Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the accompanying paper we described the induction of apoptosis by extended cyclic AMP (cAMP)-mediated signals in primary granulosa cells and the reduction in this process in transformed cells expressing SV40 T antigen. In the present work, we examined the effect of overexpression of either wild-type or mutant p53 on cAMP-mediated apoptosis in steroidogenic granulosa cell lines transfected with SV40 DNA together with the Ha-ras oncogene and a temperature-sensitive variant of p53, p53val135. In cell lines expressing low amounts of T antigen and high amounts of p53val135, growth arrest was induced by transferring the cells from 37.5 degrees to 32 degrees C, a temperature which allows the manifestation of the wild-type phenotype of p53 and the induction of the WAF1 gene. While nonstimulated cells showed only a very modest apoptotic process, rapid and massive apoptosis was evident in cells stimulated by forskolin at 32 degrees C. The presence of serum could delay, but not abolish, this phenomenon. Progesterone production in such cells treated with cAMP was significantly higher at 32 degrees C than at 37.5 degrees C, suggesting that wild-type p53 can also enhance granulosa cell differentiation. Furthermore, at least at early stages, apoptosis is correlated with increased cell differentiation. On the other hand, in lines expressing high amounts of T antigen and low amounts of p53, neither an increase in cAMP-induced differentiation nor massive apoptosis was seen at 32 degrees C. These findings demonstrate that wild-type p53 can cooperate with cAMP-generated signals in the induction of steroidogenesis and of programmed cell death in granulosa cells.
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PMID:Involvement of p53 expression in cAMP-mediated apoptosis in immortalized granulosa cells. 773 66

We investigated the sensitivity and sequential events that take place in thyroid epithelial cells after irradiation. Cell survival ratios at a dose of 2 Gy were 18 +/- 2.5%, 58 +/- 1.0%, 59 +/- 1.5%, and 98 +/- 1.8% in primary thyroid cells, papillary thyroid carcinoma cells, follicular thyroid carcinoma cells, and anaplastic thyroid carcinoma cells, respectively. Thyroid carcinoma cell lines carrying mutations in the p53 gene were resistant to ionizing radiation. Although irradiated cells were accumulated at G1 in primary thyroid cells even after low-dose irradiation (0.2 Gy), this phenomenon was not observed in the thyroid carcinoma cell lines. Wild-type p53 expression in primary thyroid cell was increased following irradiation, but mutated p53 in the thyroid carcinoma cell lines was unchanged. To clarify the signal transduction in the G1 arrest following irradiation, levels of expression of the p53 putative downstream effectors GADD45 and WAF1/Cip1 were examined. Despite the consistent level of GADD45 mRNA, the level of WAF1/Cip1 transcripts was increased in a radiation dose-dependent manner in primary thyroid cells. This increase in the WAF1/Cip1 mRNA level was observed 30 min after irradiation and continued for at least 48 h. A mobility shift assay performed using the sequence of the putative p53 DNA binding site on the WAF1/Cip1 and GADD45 genes as a probe showed that nuclear protein extracted from primary thyroid cells, anti-p53 antibody, and probe oligonucleotide-bound complex was clearly shifted. An increase in binding activity of the p53/antibody/DNA complex was observed following irradiation. In contrast, the nuclear extract from thyroid carcinoma cells could not bind the specific DNA site, suggesting that mutant p53 has lost its binding ability. Actinomycin D inhibited WAF1/Cip1 and GADD45 mRNA levels and cycloheximide stimulated up-regulation of both basal mRNA levels, but an additional increase of the mRNA expression following irradiation was observed only in the WAF1/Cip1 gene. These data suggest that p53 in postradiation acts at a transcriptional level on WAF1/Cip1 gene expression and that de novo protein synthesis is not required for this effect. These results suggest that the p53-WAF1/Cip1 pathway may play a central role in induction of G1 arrest following irradiation in human thyroid epithelial cells.
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PMID:Radiation-induced G1 arrest is selectively mediated by the p53-WAF1/Cip1 pathway in human thyroid cells. 774 5

In order to examine more precisely the role of p53 in the activation of the G1/S checkpoint by ionizing radiation, we examined two human lymphoblast cell lines derived from the same donor. The TK6 line had a doubling time of 12.2 h and expressed wild type p53, while the WTK1 line had a doubling time of 12.7 h and expressed mutant p53. The two lines differ significantly in their susceptibility to radiation-induced cell killing and apoptosis. Cells were examined by flow cytometry at regular intervals from 0 to 12 h after irradiation with two different doses designed to yield equivalent survival levels in both cell lines. In some experiments, cells were incubated with colcemid to block them in the first postirradiation mitosis and prevent contamination of the flow cytometric profiles with second cycle cells. There was no significant difference between the two cell lines in the progression of irradiated cells out of G1 and into the S and G2 phases of the cell cycle. In particular, there was no evidence for a prolonged arrest in G1 in the TK6 cell line expressing wild type p53. Furthermore, expression of the p53 downstream genes WAF1/CIP1 and RB appeared normal in TK6 cells. These results suggest that factors other than those in the p53 signal transduction pathway alone may be required to activate the G1/S checkpoint in irradiated human cells and that apoptosis and G1 arrest may utilize different pathways.
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PMID:Absence of radiation-induced G1 arrest in two closely related human lymphoblast cell lines that differ in p53 status. 774 31

Over the past year, insights have been made into the biochemistry and biological effects of p53. The high-resolution three-dimensional structure has been determined for the central core and carboxy-terminal domain of the protein, important p53 target genes (such as WAF1) have been identified, and insight has been gained into the relationship between p53-mediated growth arrest and apoptosis.
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PMID:Biochemical properties and biological effects of p53. 774 31

The combination of recombinant human fibroblast interferon (IFN-beta) and the antileukemic compound mezerein (MEZ) induces terminal differentiation with an irreversible loss of proliferative capacity in human melanoma cells. Using subtraction hybridization, cDNAs were identified that display enhanced expression in terminally differentiated and growth arrested human melanoma cells (Jiang and Fisher, 1993; Jiang et al., 1994a). A specific melanoma differentiation-associated (mda) cDNA, mda-6, is described whose expression inversely correlates with melanoma progression and growth. mda-6 is identical to WAF1/CIP1/SDI1 that encodes the M(r) 21,000 protein (p21) that is an inhibitor of cyclin-dependent kinases. Actively growing normal melanocyte, SV40-immortalized human melanocyte and dysplastic nevus cell lines synthesize elevated levels of mda-6 mRNA; whereas, actively proliferating radial and early vertical growth phase primary melanomas as well as metastatic human melanoma cells produce reduced levels of mda-6 mRNA. Treatment of primary and metastatic human melanoma cells with IFN-beta + MEZ results in growth inhibition and an increase in mda-6 expression. mda-6 expression also increases when human melanoma cells are grown to high saturation densities or when grown in serum-free medium. Using anti-p53 and anti-p21 antibodies, an inverse correlation is found between p53 and p21 protein levels during growth arrest and differentiation. Induction of growth arrest and terminal differentiation in H0-1 human melanoma cells by IFN-beta + MEZ results in a temporal decrease in wild-type p53 protein levels with a corresponding increase in p21 levels. In the Matrigel-assisted melanoma progression model, mda-6 expression decreases in early vertical growth phase primary human melanoma cells selected for autonomous or enhanced tumor formation in nude mice. In metastatic human melanoma cells displaying a loss of metastatic potential resulting from introduction of a normal human chromosome 6, mda-6 mRNA levels increase. Taken together, these studies indicate that mda-6 (p21) may function as a negative regulator of melanoma growth, progression and metastasis.
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PMID:The melanoma differentiation-associated gene mda-6, which encodes the cyclin-dependent kinase inhibitor p21, is differentially expressed during growth, differentiation and progression in human melanoma cells. 775 61

The tumor suppressor gene p53 is involved in controlling cell cycle checkpoint or triggering apoptosis. p53 may accomplish these roles by acting as a sequence-specific transcription factor. One of the downstream targets of p53 transcription control is the WAF1/CIP1 gene, whose gene product p21 interacts with several cyclins and cyclin-dependent kinases, resulting in inhibition of these kinases. In our previous studies, we have shown that the p53 protein level in mouse keratinocytes was elevated following UV-B/A irradiation. In this paper we further investigated the consequences of increased p53 protein level by characterizing p53 DNA-binding level and WAF1/CIP1 gene expression in UV-B/A-irradiated mouse keratinocytes. Consistent with the increased level of p53 protein, both p53 DNA-binding level and steady-state level of WAF1/CIP1 mRNA were elevated. We have demonstrated that the induction of WAF1/CIP1 mRNA was mediated by p53, since no WAF1/CIP1 induction was observed in p53-deficient cells upon UV-B exposure. These observations suggest an important role for the tumor suppressor gene p53 in the response of keratinocytes to the biologically relevant UV-B/A irradiation and in suppressing UV-induced skin cancer.
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PMID:UV-B/A irradiation of mouse keratinocytes results in p53-mediated WAF1/CIP1 expression. 776 Oct 96

The mechanism of cell cycle withdrawal during terminal differentiation is poorly understood. We report here that the cyclin-dependent kinase (CDK) inhibitor p21Cip1/WAF1 is induced at early times of both keratinocyte and myoblast differentiation. p21Cip1/WAF1 induction is accompanied by a drastic inhibition of total Cdk2, as well as p21Cip1/WAF1-associated CDK kinase activities. p21Cip1/WAF1 has been implicated in p53-mediated G1 arrest and apoptosis. In keratinocyte differentiation, Cip1/WAF1 induction is observed even in cells derived from p53-null mice. Similarly, keratinocyte differentiation is associated with induction of Cip1/WAF1 promoter activity in both wild-type and p53-negative keratinocytes. Induction of the Cip1/WAF1 promoter upon differentiation is abolished by expression of an adenovirus E1A oncoprotein (d1922/947), which is unable to bind p105-Rb, p107, or cyclin A but which still binds the nuclear phosphoprotein p300. Overexpression of p300 can suppress the E1A effect, independent of its direct binding to E1A. Thus, terminal differentiation-induced growth arrest in both keratinocyte and myoblast systems is associated with induction of Cip1/WAF1 expression. During keratinocyte differentiation, Cip1/WAF1 induction does not require p53 but depends on the transcriptional modulator p300.
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PMID:Involvement of the cell-cycle inhibitor Cip1/WAF1 and the E1A-associated p300 protein in terminal differentiation. 777 29

The transforming growth factor beta s (TGF-beta s) are a group of multifunctional growth factors which inhibit cell cycle progression in many cell types. The TGF-beta-induced cell cycle arrest has been partially attributed to the regulatory effects of TGF-beta on both the levels and the activities of the G1 cyclins and their kinase partners. The activities of these kinases are negatively regulated by a number of small proteins, p21 (WAF1, Cip1), p27Kip1, p16, and p15INK4B, that physically associate with cyclins, cyclin-dependent kinases, or cyclin-Cdk complexes. p21 has been previously shown to be transcriptionally induced by DNA damage through p53 as a mediator. We demonstrate that TGF-beta also causes a rapid transcriptional induction of p21, suggesting that p21 can respond to both intracellular and extracellular signals for cell cycle arrest. In contrast to DNA damage, however, induction of p21 by TGF-beta is not dependent on wild-type p53. The cell line studied in these experiments, HaCaT, contains two mutant alleles of p53, which are unable to activate transcription from the p21 promoter when overexpressed. In addition, TGF-beta and p53 act through distinct elements in the p21 promoter. Taken together, these findings suggest that TGF-beta can induce p21 through a p53-independent pathway. Previous findings have implicated p27Kip1 and p15INK2B as effectors mediating the TGF-beta growth inhibitory effect. These results demonstrate that a single extracellular antiproliferative signal, TGF-beta, can act through multiple signaling pathways to elicit a growth arrest response.
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PMID:Transforming growth factor beta induces the cyclin-dependent kinase inhibitor p21 through a p53-independent mechanism. 777 46

The regulation of p53 protein synthesis and p53-mediated gene transactivation were evaluated in cultured mouse keratinocytes maintained as basal cells or induced to differentiate by Ca2+ > 0.1 mM. p53 protein half-life, p53 protein synthesis and the level of p53 mRNA decreased during terminal differentiation, as detected by immunoprecipitation with a panel of p53-specific antibodies and Northern blotting. Thus differentiating keratinocytes have lower levels of p53 protein. This decline is not observed following growth arrest alone, or in papilloma cell lines which do not terminally differentiate in response to Ca2+. In contrast, the ability of endogenous p53 to transactivate transcription from the PG13 CAT plasmid increased during differentiation in vitro. This change in activity cannot be explained by changes in p53 conformation or nuclear localization. Consistent with these findings, mRNA for the p53-mediated genes WAF1 and mdm-2 increased with Ca(2+)-induced differentiation in a time dependent manner, suggesting activation of p53 contributes to the differentiated phenotype. However, p53-null mice exhibit histologically normal skin and epidermal keratinocytes from these mice express the appropriate markers of differentiation and suppression of DNA synthesis in vitro when the [Ca2+] is > 0.1 mM. The observation that proliferating cells have higher levels of p53 protein which is less active for its function than differentiated cell types could have a consequence for the selection of p53 gene mutations during carcinogenesis, depending upon the stage of differentiation of the tumor cell type.
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PMID:p53-mediated transcriptional activity increases in differentiating epidermal keratinocytes in association with decreased p53 protein. 778 75

In order to examine the role of p53 expression on the sensitivity of cells to radiation-induced reproductive failure, we examined the radiosensitivity of a human diploid fibroblast cell strain (AG1521) before and after transfection with the E6 or E6/E7 genes of human papillomavirus 16 (HPV16)3. HPV E6 binds to p53, promoting its degradation and abrogating wild-type p53 function. AG1521 cells transfected with either E6 or E6/E7 showed no radiation induction of either p53 or WAF1/Cip1. The radioresistance of these cells were significantly increased; the D0 of the survival curves rose from 130 +/- 4 cGy for wild type (neo-transfected) cells to 178-192 cGy for three subclones transfected with E6 alone, and 151-218 cGy for eight subclones transfected with E6/E7. The change in radiosensitivity took place before the process of cellular immortalization and transformation produced by transfection with these genes. Thus, the effect on radiosensitivity appears to be an early effect of the loss of p53 function in non-transformed cells, perhaps related to the loss of the G1 checkpoint and of the capacity for programmed death amongst radiation damaged cells.
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PMID:Abrogation of p53 function by transfection of HPV16 E6 gene enhances the resistance of human diploid fibroblasts to ionizing radiation. 778 90


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