Inhibition of DNA synthesis by TGF-beta 1 coincides with inhibition of phosphorylation and cytoplasmic translocation of p53 protein

Electroporation and carrier DNA cause p53 activation, cell cycle arrest, and apoptosis

Methods used in transient transfection of cells may alter cellular signaling pathways that in turn may lead to misinterpretation of the results. A variety of genotoxic agents cause the accumulation of the p53 protein leading to either apoptosis or growth arrest. Here we report the effect of electroporation and carrier DNA on the stability, cellular localization, and transcriptional activity of p53. We show that electroporation leads to p53-dependent and also p53-independent cell-cycle arrest and apoptosis. At the same time a chemical agent polyethylenimine that is also used for transient transfection of cells causes neither upregulation of p53 nor cellular response.

Growth arrest in G1 protects against oxygen-induced DNA damage and cell death

Although oxygen is required for normal aerobic respiration, hyperoxia (95% O(2)/5% CO(2)) damages DNA, inhibits proliferation in G1, S and G2 phases of the cell cycle, and induces necrosis. The current study examines whether growth arrest in G1 protects pulmonary epithelial cells from oxidative DNA damage and cell death. Mv1Lu pulmonary adenocarcinoma cells were chosen for studies because hyperoxia inhibits their proliferation in S and G2 phase, while they can be induced to arrest in G1 by altering culture conditions. Hyperoxia inhibited proliferation, increased intracellular redox, and rapidly reduced clonogenic survival. In contrast, Mv1Lu cells treated with transforming growth factor (TGF)-beta1, deprived of serum or grown to confluency, arrested and remained predominantly in G1 even during exposure. Growth arrest in G1 significantly enhanced clonogenic survival by 10-50-fold. Enhanced survival was not due to reduction in the intracellular redox-state of the cells, but instead was associated with reduced DNA strand breaks and p53 expression. Our findings suggest that the protective effects of G1 is mediated not simply by a reduction in intracellular ROS, but rather through an enhanced ability to limit or rapidly recognize and repair damaged DNA.

The involvement of Fas-Fas ligand pathway in fibrosing lung diseases

Pulmonary fibrosis begins with alveolitis, which progresses to destruction of lung tissue and excess collagen deposition. This process could be the result of DNA damage and a form of apoptosis. Therefore, we hypothesized that Fas ligand (FasL), which induces apoptosis in cells expressing Fas antigen (Fas), is associated with pulmonary fibrosis. We examined frozen lung tissues from seven patients with idiopathic pulmonary fibrosis (IPF), and bronchoalveolar lavage fluid (BALF) cells from 19 patients with IPF and from 17 patients with interstitial pneumonia associated with collagen vascular diseases (CVD-IP). We used five frozen lungs with normal lung parenchyma and BALF cells from 10 patients with solitary pulmonary nodule as controls. Reverse transcription-polymerase chain reaction (RT-PCR) showed that FasL messenger RNA (mRNA) was expressed in BALF cells from all patients with IPF and from 15 of 16 patients with CVD-IP. FasL mRNA was not detected in BALF cells except in one of 10 controls. RT in situ PCR detected FasL mRNA in inflammatory cells in BALF from patients with IPF. Immunohistochemistry detected FasL protein in infiltrating lymphocytes and granulocytes in all of seven frozen lung tissues of IPF, but in none of five control lung tissues. Additionally, the expression of Fas appeared to be upregulated in bronchiolar and alveolar epithelial cells in IPF compared with normal lung parenchyma by immunohistochemistry. We conclude that Fas and FasL were upregulated in fibrosing lung diseases and may associate with DNA damage or apoptosis of bronchiolar and alveolar epithelial cells in this disorder.

Study of tumor infiltrating lymphocytes and transforming growth factor-beta as prognostic factors in breast carcinoma

Cytokines and growth factors are powerful modulators of the immune response. Their aberrant expression either by the tumor cells or by the tumor infiltrating lymphocytes confers a selective advantage to the tumor to grow and suppress the cytotoxic activity of the infiltrating lymphocytes. Therefore, analysis of these soluble factors in the tumor microenvironment can provide an insight into the understanding of the tumor behavior and may be used as a prognostic factor. In the present study the nature of the tumor infiltrating lymphocytes (TILs) and cytokine profile was examined in 36 and 19 mammary carcinoma tissues, respectively, by immunohistochemistry and PCR. Phenotypic differences in the number of cytotoxic T lymphocytes (CD8+) and lymphokine activated killer cells (CD16) was observed among TILs when patients with either early disease stage (39% and 46.6%, respectively) or those alive with no residual disease (31% and 52%, respectively) were compared with late stage (9.7% and 22.8%, respectively) or those dead of disease (14.6% and 15.6%, respectively). Furthermore, analysis of the 19 tumor samples for cytokine mRNA expression by RT-PCR revealed the presence of TNF-alpha, IL-10, TGF-beta1, and IL-2. However, semi-quantitative PCR analysis demonstrated TGF-beta1 expression to be significantly higher in patients with a favorable outcome (1.0246 attomoles/micromoles) as compared to patients with a poor prognosis (0.1157 attomoles/micromoles). Our results demonstrate the potential biological significance of certain host factors, particularly TILs and TGFbeta1 expression, on the outcome of breast cancer.

Wild-type p53 gene-induced morphological changes and growth suppression in hepatoma cells

The human hepatocellular carcinoma (HCC) cell line, HLF, expresses only mutant-type p53 (mt-p53), which has an amino acid substitution at the 244th residue from glycine to alanine. HLF cells were transfected with wild-type p53 (wt-p53) cDNA construct pC53-SN3, mt-p53 cDNA construct pC53-SCX [which differs by a single nucleotide, resulting in alanine instead of valine at the 143rd residue in p53 (p53-143)], or pCMV-Neo-Bam, as a control, by a liposome method. After G418 selection, three wt-p53 stable transformants (WT), four mt-p53 transformants (MT), and three control vector transformants (VT) were obtained. We analyzed the cell growth and morphological changes of these transformants under different culture conditions [fetal calf serum (FCS), 10%, 1%, and 0%]. Whereas no difference from control in the growth rate and morphology was observed under the 10% FCS conditions, serum starvation induced remarkable phenotypical changes in all three WTs, but not in the other transformant. Corresponding to these phenotypical changes, the transcriptional activity of wt-p53 was increased more than nine fold. These results indicated that serum starvation would induce wt-p53 biological function, which is tightly linked to morphological changes and growth suppression. To induce these changes, the introduction of the wt-p53 gene itself was not sufficient, and additional triggering, i.e., serum starvation, was indispensable.

Stimulation of cell proliferation and inhibition of gap junctional intercellular communication by linoleic acid

The effect of linoleic acid (LA) on gap-junction permeability, connexin 43 mRNA level, protein level, and phosphorylation, and the numbers of gap-junctional membrane plaques were studied in the rat liver epithelial cell line WB-F344 to determine whether changes in these parameters correlated with the enhanced cell growth and the inhibition of gap-junction function. When cultured in a medium with low serum (1%), these cells exhibited a slower growth rate than in the high serum medium (7%). Addition of linoleic acid (0.01-3 mg/ml) to the low serum medium increased the growth rate and inhibited gap junctional intercellular communication (GJIC) in a dose-dependent manner. In a comparison of short-term and long-term treatments with LA, GJIC in short-term treated (1 h) WB cells was inhibited at 3 mg/ml LA but readily recovered by washing and removing LA from cells, whereas GJIC in long-term treated (6 days) WB cells did not recover by washing and removing LA from WB cells. Western blot analysis of connexin 43 showed that a short-term incubation with linoleic acid increased the relative amount of unphosphorylated connexin 43 protein, but a long-term incubation with linoleic acid decreased the amount of unphosphorylated connexin 43 protein and increased the relative amount of hyperphosphorylated connexin 43 protein. Connexin 43 and p53 mRNA levels decreased in a time- and dose-dependent manner in linoleic acid-treated cells. These results suggest that growth stimulation and gap junctional intercellular communication inhibition of rat liver epithelial cells by linoleic acid may be mediated in part through modulation of p53 expression and function.

Immunohistochemical analysis of p53 protein in transplant recipients with Kaposi's sarcoma

PURPOSE

Kaposi's sarcoma (KS) is a proliferative process of suspected viral aetiology associated with immune deficiency. In transplanted patients, lesions regress on discontinuation of immunosuppressive therapy. The purpose of this work was to analyse the expression of the p53 oncosuppressor gene product, a proliferation regulator overexpressed in both malignant and non-malignant conditions, with the aim of better qualifying KS proliferation characteristics.

METHODS

We analysed p53 expression in a group of transplanted, cyclosporin A-treated, KS patients by immunohistochemistry, utilizing the DO-7 (with and without the antigen retrieval pretreatment), and the PAb 240 monoclonal anti-p53 antibodies, the latter of which is able to detect a mutated epitope, and evaluating staining intensity and localization, whether cytoplasmic or nuclear.

RESULTS

Seventy five percent of KS lesions from transplanted patients presented both nuclear and cytoplasmic positive p53 immunostaining with DO-7 antibody, thus demonstrating a presumably functional inactivation; one case also presented immunoreactivity with the PAb 240 antibody.

CONCLUSIONS

On the basis of the results obtained and in the presence of lesion regression upon immunosuppression withdrawal, it may be concluded that KS in transplanted patients can be considered a non-malignant proliferative process, and that the cytoplasmic expression of p53 may stand for a functional inactivation pattern.

p53 Phosphorylation: biochemical and functional consequences

The p53 protein plays a vital role in suppressing the development of cancer. Posttranslational modification through phosphorylation has been postulated to be an important regulatory mechanism of p53 function. Data describing the role of phosphorylation in terms of its effects on several biochemical properties and cellular functions of p53 are examined in the context of how p53 might be "phospho-regulated."

Prognostic significance of cytoplasmic p53 overexpression in colorectal cancer. An immunohistochemical analysis

p53 overexpression was studied by immunohistochemistry in 96 consecutive colorectal cancer patients, subdividing positive specimens according to two staining patterns: cytoplasmic or nuclear. Forty-seven per cent of the cases were p53 positive, a significant correlation being found with Dukes' stage (P = 0.0036). A prevalence of nuclear staining was observed in Dukes' B and cytoplasmic in Dukes' D stages. After 36 months, 23% of the patients had a recurrence, and 45% were p53 positive, all Dukes' C-D stage with cytoplasmic staining. The Kaplan-Meier curve showed a significant correlation between p53 cytoplasmic staining and disease-free survival period (P = 0.002). With respect to disease-free survival, the Cox proportional hazard regression test, comparing p53 positivity with Dukes' stage, showed the latter to be the most significant variable. In our series of patients, advanced Dukes' stage tumours were localised in the right colon, where a higher percentage of p53 positivity (67% versus 40% of the left side), as well as a higher frequency of cytoplasmic staining was observed. In conclusion, from the data obtained, a strong correlation between p53 cytoplasmic staining and patient prognosis is clearly indicated.

Tumor suppressor p53 mutations and breast cancer: a critical analysis

Alterations in the tumor suppressor gene p53 are the most commonly identified changes in cancer, including neoplasia of the breast. The activity of p53 is regulated post-translationally. Phosphorylation state, subcellular localization, and interaction with any of a number of cellular proteins are likely to influence the function of p53. The exact effect of p53-mediated growth suppression seems to be cell-type specific but appears to be directly related to the ability of p53 to act as a specific transcriptional activator. The role that transcriptional repression plays in the function of WT p53 is less clear. It is also possible that p53 has a more direct activity in DNA replication and repair. Most documented p53 mutations result in single amino acid substitutions which may confer one or more of a spectrum of transforming abilities on the protein. Mutation may lead to nuclear accumulation of p53 protein; however, inactivation of p53 by nuclear exclusion and interaction with the mdm2 protein also appear to be important in tumorigenesis. Used in conjunction with other established factors, accumulation of cellular p53 may be a useful prognostic indicator in breast cancer. A syngeneic mouse model system yielded evidence that p53 mutations are important in the early, preneoplastic stages of mammary tumorigenesis. This murine system may provide the ability to investigate the functions of p53 in the early stages of breast cancer which are technically difficult to examine in the human system.

Transforming growth factor-beta 1 blocks interleukin 4 induced cell proliferation by inhibiting a protein tyrosine phosphatase essential for signal transduction

Transforming growth factor-beta 1 (TGF-beta 1) is a cytokine which exhibits pleiotropic effects on many cell types and cellular systems. TGF-beta 1 has been shown to play a modulatory role in haematopoiesis and immunoregulation, expressed through its ability to inhibit the activities induced by other cytokines; however, the mechanisms underlying this activity are currently unclear. The potency of this activity varies according to the selected stimulatory cytokine and we have found that the proliferation of leukaemic cell lines induced by interleukin 4 (IL-4) is particularly sensitive to inhibition by TGF-beta 1 and provides a useful model to study the mechanism of action of TGF-beta. We have previously shown that IL-4 mediated mitogenic signal transduction in human systems involves the induction of phosphatase activity leading to the dephosphorylation of an 80-kDa protein (p80). We now show that TGF-beta 1 inhibits IL-4 induced dephosphorylation of p80 in a dose responsive manner closely correlated with its ability to inhibit the biological activity of IL-4. This suggests that TGF-beta 1 is inhibiting the same protein-tyrosine-phosphatase required by IL-4 to transduce its mitogenic signal. The biochemical mechanism underlying the biological activity of TGF-beta 1 in inhibiting IL-4 bioactivity is therefore the blocking of post receptor binding signal transduction processes.

Immunohistological expression of p53 in primary pT1 transitional cell bladder cancer in relation to tumour progression

OBJECTIVE

To determine whether p53 expression is a marker of tumour progression in superficially invasive (pT1) transitional cell carcinoma of the bladder.

PATIENTS AND METHODS

The immunohistochemical status of the p53 protein in 28 pT1 primary bladder cancers was determined on frozen tissue and archival paraffin block sections using three primary antibodies (CM-1, PAB1801 and D07). The findings were compared with the patients' progress. All the patients, except for those who died during the course of the study, were followed up by check cystoscopy for a minimum of 2 years.

RESULTS

Immediately adjacent frozen sections stained identically in 10 of 16 cases for CM-1 and PAB1801. For paraffin sections, identical staining patterns were seen for PAB1801 and D07 in 21 of 26 sections. However, inter- and intra-tumour staining for p53 was very variable, even with the same antibody. The heterogeneity of p53 positive cell distribution in the tumours indicates potential for significant sampling errors if random sections are chosen as representative of p53 status.

CONCLUSION

The p53 status of the primary tumours did not relate to patient outcome. The results obtained do not support the use of immunohistological p53 expression as a discriminating prognostic indicator in pT1 transitional cell carcinoma of the bladder.

Close correlation between the dephosphorylation of p53 and growth suppression by transforming growth factor-beta 1 in nasopharyngeal carcinoma cells transduced with adenovirus early region genes

The mechanism of growth inhibition by transforming growth factor (TGF)-beta 1 was investigated. We examined the growth inhibitory effects of TGF-beta 1 on human nasopharyngeal carcinoma (KB) cells which constitutively expressed p53. TGF-beta 1 suppressed the DNA synthesis of KB cells in a dose-dependent manner. It had minimal effect on adenovirus-2-transduced KB cells expressing either adenovirus early region 1B (E1B) or 1A (E1A) product, which respectively binds to p53 or Rb product and inhibits its function, and no growth inhibition at all was observed with KB cells expressing both E1B and E1A products. Dephosphorylation of the p53 was promoted by TGF-beta 1 stimulation in KB cells, but not in E1B-producing KB cells, which sequestrate the function of p53. The growth inhibition of KB cells by TGF-beta 1 was significantly reduced by treatment with okadaic acid. These results suggest that p53 transduces the antiproliferative signal of TGF-beta 1 possibly through its dephosphorylation.

Transforming growth factor-beta 1 enhances serum-induced dephosphorylation of the P53 protein in cell lines growth-inhibited by this factor

A 24 hr TGF-beta 1 treatment (4 ng/ml) of SV40-transformed WI38 embryonic fibroblasts (VA13 cells) causes a moderate but reproducible inhibition of their serum-stimulated growth. By immunoprecipitation with the PAb122 antibody, we show that serum stimulation of previously serum-deprived cells causes a dephosphorylation of the wild type P53 protein, which is accentuated by the TGF-beta 1 treatment. The TGF-beta 1-enhanced dephosphorylation effect is also observed in two other cell lines growth-inhibited by TGF-beta 1, but which do not contain Large T (mink lung CCL64 and human KHOS cells). On the contrary, TGF-beta 1 treatment of the untransformed WI38 fibroblasts stimulates their growth, without affecting the phosphorylation of P53. Such treatment did not affect the expression of the corresponding mRNA nor the level of synthesis of the protein. The results suggest that the P53 protein could be a downstream target of TGF-beta 1 action on those cells growth-inhibited by the factor.

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.

Association of insulin-like growth-factor-I-induced DNA synthesis with phosphorylation and nuclear exclusion of p53 in human breast cancer MCF-7 cells

Human breast cancer MCF-7 cells, growth-arrested by serum starvation, were stimulated with recombinant human insulin-like growth factor-I (IGF-I). An increase in DNA synthesis was induced 20 hr later, which was as effective as that induced by serum. The increase in DNA synthesis was significantly inhibited either by antibody to the IGF-I receptor or by the tyrosine kinase inhibitor, methyl-2,5-dihydroxycinnamate (2,5-MeC). The IGF-I-induced DNA synthesis coincided with an elevated level of phosphorylation of p53 on tyrosine and an alteration in the subcellular distribution of the protein from the nucleus to the cytoplasm. Whereas the increases in DNA synthesis and p53 phosphorylation were inhibited by antibody to the IGF-I receptor and by 2,5-Mec, the nuclear exclusion of p53 was prevented by the antibody and also, although not significantly, by 2,5-Mec. The results suggest that growth stimulation of MCF-7 cells by IGF-I is accompanied by tyrosine phosphorylation and nuclear exclusion of p53.

Protein synthesis-dependent cytoplasmic translocation of p53 protein after serum stimulation of growth-arrested MCF-7 cells

p53 protein was localized in the cytoplasm of growing and in the nucleus of growth-arrested MCF-7 cells. While the absolute amount and rate of synthesis of p53 in growing and arrested cells were nearly the same, the protein in growing cells was phosphorylated to a greater extent than in arrested cells. The abilities of the cytoplasmic and nuclear p53 proteins to bind to DNA sequences specific for p53 protein binding did not differ remarkably despite their differential phosphorylation levels. Serum-induced translocation of the p53 protein from the nucleus to the cytoplasm, as well as DNA and protein synthesis, were inhibited by cycloheximide. These results suggest that the DNA synthesis-associated cytoplasmic translocation of p53 protein in response to serum stimulation depends on de novo protein synthesis and not on alteration of the protein's ability to bind to specific DNA sequences.

Receptors for the TGF-β superfamily: multiple polypeptides and serine/threonine kinases

Members of the transforming growth factor beta (TGF-beta) superfamily of peptide growth factors have profound effects on the growth and differentiation of many cell types. Insights into the poorly understood mechanisms of action of these ligands have come from the recent molecular cloning of two types of high-affinity receptors - type II and type III - for TGF-beta superfamily members. The cell surface expression of the type III receptor, a membrane-bound proteoglycan, appears to modulate the binding of ligand to the type II receptor, which is a transmembrane serine/threonine kinase. These results provide evidence for interactions between different receptor types, and suggest that serine/threonine phosphorylation is an important element in TGF-beta-induced signalling.

Phosphorylation-associated conformation shift of anti-oncogene phosphoprotein p53 in concanavalin-A activated human T lymphocytes

A new radioimmunoassay for p53, employing an anti-peptide antibody directed against conserved Domain V, exhibited specificity for a relatively dephosphorylated form of p53. This form, correlated with the monoclonal antibody PAB421+ conformation, appeared transiently in the cytosol of cycloheximide-treated T cells undergoing activation by concanavalin-A/serum. Concurrently, there were decreased levels of p53 in the nucleus that correlated with increased phosphorylation of p53. After 90 min nuclear levels of p53 increased steadily above levels of unstimulated cells. Anti-p53 antibodies introduced into cells prior to stimulation enhanced cell proliferation in response to mitogens.

Secretion of cell-adhesion-promoting factors, fibronectin, fibronectin fragments and a 53-kDa protein, by human rectal adenocarcinoma cells

Production of cell-adhesion proteins was examined in 10 cell lines and 5 cultured human cancer cells at an early passage. Two-thirds of the tested cells produced and secreted into their culture medium variable amounts of material active in promoting cell attachment. One of the rectal carcinoma cell lines, CaR-I, grew well in serum-free medium and secreted a large amount of the active principle. The active principles produced by CaR-I cells were characterized after partial purification, and were found to be fibronectin and its fragments. The presence of fibronectin and its fragments was proved by the following facts: (1) reactivity to the monoclonal antibodies which recognize different epitopes of fibronectin, and (2) reactivity to RGD peptide which is the attachment sequence of fibronectin. In addition to fibronectin and its fragments, CaR-I cells were also shown to produce a 53-kDa attachment factor. Unexpectedly, the protein was proved to be most probably the p53 suppressor gene product.