The hyaluronidase Hyal2 is a regulator of cell surface hyaluronan interactions

HA may increase cell motility, facilitate cancer cell invasion and induce angiogenesis. Many of these effects depend on HA binding to specific receptors, mostly CD44, on the cell surface and on the presence of a pericellular HA‐rich coat. We hypothesized that the ubiquitous glycosyl‐phosphatidylinositol‐anchored hyaluronidase Hyal2 could be one of the HA regulatory factors modifying cell response to HA. In stable Hyal2 transfectants of the rat fibroblastic cell line BB16, Hyal2 was detected on the plasma membrane and in vesicles. The plasma membrane localization was confirmed by tranfection of a fluorescent Hyal2 chimera and by surface biotinylation experiments. The thickness of the pericellular hyaluronidase‐sensitive coat was 1.22 ± 0.17 and 2.05 ± 0.45 (n=52; p<0.0001) in cells expressing high and low level of Hyal2, respectively. Hyal2 overexpression did not decrease the amount of endogenous cell‐associated HA nor the amount of secreted HA, but it reduced the number of apparent 125 I‐HA binding sites two‐fold (Bmax: 0.17 ± 0.07 vs 0.07 ± 0.01 μg HA/10 6 cells; n=7; p<0.05) without significant changes in their dissociation constant. The level of CD44, measured using immunofluorescence, Western blots and FACS experiments, was unchanged. Hyal2 coimmunoprecipitated with CD44 in the presence of low and high levels of extracellular HA. Thus, Hyal2 can decrease the efficiency of HA receptors, mostly CD44, and reduce cell coat. The impact of these events on cell signaling and behavior, in particular on the adhesiveness and invasiveness of transformed cells, is being explored.