Expression of bikunin mRNA in renal epithelial cells after oxalate exposure

Purpose: To determine the changes in expression of bikunin in renal epithelial cells on exposure to oxalate and calcium oxalate crystals. Materials and Methods: This study used reverse transcription polymerase chain reaction (RT-PCR) to examine bikunin mRNA expression levels in MDCK cells exposed to oxalate or calcium oxalate crystals. Poly(A)⁺ RNA was isolated directly from renal epithelial cells, then converted to cDNA with random primers and reverse transcriptase. To quantify the expression level of bikunin mRNA, we developed a competitive DNA template for competitive PCR analysis. The PCR products were resolved by electrophoresis on 1.3% agarose gel and visualized with ethidium bromide. In this system, we could quantify the exact number of bikunin mRNA transcripts. Bikunin mRNA from rat liver was expressed as a positive control. Results: Bikunin mRNAs and competitive templates from renal epithelial cells were expressed in all samples as 434 bp and 312 bp bands, respectively. Bikunin expression was significantly increased in oxalate exposed cells. Cells exposed to calcium oxalate monohydrate crystals or latex beads showed no significant change in expression of bikunin. Western blotting analysis also showed increased expression of bikunin and inter-α-inhibitor-related proteins in the culture medium of oxalate exposed cells. Conclusions: These findings suggest that renal epithelial cells express bikunin gene and have the capability to produce bikunin when stimulated by certain agents such as oxalate. This increased expression and production of bikunin may represent a protective response of renal epithelial cells to nephrotoxic challenges of oxalate.