TP53 mutations and mdm2 protein overexpression in cholangiocarcinomas.

Tumor suppressor protein p53 is a positive regulator of MDM2 gene expression and the mdm2 protein can bind to p53, preventing the transactivation of p53 responsive genes, thus mimicking TP53 mutation. The authors looked for alterations that could affect, directly and indirectly, p53 function in 13 patients with extrahepatic cholangiocarcinoma. Molecular analysis by single strand conformation polymorphism and DNA sequencing revealed that TP53 gene mutations occurred in only 2 of 13 cholangiocarcinomas. High levels of mdm2 protein were found, by immunohistochemical staining, in 61% of the cholangiocarcinomas and in almost all specimens (70%) displaying stabilized p53 protein in the absence and in the presence of TP53 mutations. The finding of co-overexpressed mdm2 and p53 proteins in cholangiocarcinomas indicates that they can upregulate the expression of mdm2 protein to a level sufficient for binding and accumulating p53 in a presumably inactive complexed form. The presence of TP53 mutations or upregulation of MDM2 gene expression in 9 of the 13 cholangiocarcinomas strongly supports that the impairment of the p53 pathway is an important and specific step in cholangiocarcinoma pathogenesis. At variance with other authors, no alteration of p16ink4/CDKN2 gene was observed in all 13 cholangiocarcinomas.     

Immunoreactivity for p53 and mdm2 and the detection of p53 mutations in human malignant mesothelioma

Previous immunohistochemical studies on malignant mesothelioma with antibodies recognizing both the wild and the mutant types of the p53 protein have shown immunoreactivity in 25–70% of cases. This study was designed to determine whether there is immunoreactivity for p53 and mdm2 protein in malignant mesothelioma and to correlate p53 expression with the detection of mutations in p53 at DNA level. In 10 of 15 cases there was immunoreactivity for p53. In 6 of these cases immunoreactivity for mdm2 was also detected. In one p53-immunonegative case, a mutation of the p53 gene resulting in a stop codon was found. These results suggest that mdm2 might be involved in the inhibition of p53 in malignant mesothelioma. Also, these data suggest the existence of other proteins than mdm2 that may associate with p53.This work was supported by the Belgian Cancer Association (Vereniging voor Kankerbestrijding) and the Flemish Biotechnology Programme of the Ministry of Economy     

TP53 alterations in relation to the cell cycle-associated proteins p21, cyclin D1, CDK4, RB,MDM2, and EGFR in cancers of the uterine corpus

In the present study, TP53 alterations have been analysed and compared with the expression of the proteins p21, cyclin D1, cdk4, RB, EGFR, and MDM2 in 53 cancers of the uterine corpus. TP53 gene mutations analysed by CDGE/DGGE and direct sequencing showed a TP53 gene mutation in 18 per cent of the cases. TP53 gene mutations were not significantly related to overexpression or down-regulation of any of the proteins. Immunohistochemically, there was an increased protein level of TP53 in 77 per cent, p21 in 36 per cent, cyclin D1 in 45 per cent, cdk4 in 77 per cent, EGFR in 8 per cent, and MDM2 in 32 per cent of the cases. Expression of RB protein was normal in all cancers. Significant association of protein expression was seen between TP53 and MDM2 (p = 0·005) and p21 and MDM2 (p = 0·001). Furthermore, there may be an association between TP53 and p21 (p = 0·038) and cyclin D1 and cdk4 (p = 0·045). The results revealed increased levels of TP53 protein in all MDM2-positive cases that did not show TP53 mutations, indicating TP53 protein stabilization and inactivation by complex formation with MDM2. In summary, the high number of cases showing an increased level of TP53 and cdk4 proteins suggests that these proteins play an important role in the neoplastic process in cancers of the uterine corpus. Copyright © 1999 John Wiley & Sons, Ltd.     

p53 gene mutation and MDM2 overexpression in a case of primary malignant fibrous histiocytoma of the jejunum

Primary malignant fibrous histiocytoma of the gastrointestinal tract is extremely rare. To date, only 10 cases of primary malignant fibrous histiocytoma arising in the small intestine have been reported in the English literature. We describe here the genetic alterations and morphologic features of a primary malignant fibrous histiocytoma arising in the jejunum. Immunohistochemically, the tumor cells expressed vimentin, CD68 and alpha-1-antitrypsin, but were negative for other markers. Ultrastructurally, they showed features of fibroblasts and histiocytes. Immunohistochemical overexpression of p53 and MDM2 was observed. Mutation analysis of the p53 gene detected a missense mutation in codon 158 of exon 5. Our results suggest that p53 gene mutations and MDM2 overexpression may play an important role in the tumorigenesis. To our knowledge, the present report is the first genetic study of this rare lesion.     

DISTINCT mdm2/p53 EXPRESSION PATTERNS IN LIPOSARCOMA SUBGROUPS: IMPLICATIONS FOR DIFFERENT PATHOGENETIC MECHANISMS

Recent findings have indicated that TP53 inactivation in sarcomas may result from mutation and/or deletion of the TP53 gene or, alternatively, from binding to the MDM2 gene products. To investigate further a possible role of the two genes in sarcomas, 24 large and deep-seated lipomas and 74 liposarcomas of various subtypes were analysed for mdm2 and p53 overexpression by immunocytochemistry. Nineteen cases of the same series were also molecularly analysed for both MDM2 gene amplification and TP53 mutations, and a further ten cases for non-random chromosomal abnormalities. In the retroperitoneal well-differentiated–dedifferentiated (WD–DD) group, 15/16 WD and 8/8 DD liposarcomas displayed the mdm2+/p53+ phenotype, consistent with MDM2 gene amplification in the absence of TP53 mutations. In the non-retroperitoneal WD–DD group, 5/11 WD liposarcomas also retained the mdm2+/p53+ phenotype whereas all DD liposarcomas showed an immunophenotype and, when assessed, a genotype consistent with mutant TP53. Null mdm2 immunophenotype, coupled with evidence of a specific chromosome translocation t(12;16), was constantly observed in both the usual and the cellular subtypes of myxoid liposarcoma, three cases of which also showed TP53 alterations at the genetic or protein level. Neither mdm2 nor p53 overexpression was observed in the lipomas. The results show the existence of three main pathogenetically distinct groups of liposarcoma. The first retroperitoneal WD–DD group, which represents a novel class of tumours within a single histological category of sarcoma, where MDM2-mediated inactivation of p53 could be related to the pathogenetic mechanism. The second is the non-retroperitoneal WD–DD group, where the TP53 mutations appear to correlate with the dedifferentiation process. The third is the myxoid group, which is characterized by its own unique cytogenetic profile and never shows any involvement of TP53 or MDM2 genes. As for diagnostic significance, the absence of mdm2 and p53 reactivity in lipomas seems to represent a useful marker for differential diagnosis from lipoma-like WD liposarcomas. © 1997 by John Wiley & Sons, Ltd.     

Overexpression of MDM2 protein in intrahepatic cholangiocarcinoma: relationship with p53 overexpression, Ki-67 labeling, and clinicopathological features

Aberration of the p53 gene is thought to be the most frequent genetic alteration in human cancers. Tp53 protein may be inactivated by the binding of the MDM2 protein. MDM2, the product of the mdm2 gene, is an oncoprotein that binds to Tp53 and inhibits the p53- mediated transactivation. MDM2 overexpression has been reported in several human cancers, but not in intrahepatic cholangiocarcinoma (ICC). Therefore, we have evaluated the immunohistochemical overexpression of MDM2 and the relationship between its expression and histological grade, clinicopathological features, Tp53 overexpression, and Ki-67 labeling index in 47 cases of ICC. MDM2 and Tp53 were found to be overexpressed in 38% and 57% of the tumor, respectively. MDM2 and Tp53 were not expressed in non-tumorous liver tissue. There was no significant difference between the MDM2 overexpression and ICC tumor grade. However, MDM2 overexpression correlated with the presence of metastases (P<0.01) and advanced tumor stage (P<0.05). MDM2 overexpression also correlated with Tp53 overexpression (P<0.03) and Ki-67 labeling index (P<0.03). Our findings suggest that MDM2 overexpression may play a role in the late stage of human ICC. Received: 6 October 1999 Accepted: 31 January 2000     

Molecular abnormalities in liposarcoma: role of MDM2 and CDK4-containing amplicons at 12q13–22

It has recently been shown that mdm2 overexpression with stabilization of p53 represents a characteristic of retroperitoneal well-differentiated-dedifferentiated, here renamed evolved (WD-E), liposarcomas at the immunocytochemical, molecular, and cytogenetic level. This make-up appears to be confined to half the cases in non-retroperitoneal well-differentiated liposarcomas. Since in different tumours MDM2 amplification involves amplicons encompassing flanking genes, such as CDK4, the possibility was investigated that in these tumours, CDK4 could act as an alternative or additional gene involved in the transformation mechanism. Forty-one retroperitoneal (R)/non-retroperitoneal (NR) well-differentiated-dedifferentiated (WD-DD) and 33 myxoid/round cell liposarcomas were reanalysed by immunocytochemical, molecular (nine cases) and fluorescence in situ hybridization (FISH) (one case) techniques. The results showed that all but one R WD-E cases carried the mdm2+, p53+, cdk4+ immunophenotype. In NR-WD liposarcomas, this immunophenotype was shared in five cases and the remainder showed mdm2+, p53−, cdk4+ in four and mdm2−, p53−, cdk4+ in one case, showing ring chromosomes by FISH analysis. TP53 mutations are confirmed to be closely correlated with NR-DD liposarcomas and no CDK4 involvement was found in the myxoid/round cell liposarcoma group. As well as confirming the synergistic effect of MDM2 and CDK4, these results are consistent with the concept that amplicon(s) excluding MDM2 may contribute to transformation and support a role of CDK4 in opposing p53 function, particularly in NR WD liposarcoma. © 1998 John Wiley & Sons, Ltd.     

Analysis of glioma cell lines for amplification and overexpression of MDM2

Recently, amplification of the gene encoding a p53 binding protein, MDM2, was determined in 8% of the cases constituting a large series of glioblastomas. Here we have utilized Southern blot analysis to examine 30 cell lines established from such tumors, and our investigation has revealed large increases in MDM2 gene dosage in two cases, one of which showed coamplification of the CDK4 gene that resides in close proximity to MDM2 in chromosomal region 12q13–14. Northern analysis demonstrated overexpression of MDM2 mRNA in the two cell lines with gene amplification, and overexpression of MDM2 protein was evident in each of these by immunohistochemical and Western blot analysis. Analysis of TP53 cDNAs revealed normal TP53 sequences in the cell lines with MDM2 amplification; these results are consistent with those of previous studies suggesting that MDM2 amplification occurs only in tumors expressing wild-type p53. In total, these data suggest that MDM2 amplification in glioblastoma cell lines occurs at a frequency (6.7%) comparable to that determined in primary tumors; occurs in cell lines expressing wild-type p53; and can involve the coamplification of additional genes.     

mdm2 gene alterations and mdm2 protein expression in breast carcinomas

This study investigates the mdm2 gene status and expression in 66 surgically resected human breast carcinomas, with correlations with clinico-pathological and biological data (histological type, grading, steroid receptor status, p53 expression, proliferative activity). Four (7.7 per cent) out of 52 informative cases bear mdm2 gene amplification (four- to ten-fold) and 8 (15.4 per cent) of 52 cases showed borderline amplification (three-fold). Nine (13.6 per cent) out of 66 cases showed strong mdm2 nuclear immunoreactivity. Twenty-seven (40.9 per cent) cases showed isolated mdm2 reactive nuclei. All cases with clear amplification showed a high percentage of mdm2 immunoreactive nuclei. The relationship between gene amplification and mdm2 protein expression is highly significant (P<0.0001). No association was observed between mdm2 gene amplification and any of the considered clinico-pathological and biological parameters, while mdm2 immunoreactivity showed a significant association only with oestrogen receptor immunoreactivity (P=0.009). p53 expression was associated neither with mdm2 gene amplification nor with mdm2 immunoreactivity. It could be tempting to hypothesize that the evaluation of the combined mdm2/p53 immunohistochemical phenotype in human breast carcinoma could give us better prognostic information than the evaluation of the expression of the p53 protein alone.     

p53 expression in CMV-infected cells: association with the alternative expression of the p53 transactivated genes p21/WAF1 and MDM2

The p53 tumour suppressor gene is a cell cycle regulator, able to induce cell cycle arrest to allow DNA repair or apoptosis. The molecular mechanisms underlying p53 action imply transactivation of p53 dependent genes such as WAF1 (for wild type p53 associated fragment 1) and the murine double minute (MDM2) gene. In some cases, inactivation of the p53 gene results from p53 gene mutations leading to p53 protein accumulation, but in others it may results from mechanisms other than mutation, such as interaction with viral or cellular proteins. The expression of p53 protein and p53 transactivated gene proteins p21/WAF1 and MDM2, combined with in situ detection of apoptosis, was studied in specimens of CMV-infected patients as an in vivo model of p53 alteration not due to point mutation. p53 positivity was found in CMV + cells in different tissues, in cells with typical inclusion bodies, and in in situ hybridization and immunohistochemistry CMV + cells without inclusions (hidden infection). Although this p53 reactivity was accompanied by the expression of MDM2 and p21/WAF1 proteins, the patterns of MDM2 and p21/WAF1 protein expression were mutually exclusive, and were associated with the presence or absence of inclusion bodies. Nuclei bearing inclusion bodies were usually MDM2 +, p21/WAF1?, while hidden infected cells were usually MDM2?, p21/WAF1 +. Apoptosis was not detected in any tissue section from CMV-infected patients. Two alternative patterns were found in CMV-infected tissues: p53 +, p21/WAF1 +, MDM2?, or p53 +, p21/WAF1?, MDM2 + protein expression. These may represent examples of p53 dependent alternative effects in the course of CMV infection. Early stages are represented by CMV + cells without inclusion bodies, which display p53 and p21/WAF1 expression, suggesting that p53 could be acting as a growth suppressor protein. Late CMV infection is represented by cells harbouring inclusion bodies. These cells showed a p53 +, p21/WAF1?, MDM2 + profile, consistent with MDM2 mediated p53 inactivation. The absence of p21/WAF1 expression and lack of apoptosis suggest that the p53 protein expressed by MDM2 + cells could be functionally inactivated in CMV-infected cells with inclusion bodies. Previous studies have suggested that p53 inactivation by MDM2 over-expression occurs in sarcomas and lymphomas. Our observations seem to indicate that this mechanism of MDM2 mediated p53 inactivation may play a role in the late phase of CMV infection.     

Pitfalls in the diagnosis of ectopic hamartomatous thymoma

We have investigated the immunohistochemical expression of p53, mdm2, p21/waf1 and bcl-2 proteins in 31 thymic epithelial tumours comprising five medullary thymomas (MDT), four mixed thymomas (MT), 12 cortical thymomas (CT), eight predominately cortical thymomas (PCT) and two well-differentiated thymic carcinomas (WDTC). We have found p53, mdm2, p21 and bcl-2 protein expression in 25/31, 8/31, 5/31 and 10/31 thymic epithelial tumours, respectively. Coexpression of p53 and mdm2 proteins was found in eight cases (three CT, four PCT and one WDTC). Five of them were also p21 positive and three p21 negative. Discordant p53+/mdm2−/p21− protein expression was found in 19 cases (three MDT, three MT, nine CT, three PCT and one WDTC). Mdm2 and p21 proteins were not expressed in the absence of p53 protein. Coexpression of bcl-2 and p53 proteins was found in seven cases (three MDT, three MT and one WDTC). Eighteen cases were p53+/bcl-2− (10 CT, seven PCT and one WDTC) and three cases (two MDT and one MT) were bcl-2+/p53−. Our findings indicate that in thymomas, p53 expression is more frequently associated with cortical histotypes while bcl-2 expression is strongly associated with medullary and mixed histotypes. In addition, there is an inverse correlation between p53 and bcl-2 protein expression in thymomas. Coexpression of p53/mdm2/p21 proteins may reflect thymomas with wild-type (wt), p53 gene since mdm2 and p21 proteins are inducible by wt p53 gene. However, in view of previous findings that p53 mutation is an early event in thymomas, the possibility of p53 gene mutation with p53-independent mdm2 and p21 expression should be considered in these cases. Discordant p53+/mdm2−/p21− protein expression may represent thymomas with p53 gene mutations unable to activate expression of mdm2 and p21 proteins.     

Dermatofibrosarcoma protuberans with fibrosarcomatous areas

 Fibrosarcomatous (FS) change in a rare, but well-known phenomenon encountered in dermatofibrosarcoma protuberans (DFSP), and an increased chance in an adverse outcome has been suggested in patients with DFSP having FS areas (DFSP-FS). As altered p53 pathway has been suggested as having a potential role in tumour progression, we analysed the p53 gene and p53 protein together with the p53-related protein mdm2 and p21^Wafl in 5 cases of DFSP-FS and 13 of DFSP to ascertain whether the p53 pathway correlates to the fibrosarcomatous transformation of DFSP. Three of the five DFSP-FSs overexpressed p53 protein immunohistochemically, and one of them had a ”missense” mutation of the p53 gene without immunohistochemical overexpression of mdm2 or p21^Wafl. The other two DFSP-FSs with p53 overexpression demonstrated increased labelling indices of both mdm2 and p21^Wafl. The three DFSP-FS patients with overexpression of p53 protein had frequent local recurrences, ranging from 3 to 5 in number with increasingly short intervals (mean 4.5 years), while one of the other two had no recurrences and the other, only one. None of the 13 DFSPs showed any alterations in the p53 gene or overexpressions of p53, mdm2 and p21^Wafl, except for one DFSP having a ”silent” mutation of the p53 gene. Three DFSPs had local recurrences once or twice with longer intervals to recurrence (mean 10.3 years). Although the number of cases examined is limited, the results suggest that alterations in the p53 pathway, such as overexpression of p53 protein by a mutated gene and mdm2 overexpression, are involved in fibrosarcomatous transformation in a subset of fibrohistiocytic tumours and possibly correlated with its more locally aggressive behaviour than that without p53 alterations or ordinary DFSP. Received: 21 January 1998 / Accepted: 25 March 1998     

Distinction Between Lipoma and Liposarcoma by MDM2 Alterations: A Case Report of Simultaneously Occurring Tumors and Review of the Literature

We investigated a lipoma and a well-differentiated/dedifferentiated liposarcoma (WD/DDL), occurring simultaneously in one patient for the possible role of p53 and mdm2 in the molecular oncogenesis of liposarcoma and tumor progression. The hypothesis tested was if there is a continuum in the development from lipoma to liposarcoma. Lipoma was characterized by a lack of p53 mutation, p53 LOH and p53 protein expression, as well as by mdm2 amplification and mdm2 protein expression. p53 mutation and p53 LOH were found neither in the well-differentiated nor in the dedifferentiated parts of the liposarcoma. In contrast, mdm2 amplification and an increase in mdm2 protein expression were found to be associated with malignancy and dedifferentiation, whereas p53 protein expression was only slightly increased. These findings indicate that mdm2 constitutes one of the most common targets for molecular aberration in WD/DDL. We suggest that mdm2 is a marker distinguishing between ordinary lipoma and well-differentiated liposarcoma, and that the genesis of these tumors is different.     

Molecular abnormalities of p53, MDM2, and H-ras in synovial sarcoma.

Forty-nine cases of synovial sarcoma were evaluated for mutation of the p53 gene, amplification of the MDM2 gene and mutation of the H-ras gene, and for the relation of these factors to overall survival and clinicopathologic parameters. All investigations were carried out on formalin-fixed paraffin-embedded materials. Furthermore, we evaluated the expression of p53 protein, MDM2, and p21(WAF1/CIP1) immunohistochemically in these cases, together with an assessment of proliferative activities using monoclonal antibody MIB-1. Nine of the 49 cases (18.4%) had p53 gene alteration detected by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and direct sequencing. Eleven cases (24%) showed nuclear accumulation of p53 protein in more than 10% of the tumor cells. Among them, only three cases contained gene mutations. There was no correlation between p53 nuclear accumulation and p53 gene alteration. MDM2 gene amplification, as shown by differential PCR, was observed in 19 out of 47 cases (40%). Nineteen out of 49 cases (38.8%) showed immunoreactivity for MDM2. MDM2 gene amplification and the expression of MDM2 protein showed a significant positive relationship (P = 0.0004). Moreover, MDM2 immunoreaction was significantly correlated with nuclear accumulation of p53 protein (P = 0.023). Positive immunoreaction for p21(WAF1/CIP1) was observed in 21 out of 48 cases (43.8%). p21(WAF1/CIP1) expression was correlated with p53 protein expression. H-ras gene mutations were seen in only three cases (6.1%). All mutations were in codon 12 (one GGC-to-AGC [Gly-to-Ser] mutation and two GGC-to-GAC [Gly-to-Ap] mutations). The gene alteration of p53, MDM2, and H-ras did not affect the patients' prognosis. Although the cases with positive immunoreaction for p53 tended to have a worse prognosis, the difference was not statistically significant (P = 0.13). No correlation was observed between MIB-1 LI and the immunohistochemical expression of p53, MDM2, and p21(WAF1/CIP1) or the mutation status of p53 and H-ras. On the other hand, high MIB-1 LI (more than 10) significantly correlated with poor prognosis (P < 0.0001). Our results suggest that p53 gene mutation does not appear to be a major prognostic factor and H-ras mutations are infrequent in synovial sarcoma.     

Deletion of chromosome arm 17p dna sequences in pediatric high-grade and juvenile pilocytic astrocytomas

In adults, loss of heterozygosity for DNA on 17p has been shown in high-grade anaplastic astrocytomas (AAs) and glioblastomas multiforme (GMs), and mutation of the TP53 tumor suppressor gene has been reported in all grades of astrocytomas. Little is known, however, about 17p deletion and TP53 mutation in juvenile pilocytic astrocytomas (JPAs), the most common low-grade tumors seen in children. To elucidate the genetic characteristics of pediatric high-grade astrocytomas and JPAs, we performed restriction fragment length polymorphism analysis with probes derived from 17p and TP53 mutational studies in 28 tumor specimens. Telomeric chromosome arm 17p markers 144-D6 and ABR were lost in 6 (75%) of 8 informative tumors classified as high-grade (7 AAs, 1 GM) and in 2 (10%) of 20 informative JPAs. Loss of 17p probes centromeric to the TP53 gene were also detected in 3 AAs and 5 JPAs. Four of the 6 (66%) JPAs with losses of 17p DNA sequences recurred rapidly despite aggressive therapy, whereas only 5 of the other 14 (36%) recurred. Mutation of the TP53 gene was detected by polymerase chain reaction and denaturing gradient gel electrophoresis in only 1 JPA and 1 AA. These tumors were also examined for MDM2 gene amplification as an alternate inactivation mechanism for TP53 gene function: no instances of alteration were identified. These results suggest that a gene or genes in addition to TP53 on 17p may be involved in the etiology or progression of high-grade astrocytomas and aggressive JPAs in children. Further, molecular genetic studies may be an important supplement to current clinical and radiologic data in predicting the outcome and guiding the therapy of children with aggressive and malignant astrocytomas.     

Methylation of p14(ARF) gene in meningiomas and its correlation to the p53 expression and mutation.

We have previously reported the statistically significant correlation of immunohistochemical expression of MIB-1 and p53 proteins among benign, atypical, and anaplastic meningiomas and p53 protein expression was high in atypical and anaplastic meningiomas. In the present study, we analyzed 22 cases of meningiomas for mutation of p53 gene in its spectrum of exon 5 to 8 using automated genetic analyzer. We did not find any mutation of p53 in any of these cases, thus suggesting the p53 protein expression is wild type. We analyzed 72 cases of meningiomas for determining the methylation status of p14(ARF) gene and the immunohistochemical expression of MDM2 protein to explain p53 protein expression in these meningiomas. We found methylation of p14(ARF) gene in five of 58 cases of benign meningiomas (8.6%), two of 10 cases of atypical meningiomas (20%), and two of four cases of anaplastic meningiomas (50%). In absence of p53 gene mutation, the high percentage of p14(ARF) gene methylation in high-grade meningioma may have been responsible for accumulation of wild-type p53 protein. In addition, we also found the loss of MDM2 protein in high-grade meningiomas. These deregulations of p14-MDM2-p53 pathway may contribute to the malignant progression of meningioma.     

Biochemical uncovering of mdm2/p53 complexes in liposarcomas parallels their immunohistochemical detection.

Recent observations indicate the existence of pathogenetically distinct groups of well-differentiated (WD) dedifferentiated (DD) liposarcomas. In the retroperitoneal WD-DD liposarcomas, the predominant phenotype is represented by the aberrant (overexpressed) mdm2+/p53+ wild-type profile. At the nonretroperitoneal site, the WD liposarcomas present a wider association of MDM2/P53 gene expression; i.e., mdm2+/p53+, mdm2+/p53-, mdm2-/p53+ and mdm2-/p53-, and TP53 mutations seem to correlate with the dedifferentiation process. A biochemical study of mdm2-p53 association in 11 tumor samples characterized by the presence of different mdm2 and p53 immunophenotypes was performed. Immunoprecipitation assays using a p53-specific antibody were performed on tumor tissue and surrounding normal tissue; the immunoprecipitated material was then investigated for the presence of p53 (control) and of coimmunoprecipitated mdm2. This biochemical analysis showed that, in mdm2+/p53+/wild-type retroperitoneal liposarcomas, a band corresponded to mdm2 protein in the cellular lysates immunoprecipitated with a p53-directed antibody. In contrast, the mdm2+/p53- liposarcoma did not evidence the presence of mdm2 protein nor was p53 protein available to direct immunoprecipitation, as in the p53 mutant tumor samples with mdm2-/p53+ and mdm2-/p53- phenotypes. From the normal counterpart of retroperitoneal liposarcoma lysates, no p53 protein was immunoprecipitated. The findings in this study agree with the molecular data and they show the physical association of mdm2 and p53 in fresh liposarcoma surgical specimens.     

Intratumour heterogeneity of p53 expression; causes and consequences

Genomic alterations in different types of cancer have been identified by comprehensive sequencing methodologies, revealing TP53 as the most frequently mutated gene across the majority of human cancer types. Cytotoxic treatments are still major cancer therapy strategies but cancer recurrence due to therapy resistance is a major challenge. Resistant cell populations may be associated with TP53 mutant clones exhibiting abnormal p53 expression patterns in tumours. Given data that levels of mutant p53 influence cancer cell growth and survival, understanding the mechanisms underlying intratumour heterogeneity of p53 can be exploited to design strategies that improve patient survival. The patterns of p53 protein examined by immunohistochemistry of both premalignant and malignant tissues are complex, ranging from intense staining of all tumour cell nuclei to complete absence of staining and with many intermediate phenotypes. Animal models that express only mutant proteins and adoption of international standards for terminology have brought greater clarity to understanding the causes of variation and are at the same time demonstrating the utility of p53 in oncology. In addition to p53 mutation, MDM2 and chaperone activities, gene copy number and TP53 mRNA levels linked to proliferative activity and differentiation are all now established as causes of variation in p53 staining, with clinical implications. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.