Zebrafish abcb4 gene (ortholog to human ABCB1 gene) serves primarily in multidrug resistance (MDR) mechanism by effluxing chemotherapeutic agents, chemicals, xenobiotics, and numerous anti-cancer drugs out of the cells. This study aims to identify the specific transcription factor binding sites (TFBS) within the promoter region of zebrafish abcb4 gene and determine the functional roles of these factors in abcb4 gene expression regulation via mutagenesis analysis. First, primers were designed to target and amplify the promoter region of zebrafish abcb4 gene through gradient PCR. The zebrafish abcb4 gene promoter was then cloned into pGL3.0 vector and sent for sequencing. The sequencing results revealed high similarity to zebrafish DNA sequence from clone DKEY-24I24 in linkage group 16, indicating a successful cloning of targeted gene. Thereafter, consensus sequence of zebrafish abcb4 gene promoter was generated with the length of 1,392 bp which was close to its expected size during primer design (1,500 bp). Using MATCH tool, 155 TFBSs were found within zebrafish abcb4 gene promoter region. Activator protein 1 (AP-1) TFBS at 1,255 bp was chosen to be mutated through site-directed mutagenesis. Mutagenic primers (forward primer: 5’ GGG CAA GGC AGT ATA AAC GTG 3’ and reverse primer: 5’ TTA TGT TTC TAG GGA TTA CGT CAC 3’) were designed to substitute AGT with GGG to remove the AP-1 TFBS. By mutating the zebrafish abcb4 gene promoter, the MDR phenomenon driven by zebrafish abcb4 gene can be elucidated and this might provide clues to the development of tumor and malignancy in human. The results from this study may enrich the knowledge in chemotherapy and cancer treatments.
Breast cancer is the commonest cancer among women worldwide and the probability of a woman dying from breast cancer is high (about 1 in 38 of total human population (2.6%)).The main factor for mortality is due to the resistance of this particular disease to chemotherapeutic agents. One of the most well-known proteins to be found to correlate significantly with breast cancer resistance to chemotherapeutic agent is the ATP-binding cassette super-family G member 2 (ABCG2). Knowledge on ABCG2 gene regulation is still lacking in terms of how the increased cytotoxic levels are closely related to induce a hype in gene transcript levels and ultimately cause of the reduction in chemotherapeutic agents. The approach taken in this study is through mutational analysis of selected transcription factor governing the expression of ABCG2. In order to achieve this, a previously cloned ABCG2 promoter which has been isolated (around 1500 bp in size) from Danio rerio and inserted into pGL3.0 plasmid, was subjected to site-directed mutagenesis. Selected transcription factor which is AP-1 was successfully mutated by deletion of 5'- TGACGCG -3' sequence at position 1113 bp from TSS+1 where it would bind in order to define their role in ABCG2 physiological function. Sequencing result after site-directed mutagenesis shows high similarities about 98% with ABCG2 gene of Danio rerio. Upon validation, it was found that the intended AP-1 binding site has been mutated. In future work, the mutated clone here will be subjected to transfection analysis where dual-luciferase assay will be conducted to verify the loss of activity from the ABCG2 promoter upon mutation of the targeted AP-1 site. Hence, the mutagenesis analysis of ABCG2 promoter are able to provide information on the involvement of AP-1 transcription factor in multidrug resistance mechanism of breast cancer and thus will be a potential target for chemotherapeutic agent.