FrzB-2: a human secreted frizzled-related protein with a potential role in chondrocyte apoptosis.
OBJECTIVE
To characterize a novel secreted frizzled-related protein (SFRP) and determine its tissue distribution at the mRNA and protein level.


METHODS
The FrzB-2 gene was identified by expressed sequence tag (EST) analysis of human tissue-derived libraries. Tissue distribution of FrzB-2 mRNA was determined by Northern blot analysis and in situ hybridization. FrzB-2 protein reactivity was localized in human OA articular cartilage by immunocytochemistry, using a polyclonal antibody against a peptide sequence unique to FrzB-2. Apoptosis was detected in articular cartilage sections using Tunel staining.


RESULTS
ESTs corresponding to FrzB-2 were found in osteoblast, chondrosarcoma, osteosarcoma, osteoclastoma and synovial fibroblast libraries. FrzB-2 mRNA is expressed in a number of tissues and cell types including bone-related cells and tissues such as primary human osteoblasts and osteoclastoma. In situ hybridization studies showed strong FrzB-2 mRNA expression in human chondrocytes in human osteoarthritic (OA) cartilage but negligible levels in normal cartilage chondrocytes. The FrzB-2 cDNA encodes a secreted 40 kDa protein consisting of 346 amino acids. FrzB-2 is 92. 5% identical to the rat orthologue, DDC-4, which has been shown to be associated with physiological apoptosis. FrzB-2 protein was selectively detected in human OA articular cartilage by immunocytochemistry, using a polyclonal antibody. Consistent with its potential role in apoptosis, positive FrzB-2 staining and Tunel positive nuclei staining were detected in chondrocyte clones in sections of human OA cartilage.


CONCLUSIONS
These data suggest that FrzB-2 may play a role in apoptosis and that the expression of this protein may be important in the pathogenesis of human OA.
James
I E
IE
Department of Bone and Cartilage Biology, SmithKline Beecham Pharmaceuticals, 709 Swedeland Road, King of Prussia, Pennsylvania 19406, USA. Ian_E_James@sbphrd.com
Kumar
S
S
Barnes
M R
MR
Gress
C J
CJ
Hand
A T
AT
Dodds
R A
RA
Connor
J R
JR
Bradley
B R
BR
Campbell
D A
DA
Grabill
S E
SE
Williams
K
K
Blake
S M
SM
Gowen
M
M
Lark
M W
MW
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D015152:Blotting, Northern; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D015870:Gene Expression; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D000099274:Frizzled-Related Proteins
D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D000099274:Frizzled-Related Proteins