Cathepsin K, but Not Cathepsins B, L, or S, Is Abundantly Expressed in Human Osteoclasts

doi:10.1074/jbc.271.21.12511

Cathepsin K, but Not Cathepsins B, L, or S, Is Abundantly Expressed in Human Osteoclasts (*)

From the (1)Departments of Cellular Biochemistry and Molecular Genetics, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406 and
(2)Human Genome Sciences, Inc., Rockville, Maryland 20850

^§To whom reprint requests should be addressed:
Dept. of Cellular Biochemistry, SmithKline Beecham Pharmaceuticals, P. O. Box 1539, King of Prussia, PA 19406.
Tel.: 610-270-4094; Fax: 610-270-5598.

Abstract

Random high throughput sequencing of a human osteoclast cDNA library was employed to identify novel osteoclast-expressed genes. Of the 5475 ESTs obtained, approximately 4% encoded cathepsin K, a novel cysteine protease homologous to cathepsins S and L; ESTs for other cathepsins were rare. In addition, ESTs for cathepsin K were absent or at low frequency in cDNA libraries from numerous other tissues and cells. In situ hybridization in osteoclastoma and osteophyte confirmed that cathepsin K mRNA was highly expressed selectively in osteoclasts; cathepsins S, L, and B were not detectable. Cathepsin K was not detected by in situ hybridization in a panel of other tissues. Western blot of human osteoclastoma or fetal rat humerus demonstrated bands of 38 and 27 kDa, consistent with sizes predicted for pro- and mature cathepsin K. Immunolocalization in osteoclastoma and osteophyte showed intense punctate staining of cathepsin K exclusively in osteoclasts, with a polar distribution that was more intense at the bone surface. The abundant expression of cathepsin K selectively in osteoclasts strongly suggests that it plays a specialized role in bone resorption. Furthermore, the data suggest that random sequencing of ESTs from cDNA libraries is a valuable approach for identifying novel cell-selective genes.

Footnotes

↵() The Nomenclature Committee of the International Union of Biochemistry and Molecular Biology has assigned the name cathepsin K (EC 3.4.22.38) to the protease described in this paper.
↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵() The abbreviations used are:

EST

expressed sequence tag

TESPA

3-aminopropyltriethoxy silane

PAGE

polyacrylamide gel electrophoresis.
↵⁽⁾ I. E. James, R. A. Dodds, E. Lee-Rykaczewski, C. F. Eichman, J. R. Connor, T. K. Hart, B. E. Maleeff, R. D. Lackman, and M. Gowen, submitted for publication.
- Received October 27, 1995.
- Revision received March 13, 1996.