Absence of association with cancer risk and low frequency of alterations at a p53 responsive PIG3 gene polymorphism in breast and lung carcinomas

PIG3 plays an oncogenic role in papillary thyroid cancer by activating the PI3K/AKT/PTEN pathway

The p53-inducible gene 3 (PIG3 or TP53I3) is a downstream gene of p53, which can be involved in the process of apoptosis induced by p53 via the production of reactive oxygen species (ROS). However, the functional significance of PIG3 in cancer remains to be determined. This aim of this study was to examine the mRNA and protein expression of PIG3 in papillary thyroid carcinoma (PTC) and normal thyroid tissues, assess the relationship between PIG3 expression and clinicopathological parameters in PTC and examine its role in the proliferation of PTC cell lines. The results showed that PIG3 was aberrantly overexpressed in the majority of specimens of PTC while the expression of p53 was lower in PTC compared with normal thyroid tissues. Anti-PIG3 immuno-reactivity positively correlated with TNM grade. In the PTC cell lines, PIG3 silencing using small interfering RNA (siRNAs) impaired their ability of proliferation and decreased the activity of the PI3K/AKT/PTEN pathway. The results suggested that PIG3 plays an oncogenic role in PTC via the regulation of the PI3K/AKT/PTEN pathway and support the exploration of PIG3 as a novel biomarker for patients with PTC.

Identification of prohibitin and prohibiton as novel factors binding to the p53 induced gene 3 (PIG3) promoter (TGYCC)(15) motif

The promoter of p53 induced gene 3 (PIG3) contains a variable number of tandem repeats (VNTRs) of pentanucleotides (TGYCC)n that is known as a p53 binding site. In this study, we investigated whether other potential molecules could bind to this PIG3 promoter (TGYCC)n motif. Ligand-chromatography combined with liquid chromatography-tandem mass spectrometry analyses indicated direct interactions of prohibitin and/or prohibiton with the (TGYCC)15 motif, which was confirmed by electrophoretic mobility shift assay and super-gel shift analysis with anti-prohibitin and anti-prohibiton antibodies. Using the chromatin immunopercipipation assay, we further demonstrated that prohibitin and prohibiton associated with the (TGYCC)15 motif in vivo regardless of the p53 status and apoptotic stress. We also found that prohibitin and prohibiton up-regulated PIG3 transcription independent of p53, although p53 obviously enhanced this process, and that the knock-down of prohibitin and prohibiton inhibited camptothecin-induced apoptosis. Taken together, our findings suggest that prohibitin and prohibiton contribute to PIG3-mediated apoptosis by binding to the PIG3 promoter (TGYCC)15 motif.

Functional repeats (TGYCC)n in the p53-inducible gene 3 (PIG3) promoter and susceptibility to squamous cell carcinoma of the head and neck

A polymorphic pentanucleotide microsatellite sequence (TGYCC)n within the p53-inducible gene 3 (PIG3) promoter is correlated with the extent of transcriptional activation by p53 and thought to modulate susceptibility to cancer. Using a PCR-silver staining-based single-strand conformation assay, we visualized variant genotypes of the PIG3 promoter (TGYCC)n motif in a subset of 100 subjects for each of four ethnic groups: non-Hispanic whites, African Americans, Hispanic Americans and Native Chinese. We found that PIG3 (TGYCC)15 was the most common allele but less frequent in non-Hispanic whites (0.660) than in Chinese (0.785) (P = 0.016). In an additional study of 616 patients with squamous cell carcinoma of the head and neck (SCCHN) and 623 cancer-free controls in a non-Hispanic white population, we found that compared with those who were PIG3 (TGYCC)15 homozygotes, subjects without the PIG3 (TGYCC)15 allele had a significantly increased SCCHN risk [adjusted odds ratio (OR) = 1.34; 95% CI = 1.04-1.73 for heterozygotes and OR = 1.69; 95% CI = 1.18-2.44 for variant homozygotes] in an allele-dose response manner (P = 0.002). Consistently, subsequent luciferase reporter assay revealed that the wild-type (TGYCC)15 allele had the highest p53-mediated transcriptional activity, compared with the other (TGYCC)n motifs. Our data suggest that the PIG3 variant polymorphic repeats alleles other than (TGYCC)15 may affect p53 binding and thus may be a marker for susceptibility to SCCHN, but our findings need to be validated in larger studies.

PIG3: a novel link between oxidative stress and DNA damage response in cancer

Reactive oxygen species (ROS), the most prominent free radicals produced in cells, can have both beneficial and detrimental effects on them. Many genes are known to be involved in ROS regulation. P53 inducible gene 3 (PIG3 or TP53I3) was identified in an analysis of genes induced by p53 before the onset of apoptosis. It is a widely conserved gene between many species. Until now it has been shown to exert two disparate cellular roles. The first is that of ROS producer linked to p53 induced apoptosis. In this context, it exhibits a NADPH dependent reductase activity with orthoquinones. The second is that of a component of the DNA damage response pathway. While it is considered as a p53 dependent pro-apoptotic gene, it is rarely affected in cancer. This data does not support an anti-tumor activity. In the present review we present and discuss aspects on the regulation and function of this factor and how it is implicated in cancer. We conclude by proposing that PIG3 may possibly have a role in cancer cell survival.

p53 polymorphisms: cancer implications

The normal functioning of p53 is a potent barrier to cancer. Tumour-associated mutations in TP53, typically single nucleotide substitutions in the coding sequence, are a hallmark of most human cancers and cause dramatic defects in p53 function. By contrast, only a small fraction, if any, of the >200 naturally occurring sequence variations (single nucleotide polymorphisms, SNPs) of TP53 in human populations are expected to cause measurable perturbation of p53 function. Polymorphisms in the TP53 locus that might have cancer-related phenotypical manifestations are the subject of this Review. Polymorphic variants of other genes in the p53 pathway, such as MDM2, which might have biological consequences either individually or in combination with p53 variants are also discussed.

A novel variable number of tandem repeats (VNTR) polymorphism containing Sp1 binding elements in the promoter of XRCC5 is a risk factor for human bladder cancer

X-ray repair cross-complementing 5 (XRCC5) is a gene involved in repair of DNA double-strand breaks. Abnormal expression of the XRCC5 protein is associated with genomic instability and an increased incidence of cancers. In our study, a polymorphism with a variable number of tandem repeats (21-bp repeat elements at position -201 to -160 relative to the initiation of transcription) in the promoter of XRCC5 was identified. As determined with gel-shift and super-shift assays, the binding affinity of the transcription factor Sp1 to the allele with two 21-bp repeats was greater than that for the allele with one 21-bp repeat. As established with a reporter assay, plasmids containing zero or one repeat element had higher transcriptional activities than plasmids containing two repeat elements. Furthermore, fewer tandem repeats in the promoter of XRCC5 was associated with enhanced levels of the XRCC5 protein in bladder cancer patients. Although, in a case-control study, the different genotypes were not associated with the risk of bladder cancer, individuals not carrying the two tandem repeats allele had an increased risk of bladder cancer compared with those carrying the allele with two repeats. These results indicated that, at least in a population in southeastern China, this polymorphism in the promoter of XRCC5 could regulate the expression of XRCC5 and thereby contribute to susceptibility to bladder cancer.

Association of the PIG3 promoter polymorphism with invasive bladder cancer in a Japanese population

PIG3 (p53-induced gene 3) is one of the targets of TP53 and is involved in apoptosis. The promoter of PIG3 contains a variable number of tandem repeats (VNTRs) of pentanucleotides (TGYCC)n (Y = C or T) and the number of VNTRs was reported to be correlated with the activation by TP53. In this study, the clinical significance of the PIG3 promoter VNTRs was analyzed in the bladder cancer patients using the genome DNAs from 338 controls and 273 bladder cancer patients. There was no significant difference in the allele frequency of the PIG3 promoter VNTRs between them. However, the presence of 14 or less repeats allele was associated with higher cancer grade (P = 0.038) and higher stage in relative risk (adjusted odds ratio = 2.31, 95% confidence interval = 1.05-5.90). These data suggested that the PIG3 promoter VNTRs was associated with generation of invasive bladder cancer.