Degree Name

Master of Science (MS)

Semester of Degree Completion

2015

Thesis Director

Gary A. Bulla

Abstract

Development in mammals requires a complex array of positive and negative regulatory signals and responses. The liver is a major organ that has been studied extensively to understand underlying genetic processes responsible for specification, establishment and maintenance of tissue identity. Hepatoma and hepatoma variant cell lines have been used as a model to understand genetic networks responsible for liver function. Whole genome analysis of these cell types has identified candidate genes that might serve as master regulators of liver identity. In this study, the role of two candidate genes - cellular repressor of E1A stimulated gene (CREG1) and paired-liked homeodomain-1 (PITX1) - on regulation of liver-specific gene expression has been determined utilizing transfection studies. Overexpression of CREG1 in a hepatoma variant cell line leads to modest activation of Hnf1, Hnf4 and Hnf3 as measured by qRT-PCR and strong activation of transcription factor Hnf6 and the downstream gene Serpina1 (a marker gene used to identify liver function). The finding suggests that CREG1 might act through HNF6 to regulate Serpina1 via the Locus Control Region (LCR). In contrast, Wnt4 and Pck1 genes were repressed by CREG1 overexpression. Overexpression of a second candidate gene, PITX1, in hepatoma cells resulted in reduced expression of some liver-enriched transcription factors (Hnf3 and Hnf6) as well as some downstream genes (Pck1 and Serpina1). This study suggests that loss of CREG1 expression, along with loss of other known liver-enriched factors, contributes to conversion of the hepatic phenotype to a de-differentiated non-hepatic phenotype. In addition, results suggest that PITX1 gene expression, activated in the hepatoma variants, may serve to actively repress liver function.

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