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Date of Award

Fall 2012

Degree Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Supervisor

Juliet M. Daniel

Language

English

Abstract

The POZ-ZF transcription factor ZBTB4 was initially identified due to its sequence homology to the dual-specificity DNA-binding transcription factor Kaiso. Subsequent characterization of ZBTB4 revealed that it is also a dual-specificity DNA-binding protein; it recognizes a specific oligonucleotide sequence CT/CGCCATC, coined the ZBTB4 Binding Sequence (Z4BS) as well as methylated CpG-dinucleotides. Interestingly, ZBTB4 also binds to the highly similar consensus Kaiso Binding Site (KBS) in vitro.

ZBTB4 is misexpressed in cancer, and follows a stage-specific pattern of expression in breast carcinoma tissues; low ZBTB4 levels are found in late stages while high ZBTB4 expression is detected in early stages of disease progression. Ongoing studies have begun to elucidate the molecular interactions that mediate ZBTB4’s apparent tumour suppressor role in tumourigenesis, however no study has investigated the nature of ZBTB4’s ability to interact with both the Z4BS and the KBS in vivo, and how this may expand ZBTB4’s repertoire of potential target genes.

Recently Kaiso has been characterized as a transcriptional repressor of the cell cycle regulatory gene cyclin D1, and thus we used cyclin D1 as a model to investigate the nature of ZBTB4’s interaction with the KBS in vivo. The cyclin D1 minimal promoter contains two partial Z4BS at the same location as the KBS sites and we found that ZBTB4 binds to the +69 Z4BS/KBS site, but not to the -1067 site. Because the +69 Z4BS/KBS is immediately flanked by a CpG dinucleotide, this interaction may be a methylation-dependent interaction. To determine the consequence of this interaction, we conducted minimal promoter luciferase assays, and observed that ZBTB4 mediates an activation of the -1748-CD1 minimal promoter activity.

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