Cathepsin K, but not cathepsins B, L, or S, is abundantly expressed in human osteoclasts.
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 selecively 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.
Drake
F H
FH
Department of Cellular Biochemistry, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, USA.
Dodds
R A
RA
James
I E
IE
Connor
J R
JR
Debouck
C
C
Richardson
S
S
Lee-Rykaczewski
E
E
Coleman
L
L
Rieman
D
D
Barthlow
R
R
Hastings
G
G
Gowen
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001862:Bone Resorption / Q000201:enzymology; D002401:Cathepsin B / Q000235:genetics; D056657:Cathepsin K; D056668:Cathepsin L; D002403:Cathepsins / Q000235:genetics*; D003546:Cysteine Endopeptidases; D018076:DNA, Complementary; D010450:Endopeptidases; D006801:Humans; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D010010:Osteoclasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D016324:Sequence Tagged Sites
D018076:DNA, Complementary; D012333:RNA, Messenger; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C534280:Ctsl protein, rat; C028217:cathepsin S; C534130:CTSK protein, human; D056657:Cathepsin K; C534133:Ctsk protein, rat