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J. Biol. Chem., Vol. 277, Issue 22, 20095-20103, May 31, 2002
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From the The cartilage-specific (V + C)
Absence of the I-10 Protein Segment Mediates Restricted
Dimerization of the Cartilage-specific Fibronectin Isoform*
,
,
¶
Department of Biomedical Sciences and the
§ Department of Microbiology and Immunology, James A. Baker
Institute for Animal Health, College of Veterinary Medicine, Cornell
University, Ithaca, New York 14853
fibronectin isoform does not efficiently
heterodimerize with other V-region splice variants of fibronectin. To
understand better the structural elements that determine this
restricted dimerization profile, a series of truncated fibronectin
expression constructs with various internal deletions in the V, III-15,
or I-10 segments were constructed and co-transfected into COS-7 cells
with either the V+C+ or the (V + C)
isoform. SDS-PAGE and immunoblot analyses of the
resulting conditioned media suggest that the I-10 segment must either
be present in both monomeric subunits of fibronectin or absent from
both subunits for efficient dimerization to occur. Further studies
suggest that the I-10 segment specifically, not simply a balanced
number of type I repeats at the carboxyl terminus of each monomeric
subunit, plays an important role in determining different fibronectin
dimerization patterns. Neither I-11 nor I-12 could be substituted for
segment I-10 without significantly reducing the formation of
heterodimers. Therefore, absence of segment I-10 explains why (V + C)
fibronectin is not found in heterodimeric
configurations with other native V-region splice variants in cartilage.
The unique dimerization pattern of (V + C)
fibronectin
does not prevent matrix formation yet is consistent with this isoform
having specialized properties in situ that are important
for either the structural organization and biomechanical properties of
cartilage or the regulation of a chondrocytic phenotype.
*
This work was supported by National Institutes of Health
Grant AR44340 and the Arthritis Foundation.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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