Cloning and expression of the mouse glomerular podoplanin homologue gp38P

Abstract

Background. Puromycin aminonucleoside nephrosis (PAN) is a rat model for human minimal change nephropathy. During PAN, severe proteinuria is induced that is paralleled by a reduced expression of a rat podocyte protein, named podoplanin. The protein probably plays a role in maintaining the unique shape of podocytes. Recently, attenuated amino acid transport has been observed in cultured mouse glomerular epithelial cells treated with puromycin amino-nucleoside (PA). In the present study, gp38P, a protein homologous to rat podoplanin was cloned from mouse glomerular epithelial cells and was found to be down-regulated by PA. A role for gp38P in membrane transport in mouse podocytes has been suggested. Methods. Based on homology to rat podoplanin, the protein gp38P was cloned from mouse glomerular epithelial cells by RT-PCR. Mouse glomerular epithelial cells, mouse cortical collecting duct cells, and Xenopus oocytes were treated with PA and the expression of gp38P was examined by RT-PCR and western blot analysis. Expression of gp38P in other mouse tissues was demonstrated by RT-PCR. The possible impact of gp38P on amino acid transport and folic acid uptake was examined in Xenopus oocytes. Results. gp38P cloned from mouse glomerular epithelial cells showed strong homologies to rat podoplanin and gp38, a protein expressed in the thymus and other tissues. RT-PCR analysis demonstrated ubiquitous expression of gp38P in epithelial and non-epithelial tissues. Quantitative RT-PCR and western blot analysis indicated down-regulation of gp38P in PA-treated glomerular epithelial cells along with loss of cell shape and cell lysis, which was not observed in other cell types. When expressed in Xenopus oocytes, gp38P had no impact on folic acid uptake or transport activity of the amino acid co-transporters CAT1, EAAC1, and rBAT. Conclusion. Cultured mouse glomerular epithelial cells express the podoplanin homologue gp38P, which is down-regulated by PAs. gp38P is ubiquitously expressed and is likely to control specifically the unique shape of podocytes.