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Loss of HNF1α function in human renal cell carcinoma: Frequent mutations in the VHL gene but not the HNF1α gene

Human renal cell carcinoma (RCC) is a common malignant disease of the kidney characterized by dedifferentiation of renal epithelial cells. Our previous experiments showed that most RCCs have a loss of function of the tissue‐specific transcription factor hepatocyte nuclear factor (HNF) 1α. Detailed analyses of the 10 exons encoding HNF1α in 32 human RCCs by single‐strand conformation polymorphism analysis and direct DNA sequencing revealed no tumor‐associated mutation, whereas with the same probes we frequently found mutations in the von Hippel‐Lindau tumor suppressor gene. No mutation leading to loss of HNF1α function was detected by analyzing the integrity of the HNF1α transcripts in the RNA derived from RCCs by the protein truncation test. Investigating human RCC cell lines by western blotting and gel retardation assays showed a dramatic loss in the expression of the tissue‐specific transcription factor HNF1α in eight of 10 cell lines. As the HNF1α‐related transcription factor HNF1β was expressed in all these tumor cell lines, the loss of HNF1α expression was a specific event and was maintained in RCC cell lines. The loss of HNF1α expression in RCC cell lines on the RNA level was confirmed by reverse transcription polymerase chain reaction. We propose that tumor‐associated mutations in the HNF1α gene do not occur in human RCC and that the loss of function is partially due to a transcriptional inactivation of the HNF1α gene. Mol. Carcinog. 24:305–314, 1999. © 1999 Wiley‐Liss, Inc.