Analysis Of Transcription Factor Promoter Binding In Rat Hepatoma/Fibroblast Hybrids

Abstract

When hepatomas (liver cancer cells) are fused with fibroblasts (undifferentiated body cells), there is complete extinguishing of all tissue-specific gene expression. Once it was discovered that many hybrid cell lines do not express needed transcription factors for liver-specific gene transcription, the factors were reintroduced and forced to express through the use of plasmids. Even if the two primary transcription factors were present in the system, downstream tissue-specific gene expression was not rescued. To examine potential mechanisms for the repression of liver-specific gene expression in hepatoma x fibroblast hybrid cells, chromatin immunoprecipitation (ChlP) was used. This procedure allows the liver-specific gene promoters to be analyzed for the binding of transcription factors in vivo.

When analyzed, it was found that some hepatoma x fibroblast hybrids, previously assigned the cell line designations FR2 and FTRl 6, actually produced the liver-specific transcription factor Hepatocyte Nuclear Factor I-alpha (HNFla.) which bind the promoter of some liver-specific genes but not others. On the contrary, the transcription factor HNF 4a. was never found to bind the promoter of liver-specific genes in hybrid cell lines. This data suggests that an intricate and variable repression system may dictate HNFla. binding while HNF4a binding may be controlled through a less complex, more uniform mechanism. Overall, the data supported the theory that the cessation of liverspecific gene expression in hepatoma x fibroblast hybrids is controlled at the level of transcription, although the discovery of liver-specific transcription factors present in the FR hybrid cell line challenges the notion that this is a universal and total effect.

Date of Award	2009
Original language	American English
Awarding Institution	Eastern Illinois University
Supervisor	Gary A. Bulla (Supervisor)