Characterization of CD44-mediated hyaluronan binding by renal tubular epithelial cells

Background. CD44 is the main receptor for theextracellular polysaccharide hyaluronan (HA). We have recently shown thatCD44 is strongly induced on renal tubular epithelial cells (TEC) inautoimmune renal injury and that HA accumulates in the renal interstitium(Kidney Int 1996; 50: 156-163 and NephrolDial Transplant 1997; 12: 1344-1353). The functionalsignificance of enhanced tubular CD44 expression and its interaction withHA are not known. The purpose of the present study was to characterizerenal tubular CD44 expression and CD44-mediated HA binding invitro and to investigate the growth modulating effects inresponse to HA binding by TEC. Methods. RT-PCRanalysis, flow cytometry, confocal microscopy and Western blotting wereused to examine cell surface and soluble CD44 expression by cultured TEC,using SV40-transformed mouse cortical tubular (MCT) cells. HA bindingcharacteristics were examined by flow cytometry and effects of HA on TECcell growth by [³H]thymidine incorporation.Results. By RT-PCR analysis MCT cells expressedpredominantly the standard form of CD44 mRNA, whereas the expression ofvariant forms was very weak. Confocal microscopy showed that CD44 wasexpressed basolaterally and apically on MCT cells with strong staining onmicrovilli. Shedding of CD44 from MCT cells could be induced withcrosslinking of anti-CD44 mAbs or with PMA stimulation. MCT cellsconstitutively bound HA and this binding could be modulated with anti-CD44mAbs. Soluble and plate-bound HA markedly inhibited MCT cell growth.Conclusions. CD44 is a regulated HA receptor on MCTcells which can be shed into the cellular environment. Upon binding of HA,CD44 functions as a growth inhibitory cell surface protein in MCT cells. Wespeculate that the interaction of CD44 with HA may have importantregulatory effects on cell proliferation in tubulointerstitial renaldiseases.