Screening of the differentially expressed genes in human renal oncocytoma

Abstract

Although renal oncocytoma is currently considered to be a rare, benign tumor occurring in the renal cortex, there have been increasing reports that tumors initially diagnosed as renal oncocytoma tend to have malignant potential and metastatic potential. The mechanisms by which some tumors initially diagnosed as renal oncocytoma become malignant tumors remain to be determined. However, it is extremely important to differentially diagnose renal oncocytoma from malignant renal cell carcinoma because the treatment modality of this benign tumor is completely different from that of the malignant tumor. In order to identify any specific molecular marker(s) of renal oncocytoma, we have performed ''Differential Display of mRNA'' technique using mRNA extracted from normal kidney tissue and renal oncocytoma obtained from 37 year-old patient. The clinical and pathological studies of this patient showed the typical characteristics of oncocytoma, including abundant mitochondria in cytoplasm. DNA now cytometry showed normal diploidy in this oncocytoma. Twenty different polymerase chain reaction (PCR) primer sets were used to compare gene expression patterns of normal and tumor tissues. Under our experimental conditions,. the differential display of mRNA technique produced approximately 55 up-regulated and 35 down-regulated bands each representing partial cDNA fragments. Among these differentially expressed cDNA fragments, we examined the cDNA sequences of 20 prominent polymerase chain reaction bands showing downregulated expression patterns in RNA from the oncocytoma tissues. The DNA sequence comparison analysis using Genbank data base revealed that most clones had unknown genes. However, one clone showed 98% identity to the yi43f06.s1 clone, which is expressed in the female placenta at birth. Two other clones showed 70% identity to yh8810.ri clone and human IFNAR gene for interferone alpha receptor. Northern blot analysis using these PCR products as a probe confirmed that the differentially detected PCR bands were not artifacts, but indeed reflected the differential expression of each mRNA during tumorigenesis. We are in the process of further characterizing these genes.