therapeutic target in certain disorders of bone mineralization.
Johnson
K
K
VA Medical Center, University of California-San Diego, La Jolla, California 92161, USA.
Moffa
A
A
Chen
Y
Y
Pritzker
K
K
Goding
J
J
Terkeltaub
R
R
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015519:Bone Density / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D017886:Durapatite / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D018014:Gene Transfer Techniques; D008081:Liposomes; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D010006:Osteoblasts / Q000502:physiology*; D010727:Phosphoric Diester Hydrolases; D011755:Pyrophosphatases
D016326:Extracellular Matrix Proteins; D008081:Liposomes; D008562:Membrane Glycoproteins; D017886:Durapatite; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases