First Place — Resident Basic Science Award 1993: Risedronate Activity in the Fetal and Neonatal Mouse

Otosclerosis, chronic otitis media with and without cholesteatoma, and Paget's disease of bone are just a few of the many diseases of the ear that exhibit abnormalities of bone modeling and remodeling. These diseases result in chronic infection, vestibular dysfunction, and hearing loss. Bisphosphonates are a promising new class of drugs potentially useful in the treatment of these disorders. Currently used in diseases with high rates of bone turnover (Paget's disease of bone, hypercalcemia of malignancy, and osteoporosis), they have been found to be strong inhibitors of bone resorption. A third generation bisphosphonate, 2-(3-pyrindyl)-hydroxyethylidene bisphosphonate (risedronate) is being investigated for toxicity, increased efficacy, and oral administration. In this study the in vitro and in vivo anti-resorptive activity of risedronate was quantified by measuring calcium release in a neonatal mouse calvarial culture system. This model was used to test direct in vitro effects, in vivo exposure in neonatal mice, and the possible effects of in utero and lacteal exposure. Calcium release activated by parathyroid hormone (PTH) was significantly inhibited when risedronate was only present in the pre-incubation media. When risedronate was administered subcutaneously to neonatal mice it resulted in a significant decrease in PTH-activated calcium release in explanted calvaria in vitro. Transplacental and lactational transfer of biologically effective risedronate was not demonstrated in this study; however, a paradoxic increase in PTH-stimulated calcium release in vitro from calvaria theoretically exposed transplacentally and lacteally was noted. This effect was unexplained by the data.

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Structural and functional studies of mutations affecting the UBA domain of SQSTM1 (p62) which cause Paget's disease of bone

Biochemical Society Transactions ◽

10.1042/bst0320728 ◽

2004 ◽

Vol 32 (5) ◽

pp. 728-730 ◽

Cited By ~ 25

Author(s):

R. Layfield ◽

B. Ciani ◽

S.H. Ralston ◽

L.J. Hocking ◽

P.W. Sheppard ◽

...

Keyword(s):

Solution Structure ◽

Paget’S Disease ◽

Paget's Disease ◽

Paget’S Disease Of Bone ◽

Missense Mutations ◽

Paget's Disease Of Bone ◽

Hydrophobic Patch ◽

Sequestosome 1 ◽

Uba Domain

Mutations affecting the UBA (ubiquitin-associated) domain of SQSTM1 (Sequestosome 1) (p62) are a common cause of Paget's disease of bone. The missense mutations resolve into those which retain [P392L (Pro392→Leu), G411S] or abolish (M404V, G425R) the ability of the isolated UBA domain to bind Lys-48-linked polyubiquitin. These effects can be rationalized with reference to the solution structure of the UBA domain, which we have determined by NMR spectroscopy. The UBA domain forms a characteristic compact three-helix bundle, with a hydrophobic patch equivalent to that previously implicated in ubiquitin binding by other UBA domains. None of the mutations affect overall folding of the UBA domain, but both M404V and G425R involve residues in the hydrophobic patch, whereas Pro-392 and Gly-411 are more remote. A simple model assuming the isolated UBA domain is functioning as a compact monomer can explain the effects of the mutations on polyubiquitin binding. The P392L and G411S mutations do however have subtle local effects on secondary structure, which may become more relevant in full-length SQSTM1. Identification of the in vivo ubiquitylated substrates of SQSTM1 will be most informative in determining the functional significance of the SQSTM1–ubiquitin interaction, and consequences of the disease-associated mutations.

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