Metastasis Suppression by the Standard CD44 Isoform Does Not Require the Binding of Prostate Cancer Cells to Hyaluronate1

Previous studies from this laboratory have demonstrated that downregulation or the standard (1)44 isoform at the niRNA and protein level is associated with the acquisition of high metastatic ability within the Dunning R-3327 system of rat prostate cancers. Additional studies dem onstrated that transfection-induced enhanced expression of the standard < 1)44 isoform suppresses the metastatic ability of the AT3.1 Dunning suhline without suppressing tumorigenicity. The standard (1)44 isoform is a major cell surface receptor for the extracellular matrix glycosaminoglycan hyaluronate. In this study, an investigation was made to resolve whether the ability of the standard CD44 isoform to suppress metastasis of the AT3.1 prostate cancer cells critically requires enhanced hyaluronate binding. Highly metastatic Dunning AT3.1 rat prostate cancer cells were transfected with expression plasmids encoding either the wild-type or mutant standard (1)44 isolili in. The mutant standard (1)44 isoform construct encoded a protein unable to bind to hyaluronate. Transfectants were isolated and characterized with regard to their level of standard ! 1)44 isoform expression, hyaluronate binding, tumorigenicity, and met astatic ability. Kxprcssion of the wild-type standard (1)44 isoform in creased the hyaluronate binding of prostate cancer cells and suppressed their metastatic ability without suppressing their tumorigenicity. Expres sion of the mutant ( '1)44 standard isoform did not increase hyaluronate binding; however, it equally suppressed the mctastatic ability of the AT3.1 prostate cancer cells. These results demonstrate that the metastasis sup pression by the standard (1)44 isoform is independent of its ability to bind to hyaluronate.