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) 1 alpha. Detailed analyses of the 10 exons encoding HNF1 alpha 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 HNF1 alpha function was detected by analyzing the integrity of the HNF1 alpha 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 HNF1 alpha in eight of 10 cell lines. As the HNF1 alpha-related transcription factor HNF1 beta was expressed in all these tumor cell lines, the loss of HNF1 alpha expression was a specific event and was maintained in RCC cell lines. The loss of HNF1 alpha 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 HNF1 alpha gene do not occur in human RCC and that the loss of function is partially due to a transcriptional inactivation of the HNF1 alpha gene. (C) 1999 Wiley-Liss, Inc.

Human renal cell carcinogenesis is usually accompanied by dedifferentiation processes including the loss of expression of tissue specifically expressed genes. Based on the hypothesis that these dedifferentiation processes might be attributed to a functional change in tissue specific transcription factors, we have analyzed the expression and function of the tissue specific transcription factor HNF4 alpha in human renal cell carcinomas. By Western blot analysis and gel retardation assay using HNF4 alpha specific antibodies, we observed that in most cases the amount as well as the binding activity of HNF4 is reduced in the tumor samples compared to the corresponding normal tissues. Furthermore, we found a clear correlation between the HNF4 alpha binding activity and the amount of another transcription factor (HNF1 alpha), which is thought to be transcriptionally activated by HNF4 alpha. We therefore speculate that disruption of the HNF4 alpha/HNF1 alpha pathway of kidney specific gene expression might be an important molecular mechanism in renal cell carcinogenesis.

The retinoic acid receptor (RAR) beta gene is located in a region on chromosome 3p, which is frequently deleted in renal cell carcinoma. Since retinoic acid (RA) can inhibit cell proliferation and tumor formation, loss of RAR beta might contribute to oncogenesis of the kidney. This prompted us to examine RAR beta expression in 12 primary kidney tumors and 11 renal cancer cell lines. Five tumors expressed RAR beta at severely reduced levels, three of which have retained one gene copy. In one tumor an aberrant larger transcript was expressed. Only three cell lines showed detectable expression of RAR beta, albeit at low levels in comparison with normal kidney cells, and in most cases RA could not inhibit cell proliferation. To investigate the involvement of RARB in RA-dependent growth control, we stably transfected RAR beta expression vectors into two of the renal cancer cell lines. RAR beta-expressing clones' derived from SK-RC-35 showed a markedly reduced proliferation in the presence of RA, whereas the growth of parental cells was not affected. Transfectants derived from SK-RC-48, also showed inhibition of growth when exposed to RA. However, these transfectants responded only to high doses of RA. Taken together, our data support the possibility that RAR beta is implicated in the development of renal cell carcinomas.