The cationic porphyrin TMPyP4 destabilizes the tetraplex form of the fragile X syndrome expanded sequence d(CGG)n

Abstract

Fragile X syndrome, the most common cause of inherited mental retardation, is instigated by dynamic expansion of a d(CGG) trinucleotide repeat in the 5'-untranslated region of the first exon of the FMR1 gene, resulting in its silencing. The expanded d(CGG)(n) tract readily folds into hairpin and tetraplex structures which may contribute to the blocking of FMR1 transcription. In this work, we report that the cationic porphyrin 5,10,15,20-tetra(N-methyl-4-pyridyl)porphin (TMPyP4) effectively destabilizes in vitro the G'2 bimolecular tetraplex structure of d(CGG)(n) while it stabilizes the G'2 tetraplex form of the telomeric sequence d(TTAGGG)(2). Similarly to TMPyP4, the hnRNP-related protein CBF-A also destabilizes G'2 tetrahelical d(CGG)(n) while binding and stabilizing tetraplex telomeric DNA. We report that relative to each agent individually, successive incubation of G'2 d(CGG)(n) with TMPyP4 followed by exposure to CBF-A results in a nearly additive extent of disruption of this tetraplex form of the repeat sequence. Our observations open up the prospect of unfolding secondary structures of the expanded FMR1 d(CGG)(n) tract of fragile X cells by their exposure to low molecular size drugs or to proteins such as TMPyP4 or CBF-A.

Evidence for the Presence of a Guanine Quadruplex Forming Region within a Polypurine Tract of the Hypoxia Inducible Factor 1α Promoter

“…These data demonstrate that telomestatin can both induce and stabilize the HIF-1R G-quadruplex. TmPyP4 is a cationic porphyrin that has been shown to bind to the telomeric G-quadruplex and the human c-myc G-quadruplex, while TmPyP2 is a positional isomer of TmPyP4 that has a lower capacity for binding to G-quadruplexes (58,63,65,83). TmPyP2 (0.1-1.0 µM) had no effect on DNA polymerase arrest in the control template nor the HIF-1R template ( Figure 7C).…”

Formation and properties of hairpin and tetraplex structures of guanine-rich regulatory sequences of muscle-specific genes

“…The T m of G′2 integrin 26 remained virtually unaffected by TMPyP2 and TMPyP3 but was somewhat decreased by TMPyP4. In this context, G′2 integrin 26 was reminiscent of G′2 d(CGG) n , which was destabilized by TMPyP4 (59). The thermal stability of G′2 integrin 26/integrin 29 DNA was not altered by TMPyP3 but was to an extent augmented by TMPyP2 and TMPyP4.…”

Development of Therapeutics for C9ORF72 ALS/FTD-Related Disorders

“…RanGAP1 has been found to be preferentially bound by sense strand HRE with a G-quadruplex tertiary structure; thus, the cationic 5,10,15,20-tetra(N-methyl-4-pyridyl) porphyrin (TMPyP4), a porphyrin that disrupts this type of structure, was successfully applied, reducing RanGAP1 sequestration in RNA foci in vitro and ameliorating nucleocytoplasmic transport in Drosophila model [18]. TMPyP4 has already been shown to destabilize the G-quadruplex of both the DNA and the RNA (CGG)n repeats of the FMR1 gene, which is linked to human pathological conditions such as fragile X syndrome and fragile X-associated tremor ataxia [46]. TMPyP4 could be particularly important if a specific target of r(GGGGCC)n RNA is not found because it is also able to prevent the sequestration of other proteins, such as hnRNPA1 and ASF/SF2, by C9ORF72-HRE [47].…”