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Linking Osteopetrosis and Pycnodysostosis: Regulation of Cathepsin K Expression by the Microphthalmia Transcription Factor Family

G. Motyckova, K. N. Weilbaecher, M. Horstmann, D. J. Rieman, D. Z. Fisher and D. E. Fisher
Proceedings of the National Academy of Sciences of the United States of America
Vol. 98, No. 10 (May 8, 2001), pp. 5798-5803
Stable URL: http://www.jstor.org/stable/3055707
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Linking Osteopetrosis and Pycnodysostosis: Regulation of Cathepsin K Expression by the Microphthalmia Transcription Factor Family
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Abstract

Various genetic conditions produce dysfunctional osteoclasts resulting in osteopetrosis or osteosclerosis. These include human pycnodysostosis, an autosomal recessive syndrome caused by cathepsin K mutation, cathepsin K-deficient mice, and mitf mutant rodent strains. Cathepsin K is a highly expressed cysteine protease in osteoclasts that plays an essential role in the degradation of protein components of bone matrix. Cathepsin K also is expressed in a significant fraction of human breast cancers where it could contribute to tumor invasiveness. Mitf is a member of a helix-loop-helix transcription factor subfamily, which contains the potential dimerization partners TFE3, TFEB, and TFEC. In mice, dominant negative, but not recessive, mutations of mitf, produce osteopetrosis, suggesting a functional requirement for other family members. Mitf also has been found-and TFE3 has been suggested-to modulate age-dependent changes in osteoclast function. This study identifies cathepsin K as a transcriptional target of Mitf and TFE3 via three consensus elements in the cathepsin K promoter. Additionally, cathepsin K mRNA and protein were found to be deficient in mitf mutant osteoclasts, and overexpression of wild-type Mitf dramatically up-regulated expression of endogenous cathepsin K in cultured human osteoclasts. Cathepsin K promoter activity was disrupted by dominant negative, but not recessive, mouse alleles of mitf in a pattern that closely matches their osteopetrotic phenotypes. This relationship between cathepsin K and the Mitf family helps explain the phenotypic overlap of their corresponding deficiencies in pycnodysostosis and osteopetrosis and identifies likely regulators of cathepsin K expression in bone homeostasis and human malignancy.

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