Smit J J, Schinkel A H, Mol C A, Majoor D, Mooi W J, Jongsma A P, Lincke C R, Borst P
The Netherlands Cancer Institute, Division of Molecular Biology, Amsterdam.
Lab Invest. 1994 Nov;71(5):638-49.
P-glycoproteins (Pgps) belong to a family of well conserved plasma membrane proteins with two members in humans: MDR1 and MDR3. The MDR1 Pgp can transport drugs; the murine homologue of MDR3, mdr2, was recently shown by us to be involved in transport of the phospholipid phosphatidylcholine (lecithin) into bile.
We have determined the MDR3 mRNA levels in a panel of human tissues by RNase protection. We have also generated polyclonal antibodies specific for the MDR3 Pgp. Detection of the MDR3 Pgp in human tissues with these antibodies was by a streptavidin-ABC procedure.
The RNase protection results show that expression of the MDR3 gene has a more restricted distribution than that of MDR1. A high level of MDR3 mRNA was detected in the liver and in low levels in the adrenal gland, heart, striated muscle, spleen, and tonsil. In all of these tissues, some of the previously described splice variants of MDR3 were abundantly expressed. No indications were found for a tissue-specific regulation of alternative splicing of the MDR3 pre-mRNA. Two MDR3 Pgp-specific antibodies stained the bile canalicular membrane of hepatocytes across the entire liver lobule. No staining was found in the epithelial cells of the bile ductules and gall bladder, indicating that the staining at these sites with C219, a monoclonal antibody that recognizes both MDR1 and MDR3 Pgp, (mainly) represents the MDR1 Pgp. No MDR3 was detected by specific antibodies in the adrenal gland, spleen, and muscle. Since no staining was reported with MDR1-specific antibodies in muscle either, our results indicate that the C219 staining in some fibers of striated muscle represents a cross-reaction with another protein. One of the human MDR3-specific antibodies cross-reacted with the highly homologous mouse mdr2 Pgp. Staining with this antibody showed that the distribution of this protein in mouse liver and striated muscle is very similar to that of MDR3 Pgp in human tissues.
The highest expression of the MDR3 Pgp was found in liver in the canalicular membranes of hepatocytes. This is in agreement with a role for MDR3 in the transport of phospholipid into bile.
P-糖蛋白（Pgps）属于一类保守的质膜蛋白家族，在人类中有两个成员：多药耐药蛋白1（MDR1）和多药耐药蛋白3（MDR3）。MDR1 Pgp可转运药物；我们最近发现，MDR3的小鼠同源物mdr2参与磷脂酰胆碱（卵磷脂）向胆汁中的转运。
我们通过核糖核酸酶保护法测定了一组人类组织中的MDR3 mRNA水平。我们还制备了针对MDR3 Pgp的多克隆抗体。用这些抗体在人类组织中检测MDR3 Pgp采用的是链霉亲和素-ABC法。
核糖核酸酶保护结果显示，MDR3基因的表达分布比MDR1更具局限性。在肝脏中检测到高水平的MDR3 mRNA，而在肾上腺、心脏、横纹肌、脾脏和扁桃体中检测到的水平较低。在所有这些组织中，一些先前描述的MDR3剪接变体大量表达。未发现MDR3前体mRNA可变剪接存在组织特异性调控的迹象。两种MDR3 Pgp特异性抗体对整个肝小叶中肝细胞的胆小管膜进行了染色。在胆小管和胆囊的上皮细胞中未发现染色，这表明用识别MDR1和MDR3 Pgp的单克隆抗体C219在这些部位的染色（主要）代表MDR1 Pgp。在肾上腺、脾脏和肌肉中，特异性抗体未检测到MDR3。由于在肌肉中也未报道MDR1特异性抗体的染色情况，我们的结果表明，横纹肌某些纤维中的C219染色代表与另一种蛋白质的交叉反应。一种人类MDR3特异性抗体与高度同源的小鼠mdr2 Pgp发生交叉反应。用该抗体染色显示，这种蛋白质在小鼠肝脏和横纹肌中的分布与人类组织中MDR3 Pgp的分布非常相似。
在肝细胞的胆小管膜中发现MDR
