Expression of transmembrane-type protein tyrosine phosphatase mRNA along rat nephron segments.

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.