Rab10-mediated Endocytosis of the Hyaluronan Synthase HAS3 Regulates Hyaluronan Synthesis and Cell Adhesion to Collagen

Background: Hyaluronan synthases (HASs) require transport to plasma membrane for the activation of hyaluronan (HA) synthesis. Results: Rab10 overexpression inhibited, whereas Rab10 silencing increased, cell surface HA coat and HAS3-dependent hyaluronan synthesis. Conclusion: Rab10 reduces the steady-state abundance of HAS3 in the plasma membrane by enhancing HAS3 endocytosis. Significance: HA synthesis is controlled by HAS3 endocytosis mediated by Rab10. Hyaluronan synthases (HAS1-3) are unique in that they are active only when located in the plasma membrane, where they extrude the growing hyaluronan (HA) directly into cell surface and extracellular space. Therefore, traffic of HAS to/from the plasma membrane is crucial for the synthesis of HA. In this study, we have identified Rab10 GTPase as the first protein known to be involved in the control of this traffic. Rab10 colocalized with HAS3 in intracellular vesicular structures and was co-immunoprecipitated with HAS3 from isolated endosomal vesicles. Rab10 silencing increased the plasma membrane residence of HAS3, resulting in a significant increase of HA secretion and an enlarged cell surface HA coat, whereas Rab10 overexpression suppressed HA synthesis. Rab10 silencing blocked the retrograde traffic of HAS3 from the plasma membrane to early endosomes. The cell surface HA coat impaired cell adhesion to type I collagen, as indicated by recovery of adhesion following hyaluronidase treatment. The data indicate a novel function for Rab10 in reducing cell surface HAS3, suppressing HA synthesis, and facilitating cell adhesion to type I collagen. These are processes important in tissue injury, inflammation, and malignant growth.