Δ133p53 coordinates ECM-driven morphogenesis and gene expression in three-dimensional mammary epithelial acini

Growing evidence indicates that p53 (encoded by TP53) has a crucial role in normal tissue development. The role of the canonical p53 (p53α) and its 12 isoforms in development and homeostasis of healthy tissue remains poorly understood. Here, we demonstrate that the Δ133p53 isoforms, the three short isoforms of p53, respond specifically to laminin-111 and play an important regulatory role in formation of mammary organoids in concert with p53α. We demonstrate that down-modulation of Δ133p53 isoforms leads to changes in gene expression of the extracellular matrix molecules fibronectin (FN), EDA+-FN, laminin α5 and laminin α3 in human breast epithelial cells. These changes resulted in increased actin stress fibers and enhanced migratory behavior of cells in two-dimensional culture. We found that α5β1-integrin coupled with the extracellularly deposited EDA+-FN activates the Akt signaling pathway in three-dimensional (3D) culture when Δ133p53 is dysregulated. Cells that do not express detectable Δ133p53 isoforms or express low levels of these isoforms failed to form polarized structures in 3D. These results uncover that Δ133p53 isoforms coordinate expression and deposition of organ-specific ECM molecules that are critical for maintenance of tissue architecture and function.

Low level of Fibrillarin, a ribosome biogenesis factor, is a new independent marker of poor outcome in breast cancer

Background

A current critical need remains in the identification of prognostic and predictive markers in early breast cancer. It appears that a distinctive trait of cancer cells is their addiction to hyperactivation of ribosome biogenesis. Thus, ribosome biogenesis might be an innovative source of biomarkers that remains to be evaluated.

Methods

Here, fibrillarin (FBL) was used as a surrogate marker of ribosome biogenesis due to its essential role in the early steps of ribosome biogenesis and its association with poor prognosis in breast cancer when overexpressed. Using 3,275 non-metastatic primary breast tumors, we analysed FBL mRNA expression levels and protein nucleolar organisation. Usage of TCGA dataset allowed transcriptomic comparison between the different FBL expression levels-related breast tumours.

Results

We unexpectedly discovered that in addition to breast tumours expressing high level of FBL, about 10% of the breast tumors express low level of FBL. A correlation between low FBL mRNA level and lack of FBL detection at protein level using immunohistochemistry was observed. Interestingly, multivariate analyses revealed that these low FBL tumors displayed poor outcome compared to current clinical gold standards. Transcriptomic data revealed that FBL expression is proportionally associated with distinct amount of ribosomes, low FBL level being associated with low amount of ribosomes. Moreover, the molecular programs supported by low and high FBL expressing tumors were distinct.

Conclusion

Altogether, we identified FBL as a powerful ribosome biogenesis-related independent marker of breast cancer outcome. Surprisingly we unveil a dual association of the ribosome biogenesis FBL factor with prognosis. These data suggest that hyper- but also hypo-activation of ribosome biogenesis are molecular traits of distinct tumors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09552-x.

Erratum: Ribosomal RNA 2' O-methylation as a novel layer of inter-tumour heterogeneity in breast cancer

[This corrects the article DOI: 10.1093/narcan/zcaa036.].

Ribosomal RNA 2'O-methylation as a novel layer of inter-tumour heterogeneity in breast cancer

Recent epitranscriptomics studies unravelled that ribosomal RNA (rRNA) 2′O-methylation is an additional layer of gene expression regulation highlighting the ribosome as a novel actor of translation control. However, this major finding lies on evidences coming mainly, if not exclusively, from cellular models. Using the innovative next-generation RiboMeth-seq technology, we established the first rRNA 2′O-methylation landscape in 195 primary human breast tumours. We uncovered the existence of compulsory/stable sites, which show limited inter-patient variability in their 2′O-methylation level, which map on functionally important sites of the human ribosome structure and which are surrounded by variable sites found from the second nucleotide layers. Our data demonstrate that some positions within the rRNA molecules can tolerate absence of 2′O-methylation in tumoral and healthy tissues. We also reveal that rRNA 2′O-methylation exhibits intra- and inter-patient variability in breast tumours. Its level is indeed differentially associated with breast cancer subtype and tumour grade. Altogether, our rRNA 2′O-methylation profiling of a large-scale human sample collection provides the first compelling evidence that ribosome variability occurs in humans and suggests that rRNA 2′O-methylation might represent a relevant element of tumour biology useful in clinic. This novel variability at molecular level offers an additional layer to capture the cancer heterogeneity and associates with specific features of tumour biology thus offering a novel targetable molecular signature in cancer.

Druggable Nucleolin Identifies Breast Tumours Associated with Poor Prognosis That Exhibit Different Biological Processes

Background: Nucleolin (NCL) is a multifunctional protein with oncogenic properties. Anti-NCL drugs show strong cytotoxic effects, including in triple-negative breast cancer (TNBC) models, and are currently being evaluated in phase II clinical trials. However, few studies have investigated the clinical value of NCL and whether NCL stratified cancer patients. Here, we have investigated for the first time the association of NCL with clinical characteristics in breast cancers independently of the different subtypes. Methods: Using two independent series (n = 216; n = 661), we evaluated the prognostic value of NCL in non-metastatic breast cancers using univariate and/or multivariate Cox-regression analyses. Results: We reported that NCL mRNA expression levels are markers of poor survivals independently of tumour size and lymph node invasion status (n = 216). In addition, an association of NCL expression levels with poor survival was observed in TNBC (n = 40, overall survival (OS) p = 0.0287, disease-free survival (DFS) p = 0.0194). Transcriptomic analyses issued from The Cancer Genome Atlas (TCGA) database (n = 661) revealed that breast tumours expressing either low or high NCL mRNA expression levels exhibit different gene expression profiles. These data suggest that tumours expressing high NCL mRNA levels are different from those expressing low NCL mRNA levels. Conclusions: NCL is an independent marker of prognosis in breast cancers. We anticipated that anti-NCL is a promising therapeutic strategy that could rapidly be evaluated in high NCL-expressing tumours to improve breast cancer management.

TP53 drives invasion through expression of its Δ133p53β variant

TP53 is conventionally thought to prevent cancer formation and progression to metastasis, while mutant TP53 has transforming activities. However, in the clinic, TP53 mutation status does not accurately predict cancer progression. Here we report, based on clinical analysis corroborated with experimental data, that the p53 isoform Δ133p53β promotes cancer cell invasion, regardless of TP53 mutation status. Δ133p53β increases risk of cancer recurrence and death in breast cancer patients. Furthermore Δ133p53β is critical to define invasiveness in a panel of breast and colon cell lines, expressing WT or mutant TP53. Endogenous mutant Δ133p53β depletion prevents invasiveness without affecting mutant full-length p53 protein expression. Mechanistically WT and mutant Δ133p53β induces EMT. Our findings provide explanations to 2 long-lasting and important clinical conundrums: how WT TP53 can promote cancer cell invasion and reciprocally why mutant TP53 gene does not systematically induce cancer progression.

DOI:http://dx.doi.org/10.7554/eLife.14734.001

Most cancers are caused by a build-up of mutations that are acquired throughout life. One gene in particular, called TP53, is the most commonly mutated gene in many types of human cancers. This suggests that TP53 mutations play an important role in cancer development.

It is widely considered that the TP53 gene normally stops tumors from forming, while mutant forms of the gene somehow promote cancer growth. Evidence from patients with cancer has shown, however, that the relationship between TP53 mutations and cancer is not that simple. Some very aggressive cancers that resist treatment and spread have a normal TP53 gene. Some cancers with a mutated gene do not spread and respond well to cancer treatments. Recent studies have shown that the normal TP53 gene produces many different versions of its protein, and that some of these naturally occurring forms are found more often in tumors that others. However, it was not clear if certain versions of TP53’s proteins contributed to the development of cancer.

Now, Gadea, Arsic, Fernandes et al. show that Δ133p53β, one version of the protein produced by the TP53 gene in human cells, helps tumor cells to spread to other organs. Tests of 273 tumors taken from patients with breast cancer revealed that tumors with the Δ133p53β protein were more likely to spread. Patients with these Δ133p53β-containing tumors were also more likely to develop secondary tumors at other sites in the body and to die within five years.

Next, a series of experiments showed that removing Δ133p53β from breast cancer cells grown in the laboratory made them less likely to invade, while adding it back had the opposite effect. The same thing happened in colon cancer cells grown in the laboratory. The experiments showed that Δ133p53β causes tumor cells with the normal TP53 gene or a mutated TP53 gene to spread to other organs.

Together the new findings help explain why some aggressive cancers develop even with a normal version of the tumor-suppressing TP53 gene. They also help explain why not all cancers with a mutant version of the TP53 gene go on to spread. Future studies will be needed to determine whether drugs that prevent the production of the Δ133p53β protein can help to treat aggressive cancers.

DOI:http://dx.doi.org/10.7554/eLife.14734.002

Abstract 855: p53 isoform Ä133p53â triple negative breast cancer and increased relapse with neoadjuvant taxanes

Background:

Studies of TP53 mutation, protein expression and modifications of the p53 network in breast cancer yield a complexity which has so far hindered substantive clinical progress. The effects of p53 mutation and p53 protein expression in breast cancer is dependent on the breast cancer subtype and stressors involved. Since identifying differential expression of p53 isoform mRNAs in breast cancer a decade ago, we have demonstrated associations between individual p53 isoforms (p53â, p53ã, Ä133p53á, Ä133p53â), breast cancer cell behaviour and clinical outcomes. Co-expressed combinations of isoforms may influence canonical p53 (p53á), whether mutant or wild type. Patterns of p53 isoform co-expression may hold the key to understanding p53 functionality, responses to therapy and disease behaviour in breast cancer.

Methods:

Expression of p53á, p53â, p53ã, Ä133p53á, Ä133p53â, Ä133p53ã by reverse-transcription PCR was analysed for the EORTC 10994 neoadjuvant breast cancer trial. In 469 available primary breast tumors, 223 patients had been randomised to a preoperative anthracycline regimen (fluorouracil, epirubicin, cyclophosphamide [FEC]) and 246 patients to receive a taxane based regimen (three cycles of docetaxel followed by three cycles of docetaxel + epirubicin [T-ET]). TP53 status was assessed by use of the yeast functional assay (FASAY) on biopsy samples that contained at least 20% tumour cells. Breast tumor subtypes: HER2 positive, triple-negative (TNBC), luminal-A, luminal-B (HER2 negative) and luminal-B (HER2 positive) were determined using the pathological markers recommended by the St Gallen breast cancer consensus guidelines. The primary endpoint was progression-free survival (PFS) with 9 years median follow up at the time of analysis.

Results:

All cancers expressed multiple p53 isoform mRNAs; none expressed canonical p53 mRNA (p53á) alone. There was a strong association between the p53 isoforms with 4 combinations of co-expressed p53 mRNAs predominated. Expression patterns included: (a) 285 tumours co-expressed p53á, p53â, p53ã, Ä133p53á, and Ä133p53ã; (b) 122 tumours co-expressed p53á, p53â, p53ã, Ä133p53á, Ä133p53â and Ä133p53ã (c) in 25 Ä133p53 negative tumors, p53á, p53â and p53ã were co-expressed (d) 22 p53â negative tumors co-expressed p53á, p53ã, Ä133p53á and Ä133p53ã. While no individual p53 isoform expression was associated with PFS, among the 104 TNBC expressing all p53 isoforms (pattern (b), Ä133p53â positive tumors), patients had 11.31 times greater risk of relapse when treated with T-ET than when treated with FEC (95%CI 1.91-66.99, p<0.0075).

Conclusions:

Corroborating the experimental and animal model data that p53 isoform expression, p53 mutation and p53 protein expression influence the pluripotent nature of p53, patients bearing Ä133p53â positive TNBC may benefit more from treatment with FEC than T-ET in the neoadjuvant setting.

Citation Format: Jean-Christophe Bourdon, Alexandra Diot, Valerie Meuray, Leen Slaets, Richard Iggo, Herve Bonnefoi, David Cameron, Alastair M. Thompson. p53 isoform Ä133p53â triple negative breast cancer and increased relapse with neoadjuvant taxanes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 855.

Detecting p53 isoforms at protein level

The human p53 protein isoforms are expressed in several cell lines and modulate p53 tumor suppressor -activity, mainly through modulation of gene expression (1-4). Thus, identifying the pattern of p53 isoforms expression in cell lines is a key step for future studies of the p53 network (5). At the moment, the detection of p53 protein isoforms is based on the use of a panel of antibodies allowing their identification by comparing their molecular weights and their detection pattern by different antibodies (6). Here, classical protocols supplemented with technical know-how are described to detect p53 protein isoforms at protein level by Western blotting and immunoprecipitation. Furthermore, a simple method to study the impact of p53 protein isoforms on p53 transcriptional activity through luciferase reporter gene assays is provided.

p53 mutant breast cancer patients expressing p53γ have as good a prognosis as wild-type p53 breast cancer patients

INTRODUCTION

Normal function of the p53 network is lost in most cancers, often through p53 mutation. The clinical impact of p53 mutations in breast cancer remains uncertain, especially where p53 isoforms may modify the effects of these p53 mutations.

METHODS

Expression of p53β and p53γ isoforms, the isoforms identified in normal breast tissue, was detected by reverse transcription polymerase chain reaction from a cohort of 127 primary breast tumours. Expression of p53β and p53γ isoforms was analysed in relation to clinical markers and clinical outcomes (5 years) by binary logistic regression, Cox proportional hazards regression and Kaplan-Meier survival analyses.

RESULTS

p53β and p53γ were not randomly expressed in breast cancer. p53β was associated with tumour oestrogen receptor (ER) expression, and p53γ was associated with mutation of the p53 gene. The patient group with the mutant p53 breast tumour-expressing p53γ isoform had low cancer recurrence and an overall survival as good as that of patients with wild-type p53 breast cancer. Conversely, patients expressing only mutant p53, without p53γ isoform expression, had a particularly poor prognosis.

CONCLUSIONS

The determination of p53γ expression may allow the identification, independently of the ER status, of two subpopulations of mutant p53 breast cancer patients, one expressing p53γ with a prognosis as good as the wild-type p53 breast cancer patients and a second one not expressing p53γ with a particularly poor prognosis. The p53γ isoform may provide an explanation of the hitherto inconsistent relationship between p53 mutation, treatment response and outcome in breast cancer.

Δ160p53 is a novel N-terminal p53 isoform encoded by Δ133p53 transcript

p53 gene expresses several protein isoforms modulating p53-mediated responses through regulation of gene expression. Here, we identify a novel p53 isoform, Δ160p53, lacking the first 159 residues. By knockdown experiments and site-directed mutagenesis, we show that Δ160p53 is encoded by Δ133p53 transcript using ATG160 as translational initiation site. This hypothesis is supported by endogenous expression of Δ160p53 in U2OS, T47D and K562 cells, the latter ones carrying a premature stop codon that impairs p53 and Δ133p53 protein expression but not the one of Δ160p53. Overall, these results show that the Δ133p53 transcript generates two different p53 isoforms, Δ133p53 and Δ160p53.

Δ160p53 is a novel N-terminal p53 isoform encoded by Δ133p53 transcript

p53 gene expresses several protein isoforms modulating p53-mediated responses through regulation of gene expression. Here, we identify a novel p53 isoform, Δ160p53, lacking the first 159 residues. By knockdown experiments and site-directed mutagenesis, we show that Δ160p53 is encoded by Δ133p53 transcript using ATG160 as translational initiation site. This hypothesis is supported by endogenous expression of Δ160p53 in U2OS, T47D and K562 cells, the latter ones carrying a premature stop codon that impairs p53 and Δ133p53 protein expression but not the one of Δ160p53. Overall, these results show that the Δ133p53 transcript generates two different p53 isoforms, Δ133p53 and Δ160p53.

Scotin expression and survival in breast cancer

e22006

Background: The Scotin gene (3p21.3) is directly trans-activated by p53 in response to ionising radiation and produces a 25kD trans-membrane protein located in the endoplasmic reticulum and nuclear membrane which induces a caspase- dependent apoptosis. This study examines the expression of scotin and scotin isoforms in breast cancer in relation to clinical and pathological parameters. Methods: Scotin was examined in 145 breast cancers by DNA sequencing, nested PCR for mRNA expression and using novel antibodies to scotin (pantropic), the C-terminal or N-terminal domain, and the scotin-5 isoform with western blotting and immunohistochemistry on a tissue microarray of breast cancers. Results: Scotin was mutated in 10% of cancers and mRNA expression lost in a further 10%. Moreover, Scotin-5 was expressed in 40% of cancers, while it was not detectable in normal breast epithelium. We established that Scotin-5 is anti-apoptotic and inhibits scotin-mediated apoptosis. Cytoplasmic staining of scotin on TMAs demonstrated that loss of scotin expression was associated with earlier relapse (Mantel-Cox log rank p<0.01) and poor survival (Mantel-Cox log rank p<0.002). Furthermore, loss of Scotin expression identified 50% of the WTp53 patients or 50% of the ER+ patients who also had a poor survival. Conclusions: Scotin may be used as an independent biomarker in breast cancer. Loss of Scotin function may account for a significant proportion of p53 malfunction even in the presence of wild type p53 in breast cancer and adds a further level of complexity to p53 directed therapy in breast cancer.

No significant financial relationships to disclose.

The clinical relevance of p53 isoforms modifying the effects of p53 mutation on survival from breast cancer

10505

Background: p53 is a key gene in the development of breast cancer and response to therapy. Nine splice variants of p53 in breast cancer have been identified, with full length p53, p53beta and p53gamma (both 46kD, C terminal truncated proteins) commonly expressed. This study examined the clinical relevance of splice variants in breast cancer. Methods: Tumors from 248 patients with primary breast cancer were examined for mutation with the Roche p53 mutation chip and p53 isoform expression detected by RT-PCR followed by nested PCR; full clinical and pathological data included median follow up of 6.4 years. Results: p53 mutation, identified in 65/248 (26%) cancers, was significantly associated by Chi square test with shorter survival (p=0.001), histological grade 3 (p<0.001) and estrogen receptor (ER) negative cancers (p<0.001), as expected. Expression of p53 beta or p53 gamma mRNA was associated with p53 mutation (p=0.002, Fisher's exact test). Intriguingly, the patient groups with a mutant p53 cancer but expressing p53 gamma or p53 beta or both isoforms had survival curves comparable to patients with cancer containing wild type p53. Similarly, p53 gamma or p53 beta was associated with ER negative cancers (Chi square; p<0.001), but the group of ER negative tumors expressing p53 gamma or p53 beta had improved survival similar to ER positive cancers. Patients with p53 mutant, p53 beta negative and ER negative cancers comprised half of those who died within 3 years of diagnosis. Conclusions: p53 beta or p53 gamma isoform expression in breast cancer is associated with better prognosis and may moderate disease behaviour even in mutant p53 and ER negative cancers. Manipulation of p53 isoforms in breast cancer may thus offer therapeutic potential.

No significant financial relationships to disclose.

Tumor susceptibility and apoptosis defect in a mouse strain expressing a human p53 transgene

Activation of apoptosis is believed to be critical for the role of p53 as a tumor suppressor. Here, we report a new mouse strain carrying a human p53 transgene in the mouse p53-null background. Expression of human p53 in these mice was comparable with wild-type murine p53; however, transactivation, induction of apoptosis, and G(1)-S checkpoint, but not transrepression or regulation of a centrosomal checkpoint, were deregulated. Although multiple functions of p53 were abrogated, mice carrying the human p53 transgene did not show early onset of tumors as typically seen for p53-null mice. In contrast, human p53 in the p53-null background did not prevent accelerated tumor development after genotoxic or oncogenic stress. Such behavior of human p53 expressed at physiologic levels in transgenic cells could be explained by unexpectedly high binding with Mdm2. By using Nutlin-3a, an inhibitor of the interaction between Mdm2 and p53, we were able to partially reconstitute p53 transactivation and apoptosis in transgenic cells. Our findings indicate that the interaction between p53 and Mdm2 controls p53 transcriptional activity in homeostatic tissues and regulates DNA damage- and oncogene-induced, but not spontaneous, tumorigenesis.

Calcium overload increases oxidative stress in old rat gastrocnemius muscle

In order to challenge in vivo muscle Ca2+ homeostasis and analyze consequences on mitochondrial H2O2 release (MHR) and sarcopenia, we injected Ca2+ ionophore A23187 (200 microg/kg, ip) in adult and old rats and measured gastrocnemius mass and mitochondrial Ca2+ content (MCC) using radioactive Ca2+ 48 h after injection. In a second experiment performed in old rats, we measured isocitrate dehydrogenase (ICDH) activity as an index of MCC, MHR, mitochondrial respiration, citrate synthase, COX and antioxydant enzyme activities 24 h after a 150 microg/kg injection. In adult rats, muscle mass and MCC were unchanged by A23187. In old rats, MCC increased 24 h after injection as reflected by a significant increase in ICDH activity; measured MCC tended to increase at 48 h. MHR and Mn-SOD activity were significantly increased at 24 h, and GPX activity was reduced. Muscle mass was unchanged but was negatively correlated with MCC in control and treated old rats. In conclusion, in old rats, A23187 probably induced a mitochondrial Ca2+ overload responsible for the observed increase in MHR without leading to muscle atrophy on a short term basis.

p53 isoforms can regulate p53 transcriptional activity

The recently discovered p53-related genes, p73 and p63, express multiple splice variants and N-terminally truncated forms initiated from an alternative promoter in intron 3. To date, no alternative promoter and multiple splice variants have been described for the p53 gene. In this study, we show that p53 has a gene structure similar to the p73 and p63 genes. The human p53 gene contains an alternative promoter and transcribes multiple splice variants. We show that p53 variants are expressed in normal human tissue in a tissue-dependent manner. We determine that the alternative promoter is conserved through evolution from Drosophila to man, suggesting that the p53 family gene structure plays an essential role in the multiple activities of the p53 family members. Consistent with this hypothesis, p53 variants are differentially expressed in human breast tumors compared with normal breast tissue. We establish that p53beta can bind differentially to promoters and can enhance p53 target gene expression in a promoter-dependent manner, while Delta133p53 is dominant-negative toward full-length p53, inhibiting p53-mediated apoptosis. The differential expression of the p53 isoforms in human tumors may explain the difficulties in linking p53 status to the biological properties and drug sensitivity of human cancer.

Due to reverse electron transfer, mitochondrial H2O2 release increases with age in human vastus lateralis muscle although oxidative capacity is preserved

Age-related changes in mitochondrial H2O2 release (MHR) could be responsible for an increase in oxidative stress in skeletal muscle and participate in the development of sarcopenia. We compared MHR in vastus lateralis biopsies obtained from young (23.5+/-2.0 year, n=6) and elderly (67.3+/-1.5 year, n=6) healthy sedentary men. Isolated mitochondria were incubated in the presence of glutamate/malate/succinate, with or without rotenone. Muscle fat oxidative capacity, citrate synthase, complex II, complex III, and cytochrome c oxidase activities were also measured. In parallel, we analyzed in gastrocnemius of young male Wistar rats (n=6), the impact of lidocaine (local anesthetic used in humans) on mitochondrial respiration and MHR. In humans, muscle oxidative capacity was preserved with age but muscle MHR was markedly enhanced in elderly subjects compared to young adults (+175%, P<0.05). Rotenone abolished this increase, demonstrating that it was due to a free radical release during reverse electron transfer from complex II towards complex I. Lidocaine can interfere with MHR measurements (intra-muscular injection in rats) but it can be avoided by minimizing contact with muscle (small multiple subcutaneous injections in humans). Physiologic consequences of the observed increase in muscle MHR with aging remain to be determined.

A Quantum Chemical Conformational Analysis of the Ethylenediamine Molecule

The conformational analysis of the ethylenediamine molecule has been studied by the LCAO-EHMO calculation method. The results indicate that the most stable conformation of the molecule is the gauche form, in which the angle N—C—C—N is ca. 63.0° measured from the cis form. This is in agreement with experimental data and can explain the fact that the ethylenediamine in its chelate complexes is always in the gauche form. In addition, the present results indicate that the trans form is the next most stable conformation of ethylenediamine in agreement with experimental results on bridging ethylenediamine metal complexes.