Soluble forms of CD44 and CD54 (ICAM-1) cellular adhesion molecules are released by human prostatic cancer cell lines

We have identified that human prostatic cancer cell lines DU145, PC3, ND1, ALVA31 and JCA1 released soluble CD44 molecules and DU145, PC3 and ND1 released soluble CD54. Both soluble and surface CD44 were not found in LNCaP, and both forms of CD54 were not expressed in LNCaP and JCA1. CD54 was found to be highly expressed on cell surface in ALVA31, but these cells did not release soluble CD54. Expression of both cell surface and soluble forms were examined after treatment of cells with IFN-γ, TGF-β1, or culturing in serum-free media. The concentration of soluble CD54 in supernatants changed to small extent after treatment with TGF-β1 and increased after treatment with IFN-γ or in serum-free media. Cell surface expression of CD54 however, changed only minimally after treatment. The levels of cell surface and soluble CD44 also changed minimally after treatment with IFN-γ and TGF-β1 but decreased in serum-free media and this was accompanied by marked elevation of soluble CD44 in supernatants. These data indicate that soluble CD44 might be released from cell surface by shedding whereas alternative splicing is the most likely mechanism of soluble CD54 release.