Molecular characterization of rat glomerular epithelial cell complement receptors

Complement receptor type 1 (CR1) has previously been isolated from cultured rat glomerular epithelial cells (GEC) by C3b affinity chromatography. In addition, the presence of Crry in GEC and in rat glomeruli has been demonstrated. Crry appears to be the rodent analogue of human decay accelerating factor, which was previously described in human GEC and in human glomeruli. In this study, the molecular biology of these rat complement receptors is examined. A specific cDNA probe for rat CR1 was generated by reverse transcription of GEC mRNA, followed by polymerase chain reaction (PCR). The oligonucleotide primers were chosen from conserved regions spanning 271 bases in human and mouse CR1. A 271-base-pair PCR product was generated from rat GEC cDNA, the nucleotide sequence of which was 70.1% and 77.2% identical to those of the respective mouse and human sequences. This PCR product, designated rCR1-p, was then used to probe for CR1 mRNA. By northern blot analysis, rCR1-p hybridized to 4.5-kilobase (kb) mRNA from both cultured GEC and rat glomeruli and also weakly hybridized to 4.5-kb CR1 mRNA from mouse spleen. In additional northern blots, a nucleotide probe for mouse Crry hybridized to mRNA of 2.1 to 2.4 kb from rat GEC, slightly larger than the 1.9- to 2.1-kb mouse Crry mRNA. Therefore, mRNA for CR1 and Crry are present in cultured rat GEC and in rat glomeruli in vivo. To further investigate the composition of rat CR1 mRNA, northern hybridizations were performed with nucleotide probes for mouse and human CR1. Although the nucleotide probe for human CR1 hybridized to rat CR1 mRNA, the probe for mouse CR1 did not. Taken together, the available data indicate that rat CR1 has greater homology to human CR1 than to mouse CR1.