Expression of p53 protein during the cell cycle measured by flow cytometry in human leukemia

Growing and dividing: how O-GlcNAcylation leads the way

Cell cycle errors can lead to mutations, chromosomal instability, or death; thus, the precise control of cell cycle progression is essential for viability. The nutrient-sensing posttranslational modification, O-GlcNAc, regulates the cell cycle allowing one central control point directing progression of the cell cycle. O-GlcNAc is a single N-acetylglucosamine sugar modification to intracellular proteins that is dynamically added and removed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. These enzymes act as a rheostat to fine-tune protein function in response to a plethora of stimuli from nutrients to hormones. O-GlcNAc modulates mitogenic growth signaling, senses nutrient flux through the hexosamine biosynthetic pathway, and coordinates with other nutrient-sensing enzymes to progress cells through Gap phase 1 (G1). At the G1/S transition, O-GlcNAc modulates checkpoint control, while in S Phase, O-GlcNAcylation coordinates the replication fork. DNA replication errors activate O-GlcNAcylation to control the function of the tumor-suppressor p53 at Gap Phase 2 (G2). Finally, in mitosis (M phase), O-GlcNAc controls M phase progression and the organization of the mitotic spindle and midbody. Critical for M phase control is the interplay between OGT and OGA with mitotic kinases. Importantly, disruptions in OGT and OGA activity induce M phase defects and aneuploidy. These data point to an essential role for the O-GlcNAc rheostat in regulating cell division. In this review, we highlight O-GlcNAc nutrient sensing regulating G1, O-GlcNAc control of DNA replication and repair, and finally, O-GlcNAc organization of mitotic progression and spindle dynamics.

Sensory acceptable equivalent doses of β-phenylethyl isothiocyanate (PEITC) induce cell cycle arrest and retard the growth of p53 mutated oral cancer in vitro and in vivo

High doses of β-phenylethyl isothiocyanate (PEITC), a phytochemical in cruciferous vegetables, are not feasible for consumption due to a strong mouth-tingling effect. This study investigated the anti-cancer effect of PEITC at sensory acceptable doses. In vitro, PEITC was selectively toxic to oral cancer cells (CAL-27, FaDu, SCC4, SCC 9, SCC15, SCC25 and TU138), compared to oral keratinocytes (OKF6/TERT2 and NOK/Si). In vivo, 5 and 10 mg kg-1 PEITC, equivalent to human organoleptically acceptable doses, retarded tumor growth and prolonged the survival of mice bearing p53-mutated oral cancer cells - TU138 xenograft. Mechanistically, PEITC induced ROS accumulation, nuclear translocation of p53 and p21 and G1/S cell cycle arrest in vitro; increased p53 and 8-oxo-dG levels; and decreased Ki-67 intense/mild staining ratios without TUNEL changes in vivo. These findings suggested that the sensory acceptable doses of PEITC selectively induced ROS-mediated cell cycle arrest leading to delayed tumor progression and extended survival. PEITC could be a functional ingredient for oral cancer prevention.

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.

N-benzyl-N-methyldecan-1-amine, a phenylamine derivative isolated from garlic cloves, induces G2/M phase arrest and apoptosis in U937 human leukemia cells

Epidemiological studies indicate that components of garlic (Allium sativum) have anti-proliferative effects against various types of cancer. In the present study, we investigated the effect of newly isolated phenylamine derivative N-benzyl-N-methyldecan-1-amine (NBNMA) from garlic cloves on the inhibition of the growth and apoptosis of human leukemia U937 cells and its potential anticancer mechanism. NBNMA exhibited an antiproliferative effect in U937 cells by inducing cell cycle arrest at the G2/M phase and apoptotic cell death. Western blot analyses revealed that NBNMA decreased the expression of the regulator genes of G2/M phase progression, cyclin dependent kinase (Cdk) 2 and Cdc2 and elevated the expression of the Cdk inhibitor p21WAF1/CIP1 in a p53-independent manner. In addition, NBNMA activated caspase-8 and caspase-9, initiator caspases of the extrinsic and intrinsic pathways of apoptosis, respectively, which led to activation of executioner caspase-3 along with degradation of poly(ADP-ribose) polymerase. NBNMA-induced apoptosis was observed in parallel with an increased ratio of pro-apoptotic Bax and Bad/anti-apoptotic Bcl-2 and Bcl-xL, and inhibition of inhibitor of apoptosis protein (IAP) family members XIAP and cIAP-1. Furthermore, NBNMA-treated cells displayed enhanced release of cytochrome c from the mitochondria into the cytosol concomitant with a loss of mitochondrial membrane potential and downregulation of Bid, suggesting that NBNMA-induced apoptosis occurred via the extrinsic and intrinsic apoptotic pathways with a possible link to Bid protein activity between the two pathways. These results indicate that NBNMA has promising potential to become a novel anticancer agent for the treatment of leukemia. We provide new insight into the mechanisms underlying the anticancer effect of NBNMA.

Momilactone B induces apoptosis and G1 arrest of the cell cycle in human monocytic leukemia U937 cells through downregulation of pRB phosphorylation and induction of the cyclin-dependent kinase inhibitor p21Waf1/Cip1

Momilactone B, a terpenoid phytoalexin present in rice bran, has been shown to exhibit several biological activities. The present study was conducted using cultured human leukemia U937 cells to elucidate the possible mechanisms by which momilactone B exerts its anticancer activity, which to date has remained poorly understood. Momilactone B treatment of U937 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death as detected by chromatin condensation, DNA fragmentation, the cleavage of poly(ADP-ribose) polymerase and Annexin V-FITC staining. Flow cytometric analysis revealed that momilactone B resulted in G1 arrest in cell cycle progression, which was associated with the dephosphorylation of retinoblastoma protein (pRB) and enhanced binding of pRB with the E2F transcription factor family proteins. Treatment with momilactone B also increased the expression of cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1 in a p53-independent manner, without any noticeable changes in G1 cyclins and cyclin-dependent kinases (Cdks), except a slight decrease in cyclin E. Moreover, in vitro kinase assay indicated that momilactone B significantly decreased Cdk4- and Cdk6-associated kinase activities through a notably increased binding of p21 to Cdk4 and Cdk6. Our results demonstrated that momilactone B caused G1 cell cycle arrest and apoptosis in U937 cells through the induction of p21 expression, inhibition of Cdk/cyclin-associated kinase activities, and reduced phosphorylation of pRB, which may be related to anticancer activity.

A small-molecule c-Myc inhibitor, 10058-F4, induces cell-cycle arrest, apoptosis, and myeloid differentiation of human acute myeloid leukemia

OBJECTIVE

The protooncogene c-Myc plays an important role in the control of cell proliferation, apoptosis, and differentiation, and its aberrant expression is frequently seen in multiple human cancers, including acute myeloid leukemia (AML). As c-Myc heterodimerizes with Max to transactivate downstream target genes in leukemogenesis. Inhibition of the c-Myc/Max heterodimerization by the recently identified small-molecule compound, 10058-F4, might be a novel antileukemic strategy.

MATERIALS AND METHODS

HL-60, U937, and NB4 cells and primary AML cells were used to examine the effects of 10058-F4 on apoptosis and myeloid differentiation.

RESULTS

We showed that 10058-F4 arrested AML cells at G0/G1 phase, downregulated c-Myc expression and upregulated CDK inhibitors, p21 and p27. Meanwhile, 10058-F4 induced apoptosis through activation of mitochondrial pathway shown by downregulation of Bcl-2, upregulation of Bax, release of cytoplasmic cytochrome C, and cleavage of caspase 3, 7, and 9. Furthermore, 10058-F4 also induced myeloid differentiation, possibly through activation of multiple transcription factors. Similarly, 10058-F4-induced apoptosis and differentiation could also be observed in primary AML cells.

CONCLUSION

Our study has shown that inhibition of c-Myc/Max dimerization with small-molecule inhibitors affects multiple cellular activities in AML cells and represents a potential antileukemic approach.

In vitro antitumor activity of cyanidin-3-O-beta-glucopyranoside

BACKGROUND

Little is currently known regarding the cancer-preventive potential of cyanidin-3-O-beta-glucopyranoside (Cy-g) apart from its antioxidant activity.

METHODS

We tested Cy-g on Jurkat and HL-60 leukemia cell lines and, to help elucidate whether the effects of Cy-g are specific for cancer cells, also on normal T lymphocytes.

RESULTS

Cy-g induced apoptosis in all three cell systems, and this indicated that Cy-g was not selective towards leukemia cells. Moreover, Cy-g caused HL-60 differentiation. The induction of apoptosis and cytodifferentiation involved different proteins, thus suggesting that Cy-g-induced apoptosis and cytodifferentiation are two distinct events.

CONCLUSIONS

Although obtained in vitro, our findings indicate that Cy-g possesses some interesting biological properties that should encourage further investigation as regards its chemotherapeutic potential.

Immunophenotypic and genotypic characterization of progression in follicular lymphomas

Progression of follicular lymphomas (FLs) is often accompanied by a spectrum of histologic changes and an aggressive clinical course. Although molecular alterations have been implicated in this event, the underlying factors are largely unknown. We studied the expression of selected tumor suppressor genes (P53 and retinoblastoma [RB]), oncogenes (MYC and BCL2), and a transferrin-receptor related protein (Trump) in sequential biopsies in 16 patients. Eleven patients progressed from grade I or II FL to aggressive B-cell lymphomas with diffuse morphology, whereas 5 patients presented with diffuse aggressive lymphomas and recurred with indolent lymphomas. Immunoreactivity for P53 correlated with higher histologic grade in lymphomas progressing from indolent to aggressive; however, only 1 patient who presented with aggressive lymphoma demonstrated a P53 gene mutation. Neither P53 immunoreactivity nor genotypic alterations correlated with presentation with an aggressive histology and relapse with FL. Growth fraction, as assessed by Ki-67 staining, and Trump expression correlated with histologic grade. Immunoreactivity for RB, BCL2, and MYC was seldom associated with progression. Eight of 9 cases tested exhibited identical immunoglobulin heavy and light chain rearrangements or identical BCL2 gene rearrangements in the sequential lymphomas. We conclude that P53 and Trump protein expression and proliferation activity correlate with histologic grade, but not with recurrence or progression of FL. Our results further indicate that progression of FL to diffuse aggressive lymphomas and presentation of an aggressive B-cell lymphoma followed by FL are clonally related.

Induction of apoptosis in two human leukemia cell lines as well as differentiation in human promyelocytic cells by cyanidin-3-O-β-glucopyranoside

Little is known about the potentially chemopreventive mechanisms of anthocyanins apart from their antioxidant activity. We investigated the in vitro capacity of the anthocyanin cyanidin-3-O-beta-glucopyranoside (Cy-g) to induce apoptosis in T-lymphoblastoid, as well as apoptosis and differentiation in HL-60 promyelocytic cells. Although Cy-g-induced apoptosis (as well as necrosis) in the two systems, HL-60 cells were much less sensitive than T-lymphoblastoid cells. Moreover, treatment of HL-60 cells with Cy-g caused differentiation into macrophage-like cells and granulocytes. Concerning the mechanism of action, the induction of apoptosis in Jurkat T cells can be explained by a modulation of p53 and bax protein expression. At the molecular level, the induction of apoptosis and cytodifferentiation in HL-60 cells involved different proteins, thus suggesting that the effects of Cy-g on apoptosis and cytodifferentiation induction are two distinct events. These interesting biological properties should encourage further investigation into the chemopreventive and/or chemotherapeutic potential of Cy-g.

Downregulation of c-Jun expression and cell cycle regulatory molecules in acute myeloid leukemia cells upon CD44 ligation

In the present study, we investigated the mechanism of CD44 ligation with the anti-CD44 monoclonal antibody A3D8 to inhibit the proliferation of human acute myeloid leukemia (AML) cells. The effects of A3D8 on myeloid cells were associated with specific disruption of cell cycle events and induction of G0/G1 arrest. Induction of G0/G1 arrest was accompanied by an increase in the expression of p21, attenuation of pRb phosphorylation and associated with decreased Cdk2 and Cdk4 kinase activities. Since c-Jun is an important regulator of proliferation and cell cycle progression, we analysed its role in A3D8-mediated growth arrest. We observed that A3D8 treatment of AML patient blasts and HL60/U937 cells led to the downregulation of c-Jun expression at mRNA and protein level. Transient transfection studies showed the inhibition of c-jun promoter activity by A3D8, involving both AP-1 sites. Furthermore, A3D8 treatment caused a decrease in JNK protein expression and a decrease in the level of phosphorylated c-Jun. Ectopic overexpression of c-Jun in HL60 cells was able to induce proliferation and prevent the antiproliferative effects of A3D8. In summary, these data identify an important functional role of c-Jun in the induction of cell cycle arrest and proliferation arrest of myeloid leukemia cells because of the ligation of the cell surface adhesion receptor CD44 by anti-CD44 antibody. Moreover, targeting of G1 regulatory proteins and the resulting induction of G1 arrest by A3D8 may provide new insights into antiproliferative and differentiation therapy of AML.

Mechanism of action for N-substituted benzamide-induced apoptosis

We have analysed the mechanism of action for induction of apoptosis by N-substituted benzamides using declopramide as a lead compound. We show here that declopramide at doses above 250 microM in the mouse 70Z/3 pre-B cell line or in the human promyeolocytic cancer cell line HL60 induced cytochrome c release into the cytosol and caspase-9 activation. The broad spectrum caspase inhibitor zVADfmk and caspase-9 inhibitor zLEDHfmk inhibited apoptosis and improved cell viability when administrated to cells 1 h before exposure to declopramide, whereas the caspase-8 inhibitor zIEDHfmk had less effect. Also, the over expression of Bcl-2 by transfection in 70Z/3 cells inhibited declopramide-induced apoptosis. Prior to the induction of apoptosis, a G(2)/M cell cycle block was induced by declopramide. The cell cycle block was also observed in the presence of broad spectrum caspase inhibitor zVADfmk and in a transfectant expressing high levels of Bcl-2. Furthermore, while p53 was induced in 70Z/3 cells by declopramide, neither the apoptotic mechanism nor the G(2)/M cell cycle block were dependent on p53 activation since both effects were also seen in p53 deficient HL60 cells after addition of declopramide.

Prevention of etoposide-induced apoptosis by proteasome inhibitors in a human leukemic cell line but not in fresh acute leukemia blasts. A differential role of NF-kappab activation

Recent research indicates that the proteasome is one of the non-caspase proteases involved in apoptotic signaling pathways. Nuclear factor-kappaB (NF-kappaB) activation, one of the key factors in apoptosis, can be prevented through abrogation of IkappaBalpha degradation by proteasome inhibition. We have investigated the effects of the proteasome inhibitors carbobenzoxyl-L-leucyl-L-leucyl-L-leucinal (MG132) and N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal (LLnL) on apoptosis and NF-kappaB activation induced by etoposide, using a human leukemia cell line (U937) and leukemia blasts freshly isolated from patients with acute leukemia. Pretreatment of U937 cells with MG132 or LLnL inhibited etoposide-induced morphological apoptosis and caspase-3 activation. Furthermore, MG132 or LLnL prevented NF-kappaB activation and IkappaBalpha degradation, but not IkappaBalpha phosphorylation at Ser32. Other inhibitors of NF-kappaB activation, including pyrrrolidine dithiocarbamate (an antioxidant) and the peptide SN50 (an inhibitor of translocation of activated NF-kappaB into the nucleus), also attenuated etoposide-induced apoptosis. In leukemia blasts, although proteasome inhibitors suppressed NF-kappaB activation induced by etoposide, they were unable to prevent morphological apoptosis. Moreover, proteasome inhibitors by themselves caused apoptosis in leukemia blasts at the concentrations employed in this study. These results suggest that the role that NF-kappaB plays in apoptosis induced by etoposide in a human leukemia cell line may be different from the role it plays in freshly isolated leukemia blasts.

Evidence of a functional role for the cyclin-dependent kinase inhibitor p21CIP1 in leukemic cell (U937) differentiation induced by low concentrations of 1-beta-D-arabinofuranosylcytosine

The functional role of the cyclin-dependent kinase inhibitor (CDKI) p21CIP1 in differentiation of human myelomonocytic leukemia cells (U937) exposed to low concentrations of the antimetabolite 1-beta-D-arabino-furanosylcytosine (ara-C) was examined utilizing a cell line stably expressing a p21CIP1 antisense construct. Continuous exposure to 50 nM ara-C led to marked induction of p21CIP1 at 48-72 h in empty-vector control cells but not in their antisense-expressing counterparts (p21AS/F4 and B8). Such treatment induced expression of the myelomonocytic differentiation marker CD11b in approximately 35% of control cells, but no evidence of maturation was noted in antisense-expressing lines. However, antisense-expressing cells exposed to low concentrations of ara-C exhibited a reciprocal increase in apoptosis, manifested by the appearance of cells with classic morphologic features and hypodiploid quantities of DNA, reduced mitochondrial membrane potential (deltapsim), an increase in cytochrome c release into the cytosol, cleavage/activation of procaspases-9 and -3, and degradation of PARP and p27Kip1. Whereas empty-vector control cells exposed to 50 nM ara-C exhibited a decline in Bcl-2 expression, dephosphorylation of pRb, and an initial accumulation in S-phase, antisense-expressing cells did not. However, c-Myc down-regulation induced by low concentrations of ara-C was, if anything, more complete in antisense-expressing cells. Exposure of control but not antisense-expressing cells to ara-C led to phosphorylation/activation of MAP kinase at 24 h; moreover, the specific MEK/MAP kinase inhibitor PD98059 enhanced low-dose ara-C-mediated apoptosis only in wild-type cells. Lastly, exposure to 50 nM ara-C for 72 h resulted in detectable levels of cytoplasmic p21CIP1, a phenomenon associated with resistance to apoptosis, only in empty vector controls. Collectively, these findings demonstrate a functional role for p21CIP1 in leukemic cell maturation induced by low concentrations of ara-C. They also indicate that, as in the case of more conventional differentiation-inducers such as phorbol esters, disruption of the p21CIP1 response after exposure to low concentrations of the cytotoxic drug ara-C prevents leukemic cells from engaging a maturation program, but instead directs them along an apoptotic pathway.

Polyamine-depletion induces p27Kip1 and enhances dexamethasone-induced G1 arrest and apoptosis in human T lymphoblastic leukemia cells

Glucocorticoid-induced apoptosis is preceded by G1 arrest and supposed to be up-regulated by polyamine-depletion, which also induces G1, arrest. In CEM leukemia cells, dexamethasone showed an antileukemic effect by inducing G1 arrest and apoptosis. DFMO, which depleted cellular polyamines by inhibiting ornithine decarboxylase, induced G1 arrest but without apoptosis, though it enhanced dexamethasone-induced G1 arrest and apoptosis. The G1 arrest was associated with hypophosphorylation of pRb. Dexamethasone inhibited the increase of mutated p53 expression but had little effect on p2Wafl/Cip1 expression. The p27Kip1, level was increased by dexamethasone or and DFMO in line with the kinetics of G1 arrest. Therefore, the up-regulation of dexamethasone-induced apoptosis by polyamine-depletion may be associated with additive down-regulation of G1 progression via the p27Kip1-pRb pathtway.

Differential regulation of E2F transcription factors by p53 tumor suppressor protein

The cell cycle is under the control of various positive and negative regulators. Two such regulators are the E2F family of transcription factors and the p53 tumor suppressor protein. While E2F proteins are implicated in promoting the S phase of the cell cycle, p53 has the potential to arrest cells in G1 phase and thereby prevent entry into S phase. Because they perform seemingly opposite functions in the control of cell growth, a possibility of functional interactions between E2F and p53 was investigated. It was found that p53 specifically inhibited activated transcription by E2F-5 but not by E2F-1. Investigation into the mechanism of action established that heterodimer formation and the DNA-binding steps were not significantly inhibited by p53. However, the transcriptional activation step of E2F-5 activity, as examined by using a Gal4 DNA-binding domain chimera, was specifically inhibited by p53. Interestingly, p53 could also inhibit transcriptional activation by E2F-4 but not by E2F-2 or E2F-3. The results indicate that p53 differentially regulates the activities of two subclasses (E2F-1/-2/-3 vs. E2F-4/-5) of E2F transcription factors. Detailed analysis using a two-hybrid approach in mammalian cells indicated lack of physical interaction between p53 and E2F-5, DP-1, or E2F-1. Reciprocal analysis revealed that whereas E2F-1 dramatically inhibited p53-activated transcription, E2F-5 or DP-1 did not. Thus, nonreciprocal functional interactions exist between various members of the E2F family of transcription factors and p53 tumor suppressor protein. The complex interplay between various positive and negative regulators of cell growth, such as E2F and p53 proteins, may be crucial in determining the ultimate outcome in terms of cell cycle arrest, cell growth, or apoptosis.

Tumor suppressor p53 as a component of the tumor necrosis factor-induced, protein kinase PKR-mediated apoptotic pathway in human promonocytic U937 cells

Despite what is known about the early signaling events in tumor necrosis factor (TNF) alpha-induced apoptosis, characterization of the downstream events remains largely undefined. It is now known that a cross-talk exists between the interferon and TNF-alpha pathways. This linkage allows recruitment of the cell proliferation suppressor PKR (dsRNA-dependent protein kinase) from the interferon pathway to play a pivotal role in TNF-alpha-induced apoptosis. In this study, we took advantage of the differential TNF-alpha susceptibilities of human promonocytic U937 subclones, deficient in or overexpressing PKR, to further characterize the role of PKR in apoptosis. By reverse transcription-polymerase chain reaction, we demonstrated that TNF-alpha transiently induces the tumor suppressor p53 in U937 cells. This p53 induction lags behind the TNF-alpha induction of PKR by 1 h. By cell viability determination, ultrastructural studies, apoptotic DNA laddering, and antisense techniques, it was shown that inhibition of p53 expression in PKR-overexpressing U937 cells abrogates the TNF-alpha-induced apoptosis in these cells. Conversely, overexpressing wild type p53 in PKR-deficient U937 cells confers the susceptibility of these cells to TNF-alpha-induced apoptosis. This latter result indicates that p53 induction is an event downstream of TNF-alpha-induced up-regulation of PKR, thereby further establishing the critical role of p53 in TNF-alpha-induced apoptosis in U937 cells. PKR-overexpressing U937 cells were found to possess a constitutively higher level of p53, which partly explains why these cells spontaneously undergo apoptosis even without TNF-alpha treatment. Finally, a model is presented on the interplay between PKR and p53 in effecting TNF-alpha-induced apoptosis in U937 cells.

Time course of cell cycle-related protein expression in diethylnitrosamine-initiated rat liver

BACKGROUND/AIMS

Cell cycle control and the relationship that exists between cellular proliferation, the expression of cell cycle control proteins and cancer have been reported. This study was designed to decipher the timing of cell cycle control protein expression during the initiation of diethylnitrosamine-induced rat hepatocarcinogenesis.

METHODS

Three-week-old female Sprague-Dawley rats were intraperitoneally injected twice in 1 week with diethylnitrosamine; after the second injection, all animals were sacrificed at 1, 2 and 24 h, and 3 and 7 days. The expression of cell cycle-related proteins such as CDK2 and 4, cyclin proteins (D1, E and cdc2), proliferating cell nuclear antigen, tumor suppressor proteins (p53 and Rb), CDK inhibitory proteins (p21waf1 and p27Kip1), and apoptosis-inhibiting protein (bcl-2) following diethylnitrosamine treatment was examined.

RESULTS

The peak induction time of each cell cycle-related protein during DEN-induced cellular proliferation was diverse, and expressions of CDK2, CDK4, cdc2, p53, bcl-2, p21Waf1 and p27Kip1 appear to be of the greatest interest.

CONCLUSIONS

Data generated from this study may provide information about cell cycle-related protein expression in the initiation stage of hepatocarcinogenic signaling pathways stimulated by a genotoxic agent such as diethylnitrosamine.

p53 Expression in B-Cell Chronic Lymphocytic Leukemia: A Marker of Disease Progression and Poor Prognosis

We have analyzed by immunocytochemistry (ICC) the frequency of p53 protein expression in 181 cases of B-cell chronic lymphocytic leukemia (CLL) followed at a single institution to assess the relationship between p53 and the clinical and morphological features of the disease, as well as the possible involvement of this protein in the pathogenesis of the more aggressive forms of CLL. The overall frequency of p53 protein positivity in CLL was 15% (27 of 181 cases). There were no significant differences in age, sex, absolute lymphocyte count, or lymphocyte doubling time between p53-positive and -negative patients. By contrast, p53-positive patients had a significantly higher percentage of prolymphocytes (P = .002) and a significantly lower percentage of residual CD3-positive T lymphocytes (P = .0001). No correlation was found between the percentage of p53-positive cells and the percentage of cells in cycle assessed by the monoclonal antibody Ki-67. When the percentage of p53 positivity was correlated with the clinical stage of the disease, the proportion of p53-positive cases increased significantly from Binet's stage A (8 of 108; 7.4%), to stage B (12 of 49; 24.4%) and C (7 of 24; 29.2%) (P = .002). p53 positivity correlated also with the phase of the disease, showing a low expression at diagnosis (8 of 112; 7.1%) and a significantly higher expression in patients studied during the course of the disease (7 of 35; 20%) and, to a further extent, with disease progression (12 of 34; 35.3%) (P = .0001). The association of p53 protein expression with mutations in the gene was confirmed by direct sequence of the entire cDNA in 15 of the 17 ICC positive cases tested (88%). A significantly shorter treatment-free interval from diagnosis (P = .003) and a poorer response to therapy (P = .007) was observed in p53-positive compared with p53-negative patients. Overall survival from the time of diagnosis, as well as from the time of p53 protein analysis, was significantly shorter in patients with p53 protein expression (P = .03 and .0001, respectively). Moreover, in multivariate analysis, p53 expression and stage C were independently associated with a short survival. The results of this study indicate that in CLL the expression of the p53 protein, analyzed by a simple and reliable immunocytochemical method, is strongly associated with p53 gene mutations, a morphological variant (CLL with >10% prolymphocytes), advanced clinical stage, progressive disease, poor response to therapy, and short survival.

p53 Expression in B-Cell Chronic Lymphocytic Leukemia: A Marker of Disease Progression and Poor Prognosis

We have analyzed by immunocytochemistry (ICC) the frequency of p53 protein expression in 181 cases of B-cell chronic lymphocytic leukemia (CLL) followed at a single institution to assess the relationship between p53 and the clinical and morphological features of the disease, as well as the possible involvement of this protein in the pathogenesis of the more aggressive forms of CLL. The overall frequency of p53 protein positivity in CLL was 15% (27 of 181 cases). There were no significant differences in age, sex, absolute lymphocyte count, or lymphocyte doubling time between p53-positive and -negative patients. By contrast, p53-positive patients had a significantly higher percentage of prolymphocytes (P = .002) and a significantly lower percentage of residual CD3-positive T lymphocytes (P = .0001). No correlation was found between the percentage of p53-positive cells and the percentage of cells in cycle assessed by the monoclonal antibody Ki-67. When the percentage of p53 positivity was correlated with the clinical stage of the disease, the proportion of p53-positive cases increased significantly from Binet's stage A (8 of 108; 7.4%), to stage B (12 of 49; 24.4%) and C (7 of 24; 29.2%) (P = .002). p53 positivity correlated also with the phase of the disease, showing a low expression at diagnosis (8 of 112; 7.1%) and a significantly higher expression in patients studied during the course of the disease (7 of 35; 20%) and, to a further extent, with disease progression (12 of 34; 35.3%) (P = .0001). The association of p53 protein expression with mutations in the gene was confirmed by direct sequence of the entire cDNA in 15 of the 17 ICC positive cases tested (88%). A significantly shorter treatment-free interval from diagnosis (P = .003) and a poorer response to therapy (P = .007) was observed in p53-positive compared with p53-negative patients. Overall survival from the time of diagnosis, as well as from the time of p53 protein analysis, was significantly shorter in patients with p53 protein expression (P = .03 and .0001, respectively). Moreover, in multivariate analysis, p53 expression and stage C were independently associated with a short survival. The results of this study indicate that in CLL the expression of the p53 protein, analyzed by a simple and reliable immunocytochemical method, is strongly associated with p53 gene mutations, a morphological variant (CLL with >10% prolymphocytes), advanced clinical stage, progressive disease, poor response to therapy, and short survival.

Chemotherapeutic drug-induced apoptosis in human leukaemic cells is independent of the Fas (APO-1/CD95) receptor/ligand system

The potential role of the Fas (CD95/APO-1) receptor/ligand system in chemotherapeutic drug-induced apoptosis was examined in a number of human leukaemic cell lines. Flow cytometric profiles of doxorubicin-treated HL-60, K562, U937 and Jurkat cells failed to show any significant increase in Fas or Fas ligand expression over 24 h, despite the induction of significant levels of apoptosis in these cells. Although preincubation of human leukaemic cells with a neutralizing anti-Fas IgG antibody blocked anti-Fas IgM-induced apoptosis, this strategy failed to inhibit chemotherapeutic drug-induced apoptosis. To determine whether recruitment of the Fas/Fas ligand complex during drug-induced apoptosis was a cell-specific event we utilized the CEM cell line. Doxorubicin treatment of CEM cells over 24 h failed to show any up-regulation in Fas or Fas ligand protein levels as detected by flow cytometry. Furthermore, neutralizing anti-Fas IgG Ab failed to inhibit chemotherapeutic drug-induced apoptosis in CEM cells. The present studies do, however, demonstrate a role for anti-Fas IgM Ab in producing a cytotoxic synergistic effect when used in combination with chemotherapeutic drugs. Low-dose anti-Fas IgM treatment in combination with doxorubicin, methotrexate, camptothecin and etoposide produced an augmented cytoxicity in CEM cells. Taken together these observations demonstrate that although recruitment of the Fas/APO-1/CD95 receptor/ligand system is not a necessary requirement for chemotherapeutic drug-induced apoptosis, combination of anti-Fas IgM and drug treatment produces a synergistic cytotoxic effect which may prove useful in the treatment of human leukaemias.

Proteasome inhibitors activate stress kinases and induce Hsp72. Diverse effects on apoptosis

Inhibition of the major cytosolic protease, proteasome, has been reported to induce programmed cell death in several cell lines, while with other lines, similar inhibition blocked apoptosis triggered by a variety of harmful treatments. To elucidate the mechanism of pro- and antiapoptotic action of proteasome inhibitors, their effects on U937 lymphoid and 293 kidney human tumor cells were tested. Treatment with peptidyl aldehyde MG132 and other proteasome inhibitors led to a steady increase in activity of c-Jun N-terminal kinase, JNK1, which is known to initiate the apoptotic program in response to certain stresses. Dose dependence of MG132-induced JNK activation was parallel with that of apoptosis. Furthermore, inhibition of the JNK signaling pathway strongly suppressed MG132-induced apoptosis. These data indicate that JNK is critical for the cell death caused by proteasome inhibitors. An antiapoptotic action of proteasome inhibitors could be revealed by a short incubation of cells with MG132 followed by its withdrawal. Under these conditions, the major heat shock protein Hsp72 accumulated in cells and caused suppression of JNK activation in response to certain stresses. Accordingly, pretreatment with MG132 reduced JNK-dependent apoptosis caused by heat shock or ethanol, but it was unable to block JNK-independent apoptosis induced by TNFalpha. Therefore, proteasome inhibitors activate JNK, which initiates an apoptotic program, and simultaneously they induce Hsp72, which suppresses JNK-dependent apoptosis. A balance between these two effects might define the fate of cells exposed to the inhibitors.

p53 expression in human carcinomas: could flow cytometry be an alternative to immunohistochemistry?

Several studies have shown that p53 expression has important clinical implications as an indicator of prognosis and response to chemotherapy or radiotherapy in different human tumor types. Determination of p53 expression by immunohistochemistry (IHC) has been incorporated into routine practice and its reliability has been consolidated. However, flow cytometric (FCM) analysis might represent an important objective and rapid approach. In the present study we determined p53 expression by IHC and FCM on a series of 118 human solid tumors. IHC determination was performed on histological sections and FCM analysis on cell suspensions. Low correlation coefficients (rs from 0.22 to 0.57) were observed between IHC and FCM data from individual tumors. By considering the IHC approach as the gold standard, high sensitivity and low specificity were found for FCM in detecting p53 expression. The FCM analysis of p53 expression and DNA content showed p53-positive cells in all cell cycle phases. Moreover, in most breast, lung, and colon aneuploid tumors (77%), p53-positive cells were detected only in the subpopulations with abnormal DNA content. In conclusion, FCM-p53 expression cannot be used alternatively to IHC determination, and its clinical relevance remains to be validated. Nevertheless, FCM may provide important information about p53 protein expression in the different subpopulations and cell cycle phases. (J Histochem Cytochem 46:41-47, 1998)

p53 protein expression in non-Hodgkin's lymphomas is infrequently related to p53 gene mutations

Accumulation of the p53 protein has been found in several types of lymphomas. However, p53 gene mutations have been infrequently demonstrated in some specific types of lymphomas. In the present study, a correlation between p53 immunoreactivity and p53 gene mutations in a large panel of non-Hodgkin's lymphoma (NHL) cases is attempted. A panel of 202 cases of NHL was evaluated by immunohistochemical staining for p53 protein. All cases that were immunohistochemically positive for p53 protein were analyzed by the polymerase chain reaction (PCR) single strand conformation polymorphism (SSCP) method to identify mutations within the p53 gene. In order to confirm the mutation, sequencing of PCR-amplified p53 gene segments was performed. Overexpression of p53 protein was found in 59 of the 202 cases of NHL, but only four of these 59 cases showed a shift on SSCP analysis, and point mutations were detected in three of them by the subsequent sequencing. p53 immunoreactivity was generally greater in high-grade lymphoma. The results of this study suggest that immunohistochemical reactivity for p53 protein is not a reliable indicator of the presence of their structural alterations of p53 gene exons 4-9 in NHL.

Detection of apoptosis-related factors and apoptotic cells in ameloblastomas: analysis by immunohistochemistry and an in situ DNA nick end-labelling method

To clarify the possible role of apoptosis in odontogenic epithelium, apoptosis-related factors and apoptotic cells were examined by immunohistochemistry and an in situ DNA nick end-labelling method. Expression of bcl-2 protein was detected in both normal and neoplastic odontogenic epithelium, whereas expression of p53 protein was detected only in neoplastic but not in normal odontogenic epithelium. The prevalence of cases positive for Lewis(y) antigen in ameloblastomas was significantly lower than in enamel organs. Correlation between these factors and apoptotic cells presented by an in situ DNA nick end-labelling method was not clear. The number of apoptotic cells in ameloblastomas was significantly greater than in normal odontogenic epithelium, and apoptotic reactions in the granular cell type ameloblastoma tended to be more frequently detected than in other types of ameloblastomas. These results suggested that apoptotic cell death might play an important role in oncogenesis and/or tissue differentiation in odontogenic epithelium.

Apoptosis-resistant phenotype selected by alternating exposure to camptothecin and etoposide

We selected an apoptosis-resistant subline (VC-33) in a human promyelocytic leukemia cell line, HL-60, by alternating exposure to camptothecin (CPT) and etoposide (VP-16). When wild-type (WT) and VC-33 cells were incubated with various concentrations of either CPT or VP-16 for 4 h, VC-33 showed several-fold resistance to apoptosis induced by these agents in comparison with WT cells. VC-33 cells also exhibited cross-resistance to apoptosis induced by 1-beta-d-arabinofuranosylcytosine, hydroxyurea, a calcium ionophore (A23187), cycloheximide, or UV irradiation. The levels of protein-DNA cross-linking induced by CPT or VP-16, and the amounts of ara-CTP generation, tended to be smaller in VC-33 cells, but the difference was not sufficient to explain the difference in the sensitivity to apoptosis. The initial rise of intracellular calcium ions with A23187 and the expression of P-glycoprotein, Bcl-2, and Bcl-Xl were comparable between WT and VC-33 cells. This mutant may represent a new phenotype of resistance to apoptosis induced by a variety of agents, and may thus be useful in the study of the mechanisms of apoptosis.

Ectopic expression of decorin protein core causes a generalized growth suppression in neoplastic cells of various histogenetic origin and requires endogenous p21, an inhibitor of cyclin-dependent kinases

Decorin belongs to a family of secreted, small, leucine-rich proteoglycans that affect matrix assembly and cellular growth. Ectopic expression of decorin proteoglycan or protein core as a mutated form lacking any glycosaminoglycan side chains induced growth suppression in neoplastic cells of various histogenetic origins, including tumor cells derived from gastrointestinal, genital, skeletal, cutaneous, or bone marrow tissues. Exogenously added recombinant decorin also suppressed overall growth of the parental cell lines. In all stably-transfected clones, growth retardation was specifically associated with induction of the potent cyclin-dependent kinase inhibitor p21, but not p27, and subsequent translocation of p21 protein into the nuclei of decorin-expressing cells. This led to a greater proportion of the cells arrested in G1 phase of the cell cycle. These changes were independent of functional p53 or retinoblastoma protein. De novo expression of decorin in HCT116 human colon carcinoma cells harboring a disrupted p21 gene failed to induce growth suppression, in contrast to the wild-type cells in which p21 and growth arrest could be induced. These findings indicate that ectopic production of decorin protein core can retard the growth of a variety of tumor cells and that endogenous p21 is a required downstream effector of this biological axis.

The relationship between the gene mutation of p53 and the protein expression of p53 and Ki-67 in non-Hodgkin's lymphomas

The relationship between the mutation of the p53 gene and the expression of the p53 protein and the Ki-67 antigen has been investigated in 115 cases with non-Hodgkin's lymphoma, using the immunohistochemical double staining technique, single-strand conformational polymorphism and DNA sequencing methods. Eighteen cases showed more than 10% of p53+ cells and the others showed a few p53+ cells presented sporadically. Alterations in the p53 gene were detected in six cases with B cell type, consisting of five cases with point mutation and one case with point mutation and 15 base pairs deletion. These six cases showed a high percentage of p53+ cells and five cases revealed that the percentage of p53+ cells was higher than that of Ki-67+ cells (p53+ cells > Ki-67+ cells). Excluding the six cases with mutation of the p53 gene, all cases revealed that the percentage of p53+ cells was less than that of Ki-67+ cells (p53+ cells < Ki-67+ cells). Moreover, there was a positive correlation between expression of the p53 protein and of the Ki-67 antigen in histologic types of B cell lymphomas and of T cell lymphomas, respectively, except in small non-cleaved (Burkitt's) and lymphoblastic types. Therefore, sporadic cases showing p53+ cells > Ki-67+ cells revealed alteration of the p53 gene, and expressed abnormal p53 protein (mutant form). Most cases showing p53+ cells < Ki-67+ cells expressed normal p53 protein (wild type), and may reflect the rapid proliferation rate.

Tumor genes and their proteins in cytologic and surgical specimens: relevance and detection systems

Oncogenesis is the consequence of a series of genetic alterations that allow unrestrained cellular growth, tissue invasion, and eventual metastases. Tumor-related genes can be classified into functional categories. Proto-oncogenes/oncogenes have a stimulatory role in cell growth, and the inactivation of cancer-suppressor genes/antioncogenes results in the loss of cell cycle regulation. More recently, three other groups of tumor-related genes have been recognized. They include the antiapoptosis genes which protect from programmed cell death, the antimetastasis genes, and multidrug resistance genes. Besides aiding in tumor diagnosis, the detection of such tumor-associated genes and their products allows the identification of individuals with an inherited predisposition to neoplastic growths, and the overexpression of many of these oncogene products has been shown to be a potential marker of tumor behavior and a predictor of treatment outcome and response. The ability to utilize DNA and RNA probes for nucleic acid hybridization and polymerase chain reaction procedures in cell and tissue preparations of solid tumors and lymphoid proliferations expands and complements the information provided by immunohistochemical techniques. These probes allow direct visualization and correlation of specific genes and their protein products with cytomorphologic features, and form a powerful addition to the armamentarium of the cytopathologist and surgical pathologist.

Detection of human papillomavirus DNA sequences in oral squamous cell carcinomas and their relation to p53 and proliferating cell nuclear antigen expression

BACKGROUND

The etiology of oral squamous cell carcinoma (SCC) is still obscure. Since human papillomavirus (HPV) DNAs are associated with carcinoma of the uterine cervix, carcinomas of the oral cavity were investigated to ascertain if these viruses are present in squamous carcinomas of this anatomic site.

METHODS

Seventy-seven oral mucosal SCCs were examined for the presence of HPV DNAs by polymerase chain reaction and dot blot hybridization. Immunohistochemical detection of proliferating cell nuclear antigen (PCNA) and p53 was performed and single strand conformation polymorphism analysis for p53 was undertaken. In situ hybridization detection of HPV-16 DNA also was performed.

RESULTS

Human papillomavirus-16 DNA was detected in 23 cases of oral SCC and both HPV-16 and HPV-18 DNA were detected in one case of tongue SCC. Human papillomavirus DNAs were detected of 11 of 33 tongue, 4 of 15 gingival, 2 of 4 palate, 2 of 5 buccal mucosa, 3 of 7 maxillary sinus, and 2 of 11 the floor of the mouth SCCs. None were detected in SCCs of the retromolar region (0/2). Immunohistochemical examination for p53 was performed in 26 cases of oral SCC and the accumulation of p53 protein was observed in 6 cases (i.e., in 4 of 17 HPV DNA-negative cases and in 2 of 9 HPV DNA-positive cases). Single strand conformation polymorphism analysis confirmed gene mutations in all 6 cases. Human papillomavirus-16 DNA was predominantly identified in cancer cells that showed a morphologic resemblance to basal cells and its hybridized signal in keratinized cells was reduced by in situ hybridization detection. Immunohistochemical detection of PCNA revealed its cooccurrence with HPV-16 DNA in cancer cells.

CONCLUSIONS

These results suggest that HPV-16 DNA sequences may have the capability to maintain the proliferative state of epithelial cells, and may contribute to the production of malignant phenotypes.

Induction of a retinoblastoma phosphatase activity by anticancer drugs accompanies p53-independent G1 arrest and apoptosis

DNA-damaging agents induce accumulation of the tumor suppressor and G1 checkpoint protein p53, leading cells to either growth arrest in G1 or apoptosis (programmed cell death). The p53-dependent G1 arrest involves induction of p21 (also called WAF1/CIP1/SDI1), which prevents cyclin kinase-mediated phosphorylation of retinoblastoma protein (RB). Recent studies suggest a p53-independent G1 checkpoint as well; however, little is known about its molecular mechanisms. We report that induction of a protein-serine/threonine phosphatase activity by DNA damage signals is at least one of the mechanisms responsible for p53-independent, RB-mediated G1 arrest and consequent apoptosis. When two p53-null human leukemic cell lines (HL-60 and U-937) were treated with a variety of anticancer agents, RB became hypophosphorylated, accompanied with G1 arrest. This was followed immediately (in less than 30 min) by apoptosis, as determined by the accumulation of pre-G1 apoptotic cells and the internucleosomal fragmentation of DNA. Addition of calyculin A or okadaic acid (specific serine/threonine phosphatase inhibitors) or zinc chloride (apoptosis inhibitor) prevented the G1 arrest- and apoptosis-specific RB dephosphorylation. The levels of cyclin E- and cyclin A-associated kinase activities remained high during RB dephosphorylation, supporting the involvement of a chemotherapy-induced serine/threonine phosphatase(s) rather than p21. Furthermore, the induced phosphatase activity coimmunoprecipitated with the hyperphosphorylated RB and was active in a cell-free system that reproduced the growth arrest- and apoptosis-specific RB dephosphorylation, which was inhibitable by calyculin A but not zinc. We propose that the RB phosphatase(s) might be one of the p53-independent G1 checkpoint regulators.

Correlative study on the expression of p53 and DNA ploidy in acute nonlymphocytic leukemia

We used the flow cytometric immunoassay to study the correlation between the rumor-suppressor gene product p53- and the DNA ploidy in 30 de novo cases of acute nonlymphocytic leukemia (ANLL). The results showed that 15 cases were positive expression for p53. As compared with p53 negative (p53) cases, the patients with positive p53 (p53+) had higher percentage of bone marrow blasts and lower peripheral leukocyte and platelet counts, which had no influence on the complete remission rate. Before treatment, DNA diploidy was seen in 18 cases including 12 p53- cases, and DNA aneuploidy in 12 cases including 9 p53+. After therapy, aneuploidy could be transformed into diploidy. Patients with P53+ or having aneuploidy in complete remission were at risk for early relapse. We believe that p53 may be involved in the process of leukemogenesis and progression of ANLL.

Role of p53 in leukemogenesis of chronic myeloid leukemia

This review attempts to provide current information on the role played by the p53 gene in normal and leukemic hematopoiesis with particular emphasis on chronic myeloid leukemia. On the basis of the currently available data we can argue that p53 acts as a negative regulator of proliferation of myeloid mature cells and CD34+ progenitors, and its action is mediated through changes in cell cycle kinetics, mainly before the S phase. The p53-dependent pathway is also regulated by several proteins, including p16, p21, p27 (cyclin-dependent kinase [CDK] inhibitors), and a few oncogenes (bcl-2, bax, MDM-2). Although there is some information about the changes in the p53 gene seen in various types of leukemia, the functions and biological importance of these changes in the pathogenesis of leukemia are still largely elusive. During the past several years, accumulated evidence suggests that changes in the p53 gene are commonly associated with blast crisis of chronic myeloid leukemia (CML) but rarely with chronic phase, and they are represented by rearrangements, deletions and point mutations. As for most of the tumors, the majority of point mutations occur between exons 4 and 8 (hot regions). In patients with CML in blastic crisis the most frequent mechanism of p53 inactivation is complete deletion of one allele in association with a point mutation in the remaining allele.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of cell kinetics and cell cycle status by treating CD34+ chronic myeloid leukaemia cells with p53 antisense phosphorothioate oligonucleotides

Mutations of the p53 tumour suppressor gene occur in 20% of chronic myeloid leukaemia (CML) patients in blastic crisis, but it is still uncertain whether this inactivation plays a role in the pathogenesis of blastic transformation or in maintaining the leukaemic proliferation in CML, as it does in several solid tumours. We have previously shown that more than 50% of both normal and CML CD34+ cells express the p53 protein. However, haemopoietic cells at different phases of the cell cycle express p53 with different conformations, suggesting that the function of p53 may be closely regulated during the cell cycle. In order to elucidate the mechanism by which p53 suppresses cell proliferation, we evaluated the effects of inhibiting p53 expression on cell cycle and cell kinetics of chronic phase CML (n = 12) and normal (n = 7) bone marrow light-density cells and purified CD34+ progenitors by using an 18-mer modified antisense oligonucleotide which targets the region covering the six base pairs immediately before the first codon and the first four coding codons of p53. We found that the number of cells positive for the cell cycle-specific nuclear antigen Ki67 and for the BrdU monoclonal antibody (McAb) was significantly increased after p53 antisense olignucleotide treatment. At the same time, p53 protein expression was completely abrogated in both light-density and CD34+ cells. In addition, DNA analysis by flow cytometry demonstrated that the number of cells in quiescent phases of the cell cycle (G0-G1) was significantly decreased after exposure of light-density cells to p53 antisense oligomers, whereas the number of cells in S or G2-M phases was increased. Furthermore, the longer the incubation time the higher the increase in cell proliferation. Treatment of CML, cells with p53 antisense oligomers also resulted in significantly increased numbers of CFU-GM colonies. Our data suggest that p53 is a negative regulator of cell proliferation and its action is mediated through changes in cell cycle kinetics, mainly before the S phase. We can further speculate that the loss of p53 function, at the time of blastic crisis of CML, may play a role, in combination with other genetic changes (p210 BCR/ABL, Rb gene abnormality, others to be defined), in inducing disturbances in cell proliferation, differentiation, and apoptosis.

P53 gene mutations in lymphoid diseases and their possible relevance to drug resistance

Mutations in the p53 tumor suppressor gene occur with a frequency of 12.5% in lymphoid malignancies. The viral-associated diseases, Adult T-cell Leukemia (ATL) and Burkitt's lymphoma, showed higher p53 mutation frequencies of 24% and 41%, respectively. Mutations occurred in the highly conserved regions of the p53 gene. Two new hot spots for mutation were noted in exon 7 at codons 239 and 245. The spectrum of p53 mutations differs among different cancers. Transition mutations occurring in colon and brain tumors also predominated in the majority of the lymphoid malignancies. However, B-cell chronic lymphocytic leukemia (B-CLL) and non-Hodgkin's lymphoma (NHL) had an unusually high frequency of G to T transversions. Among carcinomas of the lung, liver, breast and esophagus there is also a high frequency of G to T transversions. The differences in mutation spectra between different lymphoid diseases may be due to differences in mutagenic factors or differences in the biological properties of the p53 protein in different lymphoid compartments. Mutation of the p53 gene is associated with advanced stage of lymphoid disease and poor prognosis. For B-CLL disease, p53 mutations are associated with drug resistance. Overexpression of the bcl-2 protein is also associated with a block in apoptosis. Resistance to apoptosis could be a general mechanism for drug resistance in B-CLL and other lymphoid diseases.

The emerging picture of p53

1. The cellular phosphoprotein p53 is a negative regulator of the cell growth. A great majority of human malignancies expresses a mutated p53 that represents an oncogenic version of the protein. 2. However, in the meantime many tumors were identified containing a p53 protein without any mutation. Here also other events than genomic alterations of p53 might be implicated in the process of cell transformation. 3. The expression of wild-type or mutant conformation is not exclusively defined by the p53 DNA sequence but also influenced by the subcellular environment and the interaction of cellular proteins with p53. 4. In particular, the mdm-2 gene product appears to be an important partner of p53 somehow involved in these complex regulatory processes. 5. Recent findings supported a role for p53 in transcriptional regulation, perhaps by reducing the expression of genes that are needed for ongoing cell proliferation. 6. This property may be based upon the ability of p53 to bind DNA as well as different proteins from viral or cellular origin. 7. Especially transcription factors or further cellular proteins connected in any way with the regulation of cell proliferation are possible candidates. 8. Thus, it is not surprising that p53 is implicated in the regulation of the cell cycle and in the decision of a cell to replicate DNA or to go into apoptosis.

Expression of different conformations of p53 in the blast cells of acute myeloblastic leukaemia is related to in vitro growth characteristics

Expression of the wild-type p53 gene has an important role in cell differentiation, maturation and apoptosis. Mutation of the p53 gene is associated with tumour development and mutant p53 can promote cell proliferation. Recently wild-type p53 has been demonstrated to exist in two conformational variants: one acting as a suppressor (PAb240-/PAb1620+) and one as a promoter (PAb240+/PAb1620-) of cell proliferation. We have analysed the expression of p53 by flow cytometry in blast cells from 34 patients with acute myeloblastic leukaemia in relationship to the proliferation characteristics of these cells in a clonogenic assay. Blasts from three out of 34 patients did not express p53 using the antibodies: PAb421, PAb1801, PAb240 and PAb1620. The remaining 31 samples expressed p53 detected by PAb240 which recognises mutant p53 and is predicted to recognise wild-type p53 in the promoter conformation. Blasts from 19 out of 31 cells which expressed PAb240 co-expressed PAb1620, expression of PAb1620 was associated with non-autonomous growth in vitro. In contrast, the majority of blasts with the p53 phenotype of PAb240+/PAb1620- or which lacked p53 expression exhibited autonomous growth characteristics in vitro. Furthermore expression of PAb1620 in blasts with autonomous growth cells could be detected following growth inhibition using monoclonal antibodies against autocrine growth factors. Our data demonstrate that in AML cells, p53 conformation is related to the growth characteristics of the cells and is regulated by either exogenous or autocrine haematopoietic growth factors.

Localization of p53 protein and human papillomavirus in anogenital squamous lesions: immunohistochemical and in situ hybridization studies in benign, dysplastic, and malignant epithelia

p53 Protein is a 53-kd nuclear phosphoprotein believed to play an important role in controlling proliferation of neoplastic and normal cells. This "natural tumor suppressor" can be rendered ineffective (or oncogenic) by mutations in the p53 gene or by interactions with proteins synthesized by DNA-transforming viruses, including specific subtypes of human papillomavirus (HPV). We describe the localization of p53 protein in association with HPV in paraffin sections of a spectrum of benign, dysplastic, and malignant anogenital squamous epithelia using immunohistochemical and in situ hybridization techniques. p53 Was detected in 81% of the 48 cases studied. Immunoreactivity for p53 was seen in 83% of the benign and low-grade squamous intraepithelial lesions (SILs), in 73% of the high-grade SILs, and in 86% of the infiltrating squamous carcinomas. In high-grade SILs p53 staining was frequently observed in individual nuclei at various levels of the abnormal epithelium and in the basal layer of the adjacent epithelium, while in squamous metaplasia and low-grade SILs immunostaining for p53 was limited to the basal layer of the epithelium. p53 Was detected in a slightly higher percentage of HPV-positive than HPV-negative epithelia as determined by in situ hybridization. No correlation was observed between p53 immunoreactivity and HPV subtypes. p53 Protein and HPV were detected in anal lesions from a small group of human immunodeficiency virus-positive individuals. Antibodies currently available mainly demonstrate mutant forms of p53 protein that are associated with longer half-lives than the wild-type protein, but demonstration of p53 protein overexpression is not necessarily indicative of malignancy.

Analysis of the p53 gene in patients with isochromosome 17q and Ph1-positive or -negative myeloid leukemia

Increased incidence of p53 gene aberrations or chromosome 17p monosomy resulting from an isochromosome 17q [i(17q)] has been observed with transition of chronic myelogenous leukemia (CML) to myeloid blast crisis (BC), and in some patients with poor risk acute myeloid leukemia (AML) progressing from myelodysplastic syndrome (MDS). These data suggested that disease progression may be linked to bi-allelic inactivation of p53. Here, we report on p53 gene analyses of nine patients with CML-BC and AML who showed an i(17q) as characteristic cytogenetic anomaly. Using Southern blots, agarose gel electrophoresis and single-strand conformation polymorphism analyses of PCR products from genomic DNA and cDNA, spanning exons 4 through 9, we did not detect any structural abnormalities of the remaining p53 allele. These findings question the hypothesis that p53 gene alterations are the principal molecular event responsible for progression of CML chronic phase or MDS to i(17q)-positive CML-BC or AML, respectively.

Cell kinetics with in vivo bromodeoxyuridine assay, proliferating cell nuclear antigen expression, and flow cytometric analysis. Prognostic significance in acute nonlymphoblastic leukemia

BACKGROUND

The proliferative characteristics of acute nonlymphoblastic leukemia (ANLL) were studied in vivo, and data were correlated with response to chemotherapy and survival.

METHODS

Sixty-five patients with untreated ANLL and 15 patients with solid tumors and normal bone marrow (BM) received 250 mg/m2 of bromodeoxyuridine (BUdR); bivariate flow cytometric (FCM) analysis then was used to measure cell BUdR incorporation and DNA content to obtain a complete set of kinetic parameters (i.e., BM BUdR-labeling index, DNA-synthesis time, potential doubling time [Tpot], and cell production rate). The percentage of blasts with positive results for proliferating cell nuclear antigen (PCNA) also was obtained by FCM analysis on the same BM samples, and these kinetic parameters were derived specifically for the ANLL proliferating compartment (growth fraction). Induction therapy, consisting of vincristine, arabinosylcytosine, and daunomycin, was administered subsequently to the patients with ANLL.

RESULTS

Overall ANLL proliferative activity was lower than normal myelopoiesis, and a short Tpot was found to be a favorable factor for achieving complete remission (CR), the duration of CR, and survival. When the growth fraction was considered, however, ANLL proliferative activity was higher and more like that of normal BM. The kinetic differences detected in the PCNA-positive cells of patients with CR and no response and those with CR and survival durations above and below the median values for the entire series were highly significant in univariate analysis and retained a strong independent prognostic value when multivariate analysis was performed.

CONCLUSIONS

These data show the clinical feasibility of a detailed study of cell kinetics by means of new FCM-based techniques and reinforce the clinical value of pretreatment proliferative activity in ANLL.

Cell cycle analysis of p53-induced cell death in murine erythroleukemia cells

A temperature-sensitive mutant of murine p53 (p53Val-135) was transfected by electroporation into murine erythroleukemia cells (DP16-1) lacking endogenous expression of p53. While the transfected cells grew normally in the presence of mutant p53 (37.5 degrees C), wild-type p53 (32.5 degrees C) was associated with a rapid loss of cell viability. Genomic DNA extracted at 32.5 degrees C was seen to be fragmented into a characteristic ladder consistent with cell death due to apoptosis. Following synchronization by density arrest, transfected cells released into G1 at 32.5 degrees C were found to lose viability more rapidly than did randomly growing cultures. Following release into G1, cells became irreversibly committed to cell death after 4 h at 32.5 degrees C. Commitment to cell death correlated with the first appearance of fragmented DNA. Synchronized cells allowed to pass out of G1 prior to being placed at 32.5 degrees C continued to cycle until subsequently arrested in G1; loss of viability occurred following G1 arrest. In contrast to cells in G1, cells cultured at 32.5 degrees C for prolonged periods during S phase and G2/M, and then returned to 37.5 degrees C, did not become committed to cell death. G1 arrest at 37.5 degrees C, utilizing either mimosine or isoleucine deprivation, does not lead to rapid cell death. Upon transfer to 32.5 degrees C, these G1 synchronized cell populations quickly lost viability. Cells that were kept density arrested at 32.5 degrees C (G0) lost viability at a much slower rate than did cells released into G1. Taken together, these results indicate that wild-type p53 induces cell death in murine erythroleukemia cells and that this effect occurs predominantly in the G1 phase of actively cycling cells.

Cell cycle analysis of p53-induced cell death in murine erythroleukemia cells

A temperature-sensitive mutant of murine p53 (p53Val-135) was transfected by electroporation into murine erythroleukemia cells (DP16-1) lacking endogenous expression of p53. While the transfected cells grew normally in the presence of mutant p53 (37.5 degrees C), wild-type p53 (32.5 degrees C) was associated with a rapid loss of cell viability. Genomic DNA extracted at 32.5 degrees C was seen to be fragmented into a characteristic ladder consistent with cell death due to apoptosis. Following synchronization by density arrest, transfected cells released into G1 at 32.5 degrees C were found to lose viability more rapidly than did randomly growing cultures. Following release into G1, cells became irreversibly committed to cell death after 4 h at 32.5 degrees C. Commitment to cell death correlated with the first appearance of fragmented DNA. Synchronized cells allowed to pass out of G1 prior to being placed at 32.5 degrees C continued to cycle until subsequently arrested in G1; loss of viability occurred following G1 arrest. In contrast to cells in G1, cells cultured at 32.5 degrees C for prolonged periods during S phase and G2/M, and then returned to 37.5 degrees C, did not become committed to cell death. G1 arrest at 37.5 degrees C, utilizing either mimosine or isoleucine deprivation, does not lead to rapid cell death. Upon transfer to 32.5 degrees C, these G1 synchronized cell populations quickly lost viability. Cells that were kept density arrested at 32.5 degrees C (G0) lost viability at a much slower rate than did cells released into G1. Taken together, these results indicate that wild-type p53 induces cell death in murine erythroleukemia cells and that this effect occurs predominantly in the G1 phase of actively cycling cells.

Flow cytometric analysis of multidrug-resistance-associated antigen (P-glycoprotein) and DNA ploidy in human colon cancer

In many cell systems, resistance to cytotoxic drugs is acquired by the amplification and/or overexpression of the multidrug resistance (mdr) gene, which codes for the glycoprotein, p170 (P-glycoprotein). Moreover, in a variety of malignant tumours there is increasing evidence of the relationship between the DNA ploidy pattern of patients and their prognosis. In this study we aimed to evaluate these two potential indicators of constitutive drug resistance in human colorectal tumours. We employed a method to quantify simultaneously, on a per cell basis, mdr gene expression (using the C219 monoclonal antibody for P-glycoprotein) and nuclear DNA content with high-resolution bivariate flow cytometry. The study was performed on a human colon-carcinoma-derived cell line (LoVo) and its doxorubicin-resistant variant (LoVo/Dx) and on tumour samples and adjacent normal mucosa from 35 untreated patients with colon cancer. The P-glycoprotein was found in both LoVo and LoVo/Dx cells with levels slightly lower in the parental than in the resistant subline (P, NS). A multi-drug-resistant specific probe for mRNA expression and Western blot assay confirmed the specificity of p170 expression. All of the colon cancer with unimodal diploid DNA distribution and all the normal colonic mucosa samples showed P-glycoprotein expression, without a statistically significant difference in median values between tumours and normal samples. Tumours with bimodal DNA distribution showed median values of P-glycoprotein expression of their hyperdiploid cell clones significantly higher than those of their diploid clones and of the tumours with unimodal DNA distribution (P less than 0.005). Our results show the feasibility of bivariate flow-cytometric analysis of P-glycoprotein expression and DNA content on clinical material and support the hypothesis that the MDR phenotype and DNA ploidy together may influence the biological behaviour of colon cancer in vivo.

Asymmetric distribution of oncogene products at mitosis

Computer-assisted image analysis was used to demonstrate in exponentially proliferating human tumor cells the uneven postmitotic apportionment of several oncogene-encoded proteins (ras p21; erbB-2 p185; fos p55; myc p62). This observation may provide the explanation for the high degree of heterogeneity of postmitotic cells and the asynchrony in cell cycle traverse of cultured cells.

P53 protein expression in lymphomas and reactive lymphoid tissue

P53 is a tumour suppressor gene, located in the short arm of chromosome 17, which encodes for a nuclear protein involved in the control of cellular growth, regulating the entry of the cell into the S-phase. P53 mutations have been identified in a progressively increasing number of human malignancies. Nuclear p53 protein is usually present in non-tumour cells in minute concentrations, due to its short half-life. In contrast, tumours with p53 mRNA mutations show a higher nuclear protein concentration, detectable by immunohistological techniques, due to stabilization by complexing with other proteins such as heat-shock protein or wild-type p53 protein. Levels of nuclear p53 protein detected by immunohistochemistry with the monoclonal antibody PAb 1801 were measured with the aid of an image analysis system in 83 non-Hodgkin's lymphomas (NHLs) and 13 cases of Hodgkin's disease, as well as in 14 cases of normal thymus, reactive tonsils, and lymphadenitis. High levels of p53 protein (greater than 5 per cent of the cells) were present only in high-grade lymphomas (in the proportion 13/55), with a peak incidence in Burkitt's lymphoma (5/8 cases). Lower levels (less than 5 per cent) of p53 protein were detected in low-grade B- and T-cell lymphomas, as well as in most of the cases of Hodgkin's disease, where p53 protein was selectively present in Hodgkin and Reed-Sternberg cells. In 5/14 reactive tonsils or lymph nodes, occasional p53-positive cells were identified. These results suggest a relationship between levels of p53 protein and the aggressiveness of NHL.(ABSTRACT TRUNCATED AT 250 WORDS)