Human hepatocyte nuclear factor 4 isoforms are encoded by distinct and differentially expressed genes

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Hepatocyte nuclear factor 4 (HNF4) is a crucial transcription factor identified in rat liver nuclear extracts.
• HNF4 is an orphan member of the nuclear receptor superfamily, essential for early embryonic development.
• HNF4 binding sites are found in numerous tissue-specific genes.

Purpose of the Study:

• To isolate and characterize human HNF4 splice variants and subtypes.
• To determine the chromosomal locations of genes encoding HNF4 alpha and HNF4 gamma.
• To investigate the transcriptional activity and expression patterns of novel HNF4 proteins.

Main Methods:

• cDNA cloning of human HNF4 alpha 2, HNF4 alpha 4, and HNF4 gamma.
• Chromosomal mapping of HNF4 alpha and HNF4 gamma genes.
• Northern blot analysis for HNF4 expression.
• Cotransfection experiments in C2 and HeLa cells to assess transactivation potential.

Main Results:

• Isolation of cDNAs for human HNF4 alpha 4 (a novel splice variant) and HNF4 gamma (a novel subtype).
• HNF4 alpha and HNF4 gamma genes are located on human chromosomes 20 and 8, respectively.
• HNF4 gamma is expressed in kidney, pancreas, small intestine, testis, and colon, but not liver; HNF4 alpha is expressed in all tested tissues.
• HNF4 gamma exhibits significantly lower activity than HNF4 alpha 2; HNF4 alpha 4 has no detectable transactivation potential.

Conclusions:

• Novel human HNF4 variants (HNF4 gamma and HNF4 alpha 4) have been identified.
• Distinct expression patterns and varying transcriptional activities of HNF4 proteins suggest specialized roles.
• Differential expression of HNF4 isoforms likely contributes to the regulation of HNF4-dependent genes in a tissue-specific manner.