Cellular accumulation of p53 protein: an independent prognostic factor in stage II breast cancer

The p53 gene product is a tumour suppressor protein, and alterations of the protein are common in human cancer. Previous studies have focused on nuclear accumulation of p53. To investigate if cytoplasmic accumulation of p53 strengthens the relationships to different pathobiological variables and distant recurrence-free survival in breast cancer, tumours from 164 stage II patients were examined with the monoclonal antibody PAb1801. Nine per cent of the tumours were nuclear positive and 21% were cytoplasmic positive. Cellular p53 accumulation, related to the nucleus or the cytoplasm or both, showed stronger associations with pathobiological variables than nuclear accumulation alone. Accumulation of p53 was significantly correlated to tumour size over 20 mm, negative oestrogen receptor (ER) status, DNA aneuploidy, high S-phase fraction and positive erbB-2 status. Cytoplasmic p53 was significantly correlated to distance recurrence-free survival in patients negative for nuclear p53 (P < 0.0001). Cellular p53 accumulation was an independent prognostic factor, in addition to lymph node status and ER content. We conclude that consideration of cytoplasmic staining enhances the clinical importance of p53.

Tumor spectrum analysis in p53-mutant mice

BACKGROUND

The p53 tumor suppressor gene is mutated in a large percentage of human malignancies, including tumors of the colon, breast, lung and brain. Individuals who inherit one mutant allele of p53 are susceptible to a wide range of tumor types. The gene encodes a transcriptional regulator that may function in the cellular response to DNA damage. The construction of mouse strains carrying germline mutations of p53 facilitates analysis of the function of p53 in normal cells and tumorigenesis.

RESULTS

In order to study the effects of p53 mutation in vivo, we have constructed a mouse strain carrying a germline disruption of the gene. This mutation removes approximately 40% of the coding capacity of p53 and completely eliminates synthesis of p53 protein. As observed previously for a different germline mutation of p53, animals homozygous for this p53 deletion mutation are viable but highly predisposed to malignancy. Heterozygous animals also have an increased cancer risk, although the distribution of tumor types in these animals differs from that in homozygous mutants. In most cases, tumorigenesis in heterozygous animals is accompanied by loss of the wild-type p53 allele.

CONCLUSION

We reaffirm that p53 function is not required for normal mouse development and conclude that p53 status can strongly influence tumor latency and tissue distribution.

Transitional cell carcinoma of the renal pelvis and its expression of p53 protein, c-erbB-2 protein, neuron-specific enolase, Phe 5, chromogranin, laminin and collagen type IV

Expression of p53 protein, c-erbB-2 protein, neuron-specific enolase (NSE), Phe 5, chromogranin, laminin and collagen type IV was studied by immunohistochemistry in formalin-fixed and paraffin-embedded specimens from 20 patients with renal pelvic carcinoma. Positive membrane-bound c-erbB-2 staining was not found in any case. Two tumors stained for p53 protein. Focal immunoreactivity for laminin was present in 55% and for collagen type IV in 80%. 25% of the cases were NSE positive. None of the tumors stained for Phe 5 or chromogranin. The results were compared with the clinical outcome and the immunohistological findings of p53 protein and c-erbB-2 protein in 13 cases of bladder carcinoma in the same patient group. Four of the thirteen bladder cancer specimens, but only 2 of the 20 renal pelvic cancer specimens, expressed p53 protein. As for renal pelvic carcinoma, c-erbB-2 protein was not expressed in bladder carcinoma. We conclude that p53 gene abnormalities may be of importance in the development of carcinoma in the renal pelvis and urinary bladder, but c-erbB-2 protein expression does not play a major role.

Elevated wild-type p53 protein levels in human epithelial cell lines immortalized by the human papillomavirus type 16 E7 gene

The role tumor suppressors p53 and retinoblastoma (RB) play in the transformation process has become central to understanding the pathogenesis of DNA tumor viruses. The two oncoproteins of human papillomavirus (HPV)-16, E6 and E7, bind to p53 and RB, respectively, thus inactivating the function of these tumor suppressor genes. Immortalization of primary human foreskin epithelial cells by HPV requires expression of the E7 protein, and the E6 protein greatly enhances the immortalization frequency. Two of three cell lines immortalized by the HPV-16 E7 oncoprotein expressed wild-type p53 and only one of the three cell lines had acquired a p53 mutation and loss of heterozygosity at 17p during the immortalization process. All three E7-immortalized lines contained higher steady-state levels of p53 protein. Mutation of the p53 gene is not required for immortalization in the absence of the HPV-16 E6 inactivation of the p53 protein, and 16E7 expression leads to the stabilization of wild-type p53.

The mdm-2 gene is induced in response to UV light in a p53-dependent manner

Irradiation of mammalian cells with UV light results in a dose-dependent accumulation of the p53 tumor-suppressor gene product that is evident within 2 hr. UV treatment causes a dramatic increase in p53-specific transcriptional transactivation activity and an increase in expression of the p53-responsive gene mdm-2. UV-stimulated mdm-2 expression is not directly correlated with the level of p53 protein in a cell because mdm-2 induction is delayed at high UV doses even though p53 levels rise almost immediately. Cells lacking p53 protein do not respond to UV by increasing their expression of mdm-2. The delayed induction of mdm-2 at high UV doses suggests that, in addition to p53 protein levels, other factors contribute to the regulation of mdm-2 expression following UV treatment. The time of induction of mdm-2 in cells treated with UV light correlates with recovery of normal rates of DNA synthesis, presumably after DNA repair. These data indicate a possible role for mdm-2 in cell cycle progression.

Comparison of p53 protein expression and cellular localization in human and hamster pancreatic cancer cell lines

We compared the expression of p53 protein in four human pancreatic cancer cell lines (HPAF, CD11, CD18 and PANC-1) and four hamster pancreatic cancer cell lines (PC-1, PC-1.2, PC-1.0 and H2T) by the monoclonal antibodies PAb421 and PAb240. PAb421 reacted with all human pancreatic cancer cell lines but not with the hamster cells. PAb240, on the other hand, reacted with all human and hamster pancreatic cancer cell lines in immunoblotting and in immunocytochemistry. However, immunoprecipitation with PAb240 was detected only in human cell lines HPAF, CD11 and CD18 cells but not in PANC-1 or in any of the hamster cell lines. During exponential growth, immunoreactivity was detected mainly in the nucleus of PC-1, PC-1.2 and PANC-1 cells (nuclear type) and in both the nucleus and the cytoplasm of PC-1.0, H2T, HPAF, CD11 and CD18 cells (diffuse type). At the confluence, the expression of p53 was decreased in most of the human cell lines as was proliferative cell nuclear antigen. After incubation with 1 mM hydroxyurea, cells with nuclear p53 expression did not show an altered cellular distribution of p53 protein, whereas cells with a diffuse type of localization pattern showed an increase in the nuclear staining. On the other hand, cytoplasmic immunoreactivity was found in PC-1.0, PC-1, PC-1.2, HPAF, CD11 and CD18 cells that were treated with 100 ng/ml of nocodazole. After heat stress with 1 h incubation at 42 degrees C, p53 protein was detected in the cytoplasm and nucleolus of all cell lines. After 24-48 h incubation at 37 degrees C, this change in cellular distribution of p53 in response to heat stress was reverted to a preheat stress pattern. The overall results suggest that neither the p53 of PANC-1 nor the hamster pancreatic cancer cell lines are immunoprecipitated with the PAb240. It appears that cell cycle and heat stress are two of the factors that influence cellular localization of p53 protein in both human and hamster pancreatic cancer cells.

Mutational inactivation of the p53 gene in the human erythroid leukemic K562 cell line

The K562 human chronic myelogenous leukemia (CML) cell line has attained widespread use as a model for studying hematologic malignancy and erythroid differentiation. Sequencing of the p53 gene in the K562 cell line demonstrated a mutation in exon 5 characterized by a single base insertion (cytosine) between codons 135 and 136. This frameshift mutation leads to an N-terminal truncated protein of 147 amino acids. Only the mutated sequence was present suggesting that the normal allele has been lost. Reverse transcription PCR (RT-PCR) detected a p53 transcript but Western blotting and immunohistochemical staining of cells failed to detect p53 protein. The identification of an inactivation mutation of p53 in the K562 cell line further supports the argument that p53 mutations play a role in myeloid blast transformation of CML.

[Establishment and mechanistic characterization of SV40 T antigen immortalized human fetal hepatocytes]

Human fetal liver cells were cultured in serum free media enriched with hydrocortisone and infected with retrovirus containing SV40 large T gene. Replicating colonies with G-418 resistance developed in 50 days through 23 passages, while none grew in control dishes. After a crisis of 3 months duration, three colonies resumed active proliferation for over 15 months through 60 passages and became immortalized. These cells had epithelioid morphology, and were stained positively for CK-18. Southern blot and immunocytochemistry demonstrated the presence and expression of SV40 T-antigen in the immortalized cell lines. The cells expressed human albumin, especially in those while in cycle. Accumulation of p53 protein in the cell nuclei and strong expression of TGF-alpha as shown by immunocytochemistry explained at least partly the mechanism of unlimited growth of these immortalized human hepatocytes. These cells did not show anchorage-dependent growth in soft agar, nor did tumor form when inoculated into nude mice. These immortalized, differentiated, non-malignant human fetal hepatocyte lines may be useful for further studies.

Correlation between p53 mutations and antibody staining in breast carcinoma

Abnormalities of the p53 gene and protein were examined in 81 primary breast carcinoma samples. Using a polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) analysis, mutations in p53 exons 5-8 were identified in 13 of 81 tumours (16 per cent) and confirmed by DNA sequencing. Positive staining for p53 protein was detected in ten of 77 (13 per cent) of these tumours using polyclonal CM1 antibody on formalin-fixed tissue. Mutations detected by PCR-SSCP analysis were more common in grade III tumours (P = 0.015), but no correlation was found with tumour size, node status or level of epidermal growth factor receptor expression. A p53 mutation was associated with positive antibody staining in only two patients. Positive immunohistochemical staining using a p53 antibody may detect p53 protein expression, but this may not correlate directly with an underlying mutation in the hot spot region examined.

[P53 in atherosclerotic plaques]

The methylation and expression of P53 were studied in atherosclerotic plaques. Atherosclerosis was initiated in 2.5-3.0 kg New Zealand white Rabbits by feeding cholesterol, oil and endothelial debridement of the aorta. There were the methylation of the partial CCGG sites, low levels of expression of the wild-type P53 and mutant P53 protein in the plaques. These might be an important cause of the cellular proliferation during development of atherosclerosis.

Immunohistochemical detection of mutant P53 protein and human papillomavirus-related E6 protein in anal cancers

PURPOSE

The wild-type P53 protein, a product of the P53 gene, is a normal growth controlling protein. Mutation of the P53 gene generates a mutant P53 protein which promotes tumor formation through loss of growth suppression. Some of the agents responsible for P53 gene mutation are known, one of which may be tumorigenic human papillomavirus (HPV) infection. Anal cancers are demonstrating a changing trend in the affected population, from older females in the older reported series to younger males more recently. This may be a reflection of infection with tumorigenic HPV types 16 and 18. The E6 oncoprotein of these viruses inactivates the growth-controlling wild-type P53 protein. In this study, our purpose was to determine the incidence of mutant P53 and HPV-16 and 18-related E6 protein and their coexpression in anal cancers.

METHODS

We examined 29 anal cancers immunohistochemically for mutant P53 protein, HPV 16 and 18 E6 protein, and coexpression of the two.

RESULTS

Mutant P53 protein was present in 58.6 percent of anal cancers overall and in 85.7 percent of anal adenocarcinomas. E6 oncoprotein was present in five cases (17.2 percent), all of which were squamous-cell carcinomas. Coexpression of both mutant P53 and E6 proteins was seen in only three cases (10.3 percent).

CONCLUSION

Although tumorigenic HPV may be an important cause for P53 gene mutation in anal cancers, perhaps other mutagenic factors play a predominant role.

Establishment of a leukaemic cell line from a patient with acquisition of chromosomal abnormalities during disease progression in myelodysplastic syndrome

A cell line designated SKM-1 was newly established from leukaemic cells of a 76-year-old Japanese male patient with monoblastic leukaemia following myelodysplastic syndrome (MDS). The cells were obtained from peripheral blood of the patient when he lost multiple point mutations of ras genes with acquisition of chromosomal abnormalities during disease progression in MDS. The cells grew as a single floating cell, and have been continuously growing with the morphological characteristics of immature monoblasts by serial passages during the past 42 months with a doubling time of about 48 h. By cytochemical analysis, the cloned cells were positive for butyrate esterase, but negative for the Epstein-Barr virus associated nuclear antigen. Phenotypic analysis revealed the expression of myelomonocyte specific antigens such as CD4, CD13, CD33 and HLA-DR. Cells from the primary peripheral blood and those from 50 passages of the SKM-1 cell line both possessed no activated ras genes but showed karyotype abnormalities with 46,XY, del(9)(q13;q22), der(17) t(17;?)(p13;?). The SKM-1 cells have two mutations in p53 gene and overexpress the p53 products. This cell line may contribute to a better understanding of molecular mechanisms in the progression from MDS to myelogenous leukaemia.

The tumor suppressor p53 and the oncoprotein simian virus 40 T antigen bind to overlapping domains on the MDM2 protein

The oncogene mdm2 has been found to be amplified in human sarcomas, and the gene product binds to the tumor suppressor p53. In this report, we describe the dissection of the MDM2-binding domain on p53 as well as the p53-binding domain on MDM2. We also demonstrate that the oncoprotein simian virus 40 T antigen binds to the product of cellular oncogene mdm2. We have constructed several N- and C-terminal deletion mutants of p53 and MDM2, expressed them in vitro, and assayed their in vitro association capability. The N-terminal boundary of the p53-binding domain on MDM2 is between amino acids 1 and 58, while the C-terminal boundary is between amino acids 221 and 155. T antigen binds to an overlapping domain on the MDM2 protein. On the other hand, the MDM2-binding domain of p53 is defined by amino acids 1 and 159 at the N terminus. At the C terminus, binding is progressively reduced as amino acids 327 to 145 are deleted. We determined the effect of human MDM2 on the transactivation ability of wild-type human p53 in the Saos-2 osteosarcoma cell line, which does not have any endogenous p53. Human MDM2 inhibited the ability of human p53 to transactivate the promoter with p53-binding sites. Thus, human MDM2 protein, like the murine protein, can inactivate the transactivation ability of human p53. Interestingly, both the transactivation domain and the MDM2-binding domain of p53 are situated near the N terminus. We further show that deletion of the N-terminal 58 amino acids of MDM2, which eliminates p53 binding, also abolishes the capability of inactivating p53-mediated transactivation. This finding suggests a correlation of in vitro p53-MDM2 binding with MDM2's ability in vivo to interfere with p53-mediated transactivation.

Some oral carcinomas from Sri Lankan betel/tobacco chewers overexpress p53 oncoprotein but lack mutations in exons 5-9

We reported a low prevalence (11%) of p53 expression detected by immunohistochemistry in oral squamous cell carcinomas associated with betel/tobacco chewing Sri Lankans (23). Five neoplasms which over-expressed p53 protein were used in the present study of mutations. Despite extensive sequence analysis no mutations were detected in exons 5 through 9 of the p53 gene in all the DNA samples of these neoplasms. Thus, over-expression of p53 is not necessarily synonymous with mutations in the exons studied, although mutations of this gene have been reported in oral and head and neck cancer from Japan and USA. The absence of mutations in betel/tobacco related carcinomas in this population may derive from differences in aetiology, carcinogen metabolism and susceptibility, DNA repair mechanisms and/or genetic predisposition.

Expression of p53 protein in benign and malignant epidermal pathologic conditions

BACKGROUND

p53 is an oncogene and a tumor-suppressor gene whose gene product regulates the cell growth cycle. Mutations in p53 are the most common genetic alterations in human cancer.

OBJECTIVE

Our purpose was to define p53 expression and subcellular localization in normal and pathologic epidermis.

METHODS

We examined sections of normal skin, psoriasis, squamous cell carcinoma (SCC), basal cell carcinoma (BCC), keratoacanthoma, and cultured epithelial cell lines with five antibodies to p53.

RESULTS

Monoclonal antibody MAb421 and MAb1801 stained the cytoplasm of normal basal keratinocytes, suggesting that subcellular localization or sequestration of wild-type p53 regulates its activity. Polyclonal antibody reacted throughout normal epidermis, suggesting heterogeneity of species or conformational forms of p53 protein. Cytoplasmic reactivity to MAb421 was similar in normal epidermis, psoriasis, and cultured keratinocytes but was, diminished in SCC, BCC, and keratoacanthoma. CM-1 reactivity persisted in these tumors. Putative p53 mutations detected by MAb240 reactivity were present in 44% of SCC specimens.

CONCLUSION

Epidermis expresses p53 and the gene may regulate epidermal keratinocyte growth and carcinogenesis.

High-risk human papillomavirus infections and overexpression of p53 protein as prognostic indicators in transitional cell carcinoma of the urinary bladder

Ninety Japanese patients with transitional cell carcinoma of the urinary bladder were investigated for tumor incorporation of DNA for high-risk human papillomavirus (HPV) types 16, 18, and 33 by in situ hybridization with biotinylated DNA probes. In addition, immunohistochemical analysis of p53 protein expression was performed with an antibody to p53 protein. Twenty-eight tumors were positive for HPV DNA, and multiple HPV infection was detected in 17 cases. Positive nuclear staining of cancer cells by the antibody to p53 protein was detected in 32 cases. DNA for HPV 16, 18, and/or 33 and the overexpression of p53 protein were simultaneously observed in 6 tumors by using a mirror section method. The overexpression of p53 protein was frequently detected in invasive and nonpapillary tumors (P < 0.05) and in high grade tumors (P < 0.05). In contrast, HPV infection was more common in noninvasive and papillary tumors (P < 0.01). The patients with tumors positive for HPV DNA and/or p53 antibody had a significantly worse survival rate (P < 0.05). These results suggest that HPV infection or overexpression of p53 protein may be related to tumor behavior and may indicate a relatively poor prognosis in patients with transitional cell carcinoma.

Role of the p53 tumor suppressor gene in cell cycle arrest and radiosensitivity of Burkitt's lymphoma cell lines

We have assessed the role of the p53 tumor suppressor gene in cell cycle arrest and cytotoxicity of ionizing radiation in 17 Burkitt's lymphoma and lymphoblastoid cell lines. Cell cycle arrest was assessed by flow cytometry of cells 16 h following irradiation. In addition to the usual G2 arrest, the cell lines exhibited three types of responses in G1: Class I, strong arrest in G1 following radiation; Class II, minimal arrest; and Class III, an intermediate response. All Class I cells contained normal p53 genes. Of the ten lines that showed minimal G1 arrest, eight had mutant p53 alleles, and two lines were heterozygous for p53 mutations. Both of the lines showing an intermediate response contained wild-type p53. Our results are consistent with the view that mutations abrogate the ability of p53 to induce G1 arrest following radiation. Studies with the heterozygotes showed that the mutant protein can have a dominant negative influence upon wild-type p53, and the reduced ability of two normal p53 lines to arrest in G1 indicated that p53 function can be impaired by other mechanisms. The radiosensitivity of most of the lines appeared to depend on the ability of p53 to induce a G1 arrest. The mean radiation dose that inhibited proliferation of the Class I lines by 50% was 0.98 Gy. Of the eight p53 mutant cell lines tested, five lines required approximately 2.9 Gy to cause a 50% inhibition of cell proliferation. The two heterozygotes were also more resistant to radiation than the Class I cells (50% inhibitory dose, 2.1 and 2.9 Gy). Our results suggest that radioresistance is afforded by a loss of function of wild-type p53, which would normally induce a G1 arrest and promote cell death in the presence of DNA damage.

Relationship of tobacco/alcohol use to p53 expression in patients with lingual squamous cell carcinomas

This study examined p53 expression immunocytochemically in 40 lingual squamous cell carcinomas from Dutch patients with known histories of smoking and/or drinking alcohol. 30% of neoplasms showed positive p53 reactivity, suggesting increased levels of p53 protein. No alcohol or tobacco risk factors were evident in 33.3% (4/12) of p53-positive neoplasms whereas only 7.1% (2/28) of p53-negative neoplasms showed an absence of these risk factors. 25% (3/12) of p53-positive neoplasms and 71.4% (20/28) of p53-negative neoplasms were found in patients who had been exposed to both alcohol and tobacco. A similar negative association with p53 reactivity was also found when either tobacco or alcohol were used in isolation. The results contrast with previous observations in head/neck and oral carcinomas and indicate that the association of alcohol/tobacco and p53 expression remains open to question.

Dominant negative effect of a germ-line mutant p53: a step fostering tumorigenesis

Lysates derived from the fibroblasts of individuals who are homozygous for normal p53 or heterozygous for the germ-line p53 mutation characteristic of certain Li-Fraumeni cancer-prone families were assessed for p53 function utilizing the binding of p53 protein to a p53-specific consensus oligonucleotide sequence. As expected, control nuclear lysates containing only mutant p53 or no p53 displayed little or no such binding. However, the nuclear lysates from heterozygous fibroblasts containing similar amounts of normal p53 and 245D mutant p53 displayed binding that was significantly below 50% of that seen with homozygous wild-type p53 in normal cell lysates. The nuclear lysates of these heterozygous or homozygous fibroblasts exhibited similar levels of DNA binding to a consensus oligonucleotide specific for the transcription factor, AP-1. These results indicate that mutant p53 has a transdominant effect on the binding of DNA by normal p53. These findings also suggest that p53 complexes formed in vivo that contain mutant p53 are functionally impaired even if normal p53 is also present in the complex. The implications of a trans-dominant effect of mutant p53 on the cancer-prone phenotype of individuals heterozygous for mutated p53 in Li-Fraumeni families is discussed.

Mice with reduced levels of p53 protein exhibit the testicular giant-cell degenerative syndrome

Transgenic mice which carry hybrid p53 promoter-chloramphenicol acetyltransferase (CAT) transgenes were found to express CAT enzymatic activity predominantly in the testes. Endogenous levels of p53 mRNA and protein were lower than in the nontransgenic control mice. The various p53 promoter-CAT transgenic mice exhibited in their testes multinucleated giant cells, a degenerative syndrome resulting presumably from the inability of the tetraploid primary spermatocytes to complete meiotic division. The giant-cell degenerative syndrome was also observed in some genetic strains of homozygous p53 null mice. In view of the hypothesis that p53 plays a role in DNA repair mechanisms, it is tempting to speculate that the physiological function of p53 that is specifically expressed in the meiotic pachytene phase of spermatogenesis is to allow adequate time for the DNA reshuffling and repair events which occur at this phase to be properly completed. Primary spermatocytes which have reduced p53 levels are probably impaired with respect to DNA repair, thus leading to the development of genetically defective giant cells that do not mature.

p53 expression in laryngeal carcinoma

The expression of the nuclear phosphoprotein, p53, was studied in 21 cases of squamous cell carcinoma of the larynx and 16 benign laryngeal lesions using the polyclonal rabbit antibody, CM1 (Novocastra Laboratories Ltd). Fourteen of the carcinomas showed nuclear staining whereas only one of the benign lesions exhibited presence of the protein. This suggests that, as with squamous cell carcinoma of the lung, p53 plays a role in the development of malignant disease of the larynx.

Expression of p53 gene in 184 unifocal hepatocellular carcinomas: association with tumor growth and invasiveness

To elucidate the biological significance of the p53 gene expression in human hepatocellular carcinoma (HCC), the p53 protein was studied in 184 resected unifocal primary HCCs, including 102 small (< or = 5 cm) and 82 large HCCs (> 5 cm), using immunocytochemistry. The p53 mRNA expression was analyzed in 69 cases using Northern hybridization. The p53 protein, which was detected in 58 HCCs (31.5%), was overexpressed more frequently in HCC with elevated serum alpha-fetoprotein level (37.9 versus 25%, P < 0.04), in large HCC (39.0 versus 25.5%, P < 0.03), and in invasive HCC (35.1 versus 13.3%, P < 0.01). The overexpression of p53 protein closely correlated with p53 mRNA overexpression (75 versus 44.4%, P < 0.003), and p53 gene mutation (76.9 versus 19.2%, P < 1 x 10(-9)). HCCs with p53 protein expression (group A) and those negative for both p53 protein and mRNA expression (group B) had an unfavorable outcome, while HCC with no p53 protein but with p53 mRNA overexpression (group C) had the best outcome; the 4-year survival was 26.1, 26.3, and 62.5%, respectively. The p53 gene mutation was significantly higher in group A HCC (76.9%) than in groups B (27.3%) and C (23.5%), P < 0.0001. The results suggest that the p53 protein and mRNA expression patterns in HCC correlate with p53 gene mutation and tumor behavior and may serve as a molecular prognostic factor.