EXPRESSION OF TRANSMEMBRANE-TYPE PROTEIN-TYROSINE-PHOSPHATASE MESSENGER-RNA ALONG RAT NEPHRON SEGMENTS

Protein phosphorylation on tyrosine residues is one of the main cell s ignaling mechanisms. Cellular phosphotyrosyl levels are regulated by t he activities of protein tyrosine kinases (PTK) and protein tyrosine p hosphatases (PTPase). We have previously reported cDNA cloning of seve ral types of PTPase from rat kidney, including LRP (leukocyte common a ntigen-related protein; also known as the transmembrane-type tyrosine phosphatase, i.e., RPTP alpha). LRP mRNA was shown to be abundant in t he 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 distri bution along rat nephron segments. Large signals were found in inner m edulla by Northern blot analysis. By using a reverse transcription and polymerase chain reaction assay of individual microdissected tubule s egments along the nephron [proximal convoluted tubule (PCT), medullary thick ascending limb (MTAL), cortical collecting duct (CCD), outer me dullary collecting duct (OMCD), and inner medullary collecting duct (I MCD)] and glomeruli, we revealed intrarenal localization of LRP mRNA. LRP mRNA was detected in all nephron segments tested but was relativel y rich in the IMCD. Rank order of the signal intensity was IMCD > PCT = OMCD > CCD > MTAL = glomeruli. Immunohistochemistry also revealed th at 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; howeve r, further study is required to describe the function of LRP in more d etail.