Effects of depletion of CHRNA5 and/or TP53, and transient and stable overexpression of wildtype or mutant TP53 on expression of DLK1-MEG3 locus in MCF7 cells

Abstract

The expression of CHRNA5 has a prominent role in lung cancer and nicotine addiction. Besides, depletion of CHRNA5 has been identified as being tumour suppressive in breast cancer. Moreover, CHRNA5 depletion causes increases in CDKN1A expression, downregulates the 14q32.31 miRNAs and decreases DLK1 expression. This thesis examined the effects of CHRNA5 and/or TP53 downregulation, as well as TP53 overexpression, on the expression of the DLK1-DIO3 region. My findings demonstrated that CHRNA5 depletion decreased the expression of the protein-coding DLK1 and the non-protein coding MEG3 genes in this locus in the presence or absence of TP53. Since these two genes have a vital role in tumour suppression and tumorigenesis, this provided more evidence for the importance of CHRNA5 in the modulation of expression in this locus in breast cancer. Since there is a relation between CHRNA5 and TP53 induction, the expression of one of the main TP53 regulators, MDM2, was also studied. Accordingly, it was found that combining CHRNA5 depletion with TP53 depletion caused a significant decrease in expression in both the MDM2 and MDM2 sequestering elements, PDLIM7 and CDH18. Additionally, the effects of both wild-type and mutant TP53 expression levels on DLK1-MEG3 locus and CHRNA5 were investigated in stable MCF7 breast cancer cells that we have generated. I have found that even if CHRNA5 depletion induced p53 expression, TP53 overexpression did not have CHRNA5-inducing effects regardless of the functionality of TP53. However, wild-type TP53 overexpressing MCF7 cells behaved differently than mutant TP53 overexpressing cells in their DLK1 expression levels. Future research should clarify the effects of CHRNA5 depletion on DLK1-MEG3 region for a given TP53 mutation status.