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Intact insulin‐like growth factor binding protein‐5 (IGFBP‐5) associates with bone matrix and the soluble fragments of IGFBP‐5 accumulated in culture medium of neonatal mouse calvariae by parathyroid hormone and prostaglandin E 2 ‐treatment
Author(s) -
Hakeda Yoshiyuki,
Kawaguchi Hiroshi,
Hurley Marja,
Pilbeam Carol C.,
Abreu Christine,
Linkhart Thomas A.,
Mohan Subburaman,
Kumegawa Masayoshi,
Raisz Lawrence G.
Publication year - 1996
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199602)166:2<370::aid-jcp15>3.0.co;2-f
Subject(s) - medicine , endocrinology , leupeptin , parathyroid hormone , growth factor , chemistry , prostaglandin e2 , insulin like growth factor 2 , extracellular matrix , insulin like growth factor binding protein , bone resorption , biology , insulin like growth factor , biochemistry , calcium , receptor , protease , enzyme
We examined the distribution of insulin‐like growth factor binding proteins (IGFBPs) in cultured neonatal mouse calvariae. IGFBP‐3 and ‐4 were predominantly found in the conditioned medium. IGFBP‐2 was partitioned between conditioned medium and bone and extracellular matrix (BECM), while intact (31‐kDa) IGFBP‐5 was most abundant in BECM extracts. After treatment with parathyroid hormone (PTH, 10 −8 M) or prostaglandin E 2 (PGE 2 , 10 −6 M), immunoreactive IGFBP‐5 accumulated in the conditioned medium in a 21‐kDa form which did not bind IGF‐I on Western ligand blots. PTH and PGE 2 did not alter the level of steady‐state IGFBP‐5 mRNA, nor markedly stimulate IGFBP‐5 synthesis in the calvariae, and thus accumulation of 21‐kDa IGFBP‐5 was largely due to release from BECM. This accumulation of truncated IGFBP‐5 in the conditioned medium was not dependent on osteoclastic bone resorption, since it was not blocked by calcitonin or a bisphosphonate which inhibited PTH‐ and PGE 2 ‐stimulated 45 Ca‐release. The conditioned medium from PTH‐ or PGE 2 ‐treated cultures degraded recombinant human IGFBP‐5 into lower molecular weight fragments. Addition of IGF‐I at 10 −8 M into the culture resulted in accumulation of native 31‐kDa IGFBP‐5. However, even in the presence of IGF‐I, the native IGFBP‐5 was degraded and the 21‐kDa product accumulated in the culture medium. These results suggested a possible proteolytic mechanism for 21‐kDa IGFBP‐5 accumulation, responsive to PTH and PGE 2 . Aprotinin, leupeptin, cystatin, and bestatin did not inhibit the effects of PTH and PGE 2 in the cultures. The localization of IGFBP‐5 in BECM and its release and proteolysis induced by PTH and PGE 2 could play a role in the local regulation of bone metabolism. © 1996 Wiley‐Liss, Inc.