TY - JOUR
T1 - Coordinated maturational regulation of PHEX and renal phosphate transport inhibitory activity
T2 - Evidence for the pathophysiological role of PHEX in X-linked hypophosphatemia
AU - Nesbitt, Teresa
AU - Fujiwara, Ikuma
AU - Thomas, Ronald
AU - Xiao, Zhou Sheng
AU - Quarles, L. Darryl
AU - Drezner, Marc K.
PY - 1999
Y1 - 1999
N2 - The mechanism by which inactivating mutations of PHEX (phosphate- regulating gene with homologies to endopeptidases on the X chromosome) cause X-linked hypophosphatemia remains unknown. However; recent reports suggest errant PHEX activity in osteoblasts may fail to inactivate a phosphaturic factor produced by these cells. To test this possibility, we examined coordinated maturational expression of PHEX and production of phosphate transport inhibitory activity in osteoblasts from normal and hyp-mice. We assessed the inhibitory activity in conditioned medium by examining the effects on opossum kidney cell phosphate transport and osteoblast PHEX expression by reverse transcriptase-polymerase chain reaction during a 17-day maturational period. Inhibitory activity increased as a function of osteoblast maturational stage, with no activity after 3 days and persistent activity by 6 days of culture. More significantly, equal phosphate transport inhibitory activity in conditioned medium from normal and hyp-mouse osteoblasts (control 1.90 ± 0.12, normal 1.48 ± 0.10, hyp 1.45 ± 0.04 nmol/mg of protein/minute) was observed at 6 days. However, by 10 days hyp- mouse osteoblasts exhibited greater inhibitory activity than controls, and by 17 days the difference in phosphate transport inhibition maximized (control 2.08 ± 0.09, normal 1.88 ± 0.06, hyp 1.58 ± 0.06 nmol/mg of protein/minute). Concurrently, we observed absent PHEX expression in normal osteoblasts after 3 days, limited production at 6 days, and significant production by day 10 of culture, while hyp-mouse osteoblasts exhibited limited PHEX activity secondary to an inactivating mutation. The data suggest that the presence of inactivating PHEX mutations results in the enhanced renal phosphate transport inhibitory activity exhibited by hyp-mouse osteoblasts.
AB - The mechanism by which inactivating mutations of PHEX (phosphate- regulating gene with homologies to endopeptidases on the X chromosome) cause X-linked hypophosphatemia remains unknown. However; recent reports suggest errant PHEX activity in osteoblasts may fail to inactivate a phosphaturic factor produced by these cells. To test this possibility, we examined coordinated maturational expression of PHEX and production of phosphate transport inhibitory activity in osteoblasts from normal and hyp-mice. We assessed the inhibitory activity in conditioned medium by examining the effects on opossum kidney cell phosphate transport and osteoblast PHEX expression by reverse transcriptase-polymerase chain reaction during a 17-day maturational period. Inhibitory activity increased as a function of osteoblast maturational stage, with no activity after 3 days and persistent activity by 6 days of culture. More significantly, equal phosphate transport inhibitory activity in conditioned medium from normal and hyp-mouse osteoblasts (control 1.90 ± 0.12, normal 1.48 ± 0.10, hyp 1.45 ± 0.04 nmol/mg of protein/minute) was observed at 6 days. However, by 10 days hyp- mouse osteoblasts exhibited greater inhibitory activity than controls, and by 17 days the difference in phosphate transport inhibition maximized (control 2.08 ± 0.09, normal 1.88 ± 0.06, hyp 1.58 ± 0.06 nmol/mg of protein/minute). Concurrently, we observed absent PHEX expression in normal osteoblasts after 3 days, limited production at 6 days, and significant production by day 10 of culture, while hyp-mouse osteoblasts exhibited limited PHEX activity secondary to an inactivating mutation. The data suggest that the presence of inactivating PHEX mutations results in the enhanced renal phosphate transport inhibitory activity exhibited by hyp-mouse osteoblasts.
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U2 - 10.1359/jbmr.1999.14.12.2027
DO - 10.1359/jbmr.1999.14.12.2027
M3 - Article
C2 - 10620061
AN - SCOPUS:0033397492
VL - 14
SP - 2027
EP - 2035
JO - Journal of Bone and Mineral Research
JF - Journal of Bone and Mineral Research
SN - 0884-0431
IS - 12
ER -