Osteoblast tissue-nonspecific alkaline phosphatase antagonizes and regulates PC-1.
Tissue-nonspecific alkaline phosphatase (TNAP) is essential for bone matrix mineralization, but the central mechanism for TNAP action remains undefined. We observed that ATP-dependent (45)Ca precipitation was decreased in calvarial osteoblast matrix vesicle (MV) fractions from TNAP-/- mice, a model of infantile hypophosphatasia. Because TNAP hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PP(i)), we assessed phosphodiesterase nucleotide pyrophosphatase (PDNP/NTPPPH) activity, which hydrolyzes ATP to generate PP(i). Plasma cell membrane glycoprotein-1 (PC-1), but not the isozyme B10 (also called PDNP3) colocalized with TNAP in osteoblast MV fractions and pericellular matrix. PC-1 but not B10 increased MV fraction PP(i) and inhibited (45)Ca precipitation by MVs. TNAP directly antagonized inhibition by PC-1 of MV-mediated (45)Ca precipitation. Furthermore, the PP(i) content of MV fractions was greater in cultured TNAP-/- than TNAP+/+ calvarial osteoblasts. Paradoxically, transfection with wild-type TNAP significantly increased osteoblast MV fraction NTPPPH. Specific activity of NTPPPH also was twofold greater in MV fractions of osteoblasts from TNAP+/+ mice relative to TNAP-/- mice. Thus TNAP attenuates PC-1/NTPPPH-induced PP(i) generation that would otherwise inhibit MV-mediated mineralization. TNAP also paradoxically regulates PC-1 expression and NTPPPH activity in osteoblasts.
Johnson
K A
KA
Veterans Affairs Medical Center/University of California San Diego, La Jolla 92161, USA.
Hessle
L
L
Vaingankar
S
S
Wennberg
C
C
Mauro
S
S
Narisawa
S
S
Goding
J W
JW
Sano
K
K
Millan
J L
JL
Terkeltaub
R
R
D016475:3T3 Cells; D000469:Alkaline Phosphatase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002113:Calcification, Physiologic / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004195:Disease Models, Animal; D005109:Extracellular Matrix / Q000502:physiology / Q000648:ultrastructure; D015971:Gene Expression Regulation, Enzymologic; D005838:Genotype; D007014:Hypophosphatasia / Q000201:enzymology / Q000235:genetics; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000502:physiology*; D010727:Phosphoric Diester Hydrolases; D011755:Pyrophosphatases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D012886:Skull / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection
D017077:Culture Media, Conditioned; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases; D002118:Calcium