Oertli B, Fan X, Wüthrich R P
Physiological Institute, University of Zürich-Irchel, Switzerland.
Nephrol Dial Transplant. 1998 Feb;13(2):271-8. doi: 10.1093/oxfordjournals.ndt.a027818.
CD44 is the main receptor for the extracellular polysaccharide hyaluronan (HA). We have recently shown that CD44 is strongly induced on renal tubular epithelial cells (TEC) in autoimmune renal injury and that HA accumulates in the renal interstitium (Kidney Int 1996; 50: 156-163 and Nephrol Dial Transplant 1997; 12: 1344-1353). The functional significance of enhanced tubular CD44 expression and its interaction with HA are not known. The purpose of the present study was to characterize renal tubular CD44 expression and CD44-mediated HA binding in vitro and to investigate the growth modulating effects in response to HA binding by TEC.
RT-PCR analysis, flow cytometry, confocal microscopy and Western blotting were used to examine cell surface and soluble CD44 expression by cultured TEC, using SV40-transformed mouse cortical tubular (MCT) cells. HA binding characteristics were examined by flow cytometry and effects of HA on TEC cell growth by [3H]thymidine incorporation.
By RT-PCR analysis MCT cells expressed predominantly the standard form of CD44 mRNA, whereas the expression of variant forms was very weak. Confocal microscopy showed that CD44 was expressed basolaterally and apically on MCT cells with strong staining on microvilli. Shedding of CD44 from MCT cells could be induced with crosslinking of anti-CD44 mAbs or with PMA stimulation. MCT cells constitutively bound HA and this binding could be modulated with anti-CD44 mAbs. Soluble and plate-bound HA markedly inhibited MCT cell growth.
CD44 is a regulated HA receptor on MCT cells which can be shed into the cellular environment. Upon binding of HA, CD44 functions as a growth inhibitory cell surface protein in MCT cells. We speculate that the interaction of CD44 with HA may have important regulatory effects on cell proliferation in tubulointerstitial renal diseases.
CD44是细胞外多糖透明质酸（HA）的主要受体。我们最近发现，在自身免疫性肾损伤中，肾小管上皮细胞（TEC）上的CD44被强烈诱导，且HA在肾间质中蓄积（《肾脏病国际》1996年；50：156 - 163以及《肾透析与移植》1997年；12：1344 - 1353）。肾小管CD44表达增强及其与HA相互作用的功能意义尚不清楚。本研究的目的是在体外对肾小管CD44表达及CD44介导的HA结合进行特性分析，并研究TEC对HA结合的生长调节作用。
采用逆转录聚合酶链反应（RT-PCR）分析、流式细胞术、共聚焦显微镜检查及蛋白质印迹法，以SV40转化的小鼠皮质肾小管（MCT）细胞研究培养的TEC的细胞表面和可溶性CD44表达。通过流式细胞术检测HA结合特性，并用[3H]胸腺嘧啶核苷掺入法检测HA对TEC细胞生长的影响。
通过RT-PCR分析，MCT细胞主要表达CD44 mRNA的标准形式，而变异形式的表达非常弱。共聚焦显微镜检查显示，CD44在MCT细胞的基底外侧和顶端表达，微绒毛上有强染色。抗CD44单克隆抗体交联或佛波酯（PMA）刺激可诱导MCT细胞上的CD44脱落。MCT细胞组成性结合HA，且这种结合可被抗CD44单克隆抗体调节。可溶性HA和平板结合的HA均显著抑制MCT细胞生长。
CD44是MCT细胞上一种受调控的HA受体，可脱落至细胞环境中。HA结合后，CD44在MCT细胞中作为一种生长抑制性细胞表面蛋白发挥作用。我们推测，CD44与HA的相互作用可能对肾小管间质性疾病中的细胞增殖具有重要调节作用。
