p53 in chronic myelogenous leukemia. Study of mechanisms of differential expression

Emerging role and therapeutic implications of p53 in intervertebral disc degeneration

Lower back pain (LBP) is a common degenerative musculoskeletal disease that imposes a huge economic burden on both individuals and society. With the aggravation of social aging, the incidence of LBP has increased globally. Intervertebral disc degeneration (IDD) is the primary cause of LBP. Currently, IDD treatment strategies include physiotherapy, medication, and surgery; however, none can address the root cause by ending the degeneration of intervertebral discs (IVDs). However, in recent years, targeted therapy based on specific molecules has brought hope for treating IDD. The tumor suppressor gene p53 produces a transcription factor that regulates cell metabolism and survival. Recently, p53 was shown to play an important role in maintaining IVD microenvironment homeostasis by regulating IVD cell senescence, apoptosis, and metabolism by activating downstream target genes. This study reviews research progress regarding the potential role of p53 in IDD and discusses the challenges of targeting p53 in the treatment of IDD. This review will help to elucidate the pathogenesis of IDD and provide insights for the future development of precision treatments.

Synergistic effects of PRIMA-1Met (APR-246) and 5-azacitidine in TP53-mutated myelodysplastic syndromes and acute myeloid leukemia

Myelodysplastic syndromes and acute myeloid leukemia with TP53 mutations are characterized by frequent relapses, poor or short responses, and poor survival with the currently available therapies including chemotherapy and 5-azacitidine (AZA). PRIMA-1^Met(APR-246,APR) is a methylated derivative of PRIMA-1, which induces apoptosis in human tumor cells through restoration of the transcriptional transactivation function of mutant p53. Here we show that low doses of APR on its own or in combination with AZA reactivate the p53 pathway and induce an apoptosis program. Functionally, we demonstrate that APR exerts these activities on its own and that it synergizes with AZA in TP53-mutated myelodysplastic syndromes (MDS)/acute myeloid leukemia (AML) cell lines and in TP53-mutated primary cells from MDS/AML patients. Low doses of APR on its own or in combination with AZA also show significant efficacy in vivo Lastly, using transcriptomic analysis, we found that the APR + AZA synergy was mediated by downregulation of the FLT3 pathway in drug-treated cells. Activation of the FLT3 pathway by FLT3 ligand reversed the inhibition of cell proliferation by APR + AZA. These data suggest that TP53-mutated MDS/AML may be better targeted by the addition of APR-246 to conventional treatments.

Ploidy and Proliferation Evaluated by Flow Cytometry. An Overview of Techniques and Impact in Oncology

Flow cytometric methods for the assessment of nuclear and chromosomal DNA content and of cell proliferation (including methods based on pulse-chase of bromodeoxyuridine and on monoclonal antibodies against nuclear oncoproteins and proliferation-associated antigens) are illustrated by examples and analyzed critically. The impact of most of these techniques for the study of human solid tumors, with exception of nuclear DNA content evaluation, appears still limited. In particular, new studies of cell lines and clinical material from human tumors using new proliferation markers and multiparameter flow cytometry are necessary to solve a considerable number of methodologic and scientific problems.

Antitumor Effects of Blocking Protein Neddylation in T315I-BCR-ABL Leukemia Cells and Leukemia Stem Cells

Imatinib revolutionized the treatment of chronic myeloid leukemia (CML), but drug resistance and disease recurrence remain a challenge. In this study, we suggest a novel strategy based on blocking protein neddylation to address BCR-ABL point mutations and leukemia stem cells (LSC) that lie at the root of imatinib-resistant recurrences. On the basis of the finding that the NEDD8-activating enzyme subunit NAE1 is overexpressed in CML cells, we hypothesized that the function of certain neddylation-dependent protein substrates might be targeted to therapeutic ends in imatinib-resistant CML cells and LSCs. In support of this hypothesis, we demonstrated that the NAE1 inhibitor MLN4924 induced G₂-M-phase arrest and apoptosis in bulk CML cells with wild-type p53, regardless of their T315I mutation status in BCR-ABL. Moreover, MLN4924 inhibited the survival and self-renewal of primary human CML CD34⁺ cells and LSCs in CML-bearing mice via accumulation of p27^kip1 in the nucleus. Notably, p27^kip1 silencing attenuated the suppressive effect of MLN4924 on the maintenance of LSCs in CML-bearing mice. Taken together, our findings offer a preclinical proof of concept for targeting protein neddylation as a novel therapeutic strategy to override mutational and LSC-derived imatinib resistance in CML.Significance: These findings highlight a mediator of protein neddylation, a type of protein turnover mechanism, as a viable therapeutic target against imatinib-resistant forms of chronic myelogenous leukemia. Cancer Res; 78(6); 1522-36. ©2018 AACR.

p53 modulates the effect of ribosomal protein S6 kinase1 (S6K1) on cisplatin toxicity in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) is characterized by the expression of the oncoprotein, BCR-ABL. BCR-ABL inhibitors revolutionized CML chemotherapy while blast crisis (BC) CML patients are less responsive. Since suppression of ribosomal protein S6 kinase1 (S6K1) phosphorylation reverses the resistance to BCR-ABL inhibitor in CML cells and S6K1 inhibitors augment cisplatin toxicity in lung cancer cells, we speculated that combination of S6K1 inhibitor and cisplatin may be beneficial for eliminating BC CML cells. To our surprise, S6K1 inhibition decreased cisplatin-induced DNA damage and cell death only in p53^-/- BC CML cells but not in p53^+/+ BC CML cells. During the progression of CML, p53 expression either decreases or mutates. Moreover, the expression of p53 affects drug response of CML cells. Our results confirmed that S6K1 inhibition reversed cisplatin toxicity is dependent on p53 expression in CML cells. Moreover, p53 attenuated the phosphorylation and localization of S6K1 via attenuating 3-phosphoinositide dependent protein kinase-1 (PDK1) phosphorylation. Furthermore, S6K1 acts via DNA-PKcs to regulate H2AX phosphorylation and PARP cleavage, respectively. Taken together, our results suggest that p53/PDK1/S6K1 is a novel pathway regulating cisplatin toxicity in BC CML cells.

p53 causes butein‑mediated apoptosis of chronic myeloid leukemia cells

Progression of chronic myeloid leukemia, marked by the oncogenic Bcr‑Abl mutation, is tightly associated with an alteration of the p53 pathway. It is known that butein extracted from various plants represses cancer growth. Although the anticancer effects of butein are widely accepted, the mechanisms by which butein induces apoptosis of chronic myeloid leukemia cells remains to be elucidated. The present study demonstrated that butein-induced apoptosis was mediated by p53. KBM5 chronic myeloid leukemia (CML) cells expressing wild-type p53 were more sensitive to butein compared with p53-null K562 CML cells in terms of apoptotic cell death. In addition, butein arrested KBM5 cells at S-phase and altered the expression levels of certain cyclins and the p53-downstream targets, MDM2 and p21. In addition, while butein reduced the protein expression of MDM2 in the KBM5 and K562 cells, it resulted in proteasome-independent MDM2 degradation in p53-expressing KBM5 cells, however, not in p53-null K562 cells. Therefore, the present study suggested that p53 causes the butein-mediated apoptosis of leukemic cells.

MDM4 overexpressed in acute myeloid leukemia patients with complex karyotype and wild-type TP53

Acute myeloid leukemia patients with complex karyotype (CK-AML) account for approximately 10–15% of adult AML cases, and are often associated with a poor prognosis. Except for about 70% of CK-AML patients with biallelic inactivation of TP53, the leukemogenic mechanism in the nearly 30% of CK-AML patients with wild-type TP53 has remained elusive. In this study, 15 cases with complex karyotype and wild-type TP53 were screened out of 140 de novo AML patients and the expression levels of MDM4, a main negative regulator of p53-signaling pathway, were detected. We ruled out mutations in genes associated with a poor prognosis of CK-AML, including RUNX1 or FLT3-ITD. The mRNA expression levels of the full-length of MDM4 (MDM4FL) and short isoform MDM4 (MDM4S) were elevated in CK-AML relative to normal karyotype AML (NK-AML) patients. We also explored the impact of MDM4 overexpression on the cell cycle, cell proliferation and the spindle checkpoint of HepG2 cells, which is a human cancer cell line with normal MDM4 and TP53 expression. The mitotic index and the expression of p21, BubR1 and Securin were all reduced following Nocodazole treatment. Moreover, karyotype analysis showed that MDM4 overexpression might lead to aneuploidy or polyploidy. These results suggest that MDM4 overexpression is related to CK-AML with wild-type TP53 and might play a pathogenic role by inhibiting p53-signal pathway.

Nucleostemin depletion induces post-g1 arrest apoptosis in chronic myelogenous leukemia k562 cells

PURPOSE

Despite significant improvements in treatment of chronic myelogenous leukemia (CML), the emergence of leukemic stem cell (LSC) concept questioned efficacy of current therapeutical protocols. Remaining issue on CML includes finding and targeting of the key genes responsible for self-renewal and proliferation of LSCs. Nucleostemin (NS) is a new protein localized in the nucleolus of most stem cells and tumor cells which regulates their self-renewal and cell cycle progression. The aim of this study was to investigate effects of NS knocking down in K562 cell line as an in vitro model of CML.

METHODS

NS gene silencing was performed using a specific small interfering RNA (NS-siRNA). The gene expression level of NS was evaluated by RT-PCR. The viability and growth rate of K562 cells were determined by trypan blue exclusion test. Cell cycle distribution of the cells was analyzed by flow cytometry.

RESULTS

Our results showed that NS knocking down inhibited proliferation and viability of K562 cells in a time-dependent manner. Cell cycle studies revealed that NS depletion resulted in G(1) cell cycle arrest at short times of transfection (24 h) followed with apoptosis at longer times (48 and 72 h), suggest that post-G1 arrest apoptosis is occurred in K562 cells.

CONCLUSION

Overall, these results point to essential role of NS in K562 cells, thus, this gene might be considered as a promising target for treatment of CML.

Tumor protein p53 (TP53) testing and Li-Fraumeni syndrome : current status of clinical applications and future directions

Prevalent as an acquired abnormality in cancer, the role of tumor protein p53 (TP53) as a germline mutation continues to evolve. The clinical impact of a germline TP53 mutation is often dramatic and affects the full life course, with a propensity to develop rare tumors in childhood and multiple common cancers of unexpectedly early onset in adulthood. In this article, we review the clinical relevance of germline mutations in the TP53 tumor suppressor gene to current healthcare practice, including the optimal ways to identify patients with Li-Fraumeni syndrome (LFS), to recognize the core cancers associated with LFS, and to develop strategies for early detection of LFS-associated tumors. Several TP53-targeted approaches to improve outcomes in LFS patients are also reviewed. A case report is used to highlight special TP53 testing dilemmas and unique challenges associated with genetic testing decisions in the current age of rapidly advancing genomic technologies.

Propyl-2-(8-(3,4-difluorobenzyl)-2',5'-dioxo-8-azaspiro[bicyclo[3.2.1] octane-3,4'-imidazolidine]-1'-yl) acetate induces apoptosis in human leukemia cells through mitochondrial pathway following cell cycle arrest

Background

Due to the functional defects in apoptosis signaling molecules or deficient activation of apoptosis pathways, leukemia has become an aggressive disease with poor prognosis. Although the majority of leukemia patients initially respond to chemotherapy, relapse is still the leading cause of death. Hence targeting apoptosis pathway would be a promising strategy for the improved treatment of leukemia. Hydantoin derivatives possess a wide range of important biological and pharmacological properties including anticancer properties. Here we investigated the antileukemic activity and mechanism of action of one of the potent azaspiro hydantoin derivative, (ASHD).

Materials and Methods

To investigate the antileukemic efficacy of ASHD, we have used MTT assay, cell cycle analysis by FACS, tritiated thymidine incorporation assay, Annexin V staining, JC1 staining and western blot analysis.

Results

Results showed that ASHD was approximately 3-fold more potent than the parent compounds in inducing cytotoxicity. Tritiated thymidine assay in conjunction with cell cycle analysis suggests that ASHD inhibited the growth of leukemic cells. The limited effect of ASHD on cell viability of normal cells indicated that it may be specifically directed to cancer cells. Translocation of phosphatidyl serine, activation of caspase 3, caspase 9, PARP, alteration in the ratio of BCL2/BAD protein expression as well as the loss of mitochondrial membrane potential suggests activation of the intrinsic pathway of apoptosis.

Conclusion

These results could facilitate the future development of novel hydantoin derivatives as chemotherapeutic agents for leukemia.

Specific small nucleolar RNA expression profiles in acute leukemia

Apart from microRNAs, little is known about the regulation of expression of non-coding RNAs in cancer. We investigated whether small nucleolar RNAs (snoRNAs) accumulation displayed specific signatures in acute myeloblastic and acute lymphoblastic leukemias. Using microarrays and high-throughput quantitative PCR (qPCR), we demonstrate here that snoRNA expression patterns are negatively altered in leukemic cells compared with controls. Interestingly, a specific signature was found in acute promyelocytic leukemia (APL) with ectopic expression of SNORD112-114 snoRNAs located at the DLK1-DIO3 locus. In vitro experiments carried out on APL blasts demonstrate that transcription of these snoRNAs was lost under all-trans retinoic acid-mediated differentiation and induced by enforced expression of the PML-RARalpha fusion protein in negative leukemic cell lines. Further experiments revealed that the SNORD114-1 (14q(II-1)) variant promoted cell growth through cell cycle modulation; its expression was implicated in the G0/G1 to S phase transition mediated by the Rb/p16 pathways. This study thus reports three important observations: (1) snoRNA regulation is different in normal cells compared with cancer cells; (2) a relationship exists between a chromosomal translocation and expression of snoRNA loci; and (3) snoRNA expression can affect Rb/p16 cell cycle regulation. Taken together, these data strongly suggest that snoRNAs have a role in cancer development.

Apoptosis induced by genipin in human leukemia K562 cells: involvement of c-Jun N-terminal kinase in G₂/M arrest

AIM

To investigate the effect of genipin on apoptosis in human leukemia K562 cells in vitro and elucidate the underlying mechanisms.

METHODS

The effect of genipin on K562 cell viability was measured using trypan blue dye exclusion and cell counting. Morphological changes were detected using phase-contrast microscopy. Apoptosis was analyzed using DNA ladder, propidium iodide (PI)-labeled flow cytometry (FCM) and Hoechst 33258 staining. The influence of genipin on cell cycle distribution was determined using PI staining. Caspase 3 activity was analyzed to detect apoptosis at different time points. Protein levels of phospho-c-Jun, phosphor-c-Jun N-terminal kinase (p-JNK), phosphor-p38, Fas-L, p63, and Bax and the release of cytochrome c were detected using Western blot analysis.

RESULTS

Genipin reduced the viability of K562 cells with an IC(50) value of approximately 250 μmol/L. Genipin 200-400 μmol/L induced formation of typical apoptotic bodies and DNA fragmentation. Additionally, genipin 400 μmol/L significantly increased the caspase 3 activity from 8-24 h and arrested the cells in the G₂/M phase. After stimulation with genipin 500 μmol/L, the levels of p-JNK, p-c-Jun, Fas-L, Bax, and cytochrome c were remarkably upregulated, but there were no obvious changes of p-p38. Genipin 200-500 μmol/L significantly upregulated the Fas-L expression and downregulated p63 expression. Dicoumarol 100 μmol/L, a JNK1/2 inhibitor, markedly suppressed the formation of apoptotic bodies and JNK activation induced by genipin 400 μmol/L.

CONCLUSION

These results suggest that genipin inhibits the proliferation of K562 cells and induces apoptosis through the activation of JNK and induction of the Fas ligand.

Salarin C, a member of the salarin superfamily of marine compounds, is a potent inducer of apoptosis

The continuous emergence of new diseases and the development of drug-resistant cancers necessitate the development of new drugs with novel mechanisms of action. The richest marine source of natural anti-cancer products has been soft-bodied organisms that lack physical defenses against their predators, and hence rely on chemical defense mechanisms using cytotoxic secondary metabolites. Bio-guided (brine shrimp test) separation of CHCl(3)-CH(3)OH (1:1) extract from the Madagascar Fascaplysinopsis sp. sponge provided several new compounds. Here we focused on the biological activity of a panel of novel natural compounds, salarins A-J. Of these, salarin C was the most potent inhibitor of proliferation, as demonstrated on the K562 leukemia cell line. Salarin C-treated K562 cells underwent apoptotic death as monitored by cell-cycle analysis, annexin V/propidium iodide staining, cleavage of poly-ADP-ribose polymerase (PARP) and caspase 3, and caspase 9 levels. The experimental approach described herein is an essential step towards identifying the cellular pathway(s) affected by salarin C and producing potent synthetic derivatives of salarin C with potential future uses as basic research tools and/or drugs and drug leads.

Inhibition of Erythroleukemia Cell Growth by Triplex-forming RNAs

OBJECTIVE

We have previously reported that oligodeoxyribonucleotides, designed to bind in a triplex fashion to a specific p53 binding site homology, inhibit the proliferation of colon cancer cells in vitro and in vivo. The present study was designed to extend these observations and to determine whether ribonucleic acid (RNA) generated from a retroviral vector (RVV) and possessing a corresponding triplex forming site can, in a similar fashion, inhibit proliferation of p53-null K-562 leukemia cells. Viral vectors may offer advantages over oligonucleotides for tumor treatment. RVVs have the potential to be taken up more efficiently than oligonucleotides and to be expressed continuously and long-term, circumventing the need for repeated and frequent oligomer administration.

EXPERIMENTAL DESIGN

The p53-null human erythroleukemia cell line, K-562, was stably transfected with a tetracycline-repressible p53 expression construct (p53/pUHD10-3). p53 protein in these cells is expressed in the absence of tetracycline but down-regulated upon tetracycline treatment. Triplex-forming oligonucleotides [Hoog 1 (experimental) and Hoog 3 (control)] were cloned into RVVs in order to generate triplex-forming fusion mRNAs. Naive K-562 cells and p53/pUHD10-3-transfected K-562 cells (with and without tetracycline treatment) were infected with viruses that express the triplex-forming RNAs. Cell growth was measured by BrdU incorporation into DNA.

RESULTS

RVVs encoding Hoog 1, in both orientations, inhibit the growth of naive K-562 cells and p53-transfected, tet-repressed K-562 cells. p53 expression in K-562 cells decreases growth to the same extent as Hoog 1 RVV treatment. However, Hoog 1-RVV does not further inhibit growth of p53-expressing K-562 cells. Treatment with an RVV encoding the control, Hoog 3, has no growth inhibitory effect.

CONCLUSION

Triple helix-forming RNAs directed to a p53 consensus sequence homology reduce leukemia cell proliferation, suggesting a novel method of treatment.

Expression of the EWS/FLI-1 oncogene in murine primary bone-derived cells Results in EWS/FLI-1-dependent, ewing sarcoma-like tumors

Ewing sarcoma is the second most common malignant pediatric bone tumor. Over 80% of Ewing sarcoma contain the oncogene EWS/FLI-1, which encodes the EWS/FLI-1 oncoprotein, a hybrid transcription factor comprised of NH2-terminal sequences from the RNA-binding protein EWS and the DNA-binding and COOH-terminal regions of the Ets transcription factor FLI-1. Although numerous genes are dysregulated by EWS/FLI-1, advances in Ewing sarcoma cancer biology have been hindered by the lack of an animal model because of EWS/FLI-1-mediated cytotoxicity. In this study, we have developed conditions for the isolation and propagation of murine primary bone-derived cells (mPBDC) that stably express EWS/FLI-1. Early-passage EWS/FLI-1 mPBDCs were immortalized in culture but inefficient at tumor induction, whereas later-passage cells formed sarcomatous tumors in immunocompetent syngeneic mice. Murine EWS/FLI-1 tumors contained morphologically primitive cells that lacked definitive lineage markers. Molecular characterization of murine EWS/FLI-1 tumors revealed that some but not all had acquired a novel, clonal in-frame p53 mutation associated with a constitutive loss of p21 expression. Despite indications that secondary events facilitated EWS/FLI-1 mPBDC tumorigenesis, cells remained highly dependent on EWS/FLI-1 for efficient transformation in clonogenic assays. This Ewing sarcoma animal model will be a useful tool for dissecting the molecular pathogenesis of Ewing sarcoma and provides rationale for the broader use of organ-specific progenitor cell populations for the study of human sarcoma.

Novel boronated derivatives of 5,10,15,20-tetraphenylporphyrin: synthesis and toxicity for drug-resistant tumor cells

We have developed the synthesis of boronated porphyrins for potential application in cancer treatment, based on the functional derivatives of 5,10,15,20-tetraphenylporphyrin. Boronated amide derivatives starting from 5,10,15,20-tetra(p-aminophenyl)porphyrin and 9-o- and 9-m-carborane carboxylic acid chlorides were prepared. Also, the reaction of 2-formyl-5,10,15,20-tetraphenylporphyrin with closo-C-lithium-o- and m-carboranes, as well as with closo-C-lithium monocarbon carborane, yielded neutral and anionic boronated hydroxy derivatives of 5,10,15,20-tetraphenylporphyrin, respectively. Water-soluble forms of neutral compounds were prepared by deboronation of closo-polyhedra with Bu4NF into nido-7,8- and nido-7,9-dicarbaundecaborate anions. Monocarbon carborane conjugated with copper (II) complex of 5,10,15,20-tetraphenylporphyrin was active for a variety of tumor cell lines (IC50 approximately 5 microM after 48-72 h of exposure) but was inert for non-malignant fibroblasts at up to 100 microM. At low micromolar concentrations, this compound caused the death of cells that express P-glycoprotein and other mechanisms of resistance to conventional anticancer drugs.

Methyl protodioscin induces G2/M arrest and apoptosis in K562 cells with the hyperpolarization of mitochondria

Methyl protodioscin is a furostanol bisglycoside with antitumor properties. The present study investigated its effects on human chronic myelogenous leukemia K562 cells. Cell cycle analysis showed that methyl protodioscin caused distinct G2/M arrest, with the appearance of polyploidy population. The levels of cyclin B1 decreased, whereas Cdc2 kept at a steady level. Subsequent apoptosis after G2/M blockage was demonstrated through DNA fragmentation and the annexin V staining assay. Methyl protodioscin induced a biphasic alteration (i.e. an early hyperpolarization, followed by depolarization) in mitochondrial membrane potential of K562 cells. The transient decline of intracellular Ca2+ concentration was observed at early stage. The generation of reactive oxygen species was also detected. The anti-apoptotic Bcl-x(L) transiently increased and then decreased. And the pro-apoptotic Bax was markedly up-regulated. Taken together, these data demonstrated that methyl protodioscin inhibits K562 cell proliferation via G2/M arrest and apoptosis, with mitochondrial hyperpolarization and the disruption of Ca2+ homeostasis playing important roles.

Diosgenin induces cell cycle arrest and apoptosis in human leukemia K562 cells with the disruption of Ca2+ homeostasis

PURPOSE

Diosgenin is a steroidal sapogenin with estrogenic and antitumor properties. In order to elucidate the mechanism of its antiproliferative activity, we investigated its effects on the cell cycle and apoptosis in human chronic myelogenous leukemia K562 cells.

METHODS

Cell viability was assessed via an MTT assay. Apoptosis was investigated in terms of nuclear morphology, DNA fragmentation, and phosphatidylserine externalization. Cell cycle analysis was performed via PI staining and flow cytometry (FCM). Western blotting and immunofluorescence methods were used to determine the levels of p53, cell cycle-related proteins and Bcl-2 family members. FCM was also used to estimate the changes in mitochondrial membrane potential (MMP), intracellular Ca2+ concentration and reactive oxygen species (ROS) generation.

RESULTS

Cell cycle analysis showed that diosgenin caused G2/M arrest independently of p53. The levels of cyclin B1 and p21Cip1/Waf1 were decreased, whereas cdc2 levels were increased. Subsequent apoptosis was demonstrated with the dramatic activation of caspase-3. A dramatic decline in intracellular Ca2+ concentration was observed as an initiating event in the process of cell cycle arrest and apoptosis, which was followed by the hyperpolarization and depolarization of MMP. Generation of ROS was observed in the progression of apoptosis. The antiapoptotic Bcl-2 and Bcl-xL proteins were downregulated, whereas the proapoptotic Bax was upregulated.

CONCLUSIONS

Diosgenin inhibits K562 cell proliferation via cell cycle G2/M arrest and apoptosis, with disruption of Ca2+ homeostasis and mitochondrial dysfunction playing vital roles.

Mitochondrial dysfunction as an early event in the process of apoptosis induced by woodfordin I in human leukemia K562 cells

Tannins are a group of widely distributed plant polyphenols, some of which are beneficial to health because of their chemopreventive activities. In the present study, we investigated the effects and action mechanisms of woodfordin I, a macrocyclic ellagitannin dimer, on human chronic myelogenous leukemia (CML) K562 cells. The results showed that woodfordin I was able to suppress the proliferation and induce apoptosis in K562 cells. Apoptosis was evaluated by cytomorphology, internucleosomal DNA fragmentation, and externalization of phosphatidylserine. Woodfordin I treatment caused a rapid and sustained loss of mitochondrial transmembrane potential (MMP), transient generation of reactive oxygen species (ROS), transient elevation of intracellular Ca2+ concentration, and cytosolic accumulation of cytochrome c. The activation of caspase-9 and 3, but not caspase-8, was also demonstrated, indicating that the apoptotic signaling triggered by woodfordin I was mediated through the intrinsic mitochondria-dependent pathway. Western blot and immunofluorescence analysis revealed that the anti-apoptotic Bcl-2 and Bcl-xL levels were downregulated, together with the pro-apoptotic Bax protein. Significantly, woodfordin I-induced apoptosis was associated with a decline in the levels of c-Abl, Bcr-Abl, and cellular protein tyrosine phosphorylation. Considering the consequence of all the events in the process of woodfordin I-induced apoptosis, the mitochondrial dysfunction is directly responsible for the pro-apoptotic effects on K562 cells. Furthermore, because CML is a malignancy of pleuripotent hematopoietic cells caused by the dysregulated tyrosine kinase activity of Bcr-Abl, these findings suggest that woodfordin I may be a potential lead compound against CML.

Antitumor activity of bruceantin: an old drug with new promise

Bruceantin was first isolated from Brucea antidysenterica, a tree used in Ethiopia for the treatment of cancer, and activity was observed against B16 melanoma, colon 38, and L1210 and P388 leukemia in mice. Phase I and II clinical trials were then initiated, but no objective tumor regressions were observed and clinical development was terminated. Recently, the activity of bruceantin has been studied with a number of leukemia, lymphoma, and myeloma cell lines. Cell differentiation was induced and c-MYC was down-regulated, suggesting a mechanistic correlation between c-MYC down-regulation and induction of cell differentiation or cell death. Treatment of HL-60 and RPMI 8226 cell lines induced apoptosis, and this involved the caspase and mitochondrial pathways. Moreover, an in vivo study using RPMI 8226 human-SCID xenografts demonstrated that bruceantin induced regression in early as well as advanced tumors, and these significant antitumor responses were facilitated in the absence of overt toxicity. Apoptosis was significantly elevated in tumors derived from animals treated with bruceantin. In sum, bruceantin interferes with the growth of leukemia, lymphoma, and myeloma cells in culture and xenograft models. Responses of this type suggest bruceantin should be reinvestigated for clinical efficacy against hematological malignancies.

The Mitotic-Arresting and Apoptosis-Inducing Effects of Diosgenyl Saponins on Human Leukemia Cell Lines

Diosgenyl saponins are the most abundant steroid saponins, and exert a large variety of biological functions. In a previous report, we showed that dioscin was able to induce cytotoxicity and apoptosis in human myeloblast leukemia HL-60 cells. This study further investigated the action mechanisms underlying this effect. The activation of caspase-9 and -3, but not caspase-8, together with the down-regulation of anti-apoptotic Bcl-2 protein, demonstrated that the apoptotic signaling triggered by dioscin was mediated through the intrinsic mitochondria-dependent pathway. We also investigated its anti-proliferative effect on human chronic myelogenous leukemia K562 cells. Flow cytometry analysis showed that dioscin treatment induced the accumulation of cells in the G(2)/M phase. Cytomorphology with DAPI and Wright-Giemsa staining demonstrated the enlargement of cell volume and multinucleation in the treated cells. Subsequent apoptosis was delineated with phosphatidylserine externalization and DNA hypodiploidy. Trillin was one of the hydrolysates of dioscin. We demonstrated that it could induce multinucleation in HL-60, K562 and human promyelocytic leukemia NB(4) cells, suggesting its extensive mitotic-arresting effects. As the diosgenyl sapogenin, diosgenin was also shown to be able to induce multinucleation and apoptosis in K562 cells in a similar manner to dioscin. These findings suggest that diosgenyl saponins have the properties to induce mitotic arrest and apoptosis, suggesting that they may be a new kind of antimitotic agent.

Spontaneous membrane transfer through homotypic synapses between lymphoma cells

Formation of an immunological synapse by T, B, or NK cells is associated with an intercellular transfer of some membrane fragments from their respective target cells. This capture is thought to require effector cell activation by surface recognition of stimulatory ligand(s). However, spontaneous synaptic transfers between homotypic lymphoid cells has never been described. In this study, we show that without adding Ag, resting healthy lymphoid cells and several tumor cell lines are inactive. Conversely, however, some leukemia cell lines including the Burkitt's lymphoma Daudi continuously uptake patches of autologous cell membranes. This intercellular transfer does not involve cytosol molecules or exosomes, but requires cell contact. In homotypic Daudi cell conjugates, this occurs through immunological synapses, involves constitutive protein kinase C and mitogen-activated protein/extracellular signal-regulated kinase kinase activity and strongly increases upon B cell receptor activation. Thus, spontaneous homosynaptic transfer may reflect the hitherto unsuspected autoreactivity of some leukemia cell lines.

BCR/ABL activates mdm2 mRNA translation via the La antigen

In a BCR/ABL-expressing myeloid precursor cell line, p53 levels were markedly downmodulated. Expression of MDM2, the negative regulator of p53, was upregulated in a tyrosine kinase-dependent manner in growth factor-independent BCR/ABL-expressing cells, and in accelerated phase and blast crisis CML samples. Increased MDM2 expression was associated with enhanced mdm2 mRNA translation, which required the interaction of the La antigen with mdm2 5' UTR. Expression of MDM2 correlated with that of La and was suppressed by La siRNAs and by a dominant negative La mutant, which also enhanced the susceptibility to drug-induced apoptosis of BCR/ABL-transformed cells. By contrast, La overexpression led to increased MDM2 levels and enhanced resistance to apoptosis. Thus, La-dependent activation of mdm2 translation might represent an important molecular mechanism involved in BCR/ABL leukemogenesis.

Brusatol-mediated induction of leukemic cell differentiation and G(1) arrest is associated with down-regulation of c-myc

Employing the natural product quassinoid brusatol, we currently report cellular and molecular events leading to cell death or terminal differentiation in a panel of leukemic cells. Brusatol and bruceantin exerted significant cytotoxic effects with several leukemic cell lines, but not with K562 or normal lymphocytic cells. Cell lines that were less sensitive to the cytotoxic effects of brusatol responded primarily through induction of terminal differentiation. The differentiated phenotype in cell lines derived from acute or chronic myeloid leukemias (HL-60, K562, Kasumi-1, NB4, U937, BV173) was characterized for producing superoxide and non-specific esterase, and some with up-regulation of CD13 (cluster of differentiation) and down-regulation of CD15. Chronic myeloid leukemic cell lines, K562 and BV173, and acute lymphoblastic cell lines, SUPB13 and RS4;11, were induced to differentiate along the erythrocytic pathway. Withdrawal studies showed that brusatol treatment for 48 h was sufficient to induce commitment towards terminal differentiation in HL-60, K562 and SUPB13. Reh cells did not undergo maturation. Analysis of c-MYC protein expression revealed that brusatol or bruceantin down-regulated expression to undetectable levels in cell lines that were most sensitive, based on cell death or terminal differentiation. Generally, c-myc RNA was reduced, but to a lower extent than c-MYC protein levels, indicating c-myc expression was regulated by quassinoids at the post-transcriptional level. Thus, regulation of c-myc expression may represent a critical event that leads to terminal differentiation. Since these responses are facilitated at clinically achievable concentrations, quassinoids may be of value for the management of hematological malignancies.

Identification of a rare polymorphism in the human TP53 promoter

The majority of families with classic Li-Fraumeni Syndrome (LFS) and a significant proportion of Li-Fraumeni-like (LFL) families have a germline mutation in the TP53 tumor suppressor gene. However around 20% of LFS and 60% of LFL families have no identifiable genetic defect in the coding region or splice junctions of TP53, and the genetic basis for cancer susceptibility in these families remains largely uncharacterized. To determine whether promoter mutations could be responsible for the Li-Fraumeni phenotype, we sequenced the TP53 promoter in index cases from members of classic LFS and LFL families without detectable TP53 mutations. We identified an identical single nucleotide deletion within the C/EBP- like site of the promoter in two out of eighteen such families (11%), compared to only one of a total of 366 control samples (0.3%). Although this result is highly significant (P=0.006, Fischer's exact test), the mutation did not affect the expression of TP53 in our hands. We provide evidence that this site is not utilized in the wild type TP53 promoter and further, that mutation of this site in LFS/LFL does not have a functional effect. We conclude that the sequence variant is a rare polymorphism arising within the TP53 promoter. However, the significantly increased frequency of this variant in LFS/LFL remains intriguing.

GAAP-1: a transcriptional activator of p53 and IRF-1 possesses pro-apoptotic activity

The mechanisms that regulate the transcription of the tumour suppressor genes p53 and IRF-1 are poorly understood. We have characterized a 68-kDa transcription factor, GAAP-1 (gatekeeper of apoptosis activating proteins), encoded by an alternative splice product of the PRDII-BF1 gene, that recognizes a novel regulatory element within the p53 and IRF-1 promoters. Transfection of U937 cells with GAAP-1 activates p53 and IRF-1 expression and leads to apoptosis, whereas over-expression of GAAP-1 in K562 cells that lack p53 and IRF-1 induces cell differentiation. Alterations in the 6p24 locus containing the GAAP-1 gene are frequent in acute myelogenous leukemia (AML), and AML-derived cell lines display reduced GAAP-1 mRNA levels. Together, these results suggest that GAAP-1 acts as a gatekeeper at a critical point in the tumour suppressor gene pathway.

Bax translocation is crucial for the sensitivity of leukaemic cells to etoposide-induced apoptosis

Bax translocation from cytosol to mitochondria is believed to be a crucial step for triggering cytochrome c release from mitochondria. However, it is unclear whether Bax translocation is associated with Bax induction by DNA damaging agents. The induction of Bax in response to DNA damaging agents has been considered to be linked with p53. In this study, we used the p53 negative human chronic myeloid leukaemia K562 cell line. Bax up-regulation occurred at the whole cell level after DNA damage induced by etoposide. However, after incubation with etoposide, Bax failed to translocate to mitochondria and as a result, the apoptotic process was blocked. A Bax stable transfectant, the K/Bax cell line, expressed more Bax protein in the cytosol, mitochondria and nuclei. This Bax overexpression induced cytochrome c release, a reduction of cytochrome c oxidase activity and mitochondrial membrane potential (Delta(Psi)m). However, Bax-induced apoptosis was blocked downstream of mitochondria in K562 cells. The increased levels of mitochondrial Bax sensitized cells to etoposide-induced activation of caspases-2, -3 and -9 and apoptosis. However, after transient transfection with the Apaf-1 gene, K/Bax cells were sensitized to etoposide-induced caspase activation and apoptosis to a larger extent compared with Bax or Apaf-1 transfection alone. We therefore conclude that two mechanisms contribute to the resistance of K562 cells to etoposide-induced apoptosis; firstly failure of Bax targeting to mitochondria and, secondly, deficiency of Apaf-1. Uncoupling of Bax translocation from Bax induction can occur in response to etoposide-induced DNA damage.

Resveratrol, a natural dietary phytoalexin, possesses similar properties to hydroxyurea towards erythroid differentiation

Resveratrol, a natural dietary polyphenol, has been postulated to be implicated in the cardioprotective effect of red wine and the low incidence of breast and prostate cancers among vegetarians and Orientals respectively. This compound inhibits ribonucleotide reductase as does hydroxyurea, the first therapeutic agent used in the treatment of sickle cell disease. Using the human erythroleukaemic K562 cell line as an in vitro model, we show here that 50 micromol/l of resveratrol induced a higher haemoglobin production (sevenfold) in K562 cells than 500 micromol/l of hydroxyurea (3.5-fold). This erythroid differentiation was linked to a dose- and time-dependent inhibition of cell proliferation associated with an equivalent increased expression of p21 mRNA, but with a higher increased level of p21 protein (sixfold) for cells treated with resveratrol than for those treated with hydroxyurea (1.5-fold). We also show that 50 micromol/l of resveratrol and 25 micromol/l of hydroxyurea induced variable but similar enhancements of fetal haemoglobin synthesis in cultured erythroid progenitors for the majority of the sickle cell patients studied. These inductions were linked to, but not correlated with, a variable decrease in erythroid burst-forming unit clone number. Taken together, these results show that resveratrol merits further investigations in sickle cell disease therapy.

Flow cytometric detection of p53 protein after incubation of a pre-B cell line with antitumor agents

BACKGROUND

The study of new substances capable of counteracting tumor development has focused, in recent years, on several of the steps in a cell's initiation of the process of apoptosis. One of the crucial events is the activation of p53, leading to a cell cycle G1/S block or to programmed cell death.

METHODS

We report here a parallel flow cytometric method for semiquantitative detection of p53 protein and apoptosis (percent of apoptotic cells) in a pre-B leukemic cell line (NALM-6) exposed to various antitumor agents (2.35 microg/ml etoposide; 0.175 microg/ml FCE296; 0.4 microg/ml FCE624; and 1.5 microg/ml L-PAM).

RESULTS

All of the substances proved to be capable of inducing an increase of p53 after 16 or 24 h of incubation. In all experiments with antitumor agents we also found an onset of apoptosis after 24 h of incubation with the substance, as determined by the annexin V flow cytometric assay and by DNA fragmentation.

CONCLUSIONS

This technique, based on flow cytometric data of both p53 intracellular content and percentage of apoptotic cells, is suitable to determine the amount of antitumor agent needed to induce p53, and thus to dose the drug in relation to the sensitivity of a defined tumor as well as choose the more efficacious drug, depending on cell responsiveness. The study of antitumor substances that induce apoptosis, bypassing p53, could also be evaluated by this method, in view of the development of substances for the treatment of p53-mutated tumors.

p53 gene mutations and rearrangements in non-Hodgkin's lymphoma

BACKGROUND

Alterations of the p53 gene have been associated with the progression of certain human malignancies. To establish further the correlation between p53 gene alterations and progression of non-Hodgkin's lymphomas (NHLs), the authors analyzed both mutations and rearrangements of the p53 gene in a cohort of 84 NHLs.

METHODS

Eighty-four NHLs were analyzed for p53 gene alterations. Point mutations of exons 5-9 were studied by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), and DNA rearrangements were studied by Southern blot analysis. RESULTS. Point mutations and DNA rearrangements of the p53 gene were detected in 6 (7.2%) and 3 (3.6%) patients, respectively. All p53 gene abnormalities were found exclusively in B-cell NHLs. Taken together, patients with p53 gene alterations had poorer survival than other patients (P = 0.024). However, of the three patients with p53 gene rearrangements, the two who appeared to have one normal allele showed a relatively better response to chemotherapy and had longer survival (27 and 47 months). In contrast, the remaining patient who had rearranged bands much stronger than the germline, and thus appeared to have both alleles rearranged, was refractory to chemotherapy and had poorer survival (6 months).

CONCLUSIONS

Patients with NHLs of intermediate and high grades who carried point mutations or rearrangements of p53 genes had worse outcomes than other patients. Patients with one abnormal p53 allele and one residual normal allele had a more favorable prognosis than those with two abnormal alleles.

Arsenic alters cytosine methylation patterns of the promoter of the tumor suppressor gene p53 in human lung cells: a model for a mechanism of carcinogenesis

Arsenic is a potent human carcinogen to which there is significant worldwide exposure through natural contamination of food and drinking water sources. Because arsenic is detoxified via methylation using a methyltransferase (MTase) and S-adenosylmethionine (SAM) as the methyl donor, we hypothesized that a mechanism of carcinogenesis of arsenic could involve alterations of MTase/SAM-dependent DNA methylation of a tumor suppressor gene. We found that exposure of human lung adenocarcinoma A549 cells to sodium arsenite (0.08-2 microM) or sodium arsenate (30-300 microM), but not dimethylarsenic acid (2-2000 microM), produced significant dose-responsive hypermethylation within a 341-base pair fragment of the promoter of p53. This was determined by quantitative PCR/HpaII restriction site analysis to analyze methylation status of two CCGG sites. In experiments with arsenite, DNA sequencing using bisulfite to visualize 5-methylcytosine (5-MeC) over the entire promoter region confirmed data obtained by restriction analysis. Limited data using SssI methylase also suggested that over-methylation of CpG sequences may exist over the entire genome in response to arsenite exposure. We propose that alteration of DNA methylation by arsenic offers a plausible, unified hypothesis for the carcinogenic mechanism of action of arsenic, and we present a model for arsenic carcinogenesis that utilizes perturbations of DNA methylation as the basis for the carcinogenic effects of arsenic.

Constitutive Activation of U937 Promonocytic Cell Clones Selected for Their Resistance to Parvovirus H-1 Infection

The human promonocytic cell line U937 is highly sensitive to the lytic effect of the autonomous parvovirus H-1. Rare cell variants that resisted H-1 virus infection could be isolated, of which four (RU1, RU2, RU3, and RU4) were further characterized. In contrast to parental cells, the RU clones sustained an abortive H-1 virus infection. Three of the clones showed a significant decrease in the accumulation levels of the c-Myc oncoprotein and in their capacity for forming tumors in immunodeficient mice. Surprisingly, all RU clones resisted the suppressing effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on c-myc oncogene expression and cell proliferation. In contrast, RU clones exhibited the TPA-induced changes in membrane surface antigens and nonspecific esterase activities that are characteristic of monocytic differentiation. Studies of the activation steady-state of RU cells demonstrated the constitutive production of significant amounts of nitric oxide (NO) and superoxide anion (O−2⋅ ). Inhibitors of NO and O−2⋅ . production sensitized all RU cells to the killing effect of parvovirus H-1 and increased the production of infectious viral particles. These data argue for the participation of active oxygen species in macrophage defence mechanisms against parvovirus infection. Moreover, the use of parvovirus H-1 as a selective agent in a cell-colony formation assay allowed us to show that expression of defined markers of monocytic differentiation can be uncoupled from suppression of proliferation.

Constitutive Activation of U937 Promonocytic Cell Clones Selected for Their Resistance to Parvovirus H-1 Infection

The human promonocytic cell line U937 is highly sensitive to the lytic effect of the autonomous parvovirus H-1. Rare cell variants that resisted H-1 virus infection could be isolated, of which four (RU1, RU2, RU3, and RU4) were further characterized. In contrast to parental cells, the RU clones sustained an abortive H-1 virus infection. Three of the clones showed a significant decrease in the accumulation levels of the c-Myc oncoprotein and in their capacity for forming tumors in immunodeficient mice. Surprisingly, all RU clones resisted the suppressing effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on c-myc oncogene expression and cell proliferation. In contrast, RU clones exhibited the TPA-induced changes in membrane surface antigens and nonspecific esterase activities that are characteristic of monocytic differentiation. Studies of the activation steady-state of RU cells demonstrated the constitutive production of significant amounts of nitric oxide (NO) and superoxide anion (O−2⋅ ). Inhibitors of NO and O−2⋅ . production sensitized all RU cells to the killing effect of parvovirus H-1 and increased the production of infectious viral particles. These data argue for the participation of active oxygen species in macrophage defence mechanisms against parvovirus infection. Moreover, the use of parvovirus H-1 as a selective agent in a cell-colony formation assay allowed us to show that expression of defined markers of monocytic differentiation can be uncoupled from suppression of proliferation.

Chromosome 17 abnormalities and inactivation of the p53 gene in chronic myeloid leukemia and their prognostic significance

We have reviewed all the relevant studies on the loss of the short arm of chromosome 17 (17p) and inactivation of the p53 gene in chronic myelogenous leukemia (CML) in an attempt to clarify their roles in the progression of CML. Loss of a 17p (hemizygous 17p) and p53 inactivation emerged as the disease progressed and were closely associated with each other. About half of the cases with loss of a 17p, however, did not show p53 inactivation. In these cases loss of a 17p preceded p53 inactivation, which suggested that either reduction of the p53 gene dosage or inactivation of another tumor-suppressor gene on 17p might contribute to the disease progression. Both loss of a 17p and p53 inactivation may serve as poor prognostic factors but the prognostic significance of the former only emerged when metaphase cells with loss of a 17p were dominant amongst the total cell population analyzed.

Inactivation of the DCC tumor suppressor gene in a B-cell lymphoma cell line with the alteration of chromosome 18

A B-cell lymphoma cell line, designated KML-1, was established from pleural effusion of a patient with non-Hodgkin's lymphoma of large-cell type. The lymphoma arose in the pelvis and ran an aggressive clinical course. Chromosome analysis of the cell line exhibited a complex karyotype including the loss of chromosome 18. To evaluate the molecular events in the cell line that may be associated with the development of the lymphoma, we investigated the expression and/or alterations of several classes of human genes, including oncogenes, tumor suppressor genes, and cytokine genes. The expression of the DCC (deleted in colorectal cancer) gene, located on the chromosome 18q21, was extremely reduced in KML-1 cell line, as compared with that in a normal spleen tissue and other 4 lymphoma cell lines by the reverse transcription-polymerase-chain-reaction (RT-PCR) method. This finding suggests that inactivation of the DCC gene might play a role in the pathogenesis of the case of lymphoma.

Wild-type p53 regulates its own transcription in a cell-type specific manner

Wild-type (w.t.) p53 acts as a transcriptional regulator that binds to DNA and modulates transcription of several promoters. Wild-type p53 has also been shown to autoregulate its own transcription. There is no agreement, however, on whether w.t. p53 has trans-activates or downregulates its own transcription. To further explore the transcriptional autoregulation of the p53 gene, we analyzed the effect of w.t. p53 on its own promoter in different cell lines that do not express p53. A DNA domain within the human p53 promoter (-48 to -23) with the structure of ATGGGATTGGGGTTTTCCCCTCCCAT shares 8 of 10 nucleotides sequence homology with the p53 binding motif. When the human p53 promoter that included this domain was linked to a chloramphenicol acetyltransferase (CAT) gene and coexpressed with w.t. or mutated p53 in cells lacking p53 protein, w.t. p53 down-regulated its own promoter in SAOS-2 and K562 cells, but not in DP15 cells. We were unable to detect direct interaction of p53 with its promoter or to domain -48 to -23 following transfection of these cells with w.t. p53. A different pattern of protein--DNA complexes was observed, however, between the p53 promoter and nuclear extracts from SAOS-2 and DP15 cells following transfection with w.t. p53. These data suggest that w.t. p53 autoregulates its own promoter indirectly and in a cell type-specific manner.

Tumor suppressor genes and clonal evolution in B-CLL

This review highlights the genetic alterations that have been detailed in the malignant B-cell clones of patients with B-chronic lymphocytic leukemia (CLL). In particular, the alterations seen in p53 and the retinoblastoma (Rb) genes are reviewed. In addition, the multiplicity of cytogenetic alterations observed at baseline and on sequential analysis are summarized. The cytogenetic and molecular biologic analysis of B-CLL clones has revealed that there is a dynamic array of genetic events which occur within a B-cell clone. This latter data strongly suggests that clonal evolution may occur in B-CLL patients. However the relationship of the clonal instability to the patient's clinical course is still unclear. The relatively frequent detection of multiple tumor suppressor gene alterations in the B-CLL clones offer several interesting clues regarding the transformation event within B-CLL. A model is proposed which attempts to explain the potential contribution and interaction of p53 and Rb gene alterations in a malignant B-cell transformation.

Hemizygous expression of the wild-type p53 allele may confer a selective growth advantage before complete inactivation of the p53 gene in the progression of chronic myelogenous leukaemia

We analysed the expression of the p53 gene in various clinical phases of chronic myelogenous leukaemia (CML) by quantitative reverse transcriptase (RT) polymerase chain reaction (PCR). Hemizygous expression of the wild-type p53 allele was observed in two samples showing the loss of one p53 allele, and affected p53 expression was associated with p53 allelic loss rather than the clinical phase of CML. In four patients with CML showing p53 inactivation, we performed a detailed sequential analysis of p53 allelic loss, p53 mutation and expression from the onset of the disease to the patients' death. Consequently, we demonstrated that the loss of a wild-type p53 allele preceded mutation of the remaining allele, and that cells hemizygous for the wild-type p53 allele dominated those with both wild-type alleles, then were replaced by cells with complete p53 inactivation. These observations indicate that not only complete p53 inactivation but also hemizygous expression of the wild-type p53 allele may confer a selective growth advantage, and that the former is implicated in a more malignant phase than the latter. Alternatively, the inactivation of another undefined anti-oncogene on chromosome 17p may allow selective growth before the p53 mutation occurs.

Identification of a cell-surface glycoprotein associated with normal mammary and extramammary epithelial cells

The goal of the study was to identify any normal genes that may become inactivated in malignant cells, with associated modifications or loss of gene products. Consequently, attempts were made to identify such products by generating monoclonal antibodies using an immune tolerisation-immunisation procedure. Using such a technique, a plasma membrane-associated glycoprotein with an apparent molecular weight of 92 kDa was identified. The glycoprotein was termed luminal epithelial antigen (LEA.92). The pattern of expression of LEA.92 was demonstrated by an indirect immunostaining technique. Using an in vitro model system representing various stages of breast oncogenesis, LEA.92 was detected on normal or immortalised mammary epithelial cell (MEC) lines which were dependent on epidermal growth factor (EGF) and anchorage formation for growth and non-tumorigenic in nude mice. In contrast, LEA.92 was undetectable on oncogenically transformed or established lines of mammary carcinoma cell lines which were independent of EGF or anchorage formation for growth and were highly tumorigenic. The results appear to suggest a correlation between the down-regulation of LEA.92 and the development of tumorigenicity in malignant MEC lines. Furthermore, the patterns of expression of LEA.92 on breast cells in tissue mirrored those of breast epithelial cells in cell cultures. LEA.92 was detected on the surface of normal but not malignant epithelial cells, which included breast, cervix, colon, lung, pancreas and stomach. LEA.92 appeared to be distinct from receptor for epidermal growth factor, antigens associated with milk fat globule membrane and the family of epithelium-specific keratins.

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.

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

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

Deletion of chromosome 22 without bcr rearrangement and without juxtaposition of c-abl in a case of acute myeloid leukemia

We describe a patient with acute myeloid leukemia (AML) who had a deletion of chromosome 22 at q11 as a sole chromosomal abnormality, resulting in the karyotype 46,XY,del(22)(q11). Southern blot analysis showed no bcr rearrangement and fluorescence in situ hybridization indicated no juxtaposition of c-abl. This study indicates that molecular events other than bcr rearrangement and c-abl juxtaposition were involved in leukemogenesis in this patient. We hypothesize that a tumor suppressor candidate gene may be located on the long arm of chromosome 22; its loss may lead to malignant transformation.

The role of apoptosis (programmed cell death) in haemopoiesis and the immune system

Apoptosis, or programmed cell death, is a series of controlled sequential events resulting in the demise of cells without invoking an inflammatory response. It is a naturally occurring process which maintains a cellular balance during both animal development and in the mature adult. Although first described 20 years ago, there is now renewed interest in this phenomenon, particularly in the light of our greater understanding of cellular signalling pathways and their genetic control. This is especially pertinent to haemopoiesis and the overall maintenance of a functional immune system. This review broadly covers the biochemical events of apoptosis and the recognition of apoptotic cells by phagocytes. Reference is made to the selective development of T- and B-cells and to the control of inflammation. Molecular events in apoptosis are also discussed with special reference to aberrant bcl-2 gene expression in follicular B-cell lymphoma and the role of other death genes in the control of apoptosis.

Phenotypic and molecular analysis of Ph1-chromosome-positive acute lymphoblastic leukemia cell lines

We have established 2 Philadelphia chromosome (Ph1)-positive acute lymphoblastic leukemia (ALL) cell lines, designated PALL-1 and PALL-2, from distinct adult Ph1-positive ALL patients. PALL-1 was established in nude mice, and PALL-2 was established in culture. Both retained the Ph1 chromosome and expressed the ALL type bcr/abl chimeric mRNA containing the junction of the first exon of BCR gene (e1) and second exon of c-abl gene (a2). PALL-1 and PALL-2 expressed CD34 surface antigen which is characteristic of early hematopoietic progenitor cells. PALL-2 expressed antigens for both pre-B and early myeloid cells and had rearrangements of both the heavy chain of immunoglobulin gene and the beta chain of T-cell-receptor gene. Both PALL-1 and PALL-2 expressed detectable levels of p53 gene RNA. Polymerase-chain-reaction-single-strand conformation polymorphism (PCR-SSCP) analysis of the p53 gene showed a normal pattern of mobility in both cell lines. Taken together, the 2 cell lines had features of Ph1-positive ALL: (i) hematopoietic progenitor cells with pre-B-cell phenotype and, (ii) activation of e1-a2 type bcr/abl oncogene without alterations of p53 gene. These unique lines should provide a valuable tool for studying the pathogenesis of Ph1-positive ALL.

p53 expression in lymphatic malignancies

AIMS

To investigate the expression of p53 protein in malignant and benign lymphoid tissues.

METHODS

Tissue from 42 non-Hodgkin's lymphomas, 10 Hodgkin's lymphomas, three atypical hyperplasias and five benign reactive hyperplasias was studied immunohistochemically for the expression of p53 protein.

RESULTS

Of the 42 non-Hodgkin's lymphomas, 13 (31%) were positive for p53 in some of the tumour cells. In two cases the proportion of positive cells was more than 10% and in four cases it was between 1-5%. These six cases consisted of three Burkitt's lymphomas, one immunoblastic lymphoma, one centroblastic diffuse lymphoma and one angioimmunoblastic lymphoma. In seven cases the proportion of p53 positive tumour cells was less than 1%. These cases comprised three centroblastic diffuse, three centroblastic polymorphic diffuse, and one angioimmunoblastic type lymphoma. In three out of 10 (30%) Hodgkin's lymphomas, a proportion of the Reed-Sternberg cells were p53 positive. One of these was a mixed cellular subtype and two nodular sclerosing subtypes. p53 protein was not expressed in the three atypical hyperplasias or the five benign reactive hyperplasias of the lymph nodes.

CONCLUSIONS

The presence of p53 positivity in non-Hodgkin's and Hodgkin's lymphomas indicates that mutations of the p53 gene may play a part in the development of these tumours. The concentration of p53 positivity in high grade lymphomas suggests that p53 is involved in the transformation of low grade lymphomas to more aggressive types. Because no p53 positivity was observed in benign lesions of the lymph nodes, positive p53 immunohistochemical staining in a lymphoid lesion suggests malignancy.

Philadelphia chromosome-positive leukaemia: the translocated genes and their gene products

Overwhelming evidence indicates a role for the deregulated ABL protein tyrosine kinase in the aetiology of CML and Ph-positive acute leukaemia. These disorders are characterized by the generation of BCR/ABL fusion proteins with elevated tyrosine kinase activity. Although much is known concerning the transforming potential of ABL proteins in various systems, very little is understood of the normal function and mode of regulation of ABL activity. The mechanism of oncogenic activation is therefore also obscure. In spite of this, our understanding of the molecular details of these chromosomal translocations allows the design of therapies directed against their unique, leukaemia-specific proteins and RNA products.

Chromosome 17- and p53 changes in lymphoma

The clinical course of lymphoma patients in whom rearrangements or deletions of the short arm of chromosome 17 (17p) were evident by cytogenetics was rapidly progressive with a short survival. The gene for the protein designated p53 resides in 17p. We studied four lymphoma cell lines derived from human tumours, and 25 tumour samples of patients with lymphomas, for any evidence of p53 genomic changes by Southern blot technique. The four cell lines and four of the 25 tumour samples showed numerical changes of chromosome 17 or structural abnormalities of 17p (translocations or deletions). Allelic loss of the p53 gene was found in two of the four cell lines, and one of these in addition showed a rearrangement of the 3' end of the gene. Of the four tumours known to have chromosome 17 abnormality, one specimen showed allelic loss of the p53 gene. None of the remaining tumour samples showed any significant change. These studies suggest that acquisition of changes in the short arm of chromosome 17, which may be interrelated with the p53 gene, may carry a poor prognosis in patients with non-Hodgkin's lymphoma.