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Biomedical subjects

K G Wiman

Publications and source records attributed to K G Wiman.

At least 19 recordsLinked to original sources
PubMed2006

Hypoxia induces p53-dependent transactivation and Fas/CD95-dependent apoptosis.

p53 triggers apoptosis in response to cellular stress. We analyzed p53-dependent gene and protein expression in response to hypoxia using wild-type p53-carrying or p53 null HCT116 colon carcinoma cells. Hypoxia induced p53 protein levels and p53-dependent apoptosis in these cells. cDNA microarray analysis revealed that only a limited number of genes were regulated by p53 upon hypoxia. Most classical p53 target genes were not upregulated. However, we found that Fas/CD95 was significantly induced in response to hypoxia in a p53-dependent manner, along with several novel p53 target genes including ANXA1, DDIT3/GADD153 (CHOP), SEL1L and SMURF1. Disruption of Fas/CD95 signalling using anti-Fas-blocking antibody or a caspase 8 inhibitor abrogated p53-induced apoptosis in response to hypoxia. We conclude that hypoxia triggers a p53-dependent gene expression pattern distinct from that induced by other stress agents and that Fas/CD95 is a critical regulator of p53-dependent apoptosis upon hypoxia.

Apoptosis↗
PubMed2006

PRIMA-1(MET) induces nucleolar accumulation of mutant p53 and PML nuclear body-associated proteins.

We have previously identified PRIMA-1, a low molecular weight compound that restores the transcriptional transactivation function to mutant p53 and induction of apoptosis. To explore the molecular mechanism for PRIMA-1-induced mutant p53-dependent apoptosis, we examined the intracellular distribution of mutant p53 upon treatment with PRIMA-1(MET) by immunofluorescence staining. We found that PRIMA-1(MET) induced nucleolar translocation of mutant p53 and the promyelocytic leukemia (PML) nuclear body-associated proteins PML, CBP and Hsp70. Levels of Hsp70 were significantly enhanced by PRIMA-1(MET) treatment. PRIMA-Dead, a compound structurally related to PRIMA-1 but unable to induce mutant p53-dependent apoptosis, failed to induce nucleolar translocation of mutant p53. Our results suggest that redistribution of mutant p53 to nucleoli plays a role in PRIMA-1-induced apoptosis.

Active Transport, Cell Nucleus↗
PubMed2006

PRIMA-1 induces apoptosis in acute myeloid leukaemia cells with p53 gene deletion.

The p53 tumour suppressor gene located on chromosome 17p13 is the most frequently mutated gene in human tumours. About 5-8% of cases with acute myeloid leukaemia (AML) carry the p53 mutation. Recently, the compound p53-dependent reactivation and induction of massive apoptosis (PRIMA-1) has been shown to induce cytotoxic effects and apoptosis in human tumour cells by restoration of the transcriptional activity of mutated p53. This is believed to be mediated by a change in the conformation of mutated p53 protein, restoring DNA binding and activation of p53 target genes. We studied the effects of PRIMA-1 and commonly used antileukaemic drugs on AML cells from 62 patients. Cells were obtained from peripheral blood or bone marrow and were exposed to PRIMA-1, cytarabine, daunorubicin, chlorodeoxyadenosine and fludarabine. This study showed that PRIMA-1 had cytotoxic effects on AML cells. Conventional AML drugs were less effective in cells with hemizygous p53 deletion. Interestingly, our data indicated that PRIMA-1 was more effective in this subgroup of patients compared with patients with normal chromosome 17. Our data suggest that the concept of restoration of p53 protein by PRIMA-1 or a PRIMA-1-based new drug may increase the efficacy of AML treatment in patients with p53 mutations.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Effects of PRIMA-1 on chronic lymphocytic leukaemia cells with and without hemizygous p53 deletion.

The tumour suppressor gene p53 is the most commonly mutated gene in solid tumours. Although less common in haematological malignancies, 10-15% of B-cell chronic lymphocytic leukaemia (B-CLL) cases carry a p53 mutation. Recently, the compound P53-dependent reactivation and induction of massive apoptosis (PRIMA-1) has been shown to induce cytotoxic effects and apoptosis in human tumour cells by restoration of the transcriptional activity of mutated p53. This is believed to be mediated by a change in the conformation of mutated p53 protein, restoring DNA binding and activation of p53 target genes. We studied the effects of PRIMA-1 and commonly used anti-leukaemic drugs on B-CLL cells from 14 patients with and without hemizygous p53 deletion. Cells obtained from peripheral blood or bone marrow were exposed to PRIMA-1 and fludarabine alone or in combination. PRIMA-1 showed cytotoxic effects on B-CLL cells from samples with and without hemizygous p53 deletion. Furthermore, conventional B-CLL drugs were less effective in cell samples with hemizygous p53 deletion and the response depended on the size of the p53 deleted clone. Finally, we found evidence for synergistic and additive effects of PRIMA-1 in combination with fludarabine.

Antineoplastic Agents↗
PubMed2003

Small molecules that reactivate mutant p53.

Around half of all human tumours carry mutant p53. This allows escape from p53-induced cell cycle arrest and apoptosis. Many tumours express mutant p53 proteins at elevated levels. Restoration of wild-type p53 function should trigger massive apoptosis in tumour cells and thus eradicate tumours. Various types of small molecules have been identified that can restore native conformation and wild-type function to mutant p53. Such molecules may serve as leads for the development of novel efficient anticancer drugs.

Antineoplastic Agents, Phytogenic↗
PubMed2001

Human wig-1, a p53 target gene that encodes a growth inhibitory zinc finger protein.

We previously identified a novel p53-induced mouse gene, wig-1, that encodes a 290 amino acid zinc finger protein (Varmeh-Ziaie et al., 1997). Here we have identified and characterized the human homolog of mouse wig-1. The human wig-1 protein is 87% identical to the mouse protein and contains three zinc finger domains and a putative nuclear localization signal. Human wig-1 mRNA and protein is induced following activation of wild type p53 expression in our BL41-ts p53 Burkitt lymphoma cells. Wig-1 is also induced in MCF7 cells following treatment with the DNA-damaging agent mitomycin C. Northern blotting detected low levels of wig-1 mRNA in normal human tissues. Fluorescence in situ hybridization mapped wig-1 to human chromosome 3q26.3-27. FLAG-tagged human wig-1 localizes to the nucleus. Ectopic overexpression of human wig-1 inhibits tumor cell growth in a colony formation assay. These results suggest that human wig-1 has a role in the p53-dependent growth regulatory pathway.

Amino Acid Sequence↗
PubMed2001

p14ARF homozygous deletion or MDM2 overexpression in Burkitt lymphoma lines carrying wild type p53.

The hallmark of Burkitt lymphoma (BL) is a constitutively activated c-myc gene that drives tumor cell growth. A majority of BL-derived cell lines also carry mutant p53. In addition, the p16INK4a promoter is hypermethylated in most BL biopsies and BL cell lines, leading to silencing of this gene. Activation of c-myc and/or cell cycle dysregulation can induce ARF expression and p53-dependent apoptosis. We therefore investigated the p14ARF-MDM2-p53 pathway in BL cell lines. p14ARF was expressed and localized to nucleoli in all BL carrying mutant p53. Three out of seven BL carrying wt p53 had a homozygous deletion of the CDKN2A locus that encodes both p14ARF and p16INK4a. Three BL carrying wild type p53 retained the CDKN2A locus and overexpressed MDM2. DNA sequencing revealed a point mutation in CDKN2A exon 2 in one of these BL, Seraphine. However, this point mutation did not affect p14ARF's nucleolar localization or ability to induce p53. The Bmi-1 protein that negatively regulates the p14ARF promoter and co-operates with c-myc in tumorigenesis was expressed at low to moderate levels in all BL analysed. Our results indicate that inactivation of the ARF-MDM2-p53 pathway is an essential step during the development of Burkitt lymphoma, presumably as a mechanism to escape c-myc induced apoptosis.

Burkitt Lymphoma↗
PubMed2000

Downregulation of telomerase reverse transcriptase mRNA expression by wild type p53 in human tumor cells.

The p53 tumor suppressor protein inhibits the formation of tumors through induction of cell cycle arrest and/or apoptosis. In the present study we demonstrated that p53 is also a powerful inhibitor of human telomerase reverse transcriptase (hTERT), a key component for telomerase. Activation of either exogenous temperature-sensitive (ts) p53 in BL41 Burkitt lymphoma cells or endogenous wild type (wt) p53 at a physiological level in MCF-7 breast carcinoma cells triggered a rapid downregulation of hTERT mRNA expression, independently of the induction of the p53 target gene p21. Co-transfection of an hTERT promoter construct with wt p53 but not mutant p53 in HeLa cells inhibited the hTERT promoter activity. Furthermore, the activation of the hTERT promoter in Drosophila Schneider SL2 cells was completely dependent on the ectopic expression of Sp1 and was abrogated by wt p53. Finally, wt p53 inhibited Sp1 binding to the hTERT proximal promoter by forming a p53-Sp1 complex. Since activation of telomerase, widely observed in human tumor cell lines and primary tumors, is a critical step in tumorigenesis, wt p53-triggered inhibition of hTERT/telomerase expression may reflect yet another mechanism of p53-mediated tumor suppression. Our findings provide new insights into both the biological function of p53 and the regulation of hTERT/telomerase expression.

Breast Neoplasms↗
PubMed2000

Increased expression of insulin-like growth factor I receptor in malignant cells expressing aberrant p53: functional impact.

We investigated the functional impact of p53 on insulin-like growth factor I receptor (IGF-IR) expression in malignant cells. Using the BL-41tsp53-2 cell line, a transfectant carrying temperature-sensitive (ts) p53 and endogenous mutant p53 (codon 248), we demonstrated a drastic down-regulation of plasma membrane-bound IGF-IRs on induction of wild-type p53. However, a similar response was obtained by treatment of BL-41tsp53-2 cells expressing mutant ts p53 with a p53 antisense oligonucleotide. Thus, even if the negative effect of wild-type p53 predominates under a competitive condition, these data indicate that mutant p53 may be important for up-regulation of IGF-IR. To further elucidate this issue, three melanoma cell lines (BE, SK-MEL-5, and SK-MEL-28) that overexpressed p53 were investigated. The BE cell line has a "hot spot" mutation (codon 248) and expresses only codon 248-mutant p53. SK-MEL-28 has a point mutation at codon 145. SK-MEL-5 cells did not exhibit any p53 mutations, but the absence of p21Waf1 expression suggested functionally aberrant p53. Our data suggest that interaction with Mdm-2 may underlie p53 inactivation in these cells. Using p53 antisense oligonucleotides, we demonstrated a substantial down-regulation of cell surface expression of IGF-IR proteins in all melanoma cell lines after 24 h. This was paralleled by decreased tyrosine phosphorylation of IGF-IR and growth arrest, and, subsequently, massive cell death was observed (this was also seen in BL-41tsp53-2 cells with mutant conformation of ts p53). Taken together, our results suggest that up-regulation of IGF-IR as a result of expression of aberrant p53 may be important for the growth and survival of malignant cells.

Acetylcysteine↗
PubMed2000

Immunolocalization of human p14(ARF) to the granular component of the interphase nucleolus.

The human p14(ARF) protein is encoded by an alternative transcript from the INK4a/ARF locus on chromosome 9p21, a locus frequently afflicted in human tumors. By use of two novel specific antisera against p14(ARF) we show that the protein is localized mainly in nucleoli but also in the nucleoplasm. Transfection of full-length and deletion mutant GFP-p14(ARF) fusion proteins confirmed this subcellular localization and assigned the nucleolar localization signal to the exon 2-encoded C-terminal region. In order to determine p14(ARF) expression in human tumor cells, we examined p14(ARF) in 32 tumor cell lines by immunofluorescence staining. Nucleolar p14(ARF) was detected in 10 lines, all of which lacked functional p53. Double immunostaining with p14(ARF) and B23/nucleophosmin or fibrillarin antibodies using 3D microscopy revealed that p14(ARF) is located mainly in the granular component of the nucleolus. p14(ARF) was also found in distinct granular aggregates scattered throughout the nucleoplasm. RNase digestion or selective inhibition of rRNA transcription by low doses of actinomycin D caused nucleoplasmic translocation of p14(ARF). This indicates that the nucleolar localization of p14(ARF) is dependent on ongoing transcriptional activity in intact functional nucleoli.

Animals↗
PubMed2000

p53 splice acceptor site mutation and increased HsRAD51 protein expression in Bloom's syndrome GM1492 fibroblasts.

GM1492 human diploid skin fibroblasts derived from a patient with Bloom's syndrome (BS), lack detectable p53 mRNA and protein as shown by Northern and Western blotting, and express an increased RecA-like activity. Here we demonstrate that the p53 gene is grossly intact in GM1492 cells according to Southern blotting. DNA sequencing did not reveal any mutations in the promoter region of p53. A highly sensitive RT-PCR produced a p53 cDNA fragment that was shorter than expected. DNA sequence analysis of p53 cDNA showed that exon 6 was missing, explaining the shorter PCR product. Furthermore, sequencing of genomic DNA revealed a base substitution at the nucleotide preceding the AG splice acceptor site of intron 5. The omission of exon 6 creates a frameshift at the junction of exons 5 and 7, and a premature stop codon in exon 7. The aberrant transcript is predicted to encode a truncated p53 protein containing 189 amino acid residues. Moreover, Western blotting demonstrated elevated HsRAD51 protein levels in GM1492 cells. The lack of sufficient levels of wild-type p53 and increased levels of HsRad51 protein may contribute to the elevated RecA-like activity in the GM1492 fibroblasts.

Alternative Splicing↗
PubMed2000

Polyoma virus middle T and small t antigens cooperate to antagonize p53-induced cell cycle arrest and apoptosis.

Wild-type p53 triggers two distinct biological responses, cell cycle arrest and apoptosis. Several small DNA tumor viruses encode proteins that bind p53 and thus block the function of p53. This probably reflects the need of these viruses to prevent p53-induced cell cycle arrest and apoptosis to allow viral DNA replication. Unlike SV40 large T, polyoma virus large T does not bind p53, and it is still unclear how polyoma virus blocks p53 function. To address this question, we transfected polyoma virus middle T or small t alone or middle T and small t together into J3D mouse T-lymphoma cells carrying temperature-sensitive p53 (ts p53). Induction of wild-type p53 by temperature shift to 32 degrees C triggered both G1 cell cycle arrest and apoptosis in parental J3D-ts p53 cells. In contrast, J3D-ts p53 cells coexpressing middle T and small t showed only a weak G1 cell cycle arrest response after induction of wild-type p53 at 32 degrees C. Fluorescence-activated cell sorter analysis revealed that nearly half of the middle T-expressing cells, 30% of the small t-expressing cells, and a majority of the cells coexpressing middle T and small t were resistant to p53-induced apoptosis. The phosphatidylinositol 3-kinase inhibitor wortmannin partially abrogated the protective effect of middle T but not small t on p53-induced apoptosis, indicating that middle T prevents p53-induced apoptosis through the phosphatidylinositol 3-kinase signal transduction pathway. Our results thus establish a mechanism for polyoma virus-mediated inhibition of p53 function.

Androstadienes↗
PubMed1999

p53-induced apoptosis as a safeguard against cancer.

p53 acts as a potent tumor suppressor largely through its ability to induce cell death by apoptosis. Diverse cellular stress conditions, e.g., DNA damage, hypoxia, and oncogene activation, trigger p53-dependent apoptosis. ARF is a 14-kDa protein encoded by an alternative reading frame within the human INK4a locus that also encodes the p16 protein. ARF induces p53 in response to oncogene activation by preventing its degradation. This ensures the elimination of emerging tumor cells by p53-dependent apoptosis. p53 promotes apoptosis through multiple mechanisms, including transactivation of specific target genes, down-regulation of a distinct set of genes, and transcription-independent mechanisms. This may explain the frequent inactivation of ARF/p53 rather than downstream effectors during tumor development.

ADP-Ribosylation Factors↗
PubMed1999

Reactivation of mutant p53 through interaction of a C-terminal peptide with the core domain.

A synthetic 22-mer peptide (peptide 46) derived from the p53 C-terminal domain can restore the growth suppressor function of mutant p53 proteins in human tumor cells (G. Selivanova et al., Nat. Med. 3:632-638, 1997). Here we demonstrate that peptide 46 binds mutant p53. Peptide 46 binding sites were found within both the core and C-terminal domains of p53. Lys residues within the peptide were critical for both p53 activation and core domain binding. The sequence-specific DNA binding of isolated tumor-derived mutant p53 core domains was restored by a C-terminal polypeptide. Our results indicate that C-terminal peptide binding to the core domain activates p53 through displacement of the negative regulatory C-terminal domain. Furthermore, stabilization of the core domain structure and/or establishment of novel DNA contacts may contribute to the reactivation of mutant p53. These findings should facilitate the design of p53-reactivating drugs for cancer therapy.

Amino Acid Sequence↗
PubMed1998

Is conversion of solid into more anoxic ascites tumors associated with p53 inactivation?

Most solid tumors are unable to grow in the ascites form, unless selected by prolonged serial transfer of peritoneal fluid (Klein, 1955). Established ascites tumor cells grow under highly crowded, virtually anoxic conditions (Warburg and Hiepler, 1953). Hypoxia was recently identified as a powerful inducer of p53 dependent apoptosis (Graeber et al., 1996). We wished to examine whether the conversion of relatively well-vascularized solid mouse tumors into freely growing ascitic cell variants favors cell with mutated or deleted p53. We have sequenced exons 4-9 of p53 cDNA from two serially transplanted methylcholanthrene induced sarcomas (MCIM and MSWBS) that were available in the original solid and the gradually converted ascites form. We have also examined five additional solid tumors, four carcinomas and one sarcoma and six additional ascites tumors, five carcinomas and one sarcoma. Sequence analysis showed that all solid tumors carried exclusively wild type p53. Among the eight ascites tumors, five carried mutant p53 and three had only the wild type gene. In one of the two isogenic pairs, the original solid tumor line had only wild type, whereas the derived ascites line had only mutant p53. In the second pair, the solid tumor was wild type whereas the ascitic variant was heterozygous. The naturally occurring alternatively spliced p53 (p53as) mRNA was detected in all solid tumors, but not in five of the eight ascites tumors. Our findings indicate that conversion of solid into ascites tumors favors the selection of cell variants with mutated p53 and of cells that lack the alternatively spliced form of p53.

Animals↗
PubMed1998

p16/INK4a and p15/INK4b gene methylation and absence of p16/INK4a mRNA and protein expression in Burkitt's lymphoma.

The fact that the p16/INK4a and p15/INK4b genes are frequently inactivated in human malignancies and that p16/INK4a null mice spontaneously develop B-cell lymphomas prompted us to examine the status of both genes in Burkitt's Lymphoma (BL). We found a low frequency of p16/INK4a and p15/INK4b deletions and mutations in BL cell lines and biopsies. However, p16/INK4a exon 1 was methylated in 17 out of 19 BL lines (89.5%) and in 8 out of 19 BL biopsies (42%) analyzed. p15/INK4b Exon 1 was also methylated, although at a lower frequency. p16/INK4a mRNA was readily detected in BL lines carrying unmethylated p16/INK4a, but not in those carrying methylated p16/INK4a. No p16/INK4a protein was detected in any of the BL lines and biopsies examined. In contrast, only one out of seven lymphoblastoid cell lines (LCLs) examined was methylated in p16/INK4a exon 1, and three out of the six LCLs with unmethylated p16/INK4a expressed detectable levels of p16/INK4a protein. Thus, the frequent p16/INK4a methylation in BL lines correlates with downregulation of p16/INK4a expression, suggesting that exon 1 methylation is responsible for silencing the p16/INK4a gene in BL.

Blotting, Northern↗
PubMed1998

Reactivation of mutant p53: a new strategy for cancer therapy.

The specific DNA binding activity of p53 is crucial for its tumor suppression function. Naturally occurring mutant forms of p53 are deficient for specific DNA binding. However, several studies have indicated that their specific DNA binding can be reactivated. Short peptides derived from the p53 C-terminus can reactivate at least some mutant p53 proteins and trigger a p53-dependent biological response. These results may provide the basis for the design of p53-reactivating anti-cancer drugs.

Animals↗