Abstract
Liver sinusoidal endothelial cells (LECs) express two HARE proteins of 175 kDa and ∼300 kDa that endocytically clear hyaluronan (HA) from the circulation. We have characterized eight monoclonal antibodies (mAbs) raised against the partially purified 175 kDa HARE. Seven mAbs recognize the 175 kDa HARE after nonreducing SDS-PAGE and in all cases also crossreact with the ∼300 kDa HARE. Two of the mAbs inhibit 125I-HA binding and endocytosis by LECs at 37°C. We purified these two HAREs and showed that the 175 kDa HARE is a single protein, whereas the ∼300 kDa species contains three subunits at 260, 230 and 97 kDa (Zhou, et al. J. Biol. Chem. 274, 33831–33834, 1999). Two mAbs recognized both the two nonreduced HARE species and three of the four proteins present after reduction. The 97 kDa subunit was not recognized by any mAbs in Western blots. Based on their cross-reactivity with the mAbs against the 175 kDa HARE, the 175, 230 and 260 kDa proteins are related to each other. Immunocytochemistry using these mAbs shows high protein expression levels in rat liver sinusoids, the venous sinuses of the red pulp in spleen, and the medullary sinuses of lymph nodes. Little or no HARE expression was observed in muscle, heart, lung, kidney, brain, skin, eye, pancreas, thymus, testis, adipose, salivary gland, adrenal, thyroid, larynx, tongue, stomach or intestine. We propose the name HARE (HA Receptor for Endocytosis) because this receptor mediates the very rapid endocytosis of HA and its tissue distribution is not unique to liver.
Published Version
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