A model for tumor suppression using H-1 parvovirus

A model system is proposed to investigate, at the molecular level, the pathways of tumor suppression. As a tool for the selection of cells with a suppressed phenotype, we used the H-1 parvovirus that preferentially kills various neoplastic cells. From the human K562 leukemia cells, we isolated a clone, KS, that is resistant to the cytopathic effect of the H-1 virus and displays a suppressed malignant phenotype. The suppressed malignancy and the cellular resistance to H-1 killing appear to depend on the activity of wild-type p53. Whereas the KS cells express wild-type p53, the protein is undetectable in the parental K562 cells. Experiments with p53 mutants suggest that wild-type p53, in its functionally intact state, contributes to the resistance against the cytopathic effect of H-1 parvovirus.

Stabilization and expression of high levels of p53 during early development in Xenopus laevis

We previously isolated a p53 cDNA from a Xenopus oocyte library. To determine if p53 has a function in the developmental period, we have studied its expression at the RNA and protein levels during the early development of Xenopus laevis. Two p53 transcripts (3 and 2.2 kb) are expressed from the beginning of Xenopus oogenesis, and the major one (2.2 kb) reaches a level of 7 x 10(5) to 7 x 10(6) transcripts per mature oocyte. After fertilization only the 2.2-kb RNA is detected, but its level decreases and at the neurula stage p53 RNA becomes undetectable. The p53 protein is highly expressed during Xenopus development, in contrast to an undetectable level in Xenopus cells in culture. Most of the p53 protein is synthesized during late oogenesis and a stage VI oocyte contains 7 x 10(11) molecules of p53 protein. This maternal p53 store is maintained at a constant level during Xenopus development, at least until the tadpole stage. This high level of expression is mainly due to stabilization of the p53 protein. Unusually for p53, the protein is strictly located in the cytoplasm of oocytes and this localization might indicate that it is stored in an inactive form at this stage. These data are discussed relative to previous observations made in transgenic mice.

Correlation of p53 expression and proliferative activity in gastric cancer

We analyzed immunohistochemically the association between p53 tissue status and prognostic parameters of 357 gastric cancer patients, using endoscopically obtained biopsy materials, embedded in paraffin. Using PAb1801, an anti-p53 monoclonal antibody p53 immunoreactivity was detected in the nuclei of cancer cells in 113 cases (32%). The nuclear p53 immunoreaction was closely associated with positive lymph node metastasis, serosal invasion, and liver metastasis. For the estimation of proliferative activity, proliferating cell nuclear antigen (PCNA) labeling rates (LRs) of biopsy specimens were immunohistochemically measured. A significant positive correlation was found between PCNA LRs and p53 tissue status. In addition, a positive nuclear p53 immunoreaction was found to be significantly associated with shorter overall survival. Especially, in the group of patients with stages III and IV, the prognosis of patients with p53-positive tumours was significantly poorer than that of patients with p53-negative tumours. These results indicate that immunohistochemical staining for nuclear p53 in biopsied materials may be useful in deciding the therapeutic schedule of patients with gastric cancer, preoperatively.

Expression of p53 protein is an early event in ultraviolet light-induced cutaneous squamous cell carcinogenesis

BACKGROUND AND DESIGN

p53 Is known to be a tumor-suppressor gene and has been suggested to play an important role for multistep carcinogenesis of cutaneous squamous cell carcinoma (SCC). To evaluate the role of ultraviolet light (UV) in p53 mutation in squamous cell carcinogenesis, paraffin-embedded sections of SCCs were immunohistochemically stained with the CM-1 antibody for p53 protein. Positive staining suggests mutation of the p53 gene since the mutant p53 protein gains prolonged half-life to be detectable by this method. The specimen included SCCs induced by UV (SCCs on sun-exposed areas, SCCs on patients with xeroderma pigmentosum), roentgen rays, scar, and miscellaneous causes. In addition, solar keratoses that are precancerous lesions of UV-related SCCs were also analyzed.

RESULTS

Fourteen (54%) of 26 UV-related SCCs were positive, whereas five (19%) of 26 UV-unrelated SCCs were positive. Among the UV-related SCCs, five (45%) of 11 well-differentiated SCCs and nine (60%) of 15 moderately to poorly differentiated SCCs were positive. Eleven (48%) of 23 solar keratoses were positive for p53.

CONCLUSIONS

These results indicate that UV acts as a mutagen for the p53 gene, and this event may occur at a relatively early stage of multistep UV carcinogenesis.

Effect of sodium butyrate on the expression of retinoblastoma (RB1) and P53 gene and phosphorylation of retinoblastoma protein in human colon tumor cell line HT29

Sodium butyrate is known to induce morphological and biochemical changes associated with cell differentiation in some colon tumor cell lines including HT29. In our present study we observed that sodium butyrate treatment caused a decrease in the level of expression of RB1 gene on day seven of butyrate treatment but a gradual six to sevenfold decrease in the level of expression of p53 gene. Western blot analysis revealed a decrease in the level of the phosphorylated form of Rb protein (pRb) and an increase in the level of underphosphorylated pRb as compared to the control cells. These changes in the phosphorylation level were observed from day three of sodium butyrate treatment. In addition, the flat foci forming large differentiated cells also began to appear after 3 days of sodium butyrate treatment. In this study, we are able to show that, besides induction of differentiation, sodium butyrate treatment can also cause a reversal in the phosphorylation status of the pRb in colon tumor cell line HT29. These results suggest that the phosphorylation level of pRb could be associated with the cell differentiation process in human colonic epithelium and as a consequence in its neoplastic development.

P53 protein expression in Hodgkin's disease

P53 is an oncosuppressor gene which is located on chromosome 17. Mutations of the p53 gene are closely associated with malignant transformation under in vitro conditions and are the most common genetic alteration in human malignancy. Unlike normal p53 protein which is unstable and usually cannot be detected by immunohistology, mutated p53 shows a decreased cell turnover rate and overexpression as compared with the wild-type protein. In this study a panel of four anti-p53 antibodies (PAb240, PAb421, PAb1801 and DO7) was applied to 52 cases of Hodgkin's disease: three cases of nodular lymphocytic predominance (LP), 33 cases of nodular sclerosis (NS), and 16 cases of mixed cellularity (MC). The results show that 53 protein is present in the Hodgkin's- and Reed-Sternberg cells in 82% of NS and 94% of MC, but not in nodular LP. It is suggested that mutations of the p53 gene and loss of normal p53 function are frequent in Hodgkin's disease and may be implicated in the pathogenesis of this disease.

Effect of estradiol on tumor growth, cell kinetics and p53 oncoprotein expression in human endometrial adenocarcinoma heterotransplanted into nude mice

To study the importance of estradiol concentrations in which tumors are growing to progression of tumor growth and cell kinetics, we have used a human tumor-nude mice model. In this model a human endometrial adenocarcinoma with estradiol independent but estradiol-responsive growth phenotype (i.e. the tumor was capable of growing in absence of estradiol but its growth could be stimulated by estradiol at the start of preparation phase) was examined. In the preparation phase pieces from this tumor were transplanted into nude mice, randomly divided into two groups, one with and one without estradiol treatment. After 18 months growth in these different hormone conditions the tumors were measured for p53 protein expression and pieces from both these groups were again transplanted into oophorectomized nude mice, each group being randomly allocated to two subgroups, one with and one without estradiol treatment (experimental phase). Tumor growth was measured during the experimental phase, whereas cell kinetic parameters and steroid receptor concentrations were analyzed after the experimental phase. Our findings indicate that progression of the growth phenotype is independent of estradiol conditions in which human endometrial adenocarcinomas are grown. Long-term growth in estradiol-poor conditions results in estradiol resistance of the cell cycle, probably accompanied by overexpression of the p53 protein. Tumor growth in estradiol-rich conditions, however, may protect, at least to some extent, the same tumor, which retains higher sensitivity of cell proliferation to estradiol and normal production of the p53 protein despite progressive changes in growth regulation.

Large E1B proteins of adenovirus types 5 and 12 have different effects on p53 and distinct roles in cell transformation

The formation of complexes between oncoproteins of DNA tumor viruses and the cellular protein p53 is thought to result in inactivation of the growth suppressor function of p53. In cells transformed by nononcogenic human adenovirus type 5 (Ad5), the 55-kDa protein encoded by E1B forms a stable complex with p53 and sequesters it in the cytoplasm. However, the homologous 54-kDa protein of highly oncogenic Ad12 does not detectably associate with p53. Yet in Ad12-transformed cells, p53 is metabolically stable, is present at high levels in the nucleus, and contributes to the oncogenicity of the cells. Such properties have previously been described for mutant forms of p53. Here, we show that stable p53 in Ad12-transformed cells is wild type rather than mutant and that stabilization of p53 is a direct consequence of the expression of the Ad12 E1B protein. We also compared the effects of the E1B proteins on transformation of rodent cells by different combinations of oncogenes. A synergistic interaction was observed for the gene encoding the 54-kDa E1B protein of Ad12 with myc plus ras oncogenes, resembling the effect of mutant p53 on myc plus ras. In contrast, the Ad5 55-kDa E1B protein strongly inhibited transformation by myc plus ras but stimulated transformation by E1A plus ras. The data are explained in terms of different interactions of the two E1B proteins with endogenous p53. The results suggest that in cultured rat cells, endogenous wild-type p53 plays an essential role in cell proliferation, even in the presence of myc plus ras. The dependence on p53 is lost, however, when the adenovirus E1A oncogene is present.

[Expression of mutant P53 gene protein product in human bladder carcinoma]

Expression of P53 protein was detected immunohistochemically in formalin-fixed, paraffin-embedded tissues from 67 patients with bladder carcinoma and 6 normal bladder controls. P53 protein was found positively in 34 of the 67 tumors, whereas no normal bladder controls and no non-cancer tissue cells on tumor sections was stained positively for P53 protein. The percentage of staining for P53 was higher in poorly-differentiated and in invasive tumors than in well and moderately differentiated and in superficial tumors. We also found that P53 positive staining was closely related to tumors recurrence. Hence, the expression of P53 may be used as a tumor marker predicting the histograde, clinical stage and recurrence.

Expression of differentially phosphorylated Rb and mutant p53 proteins in myeloid leukemia cell lines

We studied the structure and expression of Rb and p53 genes in six myeloid leukemia cell lines (HL-60, KBM3, K562, KBM5, EM2, KBM7) in the light of the published reports that structural abnormalities of these genes are rarely seen in leukemic cells and also a recent finding that Rb gene expression can be regulated by the p53 protein. Except for HL-60 cells which have a truncated p53 gene, none of the other cell lines revealed any gross structural abnormalities in the Rb and p53 genes. KBM3, KBM5 and EM-2 expressed lower levels of Rb mRNA than HL-60, K562 and KBM7. The amount of Rb protein was lowest in KBM3 cells and in this and two other cell lines (KBM5, KBM7) Rb was markedly hypophosphorylated compared to the other three cell lines. HL-60 and K562 did not express p53 m-RNA, while the other four cell lines all expressed high levels of mutant p53 protein. Thus even in the absence of gross structural alterations, subtle abnormalities in the expression pattern of Rb and p53 genes occur in myeloid leukemia cells.

c-erbB-2 oncogene related to p53 expression, cell proliferation and prognosis in breast cancer

A series of 193 archival breast cancer biopsies were analysed immunohistochemically to detect over-expression of c-erbB-2 oncoprotein. Altogether, 59/193 (31%) of the tumours were positive for c-erbB-2, the staining being located at the cell membranes with weak cytoplasmic staining in some samples. The expression of c-erbB-2 was positively correlated with a number of parameters analysed: ductal type, intraductal growth pattern, high tumour grade, density of tumour infiltrating lymphocytes (TIL), DNA aneuploidy, steroid (ER, PR) receptor negativity, high S-phase fraction, high mitotic frequency, high values of nuclear factors, and accumulation of p53 protein. c-erbB-2 expression showed a weak association with a low survival probability (p = 0.07) and with a short recurrence-free survival (p = 0.1). In local tumours or in axillary lymph node positive tumours, c-erB-2 expression had no significant prognostic value. Also in multivariate analysis, c-erbB-2 expression had no independent prognostic value superior to the axillary lymph node status, tumour diameter and mitotic frequency. The results show that c-erbB-2 expression in related to several histopathological features of malignancy and cell proliferation in breast cancer, but it has no independent prognostic value better than that of the established prognostic factors.

Expression of p53 protein related to the presence of human papillomavirus (HPV) DNA in genital carcinomas and precancer lesions

The E6 protein of the high-risk human papillomavirus (HPV) types 16 and 18 is capable of complexing with the wild-type p53 tumor suppressor gene product, leading to loss of the normal p53 function as an anti-oncogene, whereas the low-risk HPV types 6 and 11 lack this binding property. The malignant potential of HPV 16 and 18 has been ascribed to this complexing of E6 with p53, which regularly leads to undetectable expression of the latter in HPV-positive lesions. To assess the role of p53 in HPV-associated genital carcinogenesis, the expression of p53 protein was studied immunohistochemically in 22 genital carcinomas and precancer lesions; 8 vulvar carcinomas, 1 VIN (vulvar intraepithelial neoplasia), 5 cervical carcinomas and 8 CIN (cervical intraepithelial neoplasia) using monoclonal antibody PAb 1801. Presence of HPV was demonstrated by PCR using HPV consensus primers, and amplified HPV-DNA was digested with the restriction enzymes giving distinct patterns for various HPV-types in gel electrophoresis. HPV-typing was confirmed by in situ hybridization with biotinylated DNA probes. Altogether, 17 of the 22 specimens (77%) showed p53 expression: 67% of the precancer lesions and 83% of carcinomas. Expression was more frequent (89%) in the vulvar than (70%) in cervical lesions. Using PCR,HPV DNA was detected in 19/22(86%) of the samples. The following HPV types were identified: HPV 6 (2 samples), HPV 11 (3 cases), HPV 16 (5 cases), HPV 33 (3 cases), and 6 contained unidentified HPV types. All HPV DNA-negative specimens showed p53 expression. Of the 19 HPV DNA-positive lesions, 5 were p53-negative, three of these being HPV 16 positive CIN lesions. The remaining two HPV 16 lesions were invasive carcinomas with a weak p53 expression. HPV 6 and 11-positive lesions showed a weak p53 expression more frequently than HPV-negative cases and HPV 33 lesions. The results indicate that p53 expression is detectable, but it is less frequent and less intense in HPV DNA-positive genital precancer lesions and carcinomas (particularly those with HPV 16 DNA) as compared with HPV DNA-negative lesions.

The tumor suppressor p53 regulates its own transcription

The ability of p53 to suppress transformation correlates with its ability to activate transcription. To identify targets of p53 transactivation, we examined the p53 promoter itself. Northern (RNA) analysis and transient transfection experiments showed that p53 transcriptionally regulated itself. A functionally inactive mutant p53 could not regulate the p53 promoter. Deletion analysis of the p53 promoter delineated sequences between +22 and +67 as being critical for regulation. Electrophoretic mobility shift analysis and methylation interference pinpointed the p53 DNA responsive element. When oligomerized in front of a heterologous minimal promoter, this element was regulated by wild-type p53 and not by mutant p53. Point mutations in the DNA element that eliminated protein-DNA interactions also resulted in a nonresponsive p53 promoter. The DNA element in the p53 promoter responsive to p53 regulation is similar to the p53 consensus sequence. However, we have been unable to detect a direct interaction of p53 with its promoter.

Overexpression of p53 protein and c-erbB-2 protein in small cell carcinoma of the cervix uteri

Twenty-eight primary small cell carcinomas of the cervix uteri were examined immunohistochemically for overexpression of p53 protein and c-erbB-2 protein. Twenty-one per cent of the cases showed positive immunostaining for p53 protein, whereas no staining was observed using the antibody against c-erbB-2. Our results indicate that altered expression of p53 protein may be involved in the development of small cell carcinoma of the cervix uteri.

An immunocytochemical study of p53 and bcl-2 protein expression in Hodgkin's disease

In view of their reported reciprocal effects on apoptosis, the expression of p53 and bcl-2 proteins was studied in 46 cases of Hodgkin's disease by immunocytochemical labeling. We found p53 protein in Reed-Sternberg cells and their mononuclear variants in 16 of the 46 cases (34.7%) of Hodgkin's disease, mainly in a nuclear pattern. This restricted expression on Reed-Sternberg cells and variants supports their neoplastic nature. This overexpression of p53 protein in one third of Hodgkin's disease cases is similar to that seen in many other human malignancies. bcl-2 protein was present in mantle zone B cells and scattered T cells in all cases, and in 17 cases (37.7%) of Hodgkin's disease in Reed-Sternberg cells and their mononuclear variants. Six cases coexpressed both proteins, whereas in 18 cases neither was identified. There is no apparent relationship between p53 and bcl-2 protein expression, and on the basis of the present results there is no reason to suppose that they have any particular complementary effects on the neoplastic transformation in Hodgkin's disease.

Exposure to cigarette smoke and expression of the protein encoded by the p53 gene in bronchial carcinoma

Mutation of the onco-suppressor gene encoding the protein known as p53 may cause synthesis of a mutant p53 protein which can bind to and inactivate its wild-type equivalent. This protein is detectable in many malignant neoplasms, including bronchial carcinoma, and has been associated with cigarette smoking. Of 59 tissue biopsy specimens of primary bronchial malignancies immunolabeled for p53 by the avidin-biotin technique using the antibodies PAb 1801, CM1, and D07, 13 (22%) expressed the protein. Of these 13 patients, 10 (77%) smoked more than 20 cigarettes a day and their mean total exposure was 53 pack-years. Corresponding figures for those with p53-negative tumors were 21 (46%) smoking more than 20 cigarettes a day with a mean total exposure of 36 pack-years. There was, however, no difference between the groups in total duration of exposure (46 vs. 47 years). Although p53 was expressed more commonly in adenocarcinoma (30% of 10) and squamous carcinoma (28% of 29) than in small cell tumors (10% of 20), this could be accounted for by the smoking history. This study supports a relationship between mutations of the p53-encoding gene associated with overexpression of its protein product and intensity of exposure to cigarette smoke.

[Expression of P53 protein in cutaneous melanoma]

P53 protein in cutaneous melanoma. We report the results of an immunohistochemical analysis about the nuclear phosphoprotein P53 expression performed on 48 primary and 10 metastatic cutaneous melanoma in order to assess the prevalence of the expression of mutant P53 protein (m-P53) in this skin tumour. In our study m-P53 was found in about 46% of primary tumours without any significant relationship with the corresponding metastatic lesions. Therefore the P53 count in cutaneous melanoma is not a prognostic marker of tumour spread and aggressiveness.

p53 mutations in human immortalized epithelial cell lines

Although rodent cells have been immortalized following transfection with a mutant p53 gene, the role of p53 in the immortalization of human cells is unknown. Therefore, human epithelial cell lines were examined for p53 mutations in exons 4-9 which include the evolutionarily conserved regions. A spontaneously immortalized skin keratinocyte cell line, HaCat, and three ras-transfected clones, have a p53 mutational spectrum that is typical of ultraviolet light induced mutations. A normal finite lifespan cell strain (184) and two benzo[a]pyrene immortalized mammary epithelial cell lines derived from 184 (184A1 and 184B5) contain wild type p53 sequences in exons 4-9, although elevated levels of nuclear p53 indicate an alteration in the stability of the normally transient protein. Wild type p53 was found in human bronchial, esophageal and hepatic epithelial cells immortalized by SV40 T antigen gene and human renal epithelial cells immortalized by adenovirus 5. BEAS-2B, an SV40 T antigen immortalized bronchial epithelial cell line and two subclones, have a germline polymorphism at codon 47. Inactivation of p53 by mechanisms such as mutation or complexing with proteins of DNA tumor viruses appears to be important in the immortalization of human epithelial cells.

p53 protein expression in central nervous system tumors: an immunohistochemical study with CM1 polyvalent and DO-7 monoclonal antibodies

Formalin-fixed, paraffin-embedded surgical specimens from 137 primary central nervous system tumors, including 26 astrocytomas (21 fibrillary, 1 protoplasmic, 1 gemistocytic and 3 pilocytic), 26 anaplastic astrocytomas, 9 glioblastomas, 1 gliosarcoma, 8 oligodendrogliomas, 4 ependymomas, 1 anaplastic ependymoma, 2 subependymomas, 3 paragangliomas, and 57 meningiomas, were immunostained with the CM1 polyclonal (pAb) and the DO-7 monoclonal (mAb) antibodies against the p53 protein, using the streptavidin/peroxidase method. In addition, two series of 17 and 9 medulloblastomas were also immunostained with the above pAb and mAb, respectively. p53 protein expression was observed in 7 fibrillary astrocytomas, 17 anaplastic astrocytomas, 5 glioblastomas, 1 gliosarcoma, 1 oligodendroglioma, 1 anaplastic ependymoma, and 4 meningiomas with the CM1 pAb. An additional 10 cases (i.e., 3 anaplastic astrocytomas and 7 meningiomas) were found to be p53 protein positive with the DO-7 mAb. Of the medulloblastomas, 8 (of the 17) and 4 (of the 9) were found to express p53 protein with CM1 pAb and DO-7 mAb, respectively. Our results indicate that p53 protein is expressed in a number of central nervous system neoplasms, and suggest that in astrocytic tumors a possible association may exist between p53 protein expression and tumor progression through increasing histological grades of malignancy.

Expression and stability of p53 protein in normal human mammary epithelial cells

To examine the p53 protein expressed in human mammary epithelial cell strains grown in vitro we first established the presence of only wild-type p53 and lack of any missense mutations in a representative normal mammary epithelial cell strain, 76N, by cloning and sequencing the entire coding region of the p53 mRNA. The p53 protein expressed in this cell strain and a number of similarly derived normal mammary epithelial cell strains was compared with mammary epithelial tumor cell lines having known p53 mutations and with fibroblasts derived from normal mammary tissue. In all cell strains, immunoprecipitation from metabolically labelled cells using monoclonal antibodies (mAb) PAb 1801 and PAb 122 revealed easily detectable p53 protein. Surprisingly, mAb PAb 1620 (wild type-specific) and PAb 240 (mutant-specific) each immunoprecipitated p53 protein from both normal and tumor cells. Furthermore, p53 protein in normal mammary epithelial cells was shown to be markedly more stable (half-life of approximately 3 h) compared to that in mammary fibroblasts or rodent fibroblasts (half-life < 30 min). Immunocytochemistry with PAb 1801 showed detectable p53 protein in normal mammary epithelial cells with a predominantly nuclear staining; however, p53 protein was undetectable in fibroblasts by immunocytochemistry. Together, these results reveal unusual features of wild-type p53 protein in normal human mammary epithelial cells, suggesting a cell type-specific regulation of its expression and function.

Induction of Sp1-p53 DNA-binding heterocomplexes during granulocyte/macrophage colony-stimulating factor-dependent proliferation in human erythroleukemia cell line TF-1

The involvement of Sp1 in regulating cell proliferation in myeloid leukemia cells was determined by measuring the levels and DNA binding activity of Sp1 in TF-1 cells, a human erythroleukemia cell line dependent on granulocyte/macrophage colony-stimulating factor (GM-CSF) for viability and cell growth. DNA binding of Sp1 to a specific double-stranded oligodeoxynucleotide was increased markedly in a dose-dependent manner in proliferating cells in response to GM-CSF compared with growth-arrested or apoptotic cells. Competition experiments and mobility shift interference assays with antibodies against Sp1 as well as wild-type or mutant p53 indicated that GM-CSF-inducible DNA-binding complexes contained both Sp1 and p53 and that these heterocomplexes bound to both p53- and Sp1-binding sequences with high affinity. Immunoprecipitation of nuclear extracts with a p53 antibody indicated that Sp1 was associated as a heterocomplex with p53. Formation of this complex was dependent on the level of p53 since p53 was more abundant in proliferating cells and decreased upon induction of growth arrest and apoptosis by withdrawal of GM-CSF while Sp1 levels remained unchanged. These results suggest that the association of Sp1 with p53 may represent a novel mechanism of growth regulation in cytokine-dependent leukemia cells.

Overexpression of wild-type p53 and c-Myc in human fetal cells transformed with adenovirus early region 1

The expression of p53 in a large panel of adenovirus (Ad) 2/5- and 12-transformed human, rat, and mouse cells has been examined. In all cases, in the absence of the larger Ad E1B protein, the level of p53 is very low. In human and rat cells when the Ad 12 E1B 54K polypeptide is expressed, p53 is much more abundant, although this is not the case in Ad 12 E1-transformed mouse cells. We conclude that expression of p53 is determined by virus serotype, host cell type, and viral proteins expressed. p53 in Ad 12 E1-transformed human cells is wild type but has an extended half-life. Stabilization is not through protein-protein interaction with the Ad E1B protein. The level of expression of c-Myc is also elevated in Ad-transformed human cells but this does not correlate with the presence of the E1B protein or with p53. However, Northern blot analysis indicates a direct correlation between mRNA and protein levels. We conclude that c-Myc is regulated at the transcriptional level, whereas p53 is regulated at the post-translational level in adenovirus transformants.

Molecular genetic alterations of chromosome 17 and p53 nuclear overexpression in human bladder cancer

We set out to define the alterations of chromosome 17 in human bladder tumors and to correlate p53 nuclear over-expression with 17p deletions in those neoplasms. We studied 60 bladder tumors by restriction fragment-length polymorphism analysis directed at five different loci on chromosome 17. The same tumors were studied with a panel of mouse monoclonal antibodies (PAb1801, PAb240, and PAb1620) to mutant and wild-type p53 proteins using immunohistochemistry. Deletion of 17p correlated with grade (p = 0.039), stage (p = 0.004), and the presence of vascular invasion (p = 0.056). None of the pathologic parameters correlated with 17q deletions. p53 nuclear overexpression correlated with grade (p = 0.027), stage (p = 0.008), vascular invasion (p = 0.021), and the presence of nodal metastases (p = 0.007). In superficial (Ta) lesions, 17p was not deleted, whereas 55% of T1 and T2-T4 tumors showed a loss of heterozygosity. Mutations of p53 as detected by immunohistochemistry were seen in superficial as well as invasive tumors, whereas loss of heterozygosity was seen only in invasive tumors. A strong correlation was found between the presence of mutation and the loss of heterozygosity of the remaining allele (p = 0.0003). Additional follow-up and further studies are required to better define the role of p53 nuclear overexpression and 17p deletions as markers of tumor progression in human bladder cancer.

Nuclear overexpression of p53 protein in transitional cell bladder carcinoma: a marker for disease progression

BACKGROUND

Approximately one third of the patients with superficially infiltrative transitional cell (T1-TNM pathological staging system) bladder carcinoma who are treated with transurethral resection alone have disease progression. Despite precise pathologic staging and grading, clinical outcome in these patients is not predictable. Recent reports reveal that mutations of the p53 tumor suppressor gene (also known as TP53) occur commonly in bladder cancers.

PURPOSE

The aim of this study was to investigate the hypothesis that altered patterns of expression of the protein product(s) of the mutated p53 tumor suppressor gene are associated with tumor progression in patients with T1 bladder cancer.

METHODS

We examined deparaffinized tumor tissue specimens from transurethral resection in 43 patients with T1 bladder cancer who had not received adjuvant therapy. Nuclear overexpression of p53 protein was detected by immunohistochemical analysis using the mouse monoclonal antibody PAb1801, which stains both wild-type and mutant p53 proteins. The data were then correlated with the following conventional prognostic variables: age, sex, histologic presence of associated carcinoma in situ, and vascular invasion of tumor. Disease progression rates per 100 person-years were calculated.

RESULTS

Median follow-up was 119 months. None of the urothelial and stromal cells from normal bladder specimens showed nuclear overexpression of p53 protein, but patients with T1 bladder tumors could be stratified into two groups with different patterns of staining for p53 protein. Eighteen patients (42%) had no more than 20% tumor cells with positive nuclear staining (group A), while the remaining 25 patients (58%) had 20% or more tumor cells with nuclear immunoreactivity (group B). Patients in group B had a significantly lower progression-free interval (P < .001). Disease progression rates were 20.5% per year for group B and 2.5% for group A.

CONCLUSION

These results suggest that T1 bladder cancers exhibiting nuclear overexpression of p53 protein have a higher probability of disease progression. This study also suggests that p53 overexpression is an important prognostic factor in these patients and may be useful in selecting appropriate therapy.

IMPLICATIONS

Large prospective studies are needed to confirm these results and to evaluate nuclear overexpression of p53 protein as a prognostic marker in bladder cancer.