Published in Cancer Detection and Prevention 1998; 22(Supplement 1).
Cell surface CD44 activation of lymphoma cells is associated with the synergistic effect of phorbol ester-dependent signaling and receptor deglycosylation1The Lautenberg Center for General and Tumor Immunology Jerusalem, Israel 91120, 2 Karlsruhe Research Center, Institute of Genetics D-76344, Karlsruhe, Germany
AIM: Migration of inflammatory cells and of some tumor cells, and their lodgment in target organs, is dependent on the activation of cell surface CD44 receptor, usually detected by its ability to bind hyaluronic acid (HA) or other ligands. The aim of the project was to characterize activated CD44 both functionally and structurally. METHODS In an attempt to reveal the mechanism of CD44 activation, we compared the physical and chemical properties of CD44 in resting LB cell lymphoma with those in phorbol 12-myristate 13-acetate (PMA) -activated LB cells and of an LB cell subline (designated HA9) expressing constitutively-active CD44. RESULTS In contrast to resting LB cells, PMA-activated LB cells and HA9 cells displayed a CD44-dependent ability to bind HA. The ability of activated cell CD44 to bind HA was not dependent on microfilament or microtubule integrity or on changes in CD44 mobility on the membrane plane, indicating that the CD44 activation status is not associated with cytoskeleton function. Aside from the increased expression of CD44 on the surface of PMA-activated LB cells and HA9 cells, qualitative differences between the CD44 of resting and activated LB cells were also detected: the CD44 of the activated lymphoma was (i) larger in molecular size, (ii) displayed a broader CD44 isoform repertoire, and (iii) its glycoprotein contained less sialic acid. Indeed, after removal of sialic acid from their cell surface by neuraminidase, LB cells acquired the ability to bind HA. However, a reduced dose of neuraminidase did not confer HA binding on LB cells, unless they were also activated by a low concentration of PMA which, by itself, was ineffective. Similarly, under suboptimal conditions, a synergistic effect was obtained with tumicamycin and PMA; each one alone was ineffective but in combination they induced the acquisition of HA binding by the lymphoma cells. CONCLUSIONS The unveiling of the activation mechanism of CD44 is not only of academic importance, but it also has practical implications, as activated CD44 may be involved in supporting tumor progression.
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Paper presented at the International Symposium on the Impact of Biotechnology on Prediction, Prevention and Treatment of Cancer; Nice, France; October 24 - 27, 1998; in the section on Immunotherapy.