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Expression of full-length p53 and its isoform Deltap53 in breast carcinomas in relation to mutation status and clinical parameters.

Baumbusch LO, Myhre S, Langerød A, Bergamaschi A, Geisler SB, Lønning PE, Deppert W, Dornreiter I, Børresen-Dale AL - Mol. Cancer (2006)

Bottom Line: Patients expressing mutated full-length p53 and non-mutated (wild-type) Deltap53, "mutational hybrids", showed a slightly higher frequency of patients with distant metastasis at time of diagnosis compared to other patients with p53 mutations, but otherwise did not differ significantly in any other clinical parameter.Expression of p53 is accompanied by the functionally different isoform Deltap53 at the mRNA level in cell lines and human breast tumors.Investigations of "mutational hybrid" patients highlighted that wild-type Deltap53 does not compensates for mutated p53, but rather may be associated with a worse prognosis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics, Institute for Cancer Research, Rikshospitalet-Radiumhospitalet Medical Center, 0310 Oslo, Norway. lars.baumbusch@medisin.uio.no

ABSTRACT

Background: The tumor suppressor gene p53 (TP53) controls numerous signaling pathways and is frequently mutated in human cancers. Novel p53 isoforms suggest alternative splicing as a regulatory feature of p53 activity.

Results: In this study we have analyzed mRNA expression of both wild-type and mutated p53 and its respective Deltap53 isoform in 88 tumor samples from breast cancer in relation to clinical parameters and molecular subgroups. Three-dimensional structure differences for the novel internally deleted p53 isoform Deltap53 have been predicted. We confirmed the expression of Deltap53 mRNA in tumors using quantitative real-time PCR technique. The mRNA expression levels of the two isoforms were strongly correlated in both wild-type and p53-mutated tumors, with the level of the Deltap53 isoform being approximately 1/3 of that of the full-length p53 mRNA. Patients expressing mutated full-length p53 and non-mutated (wild-type) Deltap53, "mutational hybrids", showed a slightly higher frequency of patients with distant metastasis at time of diagnosis compared to other patients with p53 mutations, but otherwise did not differ significantly in any other clinical parameter. Interestingly, the p53 wild-type tumors showed a wide range of mRNA expression of both p53 isoforms. Tumors with mRNA expression levels in the upper or lower quartile were significantly associated with grade and molecular subtypes. In tumors with missense or in frame mutations the mRNA expression levels of both isoforms were significantly elevated, and in tumors with nonsense, frame shift or splice mutations the mRNA levels were significantly reduced compared to those expressing wild-type p53.

Conclusion: Expression of p53 is accompanied by the functionally different isoform Deltap53 at the mRNA level in cell lines and human breast tumors. Investigations of "mutational hybrid" patients highlighted that wild-type Deltap53 does not compensates for mutated p53, but rather may be associated with a worse prognosis. In tumors, both isoforms show strong correlations in different mutation-dependent mRNA expression patterns.

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Kaplan-Meier plot of survival rates for patientswith mutated and unmutated full-length p53 and Δp53. Cumulative breast cancer survival for a subset of patients (50) is shown for three groups of patients, depending on their mutational status of p53 versus Δp53: patients with wild-type Δp53 and wild-type p53 (Wt Δp53 – Wt p53; n = 24), "mutational hybrid" patients with non-mutated (wild-type) Δp53 and mutated full-length p53 (Wt Δp53 - M p53; n = 7), and patients with mutations in Δp53 and p53 (M Δp53 – M p53; n = 19); the significance is p = 0.0498.
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Figure 3: Kaplan-Meier plot of survival rates for patientswith mutated and unmutated full-length p53 and Δp53. Cumulative breast cancer survival for a subset of patients (50) is shown for three groups of patients, depending on their mutational status of p53 versus Δp53: patients with wild-type Δp53 and wild-type p53 (Wt Δp53 – Wt p53; n = 24), "mutational hybrid" patients with non-mutated (wild-type) Δp53 and mutated full-length p53 (Wt Δp53 - M p53; n = 7), and patients with mutations in Δp53 and p53 (M Δp53 – M p53; n = 19); the significance is p = 0.0498.

Mentions: We analyzed the existence and expression of the Δp53 isoform in breast tumors from patients with advanced disease at the mRNA level and asked whether mutations present in both isoforms had different effects on clinical and molecular parameters compared to mutations found only in the full-length form. These patients have previously been analyzed by whole genome expression microarrays and grouped according to their expression profile ([40-43] for cohorts A, B and D, and unpublished results for cohort C). Gel electrophoresis followed by qRT-PCR confirmed that Δp53 together with full-length p53 was present in all tumor samples. Patients with tumors harbouring mutations residing inside the spliced out region of the Δp53 isoform represented the rare mutational genotype of mutated full-length p53 and wild-type Δp53 and were termed "mutational hybrids" (Wild type Δp53/Mutant p53 = WtM). These patients where grouped (11 patients) and compared to patients with mutations before and after the spliced region affecting both isoforms (27 patients), and to patients without mutations (50 patients). Of the 27 tumors with mutations affecting both isoforms 14 were missense mutations, two were in frame mutations, one a nonsense mutation, four were splice mutations, and six had frame shift mutations. (For a full description of the various mutations see Additional file 2). Based on the mutation type the p53/Δp53 double mutant group (MM) was further subdivided into the MI group with missense and in frame mutations, and the MII group with nonsense, frame shift and splice mutations (Table 1). Kruskal Wallis rank tests were performed for differences in clinical and molecular parameters in three (WtWt-WtM-MM) or four classes (WtWt-WtM-MIMI-MIIMII) and the Mann-Whitney test was used to test for independent association between subgroups. A slightly higher frequency of patients with distant metastasis at time of diagnosis was observed in the WtM group compared to the MIMI group (p < 0.07). No other significant differences were observed for the "mutational hybrid" group weighted against the other groups. We analyzed whether the "mutational hybrid" genotype had an effect on patient survival time in a subset of patients from two prospective studies [44,45] of comparable treatment and uniformity. In the Kaplan-Meier plot (Figure 3) survival data for a total of 50 patients without distant metastases at time of diagnosis are shown. The survival rates in patients with the "mutational hybrid" genotype (Wt Δp53 – M p53) was similar to the survival rate in patients with mutations in both p53 and Δp53 (M Δp53 – M p53), and the survival rates in these two groups were significantly different compared to patients with wild-type Δp53 and p53 (Wt Δp53 – Wt p53) (p < 0.05).


Expression of full-length p53 and its isoform Deltap53 in breast carcinomas in relation to mutation status and clinical parameters.

Baumbusch LO, Myhre S, Langerød A, Bergamaschi A, Geisler SB, Lønning PE, Deppert W, Dornreiter I, Børresen-Dale AL - Mol. Cancer (2006)

Kaplan-Meier plot of survival rates for patientswith mutated and unmutated full-length p53 and Δp53. Cumulative breast cancer survival for a subset of patients (50) is shown for three groups of patients, depending on their mutational status of p53 versus Δp53: patients with wild-type Δp53 and wild-type p53 (Wt Δp53 – Wt p53; n = 24), "mutational hybrid" patients with non-mutated (wild-type) Δp53 and mutated full-length p53 (Wt Δp53 - M p53; n = 7), and patients with mutations in Δp53 and p53 (M Δp53 – M p53; n = 19); the significance is p = 0.0498.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1636663&req=5

Figure 3: Kaplan-Meier plot of survival rates for patientswith mutated and unmutated full-length p53 and Δp53. Cumulative breast cancer survival for a subset of patients (50) is shown for three groups of patients, depending on their mutational status of p53 versus Δp53: patients with wild-type Δp53 and wild-type p53 (Wt Δp53 – Wt p53; n = 24), "mutational hybrid" patients with non-mutated (wild-type) Δp53 and mutated full-length p53 (Wt Δp53 - M p53; n = 7), and patients with mutations in Δp53 and p53 (M Δp53 – M p53; n = 19); the significance is p = 0.0498.
Mentions: We analyzed the existence and expression of the Δp53 isoform in breast tumors from patients with advanced disease at the mRNA level and asked whether mutations present in both isoforms had different effects on clinical and molecular parameters compared to mutations found only in the full-length form. These patients have previously been analyzed by whole genome expression microarrays and grouped according to their expression profile ([40-43] for cohorts A, B and D, and unpublished results for cohort C). Gel electrophoresis followed by qRT-PCR confirmed that Δp53 together with full-length p53 was present in all tumor samples. Patients with tumors harbouring mutations residing inside the spliced out region of the Δp53 isoform represented the rare mutational genotype of mutated full-length p53 and wild-type Δp53 and were termed "mutational hybrids" (Wild type Δp53/Mutant p53 = WtM). These patients where grouped (11 patients) and compared to patients with mutations before and after the spliced region affecting both isoforms (27 patients), and to patients without mutations (50 patients). Of the 27 tumors with mutations affecting both isoforms 14 were missense mutations, two were in frame mutations, one a nonsense mutation, four were splice mutations, and six had frame shift mutations. (For a full description of the various mutations see Additional file 2). Based on the mutation type the p53/Δp53 double mutant group (MM) was further subdivided into the MI group with missense and in frame mutations, and the MII group with nonsense, frame shift and splice mutations (Table 1). Kruskal Wallis rank tests were performed for differences in clinical and molecular parameters in three (WtWt-WtM-MM) or four classes (WtWt-WtM-MIMI-MIIMII) and the Mann-Whitney test was used to test for independent association between subgroups. A slightly higher frequency of patients with distant metastasis at time of diagnosis was observed in the WtM group compared to the MIMI group (p < 0.07). No other significant differences were observed for the "mutational hybrid" group weighted against the other groups. We analyzed whether the "mutational hybrid" genotype had an effect on patient survival time in a subset of patients from two prospective studies [44,45] of comparable treatment and uniformity. In the Kaplan-Meier plot (Figure 3) survival data for a total of 50 patients without distant metastases at time of diagnosis are shown. The survival rates in patients with the "mutational hybrid" genotype (Wt Δp53 – M p53) was similar to the survival rate in patients with mutations in both p53 and Δp53 (M Δp53 – M p53), and the survival rates in these two groups were significantly different compared to patients with wild-type Δp53 and p53 (Wt Δp53 – Wt p53) (p < 0.05).

Bottom Line: Patients expressing mutated full-length p53 and non-mutated (wild-type) Deltap53, "mutational hybrids", showed a slightly higher frequency of patients with distant metastasis at time of diagnosis compared to other patients with p53 mutations, but otherwise did not differ significantly in any other clinical parameter.Expression of p53 is accompanied by the functionally different isoform Deltap53 at the mRNA level in cell lines and human breast tumors.Investigations of "mutational hybrid" patients highlighted that wild-type Deltap53 does not compensates for mutated p53, but rather may be associated with a worse prognosis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics, Institute for Cancer Research, Rikshospitalet-Radiumhospitalet Medical Center, 0310 Oslo, Norway. lars.baumbusch@medisin.uio.no

ABSTRACT

Background: The tumor suppressor gene p53 (TP53) controls numerous signaling pathways and is frequently mutated in human cancers. Novel p53 isoforms suggest alternative splicing as a regulatory feature of p53 activity.

Results: In this study we have analyzed mRNA expression of both wild-type and mutated p53 and its respective Deltap53 isoform in 88 tumor samples from breast cancer in relation to clinical parameters and molecular subgroups. Three-dimensional structure differences for the novel internally deleted p53 isoform Deltap53 have been predicted. We confirmed the expression of Deltap53 mRNA in tumors using quantitative real-time PCR technique. The mRNA expression levels of the two isoforms were strongly correlated in both wild-type and p53-mutated tumors, with the level of the Deltap53 isoform being approximately 1/3 of that of the full-length p53 mRNA. Patients expressing mutated full-length p53 and non-mutated (wild-type) Deltap53, "mutational hybrids", showed a slightly higher frequency of patients with distant metastasis at time of diagnosis compared to other patients with p53 mutations, but otherwise did not differ significantly in any other clinical parameter. Interestingly, the p53 wild-type tumors showed a wide range of mRNA expression of both p53 isoforms. Tumors with mRNA expression levels in the upper or lower quartile were significantly associated with grade and molecular subtypes. In tumors with missense or in frame mutations the mRNA expression levels of both isoforms were significantly elevated, and in tumors with nonsense, frame shift or splice mutations the mRNA levels were significantly reduced compared to those expressing wild-type p53.

Conclusion: Expression of p53 is accompanied by the functionally different isoform Deltap53 at the mRNA level in cell lines and human breast tumors. Investigations of "mutational hybrid" patients highlighted that wild-type Deltap53 does not compensates for mutated p53, but rather may be associated with a worse prognosis. In tumors, both isoforms show strong correlations in different mutation-dependent mRNA expression patterns.

Show MeSH
Related in: MedlinePlus