The MDM2 inducible promoter folds into four-tetrad antiparallel G-quadruplexes targetable to fight malignant liposarcoma

Abstract

Well-differentiated liposarcoma (WDLPS) is a malignant neoplasia hard to diagnose and treat. Its main molecular signature is amplification of the MDM2-containing genomic region. The MDM2 oncogene is the master regulator of p53: its overexpression enhances p53 degradation and inhibits apoptosis, leading to the tumoral phenotype. Here, we show that the MDM2 inducible promoter G-rich region folds into stable G-quadruplexes both in vitro and in vivo and it is specifically recognized by cellular helicases. Cell treatment with G-quadruplex-ligands reduces MDM2 expression and p53 degradation, thus stimulating cancer cell cycle arrest and apoptosis. Structural characterization of the MDM2 G-quadruplex revealed an extraordinarily stable, unique four-tetrad antiparallel dynamic conformation, amenable to selective targeting. These data indicate the feasibility of an out-of-the-box G-quadruplex-targeting approach to defeat WDLPS and all tumours where restoration of wild-type p53 is sought. They also point to G-quadruplex-dependent genomic instability as possible cause of MDM2 expansion and WDLPS tumorigenesis.

Promoter G-quadruplexes and transcription factors cooperate to shape the cell type-specific transcriptome

“…Stacked planar quartets stabilized by Hoogsteen hydrogen bonds connecting Gs of adjacent G-tracts form the G4 core 1 . Computational analysis of regular G4 sequence pattern predicted the abundance of putative G4s (pG4s) in genomic regulatory regions, such as oncogene promoters, splice and recombination sites, and telomeric ends [2][3][4][5][6] . Experimental analysis has in particular investigated and reported the implication of DNA G4s in the regulation of transcription: G4s were initially shown to represent physical obstacles to RNA polymerase processivity in vitro [7][8][9][10][11][12][13] ; vice versa in the cellular environment using selective antibodies [14][15][16][17][18] , chemical probing [19][20][21][22] , and ligands [23][24][25][26][27][28] , G4s were mapped and correlated to high gene expression 19,29 .…”

Evaluating the Influence of a G-Quadruplex Prone Sequence on the Transactivation Potential by Wild-Type and/or Mutant P53 Family Proteins through a Yeast-Based Functional Assay

“…Interestingly, G4s are often located in promoter sequences as shown for many human genes [69][70][71], including P53 targets; in fact, the presence of G4 prone sequences has been found around P53 RE in the promoter of the P53-induced apoptotic PUMA protein [34]. Therefore, the presence and the formation of a G4 structure could be an important transcriptional regulatory element, as previously observed in various organisms including humans [72][73][74].…”

Quadruplex Ligands in Cancer Therapy

“…In addition, another NDI derivative binds to G4s in MDM2 oncogene, which is a master regulator of TP53, reducing MDM2 transcription. Such an approach could be used to defeat all tumors in which the restoration of wild-type TP53 is sought [81]. Recently, our research group unveiled G4s in ribosomal DNA as new targets for NDIs [82].…”