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Mol. Cell. Biol., Mar 1996, 925-931, Vol 16, No. 3
T Drewes, S Senkel, B Holewa and GU Ryffel
Hepatocyte nuclear factor 4 (HNF4) was first identified as a DNA binding
activity in rat liver nuclear extracts. Protein purification had then led
to the cDNA cloning of rat HNF4, which was found to be an orphan member of
the nuclear receptor superfamily. Binding sites for this factor were
identified in many tissue-specifically expressed genes, and the protein was
found to be essential for early embryonic development in the mouse. We have
now isolated cDNAs encoding the human homolog of the rat and mouse HNF4
splice variant HNF4 alpha 2, as well as a previously unknown splice variant
of this protein, which we called HNF alpha 4. More importantly, we also
cloned a novel HNF4 subtype (HNF4 gamma) derived from a different gene and
showed that the genes encoding HNF 4 alpha and HNF4 gamma are located on
human chromosomes 20 and 8, respectively. Northern (RNA) blot analysis
revealed that HNF4 GAMMA is expressed in the kidney, pancreas, small
intestine, testis, and colon but not in the liver, while HNF4 alpha RNA was
found in all of these tissues. By cotransfection experiments in C2 and HeLa
cells, we showed that HNF4 gamma is significantly less active than HNF4
alpha 2 and that the novel HNF4 alpha splice variant HNF4 alpha 4 has no
detectable transactivation potential. Therefore, the differential
expression of distinct HNF4 proteins may play a key role in the
differential transcriptional regulation of HNF4-dependent genes.
Copyright © 1996, American Society for Microbiology
Human hepatocyte nuclear factor 4 isoforms are encoded by distinct and differentially expressed genes
Institut fur Zelbiologie, Universitatsklinikum Essen, Germany.
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