PIN3 duplication may be partially responsible for TP53 haploinsufficiency

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Cancer cells may silence wild-type TP53, degrade its mRNA, or overproduce mutated TP53 mRNA.
• Sequencing revealed discrepancies between TP53 DNA and cDNA, suggesting allele-specific expression differences.
• The polymorphism within intron 3 (PIN3) was hypothesized to cause unequal TP53 gene expression levels between alleles.

Purpose of the Study:

• To investigate if PIN3 polymorphic variants (A1 or A2) in heterozygotes are linked to higher TP53 expression.
• To determine if this differential expression contributes to TP53 haploinsufficiency.
• To explore the role of PIN3 in TP53 mRNA expression regulation.

Main Methods:

• Analysis of 250 tumor samples.
• Bacterial subcloning and sequencing to assess PIN3 variant involvement in TP53 mRNA expression.
• Dual luciferase reporter assays to quantify allelic expression.
• Bioinformatic analysis to identify DNA structural influences.

Main Results:

• Haplotype analysis indicated mutated TP53 templates predominated in cDNA sequencing for samples with heterozygous TP53 mutations and PIN3 heterozygosity.
• Of 30 samples with TP53 mutations and biased allelic expression, 6 were heterozygous for PIN3 (A1/A2), all with mutations in the longer allele (A2) (p = 0.04).
• Reporter assays showed significantly higher luciferase activity for the A2 construct compared to A1 (A2/A1 ratio 1.16-1.59, p < 0.019).
• Bioinformatic analysis revealed PIN3 duplication stabilizes G-quadruplexes.

Conclusions:

• TP53 alleles are not equivalent in regulating TP53 mRNA expression.
• In PIN3-heterozygous individuals, a single TP53 mutation in the longer allele may be sufficient to impair function.
• Secondary DNA structures like quadruplexes may contribute to PIN3-dependent TP53 haploinsufficiency.