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 E2-treatment
✍ Scribed by Yoshiyuki Hakeda; Hiroshi Kawaguchi; Marja Hurley; Carol C. Pilbeam; Christine Abreu; Thomas A. Linkhart; Subburaman Mohan; Masayoshi Kumegawa; Lawrence G. Raisz
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 668 KB
- Volume
- 166
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
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, M) or prostaglandin E2 (PGE2, 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, 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,-stimulated 45Carelease. The conditioned medium from PTH-or PGE,-treated cultures degraded recombinant human IGFBP-5 into lower molecular weight fragments. Addition of IGF-I at 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 PGE2. Aprotinin, leupeptin, cystatin, and bestatin did not inhibit the effects of PTH and PGE, in the cultures. The localization of IGFBP-5 in BECM and its release and proteolysis induced by PTH and PGE, could play a role in the local regulation of bone metabolism. o