Identification of the Hyaluronan Receptor for Endocytosis (HARE)

Abstract

Rat liver sinusoidal endothelial cells (LECs) express two hyaluronan (HA) receptors, of 175 and 300 kDa, responsible for the endocytic clearance of HA. We have characterized eight monoclonal antibodies (mAbs) raised against the 175-kDa HA receptor partially purified from rat LECs. These mAbs also cross-react with the 300-kDa HA receptor. The 175-kDa HA receptor is a single protein, whereas the 300-kDa species contains three subunits, ␣, ␤, and ␥ at 260, 230, and 97 kDa, respectively (Zhou, B., Oka, J. A., and Weigel, P. H. (1999) J. Biol. Chem. 274, 33831-33834). The 97-kDa subunit was not recognized by any of the mAbs in Western blots. Based on their cross-reactivity with these mAbs, the 175-, 230-, and 260-kDa proteins appear to be related. Two of the mAbs inhibit 125 I-HA binding and endocytosis by LECs at 37°C. All of these results confirm that the mAbs recognize the bone fide LEC HA receptor. Indirect immunofluoresence shows high protein expression in liver sinusoids, the venous sinuses of the red pulp in spleen, and the medullary sinuses of lymph nodes. Because the tissue distribution for this endocytic HA receptor is not unique to liver, we propose the name HARE (HA receptor for endocytosis). HA1 is an important and often abundant extracellular matrix component of all tissues, in particular cartilage, skin, and vitreous humor (1). HA plays a key role in development, morphogenesis, and differentiation, in cell adhesion and proliferation, and in inflammation and wound healing (1-4). In humans the total body turnover of HA is several grams per day (1). Although local turnover of HA occurs in avascular tissues, particularly cartilage (5, 6), two major clearance systems are responsible for HA degradation and removal in the body (4). The first is the lymphatic system, which accounts for ϳ85% of the HA turnover, and the second is in the liver, which accounts for the other ϳ15% of the total body HA turnover. Throughout the body, HA is continuously synthesized and degraded in almost all tissues. At the same time, chondroitin sulfate and other glycosaminoglycans are also released from the cleavage of proteoglycans, especially aggregating proteoglycans associated with HA. Large native HA molecules (ϳ10 7 Da) are partially degraded to large fragments (ϳ10 6 Da) that are released from the matrix and enter the lymphatic system, flowing to lymph nodes.The lymph nodes completely degrade the majority of HA (ϳ85%) by unknown mechanisms. Neither the responsible cell type, the receptor involved, nor the location in lymph nodes at which HA uptake and degradation occurs has been determined. The remaining HA (ϳ15%) that escapes degradation in the lymph nodes ultimately flows into the blood at the thoracic duct. Since HA is an exceptionally viscous polysaccharide in solution, it would be deleterious for the blood concentration of HA, even at relatively low molecular weight, to increase. Clearance of this circulating HA and the other glycosaminoglycan degradation fragments is presumably important for normal health (1, 4). Elevate...

Hyaluronan Anchored to Activated CD44 on Central Nervous System Vascular Endothelial Cells Promotes Lymphocyte Extravasation in Experimental Autoimmune Encephalomyelitis

“…Another candidate is the HA receptor for endocytosis. It can be expressed on the cell surface, but it predominately localizes within sinusodial endothelia and its expression by lymphocytes has not been reported (35,36). Interestingly, antibody blockage of HA binding to HA receptor for endocytosis impairs tumor cell metastasis, a process likened to active lymphocyte extravasation (37,38).…”

Anticancer Therapeutics: Targeting Macromolecules and Nanocarriers to Hyaluronan or CD44, a Hyaluronan Receptor

“…The short half-life of HMW-HA conjugates 57,65,66 is most likely due to HA clearance from the blood by the HARE receptor present in the liver and spleen. 5 Improvement in the distribution of HA conjugated drugs in vivo may be achieved by reducing endogenous HA blood clearance mechanisms. Luo et al suggested that systemic HA clearance can be reduced by pre-treatment with a high molecular weight saccharide that competes with HA for binding during clearance but not during target cell drug internalization.…”

“…3 HA turnover is due to local cellular catabolism, removal by an HA endocytosing receptor (LYVE-1) on cells located in the lymphatics, 4 and systemic clearance from the blood by the HARE receptor on liver sinusoidal endothelial cells. 5 In skin, HA has a half-life of over a day. 6 In contrast, circulating high molecular weight HA (HMW-HA) has a half-life of two to five minutes.…”

Rapid cell corpse clearance by stabilin-2, a membrane phosphatidylserine receptor

“…It is expressed at high levels in the sinusoidal endothelial cells of the spleen, lymph nodes, and liver. 18,21 In this study, we present evidence that stabilin-2 is also expressed in human monocyte-derived macrophages (HMDMs). These findings compelled us to speculate that stabilin-2 may participate in the recognition and engulfment of apoptotic and aged cells in macrophages.…”

“…16 Stabilin-2 is a large multifunctional receptor, which harbors seven FAS1 domains, four EGF-like repeats, and a link domain. Stabilin-2 was initially identified as the endocytic hyaluronan receptor on rat liver sinusoidal endothelial cells 17,18 and has also been reported to function as a scavenger receptor, which effects the endocytosis of modified LDL and glycation end products. 19,20 Stabilin-2 also has been shown to bind to Gram-negative and Gram-positive bacteria, thereby suggesting the potential involvement of stabilin-2 in the immune response.…”