INDUCIBLE BINDING OF HUMAN-LYMPHOCYTES TO HYALURONATE VIA CD44 DOES NOT REQUIRE CYTOSKELETON ASSOCIATION BUT DOES REQUIRE NEW-PROTEIN SYNTHESIS

We have examined molecular mechanisms of the PMA-inducible HA binding ability of human lymphocytes. Newly established OS/6 and OS/37, specif ic for human CD44, specifically inhibited PMA-induced HA binding of se veral human cell lines, suggesting that both mAb detect HA binding epi tope(s) on CD44. Sequential staining revealed that these mAb cross-blo cked each other's binding to Molt-4, T lymphoblast lines, and that nei ther of them interfered with staining of Molt-4 by other anti-CD44 mAb which induced significant homotypic cell aggregation. Biochemical and PCR analyses did not provide any evidence that PMA stimulation induce d dramatic changes in molecular weight or molecular isoforms of CD44. Interestingly, HA binding was not affected and rather slightly increas ed by cytochalasin B which disrupts F-actin microfilament integrity. T his suggests that the ability of CD44 to bind to HA does not correlate with the association of CD44 with the cytoskeleton. On the other hand , protein synthesis inhibitors, cycloheximide and anisomycin clearly i nhibited the induction of HA binding of PMA-activated Molt-4 without a ffecting the expression of CD44 at the same time after stimulation. Th e same treatment had no effect on PMA-induced FN binding of the cells, which was mediated by VLA integrins. These results suggest that the a dhesion functions of CD44 and integrins are differently regulated desp ite the fact that both are induced by PMA stimulation, and that new pr otein synthesis is essential for the PMA-induced HA binding by CD44.