Kaneko T, Moriyama T, Imai E, Akagi Y, Arai M, Inoue T, Xia C, Noguchi T, Kamada T, Ueda N
First Department of Medicine, Osaka University School of Medicine, Japan.
Am J Physiol. 1995 Jun;268(6 Pt 2):F1102-8. doi: 10.1152/ajprenal.1995.268.6.F1102.
Protein phosphorylation on tyrosine residues is one of the main cell signaling mechanisms. Cellular phosphotyrosyl levels are regulated by the activities of protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTPase). We have previously reported cDNA cloning of several types of PTPase from rat kidney, including LRP (leukocyte common antigen-related protein; also known as the transmembrane-type tyrosine phosphatase, i.e., RPTP alpha). LRP mRNA was shown to be abundant in the kidney; however, our understanding of the functional role of LRP in the kidney is very limited. To gain keener insight into the function of LRP in the kidney, our first approach was to reveal its mRNA distribution along rat nephron segments. Large signals were found in inner medulla by Northern blot analysis. By using a reverse transcription and polymerase chain reaction assay of individual microdissected tubule segments along the nephron [proximal convoluted tubule (PCT), medullary thick ascending limb (MTAL), cortical collecting duct (CCD), outer medullary collecting duct (OMCD), and inner medullary collecting duct (IMCD)] and glomeruli, we revealed intrarenal localization of LRP mRNA. LRP mRNA was detected in all nephron segments tested but was relatively rich in the IMCD. Rank order of the signal intensity was IMCD > PCT = OMCD > CCD > MTAL = glomeruli. Immunohistochemistry also revealed that LRP was abundant in IMCD. This pattern of expression gives rise to an interesting possibility that LRP might be involved in the specific renal tubule function, such as urinary concentrating mechanism; however, further study is required to describe the function of LRP in more detail.
酪氨酸残基上的蛋白质磷酸化是主要的细胞信号传导机制之一。细胞磷酸酪氨酸水平受蛋白质酪氨酸激酶（PTK）和蛋白质酪氨酸磷酸酶（PTPase）活性的调节。我们之前报道了从大鼠肾脏中克隆出几种类型的PTPase的cDNA，包括LRP（白细胞共同抗原相关蛋白；也称为跨膜型酪氨酸磷酸酶，即RPTPα）。LRP mRNA在肾脏中含量丰富；然而，我们对LRP在肾脏中的功能作用了解非常有限。为了更深入地了解LRP在肾脏中的功能，我们的首要方法是揭示其mRNA沿大鼠肾单位各节段的分布。通过Northern印迹分析在内髓质中发现了大的信号。通过对沿肾单位[近端曲管（PCT）、髓质厚升支（MTAL）、皮质集合管（CCD）、外髓质集合管（OMCD）和内髓质集合管（IMCD）]和肾小球的各个显微切割的肾小管节段进行逆转录和聚合酶链反应分析，我们揭示了LRP mRNA在肾内的定位。在所有测试的肾单位节段中都检测到了LRP mRNA，但在内髓质集合管中相对丰富。信号强度的排序为IMCD > PCT = OMCD > CCD > MTAL = 肾小球。免疫组织化学也显示LRP在内髓质集合管中含量丰富。这种表达模式引发了一种有趣的可能性，即LRP可能参与特定的肾小管功能，如尿液浓缩机制；然而，需要进一步研究来更详细地描述LRP的功能。
