CD44 is not an adhesive receptor for osteopontin

Osteopontin is a secreted glycoprotein with adhesive and migratory function s. Cellular interactions with osteopontin are mediated through integrin rec eptors which recognize the RGD domain. Recently, CD44, a non-integrin, mult ifunctional adhesion molecule was identified as an osteopontin receptor. CD 44 is a ubiquitous surface molecule that exists as a number of different is oforms, generated by alternative splicing. To analyze which forms of CD44 m ediate binding to osteopontin, we used the standard form of CD44 as CD44-hu man immunoglobulin fusion proteins and several splice variants in enzyme-li nked immunosorbant assays. Multiple preparations of osteopontin were used i ncluding native osteopontin derived from smooth muscle cells, human urinary osteopontin, full-length recombinant osteopontin, and two recombinant oste opontin fragments expected to be formed following thrombin cleavage. Our da ta show that although the CD44-hIg fusion proteins could interact with hyal uronic acid as expected, there was no interaction between CD44H, CD44E, CD4 4v3,v8-v10, or CD44v3 with osteopontin. These studies suggest that CD44-ost eopontin interactions may not be common in vivo and may be limited to a spe cific CD44 isoform(s), and/or a particular modified form of osteopontin. J. Cell. Biochem. 73:20-30, 1999. (C) 1999 Wiley-Liss, Inc.