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J. Cell Biol.,
Volume 141, Number 6, June 15, 1998 1467-1476

* Department of Medicine, Osteoclasts are multinucleated cells of hemopoietic origin that are responsible for bone resorption during physiological bone remodeling and in a variety of bone diseases. Osteoclast development requires
direct heterotypic cell-cell interactions of the hemopoietic osteoclast precursors with the neighboring osteoblast/stromal cells. However, the molecular mechanisms underlying these heterotypic interactions are
poorly understood. We isolated cadherin-6 isoform, denoted cadherin-6/2 from a cDNA library of human osteoclast-like cells. The isolated cadherin-6/2 is 3,423 bp
in size consisting of an open reading frame of 2,115 bp,
which encodes 705 amino acids. This isoform lacks 85 amino acids between positions 333 and 418 and contains 9 different amino acids in the extracellular domain
compared with the previously described cadherin-6.
The human osteoclast-like cells also expressed another
isoform denoted cadherin-6/1 together with the cadherin-6. Introduction of cadherin-6/2 into L-cells that
showed no cell-cell contact caused evident morphological changes accompanied with tight cell-cell association, indicating the cadherin-6/2 we isolated here is
functional. Moreover, expression of dominant-negative or antisense cadherin-6/2 construct in bone marrow-derived mouse stromal ST2 cells, which express
only cadherin-6/2, markedly impaired their ability to
support osteoclast formation in a mouse coculture
model of osteoclastogenesis. Our results suggest that
cadherin-6 may be a contributory molecule to the heterotypic interactions between the hemopoietic osteoclast cell lineage and osteoblast/bone marrow stromal
cells required for the osteoclast differentiation. Since
both osteoclasts and osteoblasts/bone marrow stromal
cells are the primary cells controlling physiological bone remodeling, expression of cadherin-6 isoforms in
these two cell types of different origin suggests a critical
role of these molecules in the relationship of osteoclast
precursors and cells of osteoblastic lineage within the
bone microenvironment.
Division of Hematology, University of Texas
Health Science Center, San Antonio, Texas 78284-7877; and § Department of Biochemistry, Osaka University Faculty of
Dentistry, Osaka 565, Japan
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