Liver-Enriched Transcription Factors Uncoupled from Expression of Hepatic Functions in Hepatoma Cell Lines

Abstract

Among the liver-enriched transcription factors identified to date, only expression of hepatocyte nuclear factor 4 (HNF4) and hepatocyte nuclear factor 1 (HNF1) is in strict correlation with hepatic differentiation in cultured rat hepatoma cells. Indeed, differentiated hepatoma cells that stably express an extensive set of adult hepatic functions express liver-enriched transcription factors, while dedifferentiated cells that have lost expression of all these hepatic functions no longer express HNF4 and HNF1. We describe a new heritable phenotype, designated as uncoupled, in which there is a spontaneous dissociation between the expression of these transcription factors and that of the hepatic functions. Cells presenting this phenotype, isolated from differentiated hepatoma cells, cease to accumulate all transcripts coding for hepatic functions but nevertheless maintain expression of HNF4 and HNF1. Transitory transfection experiments indicate that these two factors present in these cells have transcriptional activity similar to that of differentiated hepatoma cells. Characterization of the appropriate intertypic cell hybrids demonstrates that this new phenotype is recessive to the dedifferentiated state and fails to be complemented by differentiated cells. These results indicate the existence of mechanisms that inhibit transcription of genes coding for hepatocyte functions in spite of the presence of functional HNF4 and HNF1. Cells of the uncoupled phenotype present certain properties of oval cells described for pathological states of the liver.Genetic analysis of hepatoma-derived cell lines revealed, many years ago, that expression of differentiated functions is regulated in trans by mechanisms whose final effects are negative (extinction) or positive (activation) (78). More recent studies of these hepatoma lines further showed that maintenance of the hepatic phenotype is an active process operating at the level of transcription (21,42). By analysis of DNA sequences implicated in liver-specific transcription, the identification and cloning of members of four major families of liverenriched transcription factors (LETF) have been achieved. These families, each characterized by structurally related DNA binding domains, include the hepatocyte nuclear factor families HNF1, HNF3, and HNF4 and the CCAAT enhancer binding protein (C/EBP) family (13,82). Determination of the tissue distribution of these factors and analysis of their hierarchical relations led to the hypothesis that the combinatorial action of LETF together with the ubiquitous transcriptional machinery of the cell is necessary and maybe even sufficient for the maintenance of liver-specific gene transcription (30, 81). Indeed, the H4IIEC3 differentiated rat hepatoma cells and their derivatives that stably express an extensive set of adult hepatic functions express all the LETF identified to date, while in the rare dedifferentiated rat hepatoma cells that have lost expression of all these hepatic functions, HNF4 and HNF1 are systematically absent. In addition,...

Dissociation of the Hepatic Phenotype from HNF4 and HNF1α Expression

“…The M29 cells have a phenotype similar to cells reported by Chaya et al [58], in which a hepatoma derived cell line showed that liver gene expression appeared to be uncoupled from expression of HNF4 and HNF1a. Specifically, liver gene expression ceased despite the presence of HNF4 and HNF1a.…”

“…The third class of cells described by Weiss et al were chromosomally reduced hepatoma x fibroblast hybrid cells in which the liver phenotype could be completely rescued with the introduction of either HNF4 or HNF1a [58]. This in contrast to karyotypically complete cell hybrids, which are refractory to activation by the introduction of transacting factors with the exception that HNF4 rescued HNF1a expression (but not downstream HNF1a-responsive genes) [8].…”

“…The H5 cells were similar to cells derived in our laboratory (H11 and M38 cells) using a selection strategy in which introduction of these transacting factors rescued several liver-specific genes [29]. In contrast, the C5 cells were refractory to activation by either HNF4 or HNF1a [58]. Neither endogenous HNF4 nor HNF1a were rescued by the other in the C5 cells.…”

Dexamethasone protects primary cultured hepatocytes from death receptor-mediated apoptosis by upregulation of cFLIP

“…25 However, DEX can inhibit apoptosis in some cells such as neutrophils and tumors. 6,12,26 The antiapoptotic effect by DEX has been shown to be due to the upregulation of the Bcl-2 family proteins such as Bcl-2 and Bcl-xL in hepatocytes. 8 These protein levels have been shown to be upregulated in hepatocytes only after long-term treatment with DEX Figure 6 Pretreatment with DEX protects hepatocytes from Jo2-induced apoptosis by inhibiting DISC formation and caspase-8 activation.…”

The HNF-4/HNF-1α transactivation cascade regulates gene activity and chromatin structure of the human serine protease inhibitor gene cluster at 14q32.1

“…For example, HNF-4 (28) is a major activator of the gene encoding HNF-1␣ (29,30), a member of the HNF-1 family (31-33), and HNF-1␣ itself activates expression of more than 20 liver genes, including ␣1-antitrypsin (␣1AT, gene symbol PI) (34,35). The expression patterns of HNF-1␣ and HNF-4 closely correlate with the differentiated state of cultured hepatic cells, and studies using dedifferentiated hepatoma variants, transactivator-deficient hepatoma variants, and somatic cell hybrids have suggested that the HNF-4͞HNF-1␣ activation pathway is involved in both the determination and maintenance of hepatic phenotype (30,(35)(36)(37)(38)(39)(40).…”