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Temporal studies on the tissue compartmentalization of bone sialoprotein (BSP), osteopontin (OPN), and SPARC protein during bone formation in vitro.

Abstract：

:To study the role of noncollagenous proteins in bone formation, the synthesis and tissue distribution of BSP (bone sialoprotein), OPN (osteopontin) and SPARC (secreted protein acidic and rich in cysteine) were analyzed using pulse-chase and continuous labeling protocols during bone formation by cultures of rat calvarial cells. Following a 1 h labeling period with [35S]methionine or [35SO4], radiolabeled BSP was rapidly lost from the cells and appeared transiently in the culture medium and in a 4 M GuHCl extract (G1) of the mineralized tissue. Coinciding with the loss of BSP from these compartments, radiolabeled BSP increased in demineralizing, 0.5 M EDTA extracts (E) of the bone, in a subsequent GuHCl extract (G2), and in a bacterial collagenase digest (CD fraction) of the extracted tissue, over a 24 h chase period. In comparison, the 55 kDa form of OPN, with a small amount of the 44 kDa OPN, was secreted almost entirely into the culture medium. Most of the 44 kDa OPN, together with some 55 kDa OPN, accumulated rapidly in the E extract but could not be detected in either G extract or in the CD fraction. SPARC appeared transiently in the G1 extract, but was otherwise quantitatively secreted into the culture medium from where it was lost by complexing and/or degradation. When cultures were continuously labeled over a 12 day period with [35S]methionine, radiolabeled BSP and 44 kDa OPN accumulated in the E extract together with a small amount of SPARC. Some radiolabeled BSP also accumulated in the G2 extract. From the relative incorporation of [35SO4] over the same time period, a time-dependent loss in sulphate from the BSP was evident. Using a 24 h pulse-labeling protocol, the amount of radiolabeled BSP and OPN in the E extract and the BSP in the G2 extract were not altered significantly over a 12-day chase period. These studies demonstrate that the 44 kDa OPN and most of the BSP are rapidly bound to the hydroxyapatite crystals where they may regulate crystal formation and growth during bone formation. Some BSP is deposited in the osteoid and appears to become masked by the formation of hydroxyapatite, indicating a potential role for this protein in epitactic nucleation of hydroxyapatite crystal formation.

journal_name

J Cell Physiol

journal_title

Journal of cellular physiology

authors

Kasugai S,Nagata T,Sodek J

doi

10.1002/jcp.1041520305

keywords:

subject

Has Abstract

pub_date

1992-09-01 00:00:00

pages

467-77

issue

eissn

0021-9541

issn

1097-4652

journal_volume

152

pub_type

杂志文章

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Temporal studies on the tissue compartmentalization of bone sialoprotein (BSP), osteopontin (OPN), and SPARC protein during bone formation in vitro.