2011 Theses Doctoral

Negative regulation of gene expression by the tumor suppressor p53

Barsotti, Anthony M.

The tumor suppressor p53 inhibits the expression of a substantial number of genes whose protein products serve to promote cell survival or cell cycle progression, thereby ensuring efficient execution of p53-dependent apoptosis, cell-cycle arrest or senescence. Furthermore, p53-mediated repression has also been shown to participate in pathways that regulate diverse cellular processes, including angiogenesis, maintenance of pluripotency, and metabolic flux. p53 inhibits gene expression by both direct and indirect means. Briefly, p53 can block transcription through direct DNA binding, association with transcription factors, and through the induction of genes whose functional products facilitate downstream repression. Indirect regulation of gene repression by p53 often involves induction of intermediary factors that fall into several categories: proteins (e.g. p21), microRNAs (e.g. miR-34a), and lincRNAs (lincRNA-p21).

This dissertation discusses multiple aspects of p53-dependent gene repression and presents novel targets of p53-mediated regulation. Specifically, we have found that p53 down-regulates the transcription of the oncogenic transcription factor FoxM1. Mechanistically, this repression is largely dependent upon the p53-inducible gene p21, and consequently involves the Rb-family of tumor suppressors. Functionally, p53-dependent repression of FoxM1 contributes to the maintenance of a stable G2 cell cycle arrest in response to DNA-damage. In addition, we have identified PVT1 as a novel target of p53-transactivation. PVT1 encodes both spliced non-coding RNAs (ncRNA), as well as a series of microRNAs (miR-1204, miR-1205, miR-1206, miR-1207-5p, miR-1207-3p and miR-1208). p53 upregulates PVT1 ncRNA, primary microRNAs, and mature miR-1204. Ectopic expression of miR-1204 induces changes in cell fate that are consistent with the role of p53 (cell death, cell cycle arrest), thus miR-1204 is likely to represent a functional target of p53 at the PVT1 locus.