PURIFICATION, CHARACTERIZATION AND DIFFERENTIATION-DEPENDENT EXPRESSION OF A PERCHLORIC-ACID SOLUBLE-PROTEIN FROM RAT-KIDNEY

We have recently reported the presence of a novel perchloric acid solu ble protein in rat liver (PSP1) that inhibits cell-free protein synthe sis in a rabbit reticulocyte system. While studying the perchloric aci d soluble proteins from different tissues of rats, we found that the k idney protein cross-reacted with antibody against the PSP1. In this in vestigation, we have purified a perchloric acid soluble protein from t he rat kidney and studied its characterization and expression. The pro tein extracted from the postmitochondrial supernatant fraction with 5% perchloric acid was purified by ammonium sulfate fractionation and CM -Sephadex chromatography. By immunoscreening with the rabbit antisera against the PSP1, we detected a cDNA that contained an open reading fr ame of 411 bp, encoding a 137 amino-acid protein with a molecular mass of 14,149 daltons. The deduced amino acid sequence was completely ide ntical with that of PSP1 from rat liver. The perchloric acid soluble p rotein from rat kidney (K-PSP1) also inhibited cell-free protein synth esis in the rabbit reticulocyte lysate system in a different manner th an RNase A. Immunohistochemistry showed that the expression of K-PSP1 increased from fetal 17th day to postnatal 4th week, and it remained a lmost the same until the 7th week of postnatal age. Furthermore, the e xpression of K-PSP1 in the kidney of the nephrotic rat model was shown to be differentiation dependent. On the other hand, the expression of K-PSP1 in renal tumor cells was downregulated as compared with intact tissue. These results suggest that the expression of K-PSP1 is regula ted in a differentiation-dependent manner in the kidney.