We have previously reported that HYBID (hyaluronan (HA)-binding protein involved in HA depolymerization/KIAA1199/CEMIP) is a specific HA-binding protein that is essential for HA depolymerization in skin and synovial fibroblasts. HA is incorporated into cells in the presence of HYBID and clathrin, degraded in endosomes, and excreted into the extracellular space. However, it is not yet clear whether HYBID itself catalytically cleaves HA. A recent report on transmembrane protein 2 (TMEM2)-a novel cell surface hyaluronidase-prompted us to investigate whether TMEM2 is essential for HYBID-mediated HA depolymerization. In the present study, we found that transforming growth factor beta 1 (TGF-β1), which suppressed HA depolymerization with a concomitant decrease in HYBID expression, upregulated TMEM2 expression conversely in human skin fibroblasts. TMEM2 expression was not affected by histamine, which significantly increased HA depolymerization accompanied by an increase in HYBID expression. We confirmed a similar response in two other cell lines: KEL FIB keloid fibroblasts and HT1080 fibrosarcoma cells. TGF-β1 was the only inducer of TMEM2 expression among growth factors including epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and platelet-derived growth factor-BB (PDGF-BB), which suppressed HYBID expression. Moreover, HYBID knockdown completely suppressed HA depolymerization, whereas TMEM2 knockdown unexpectedly enhanced it. These findings clearly indicate that HYBID is indispensable, but TMEM2 is not involved in the HYBID-mediated HA depolymerization system as a catalytic hyaluronidase in human skin fibroblasts.
Keywords: Fibroblast; HYBID; Hyaluronan; Hyaluronan depolymerization; TGF-β1; TMEM2.
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