Interleukin 3 protects murine bone marrow cells from apoptosis induced by DNA damaging agents

Molecular abnormalities in chronic myeloid leukemia: deregulation of cell growth and apoptosis

Chronic myeloid leukemia (CML) is a disease of the hematopoietic system, characterized by the presence of the Bcr-Abl oncoprotein. The main characteristics of this disease include adhesion independence, growth factor independence, and resistance to apoptosis. Loss or mutation of the tumor suppressor gene, p53, is one of the most frequent secondary mutations in CML blast crisis. The transition between chronic phase and blast crisis is associated with increased resistance to apoptosis correlating with poor prognosis. This review focuses on the involvement of these two oncoproteins in the development and progression of the apoptotic-resistant phenotype in CML.

The combined administration of daniplestim and Mpl ligand augments the hematopoietic reconstitution observed with single cytokine administration in a nonhuman primate model of myelosuppression

This study evaluated the ability of daniplestim, a high affinity interleukin 3 receptor agonist, to enhance the hematopoietic response of Mpl ligand (Mpl-L) administration in nonhuman primates following severe, radiation-induced myelosuppression. Rhesus monkeys were total body x-irradiated (TBI) to 600 cGy, midline tissue dose. Beginning on day 1 post-TBI, animals were s.c. administered daniplestim (100 microg/kg bid; n = 4), Mpl-L (10 microg/kg qd; n = 3), daniplestim (100 microg/kg bid) plus Mpl-L (10 microg/kg qd) (n = 4) or 0.1% autologous serum (AS) (n = 11) for 18 days. CBCs were monitored for 60 d after TBI. The duration of thrombocytopenia (platelet count; PLT <20,000/microl) was significantly decreased by the administration of daniplestim (6.5 d, p = .01), Mpl-L (3.0 d, p = .003) and the coadministered daniplestim/Mpl-L (1.3 d, p = .001) compared to controls (10.4 d). As monotherapy Mpl-L but not daniplestim significantly improved the PLT nadir (21,000/microl, p = .023 and 5,000/microl, p = .266, respectively) compared to the control (3,000/microl). The combined administration of daniplestim and Mpl-L significantly improved the PLT nadir (28,000/microl, p = .007) compared to both the control cohort (3,000/microl) and the daniplestim only cohort (5,000/microl, p = .043). Recovery of PLT to preirradiation values occurred earlier in the daniplestim only (d 21) or the daniplestim/Mpl-L cohorts (d 18) than in the Mpl-L only or control cohorts (d 28, d 29, respectively). The administration of daniplestim or Mpl-L alone neither shortened the duration of neutropenia (ANC<500/microl) compared to the controls (15.8 d, 16.0 d versus 16.2 d, respectively), nor improved the recovery time of neutrophils to baseline values (d 22, d 25, and d 23, respectively). The ANC nadir was significantly improved by daniplestim alone but not Mpl-L administration (76/microl, p = .001 and 50/microl, p = .093, respectively) compared to the controls (8/microl). Coadministration of daniplestim and Mpl-L significantly improved the ANC nadir (196/microl, p = .001) compared to either the AS- or the monotherapy-treated cohorts. Also the duration of neutropenia observed in the AS-controls (16.2 d) was significantly reduced in the daniplestim/Mpl-L cohort (10.8 d, p = .002). The combined administration of daniplestim and Mpl-L significantly improved hematopoietic recovery and further enhanced the stimulatory effect of cytokine monotherapy, as well as reducing clinical support requirements after radiation-induced bone marrow myelosuppression.

Apoptosis of haematopoietic cells upon thymidylate synthase inhibition is independent of p53 accumulation and CD95-CD95 ligand interaction

Treatment of haematopoietic BA/F3 cells with the thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FUdR) activated apoptosis through a mechanism that required continuous protein synthesis and was inhibited by Bcl-2 over-expression. Analysis of p53 levels in cells treated with FUdR indicated a marked accumulation of this protein. Accumulation of p53 was also observed in cells over-expressing Bcl-2. In BA/F3 cells transfected with a cDNA coding for the human papilloma virus protein E6, p53 accumulation after FUdR treatment was inhibited markedly. However, apoptosis was induced in both control and E6 cells to a similar extent. The role of the CD95/CD95 ligand (CD95L) system in FUdR-induced apoptosis was also assessed. As determined by reverse transcriptase PCR, BA/F3 expressed a low constitutive level of CD95L mRNA, which decreased following FUdR treatment. Moreover, blocking CD95-CD95L interactions with antagonistic CD95 monoclonal antibody did not prevent drug-induced apoptosis. Furthermore, analysis of caspase involvement showed important differences in apoptosis induced by CD95-triggering or FUdR treatment. In summary, these results suggest that apoptosis induced by thymineless stress in haematopoietic BA/F3 cells occurs by a mechanism that does not require accumulation of p53 and which is independent of CD95-CD95L interactions.

Thrombopoietin and the TPO receptorduring platelet storage

BACKGROUND

For most cells, the addition of a specific growth factor has improved cellular viability by preventing programmed cell death (apoptosis). To determine whether the platelet-specific hematopoietic growth factor thrombopoietin (TPO) might improve platelet viability, endogenous TPO and the platelet TPO receptor were analyzed during storage, and the effect of recombinant TPO on platelet viability was assessed.

STUDY DESIGN AND METHODS

During platelet storage, TPO stability was assessed by SDS-PAGE, TPO receptor function was measured, and the platelet TPO receptor was characterized by a (125)I-rHuTPO competitive-binding assay. A recombinant TPO, pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), was added to platelet concentrates during storage, and its effect on pH, LDH, and metabolic activity was determined.

RESULTS

During storage, the molecular weight and concentration of endogenous TPO (125 +/- 19 pg/mL) and exogenous TPO (5720 +/- 140 pg/mL) were constant for 12 days; the number (33 +/- 4), binding affinity (149 +/- 33 pM), and function of the platelet TPO receptors were constant for 7 days. Metabolic activity measured with the MTT and MTS assays closely correlated with changes in the pH and LDH. The addition of PEG-rHuMGDF did not alter the pH, LDH, or metabolic activity of platelets during storage, but it did increase by 65 percent the uptake of (35)S-methionine into platelets. Finally, platelet concentrates obtained from donors treated with PEG-rHuMGDF retained normal metabolic activity for 12 days, as compared with 5 to 6 days for normal platelet concentrates.

CONCLUSIONS

TPO and its platelet receptor are present in normal amounts and have normal function during platelet storage. The addition of recombinant TPO increased platelet methionine transport but did not alter platelet viability during storage. Other means to prevent apoptosis during platelet storage should be considered, and the measurement of platelet metabolic activity by MTT and MTS assays may assist this effort.

Involvement of p53 and interleukin 3 in the up-regulation of CD95 (APO-1/Fas) by X-ray irradiation

Interleukin 3-dependent bone marrow and Ba/F3 cells present constitutive Fas expression. A dose dependent increase in Fas surface expression was induced in these cells by X-ray irradiation. Using primary cell cultures and established cell lines derived from p53-null mice (p53-/-), we demonstrated that the increase in Fas expression upon X-ray irradiation is dependent on the presence of at least one wild-type p53 allele. Fas induction by X-ray irradiation was negatively modulated by IL-3; an earlier Fas induction was observed in the absence of IL-3 or at low IL-3 concentrations. However, IL-3 withdrawal in non-irradiated cells did not induce an increase in Fas expression. X-ray irradiation of Ba/F3 cells induced the expression of functional Fas receptors. Therefore, in IL-3-dependent cells, IL-3 regulates the rate of Fas expression, which is correlated with the degree of apoptosis observed in X-irradiated cells. Finally, we demonstrate that IL-3 controls the degree of Fas expression induced by irradiation through a p53-mediated pathway.

The role of p53 in death of IL-3-dependent cells in response to cytotoxic drugs

This report examines the cytotoxicity of chemotherapeutic agents to primary bone marrow-derived IL-3-dependent cells. Such cells derived from p53-null mice were resistant to almost 100-fold higher concentrations of the inhibitors of deoxyribonucleotide synthesis FUdR, methotrexate and hydroxyurea than cells with wild-type p53. In contrast, the cytotoxicity of the DNA damaging agents X-irradiation, cisplatin or bleomycin was p53-independent. The topoisomerase II inhibitor etoposide induced p53-dependent death, which suggests that DNA damage may not be its primary mechanism of cytotoxicity in this cell type. An IL-3-dependent cell line which expresses wild-type p53 was used to demonstrate that the ability of cytotoxic drugs to increase p53 expression level does not control their ability to induce p53-dependent loss of clonigenicity. Finally, comparison with a p53-null IL-3-dependent cell line was used to show that absence of p53 delays the rate of entry into apoptosis following treatment with either DNA damaging agents or inhibitors of deoxyribonucleotide synthesis. This distinguishes short-term effects of p53 on rate of entry into apoptosis from its role in controlling ultimate cell survival. Oncogene (2000) 19, 3556 - 3559

Analysis of antiapoptosis activity of human GM-CSF receptor

Human GM-CSF (hGM-CSF) induces proliferation and sustains the viability of a mouse IL-3-dependent lymphoid cell line BA/F3 that expresses the functional hGM-CSF receptor (hGMR). To reveal an antiapoptotic mechanism of hGM-CSF, we analyzed various apoptotic markers of BA/F3 cells in various conditions. Within 24 hours of factor depletion, caspase 3-like, but not caspase 1-like, enzyme activity and DNA fragmentation were augmented. Analysis with the tyrosine kinase inhibitor (genistein) and an MEK1 inhibitor (PD98059) on antiapoptosis activity indicates that the activation of either the genistein-sensitive signaling pathway or the PD98059-sensitive signaling pathway of the betac subunit may be sufficient to suppress apoptosis through hGMR. Because hGMR mutants (which activate JAK2 but neither STAT5 nor the MAPK cascade) have antiapoptotic activity in BA/F3 cells, the involvement of JAK2, excluding the molecules mentioned earlier, for antiapoptosis activity seems likely. Because the JAK2 inhibitor AG-490 suppressed the antiapoptotic activity of hGM-CSF, the essential role for JAK2 activation to maintain the viability is considered. Interestingly, hGMR mutants, which lack MAPK cascade activation, require a higher dose of hGM-CSF than that for wild-type hGMR. Because the expression level and affinity to hGM-CSF among wild-type hGMR and mutant hGMR are the same, we speculated that biologic response is determined by a combination of strength of various signaling events.

Hematologic abnormalities and acute myeloid leukemia in children and adolescents administered intensified chemotherapy for the Ewing sarcoma family of tumors

PURPOSE

Current treatment of the Ewing sarcoma family of tumors (ESFT) includes intensive multiagent chemotherapy with topoisomerase II inhibitors, alkylating agents, and granulocyte colony-stimulating factor (G-CSF). This treatment approach has been associated with myelodysplasia and acute myeloid leukemia. Because macrocytosis and thrombocytopenia are distinctive features of myelodysplasia, the authors evaluated a cohort of patients treated for ESFT to determine the degree and duration of macrocytosis and thrombocytopenia and their relation with the development of therapy-related hematologic malignancies.

PATIENTS AND METHODS

The study group consisted of 73 patients with ESFT treated on two consecutive protocols (EW92 and EW87). Both chemotherapy regimens incorporated the same agents but differed in cumulative drug dose, dose per course, and the use of G-CSF. Platelet counts and the mean corpuscular volume (MCV) of erythrocytes were determined at diagnosis and during follow-up visits after completion of treatment.

RESULTS

Patients in the EW92 group had significantly greater MCVs after treatment than did the less intensively treated EW87 group. These changes persisted throughout the 40-month observation period. Patients in the EW92 group also had lesser mean platelet counts after treatment than those in the EW87 group. MCV differences (from baseline) were inversely related to platelet counts. The cumulative incidence of treatment-related acute myeloid leukemia was 7.8%+/-4.7% at 4 years in the EW92 group and zero in the EW87 group.

CONCLUSION

Patients treated for ESFT with intensive chemotherapy that includes large doses of alkylators, topoisomerase II inhibitors, and G-CSF characteristically have persistently elevated MCVs and decreased platelet counts after completion of therapy. These hematologic abnormalities may represent stem cell damage, predisposing patients to myelodysplasia and acute myeloid leukemia, but further study is needed to establish this relation.

The staurosporine analog, Ro-31-8220, induces apoptosis independently of its ability to inhibit protein kinase C

A series of bisindolylmaleimide (Bis) compounds were designed as analogs of the natural compound staurosporine (STS), which is a potent inducer of apoptosis. Many of the Bis analogs appear to be highly selective inhibitors of the protein kinase C (PKC) family, including PKC-alpha, -beta, -gamma, -delta, -epsilon, and -zeta, unlike STS, which is an inhibitor of a broad spectrum of protein kinases. In this report we describe the effects of the Bis analogs, Bis-I, Bis-II, Bis-III and Ro-31-8220 on the survival and proliferation of HL-60 cells, which have been widely used as a model cell system for studying the biological roles of PKC. Treatment of HL-60 cells with Bis-I, Bis-II, Bis-III, or Ro-31-8220 blocked phosphorylation of the PKC target protein Raf-1 with equal potency but did not appear to affect the general phosphorylation of proteins by other kinases. However, the biological effects of the Bis compounds were different: Bis-I and Bis-II had no observable effects on either cell survival or proliferation; Bis-III inhibited cell proliferation but not survival, whereas Ro-31-8220 induced apoptosis. These results indicated that the members of the PKC family which could be inhibited by the Bis analogs were required neither for survival nor proliferation of HL-60 cells. Analyses of cells treated with Ro-31-8220 showed that the apoptotic effect of Ro-31-8220 on HL-60 cells was mediated by a well-characterized transduction process of apoptotic signals: i.e., mitochondrial cytochrome c efflux and the activation of caspase-3 in the cytosol. Moreover, the ability of Ro-31-8220 to induce apoptotic activation was completely inhibited by the over-expression of the apoptotic suppressor gene, Bcl-2, in the cells. Interestingly, proliferation of the Bcl-2-over-expressing cells was still sensitive to the presence of Ro-31-8220, suggesting that the inhibitory effects of Ro-31-8220 on viability and cell proliferation were mediated by different mechanisms. In particular, the apoptotic effect of Ro-31-8220 on cells was not altered by the presence of an excess amount of the other Bis analogs, suggesting that this effect is mediated by a factor(s) other than PKC or by a mechanism which was not saturable by the other Bis analogs. Finally, structure-function analyses of compounds related to Ro-31-8220 revealed that a thioamidine prosthetic group in Ro-311-8220 was largely responsible for its apoptotic activity.

Ceramide induces apoptosis in neuroblastoma cell cultures resistant to CD95 (Fas/APO-1)-mediated apoptosis

BACKGROUND/PURPOSE

Spontaneous tumor regression is a well-known characteristic in neuroblastomas. Because preliminary reports have shown that regression may be caused by apoptosis (a lethal cascade mediated by the CD95 (APO-1/Fas)-receptor), we analyzed the expression of CD95-receptors in 5 human neuroblastoma cell lines. Ceramides (known stimuli of apoptosis downstream from the CD95-receptor complex) also were used to test whether apoptosis would be induced in neuroblastoma cell cultures resistant to CD95-mediated programmed cell death.

METHODS

The expression of the CD95-receptor was assessed by flow cytometry after incubation with either fluorisothiocyanate-conjugated (FITC) anti-CD95-antibody (UB2) or CD95-ligand for 16 hours. Apoptotic cell death was detected via microscopy, cell viability testing (MTT, 3-[4,5 dimehylthiazole-2-yl]-2,5 diphenyltetrazoliumbromide), and flow cytometric analysis after propidium iodide staining of the DNA.

RESULTS

CD95-receptor expression was found on all neuroblastoma cell lines. Stimulation of the CD95-receptor of the malignant glioblastoma cell line LN229 (positive control) with either anti-CD95-antibody or CD95-ligand induced apoptosis. Apoptosis was not seen, however, in any of the neuroblastoma cell lines when the CD95-receptor was stimulated with anti-CD95-antibody or the CD95-ligand. Significant apoptosis was detected in all neuroblastoma cell lines after the addition of 25 micromol/L C2- and C6-ceramide.

CONCLUSIONS

CD95-receptors are present on neuroblastoma cell lines, and these cells are resistant to apoptosis stimulated by anti-CD95-antibody or CD95-ligand. Apoptosis is induced, however, when these cells are treated with ceramide. A signal blockage downstream from the CD95-receptor complex and upstream of ceramide may account for this finding, and the "cellular FLICE inhibitory protein" (cFLIP) may be primarily responsible.

Myelopoietin, an engineered chimeric IL-3 and G-CSF receptor agonist, stimulates multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression

Myelopoietins (MPOs) constitute a family of engineered, chimeric molecules that bind and activate the IL-3 and G-CSF receptors on hematopoietic cells. This study investigated the in vivo hematopoietic response of rhesus monkeys administered MPO after radiation-induced myelosuppression. Animals were total body irradiated (TBI) in 2 series, with biologically equivalent doses consisting of either a 700 cGy dose of Cobalt-60 (60Co) γ-radiation or 600 cGy, 250 kVp x-irradiation. First series: On day 1 after 700 cGy irradiation, cohorts of animals were subcutaneously (SC) administered MPO at 200 μg/kg/d (n = 4), or 50 μg/kg/d (n = 2), twice daily, or human serum albumin (HSA) (n = 10). Second series: The 600 cGy x-irradiated cohorts of animals were administered either MPO at 200 μg/kg/d, in a daily schedule (n = 4) or 0.1% autologous serum (AS) , daily, SC (n = 11) for 23 days. MPO regardless of administration schedule (twice a day or every day) significantly reduced the mean durations of neutropenia (absolute neutrophil count [ANC] &lt; 500/μL) and thrombocytopenia (platelet &lt; 20 000/μL) versus respective control-treated cohorts. Mean neutrophil and platelet nadirs were significantly improved and time to recovery for neutrophils (ANC to &lt; 500/μL) and platelets (PLT &lt; 20 000/μL) were significantly enhanced in the MPO-treated cohorts versus controls. Red cell recovery was further improved relative to control-treated cohorts that received whole blood transfusions. Significant increases in bone marrow-derived clonogenic activity was observed by day 14 after TBI in MPO-treated cohorts versus respective time-matched controls. Thus, MPO, administered daily was as effective as a twice daily schedule for multilineage recovery in nonhuman primates after high-dose, radiation-induced myelosuppression.

Analysis of mechanisms involved in the prevention of gamma irradiation-induced apoptosis by hGM-CSF

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) induces proliferation and sustains viability of the mouse interleukin (IL)-3 dependent lymphoid cell line BA/F3 expressing the hGM-CSF receptor. Caspase-3 like enzyme activity and DNA fragmentation were augmented by depletion of this factor from the cell, and exposure to gamma irradiation accelerated kinetics of these events. Anti gamma irradiation-induced apoptosis occurred through various mutant GM-CSF receptors and only the box1 region was essential while the C terminal region, including tyrosine residues which are required for MAPK cascade activation, was dispensable. Consistent with this notion, the addition of PD98059 had no effect on this activity thereby indicating that activation of MAPK is not essential for the activity. As expected, gamma irradiation increased p53 protein and bax mRNA levels and the presence of hGM-CSF dramatically modulated bax/bcl-X(L) ratio. The PI-3K specific inhibitor wortmannin did not affect hGM-CSF dependent anti gamma irradiation induced apoptosis nor bcl-X(L) induction, thus bcl-X(L) but not PI-3K pathway seems to be involved in hGM-CSF dependent anti gamma irradiation-induced apoptosis. It is well documented that the boxl region is essential for GM-CSF dependent activation of JAK2 and JAK2 specific inhibitor AG490 suppressed anti gamma, irradiation-induced apoptosis by hGM-CSF. An artificial JAK2 activating molecule in which extracellular and the transmembrane of beta(c) fused with whole JAK2 can sustain BA/F3 cells survival and proliferation mIL-3 independently, but these cells are susceptible to gamma irradiation. Furthermore GyrB/Jak2, which can activate STAT5 but not the MAPK cascade nor survival of BA/F3 cells, also could not prevent gamma irradiation-induced apoptosis. Although JAK2 is essential for hGM-CSF dependent anti gamma irradiation-induced apoptosis, it appeared that JAK2 does not seem sufficient for the activity.

Cleistanthin A causes DNA strand breaks and induces apoptosis in cultured cells

Cleistanthin A is a novel anticancer agent isolated from Cleistanthus collinus (Rox B). It caused chromatid aberrations in a dose dependent manner. However, the concentrations that induced the aberrations, neither affected viability nor induced DNA strand breaks. Only at higher concentrations and after long exposure, DNA strand breaks were observed. Cleistanthin A induced apoptosis in Chinese hamster ovary (CHO) cells, in cervical carcinoma (Si Ha) cells and in a p53 deficient cell line K562. Cleistanthin A-induced cell death was low in bcl-2 transfected cells. Cleistanthin A inhibited the incorporation of [3H]thymidine into DNA; however, it did not affect the transport of [3H]thymidine into these cells. These studies indicate that the cytotoxic effects of cleistanthin A are mediated by the inhibition of DNA synthesis, induction of DNA damage and apoptosis.

Apoptosis and the nervous system

Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6-7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1beta converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.

Two distinct signaling pathways downstream of Janus kinase 2 play redundant roles for antiapoptotic activity of granulocyte-macrophage colony-stimulating factor

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) induces proliferation and sustains the viability of the mouse interleukin-3-dependent cell line BA/F3 expressing the hGM-CSF receptor. Analysis of the antiapoptosis activity of GM-CSF receptor betac mutants showed that box1 but not the C-terminal region containing tyrosine residues is essential for GM-CSF-dependent antiapoptotic activity. Because betac mutants, which activate Janus kinase 2 but neither signal transducer and activator of transcription 5 nor the MAPK cascade sustain antiapoptosis activity, involvement of Janus kinase 2, excluding the above molecules, in antiapoptosis activity seems likely. GM-CSF activates phosphoinositide-3-OH kinase as well as Akt, and activation of both was suppressed by addition of wortmannin. Interestingly, wortmannin did not affect GM-CSF-dependent antiapoptosis, thus indicating that the phosphoinositide-3-OH kinase pathway is not essential for cell surivival. Analysis using the tyrosine kinase inhibitor genistein and a MAPK/extracellular signal-regulated kinase (ERK) kinase 1 inhibitor, PD98059, indicates that activation of either the genistein-sensitive signaling pathway or the PD98059-sensitive signaling pathway from betac may be sufficient to suppress apoptosis. Wild-type and a betac mutant lacking tyrosine residues can induce expression of c-myc and bcl-x(L) genes; however, drug sensitivities for activation of these genes differ from those for antiapoptosis activity of GM-CSF, which means that these gene products may be involved yet are inadequate to promote cell survival.

Prognostic value of apoptotic index in cutaneous basal cell carcinomas of head and neck

Basal cell carcinoma (BCC) is the most common type of human cancer, often locally invasive, and following a benign clinical course. However, a proportion of BCCs do recur after treatment, causing extensive local tissue destruction, seldom metastasizing. Morphological methods to unequivocally distinguish the aggressive forms of these tumors (BCC2) from the ordinary ones (BCC1) have so far been lacking. Apoptosis, or programmed cell death, is thought to be important for the death of tumor cells in various stages of carcinogenesis. We analyzed the extent of apoptosis in BCCs of head and neck in a morphological, morphometric, and electron-microscopic study, to estabilish on a retrospective basis, the relative frequency of recurrence of tumors showing different apoptotic rates. We found that BCC1 showed lower apoptotic index (AI) than BCC2 [BCC1: AI from 2.03 to 10.45% (mean value: 5.98%) BCC2: AI from 21. 91 up to 43.82% (mean value: 39.82%)]. The morphometric analysis of both BCC1 and BCC2 revealed significant differences between the values concerning nuclear area, length, perimeter, and roundness of the apoptotic cells with respect to the 'viable' neoplastic cells. Electron-microscopy confirmed that the features of morphological apoptotic cells were characteristic of programmed cell death. We hypothesized that low apoptotic rates in BCC1 could be indicative of a good prognosis. In fact, this corresponded to an 'expansive' but not still invasive neoplastic state. In this phase, however, the tumor cells may constitute the target for genetic changes triggered by enviromental physical or chemical mutagenic agents, such as UV rays. BCC2, then, could be the result of newly selected mutated neoplastic cellular clones, with more aggressive biological behavior. The high apoptotic level found in BCC2 could thus be used as an indirect alarm signal from pathologists. This hypothesis seems to be supported by most of the current data in the literature and by the clinical outcome of BCC2 of our series. In our opinion, routine evaluation of apoptosis in BCCs could be proposed to facilitate their sub-classification, contributing toward the evaluation of the prospective outcome of the individual patients.

The reduction of in vitro radiation-induced Fas-related apoptosis in CD34+ progenitor cells by SCF, FLT-3 ligand, TPO, and IL-3 in combination resulted in CD34+ cell proliferation and differentiation

Recovery from radiation-induced (RI) bone marrow aplasia depends on appropriate cytokine support. The early effects of exogenous cytokines at the hematopoietic stem and progenitor cell (HSPC) level following irradiation are still largely unknown, especially those of survival factors such as stem cell factor (SCF) and Flt-3 ligand (FL). This study was aimed at A) clarifying Fas/Fas-Ligand (Fas-L) implication in RI apoptosis of CD34+ cells and B) assessing the capacity of a combination of cytokines to mitigate RI apoptosis in HSPCs in vitro. We showed that most of in vitro gamma-irradiated CD34+ HSPCs incubated in a medium devoid of cytokines underwent progressive apoptosis-related changes from 6 h (i.e., decreased CD34 antigen expression, Annexin V binding); then Fas/Fas-L coexpression occurred from 10 h on. A strong DNA fragmentation, as assessed by TUNEL assay and propidium iodide staining, was observed at 24 h. Within a 2.5- to 6-Gy dose range, the RI apoptotic process finally led to 97% CD34+ cell death within 48 h with a complete loss of functionality. Unirradiated cells incubated in the same conditions displayed a significantly reduced apoptotic pattern. The early addition of a combination of SCF, FL, thrombopoietin, and interleukin 3 (4F) after cell irradiation prevented 15% (2.5 Gy) and 12% (4 Gy) of HSPCs, respectively, from RI apoptosis, whereas these cytokines used as single factors were inefficient. Furthermore, irradiated HSPCs (2.5 Gy) incubated with 4F in a serum-free culture system for seven days proliferated, giving rise to an increase in the number of total cells (x5.6-fold) and CD34+ cells (x4.2-fold) and to megakaryocytic and granulomonocytic precursors. These results show that the prevention of apoptosis in in vitro irradiated HSPCs depends on an early combination cytokine support. These data suggest that the early therapeutic administration of anti-apoptotic cytokines may be critical for preserving functional HSPCs from in vivo radiation damage.

Effects of glucocorticoids and mineralocorticoids on proliferation and maturation of human peripheral blood stem cells

It has been shown that hematopoietic progenitors can be expanded ex vivo in the presence of various cytokine combinations. Glucocorticoids (GC) are involved in the self-renewal of erythroid progenitors in chicken. To see whether GC have a similar effect on hematopoiesis in humans, CD34(+) peripheral blood stem cells were cultured in serum free medium in the presence of a GC, triamcinolone acetonide. However, our results demonstrate an inhibition of both erythroid and granulocyte-macrophage (GM) proliferation and a modification of erythroid colony morphology. Furthermore, RU38486 (Mifepristone), a potent GC antagonist, was unable to reverse the inhibitory effect of triamcinolone acetonide. We also identified and characterized another steroid subfamily, the mineralocorticoid (MC) subfamily, in human PB CD34(+) cells. The MC, aldosterone, significantly enhanced GM colony formation and diminished the erythroid colony number. Neither of effects were inhibited by ZK91587, an antagonist specific to the MC receptor (MCR). In contrast, ZK91587 reversed the stimulatory effect of deoxycorticosterone on GM colony formation. Cytoplasmic staining for MCR was observed in CD34(+) cells incubated with a polyclonal antiserum raised against human MCR. To our knowledge, this is the first demonstration of the presence of MCR in human PB CD34(+) cells.

Physical interaction and functional antagonism between the RNA polymerase II elongation factor ELL and p53

ELL was originally identified as a gene that undergoes translocation with the trithorax-like MLL gene in acute myeloid leukemia. Recent studies have shown that the gene product, ELL, functions as an RNA polymerase II elongation factor that increases the rate of transcription by RNA polymerase II by suppressing transient pausing. Using yeast two-hybrid screening with ELL as bait, we isolated the p53 tumor suppressor protein as a specific interactor of ELL. The interaction involves respectively the transcription elongation activation domain of ELL and the C-terminal tail of p53. Through this interaction, ELL inhibits both sequence-specific transactivation and sequence-independent transrepression by p53. Thus, ELL acts as a negative regulator of p53 in transcription. Conversely, p53 inhibits the transcription elongation activity of ELL, suggesting that p53 is capable of regulating general transcription by RNA polymerase II through controlling the ELL activity. Elevated levels of ELL in cells resulted in the inhibition of p53-dependent induction of endogenous p21 and substantially protected cells from p53-mediated apoptosis that is induced by genotoxic stress. Our observations indicate the existence of a mutually inhibitory interaction between p53 and a general transcription elongation factor ELL and raise the possibility that an aberrant interaction between p53 and ELL may play a role in the genesis of leukemias carrying MLL-ELL gene translocations.

Tumor necrosis factor is a survival and proliferation factor for human myeloma cells

Interleukin-6 (IL-6) is a major survival factor for malignant plasma cells. In patients with multiple myeloma (MM), cell lines whose survival and proliferation are dependent upon addition of exogenous IL-6 have been obtained. We show here that tumor necrosis factor-alpha (TNF-alpha) is also a survival factor for myeloma cell lines, although less potent than IL-6. The survival activity of TNF-alpha is not affected by anti-IL-6 or anti-gp130 monoclonal antibodies (mAbs). TNF-alpha also induces myeloma cells in the cell cycle and promotes the long-term growth of malignant plasma cell lines. As TNF-alpha is produced in patients with MM and associated with a poor prognosis, these results suggest that anti-TNF-alpha therapies could be useful in this disease.

Growth hormone prevents human monocytic cells from Fas-mediated apoptosis by up-regulating Bcl-2 expression

Apoptosis and particularly Fas-mediated apoptosis has been proposed to play a key role in controlling monocyte homeostasis. We and others have documented the regulatory function of human growth hormone (hGH) on monocytic cells, which prompted us to investigate the role of hGH on their response to Fas antigen cross-linking. Using human promonocytic U937 cells constitutively producing hGH upon gene transfer and human primary monocytes cultured in the presence of recombinant hGH, we demonstrated that hGH diminished Fas-mediated cell death by enhancing the expression of the antiapoptotic oncoprotein Bcl-2 as well as the level of bcl-2alpha mRNA. In parallel, we established that overexpression of Bcl-2 through gene transfer into normal U937 cells also diminished Fas-induced apoptosis. Further, as a result of Bcl-2 overexpression, we found that hGH greatly depressed Fas-induced activation of the cysteine protease caspase-3 (CPP32), which in turn affected the cleavage of poly(ADP-ribose) polymerase. Altogether, these data provide evidence that hGH mediates its protective effect through a Bcl-2-dependent pathway, clearly a crucial step in enhanced survival of monocytic cells exposed to Fas-induced death.

Ionizing radiation-induced MEK and Erk activation does not enhance survival of irradiated human squamous carcinoma cells

PURPOSE

Ionizing radiation (IR) triggers several intracellular signaling cascades that have commonly been regarded as mitogenic, including the Raf-MEK-Erk kinase cascade. In addition to promoting proliferation, activated MEK and Erk may also prevent cell death induced by cytotoxic stimuli. Because Raf, MEK, and Erk are activated by IR in some tumor cell lines, this suggests that IR-induced activation of the kinase cascade may enhance the survival of irradiated cells.

METHODS AND MATERIALS

IR-induced activation of MEK and Erk was assessed in irradiated UM-SCC-6 cells, a human squamous carcinoma cell line. Activation of MEK and Erk was blocked with the pharmacological inhibitor of MEK activation, PD098059. Clonogenic survival was assessed in irradiated UM-SCC-6 cells that were pretreated with nothing or with the MEK inhibitor.

RESULTS

In UM-SCC-6 cells, IR doses as low as 2 Gy rapidly activated MEK and Erk. Pretreatment of the cells with the pharmacological inhibitor of MEK activation, PD098059, effectively blocked IR-induced activation of MEK and Erk. However, inhibition of the kinase cascade did not affect the clonogenic survival of irradiated cells in either early or delayed-plating experiments.

CONCLUSION

Taken together, these results suggest that although MEK and Erk are rapidly activated by IR treatment, these protein kinases do not affect the clonogenic survival of irradiated UM-SCC6 cells.

Survival factors and apoptosis

This chapter will explore the role of survival factors in suppression of apoptosis, and illustrate how survival signals play a critical role in the survival of both normal and tumor cells. Survival factors necessary for the development and maintenance of the nervous system and hemopoietic system will be surveyed. This will be followed by a detailed discussion of the role of insulin-like growth factor I (IGF-I) and its receptor in suppression of apoptosis. The importance of survival signals from the IGF-IR for development and tumorigenesis will be discussed, and results of a mutational analysis of the receptor to assign domains necessary for suppression of apoptosis will be summarized. Finally, a discussion of the signal transduction pathways involved in survival factor-signaling will review the roles played by PI-3 kinase and AKT and speculate on how activation of these kinases by survival factors might regulate the apoptotic pathway.

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.

Inhibited apoptosis and drug resistance in acute myeloid leukaemia

Despite extensive investigation into mechanisms of drug resistance in acute myeloid leukaemia (AML), the aetiology of therapeutic resistance is unclear. We found that five leukaemia cell lines (K562, HL-60, CEM. CEM induced to overexpress bcl-2, and REH) displayed parallel sensitivity to four antileukaemia drugs with different mechanisms of action, with K562 generally being the least sensitive and REH being the most sensitive. The amount of spontaneous apoptosis in the cell lines after serum-free culture paralleled their drug sensitivity: K562 cells displayed the least apoptosis at 24h (2.50 +/- 0.24%) and REH the most (24.47 +/- 8.22%). The extent of spontaneous apoptosis of leukaemic blasts from 39 patients with newly diagnosed de novo AML also correlated with the success of the intensive, infusional cytarabine-based induction therapy. There was a median of 19.5% (range 3.6-64%) apoptotic AML cells after 24 h of serum-free culture in patients who entered a complete remission compared with 4.2% (1.8-7.0%) apoptotic AML cells in patients who did not achieve a complete remission (P = 0.0007). Thus, inhibited apoptosis was associated with both in vitro and in vivo pan-resistance to antileukaemic chemotherapy. The cause of inhibited apoptosis in AML is probably a function of interactions among multiple signals that influence apoptosis. Assessment of spontaneous apoptosis may serve as an important prognostic factor for AML.

p53 suppresses cytokine induced, Stat5 mediated activation of transcription

p53 is a tumor suppressor which exerts its function through the regulation of genes mediating cell cycle arrest and the induction of apoptosis. Cellular survival and proliferation can be positively regulated through the action of cytokines. These signals act through the activation of cell surface receptors, and the phosphorylation of intracellular signaling components, e.g. members of the Stat family (signal transducers and activators of transcription). The signaling effects of p53 and the cytokine receptors on the cellular phenotype are counteracting. We investigated the influence of p53 on the transactivation potential of Stat5. p53 repressed the prolactin induction of the Stat5 mediated transcription of the beta-casein promoter-luciferase reporter gene, but did not affect IFN-gamma induced, Stat1 dependent transcription of the IRF-1 promoter. The inhibition was not due to a decrease in the cellular concentration of Stat5 or to interference with its specific DNA binding activity. No repression of the basal transcriptional activity of the beta-casein promoter was observed. p53 mutants defective in their DNA binding or oligomerization functions had only weak inhibitory effects, but a mutant of p53 in the transactivation domain, efficiently repressed Stat5 dependent induction. The repressive function of p53 on Stat5 activity is independent of the amino-terminal transactivation domain, but requires a functional DNA binding domain and the carboxyl-terminal domain. Our experiments show that p53 counteracts Stat5 mediated cytokine induction of gene transcription. The effect is specific for Stat5 and independent of p53 induced apoptosis.

Cytochrome c Induces Caspase-Dependent Apoptosis in Intact Hematopoietic Cells and Overrides Apoptosis Suppression Mediated by bcl-2, Growth Factor Signaling, MAP-Kinase-Kinase, and Malignant Change

It has been shown that cytochrome c is released from mitochondria during apoptosis, activates pro-caspase CPP32 (caspase III), and induces DNA fragmentation in mixtures of cytosolic extracts and isolated nuclei. To establish whether cytochrome c can primarily induce apoptosis in intact cells, we used direct electroporation of cytochrome c into murine interleukin-3 (IL-3)–dependent cells. Electroporation of micromolar external concentrations of cytochrome c rapidly induced apoptosis (2 to 4 hours) that was concentration-dependent, did not affect mitochondrial transmembrane potential, and was independent of cell growth. Only certain isoforms of cytochrome c were apoptogenic; yeast cytochrome c and other redox proteins were inactive. Cytochrome c-induced apoptosis was dependent on heme attachment to the apo-enzyme and was completely abolished by caspase inhibitors. Nonapoptogenic isoforms of cytochrome c did not compete for apoptogenic cytochrome c. Although apoptosis induced by IL-3 withdrawal was inhibited by bcl-2 overexpression and expression of an activated MAP-kinase-kinase (MAP-KK), cytochrome c induced apoptosis in the presence of IL-3 signaling, bcl-2 over-expression, expression of activated MAP-KK, and the combined antiapoptotic action of all three. Cytochrome c also induced apoptosis in the leukemic cell line WEHI 3b. However, human HL60 and CEM cells were resistant to cytochrome c-induced apoptosis. HL60 cells did not electroporate, but CEM cells were efficiently electroporated. Our studies with IL-3–dependent cells confirm that the apoptogenic attributes of cytochrome c are identical in intact cells to those in cell extracts. We conclude that cytochrome c can be a prime initiator of apoptosis in intact growing cells and acts downstream of bcl-2 and mitochondria, but that other cells are resistant to its apoptogenic activity. The system described offers a novel, simple approach for investigating regulation of apoptosis by cytochrome c and provides a model linking growth factor signaling to metabolism, survival, and apoptosis control.

© 1998 by The American Society of Hematology.

Cytochrome c Induces Caspase-Dependent Apoptosis in Intact Hematopoietic Cells and Overrides Apoptosis Suppression Mediated by bcl-2, Growth Factor Signaling, MAP-Kinase-Kinase, and Malignant Change

It has been shown that cytochrome c is released from mitochondria during apoptosis, activates pro-caspase CPP32 (caspase III), and induces DNA fragmentation in mixtures of cytosolic extracts and isolated nuclei. To establish whether cytochrome c can primarily induce apoptosis in intact cells, we used direct electroporation of cytochrome c into murine interleukin-3 (IL-3)–dependent cells. Electroporation of micromolar external concentrations of cytochrome c rapidly induced apoptosis (2 to 4 hours) that was concentration-dependent, did not affect mitochondrial transmembrane potential, and was independent of cell growth. Only certain isoforms of cytochrome c were apoptogenic; yeast cytochrome c and other redox proteins were inactive. Cytochrome c-induced apoptosis was dependent on heme attachment to the apo-enzyme and was completely abolished by caspase inhibitors. Nonapoptogenic isoforms of cytochrome c did not compete for apoptogenic cytochrome c. Although apoptosis induced by IL-3 withdrawal was inhibited by bcl-2 overexpression and expression of an activated MAP-kinase-kinase (MAP-KK), cytochrome c induced apoptosis in the presence of IL-3 signaling, bcl-2 over-expression, expression of activated MAP-KK, and the combined antiapoptotic action of all three. Cytochrome c also induced apoptosis in the leukemic cell line WEHI 3b. However, human HL60 and CEM cells were resistant to cytochrome c-induced apoptosis. HL60 cells did not electroporate, but CEM cells were efficiently electroporated. Our studies with IL-3–dependent cells confirm that the apoptogenic attributes of cytochrome c are identical in intact cells to those in cell extracts. We conclude that cytochrome c can be a prime initiator of apoptosis in intact growing cells and acts downstream of bcl-2 and mitochondria, but that other cells are resistant to its apoptogenic activity. The system described offers a novel, simple approach for investigating regulation of apoptosis by cytochrome c and provides a model linking growth factor signaling to metabolism, survival, and apoptosis control.

© 1998 by The American Society of Hematology.

MDM2 Protein Overexpression Inhibits Apoptosis of TF-1 Granulocyte-Macrophage Colony-Stimulating Factor–Dependent Acute Myeloblastic Leukemia Cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a growth factor for acute myeloblastic leukemia (AML) cells. Murine double minute 2 (MDM2) oncoprotein, a potent inhibitor of wild-type p53 (wtp53), can function both to induce cell proliferation and enhance cell survival, and is frequently overexpressed in leukemias. Therefore, we focused on the importance of MDM2 protein in GM-CSF–dependent versus GM-CSF– independent growth of AML cells. The TF-1 AML cell line, which has both wtp53 and mutant p53 genes, showed GM-CSF–dependent growth; deprivation of GM-CSF resulted in G1 growth arrest and apoptosis. MDM2 mRNA and protein were highly expressed in proliferating TF-1 cells in the presence of GM-CSF and decreased significantly with deprivation of GM-CSF. In contrast, p53 protein increased with GM-CSF deprivation. Ectopic overexpression of MDM2 in TF-1 AML cells conferred resistance to GM-CSF deprivation, and is associated with decreased p53 protein expression. Moreover, a variant of TF-1 cells that grows in a GM-CSF–independent fashion also expressed high levels of MDM2 and low levels of p53. These results suggest that GM-CSF–independent growth of AML cells is associated with overexpression of MDM2 protein and related modulation of p53 expression.

© 1998 by The American Society of Hematology.

MDM2 Protein Overexpression Inhibits Apoptosis of TF-1 Granulocyte-Macrophage Colony-Stimulating Factor–Dependent Acute Myeloblastic Leukemia Cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a growth factor for acute myeloblastic leukemia (AML) cells. Murine double minute 2 (MDM2) oncoprotein, a potent inhibitor of wild-type p53 (wtp53), can function both to induce cell proliferation and enhance cell survival, and is frequently overexpressed in leukemias. Therefore, we focused on the importance of MDM2 protein in GM-CSF–dependent versus GM-CSF– independent growth of AML cells. The TF-1 AML cell line, which has both wtp53 and mutant p53 genes, showed GM-CSF–dependent growth; deprivation of GM-CSF resulted in G1 growth arrest and apoptosis. MDM2 mRNA and protein were highly expressed in proliferating TF-1 cells in the presence of GM-CSF and decreased significantly with deprivation of GM-CSF. In contrast, p53 protein increased with GM-CSF deprivation. Ectopic overexpression of MDM2 in TF-1 AML cells conferred resistance to GM-CSF deprivation, and is associated with decreased p53 protein expression. Moreover, a variant of TF-1 cells that grows in a GM-CSF–independent fashion also expressed high levels of MDM2 and low levels of p53. These results suggest that GM-CSF–independent growth of AML cells is associated with overexpression of MDM2 protein and related modulation of p53 expression.

© 1998 by The American Society of Hematology.

Bcl-2 and drugs used in the treatment of cancer: new strategies of biotherapy which should not be underestimated

The theory that an imbalance in the control of the cell cycle contributes to the appearance and progression of neoplastic disease is gaining more ground all the time. This new line of research into tumor disease is a result of the progress made in the comprehension of cell death (apoptosis) and the discovery of alterations in the apoptotic pathway in patients with cancer, which have also been correlated to disease mechanisms. Alterations in the cycle of events that brings about apoptosis can result in tumor cells resistant to chemotherapy. In fact one of the inherent risks of chemotherapy is the generation of new, more aggressive, clonal variants and destruction of healthy cells with deleterious effects on the organism. This review examines the results of studies concerning the identification of the alterations in apoptotic mechanisms in carcinogenesis and the mechanisms governing their regulation. The aim was to evaluate if such data could be of use in identifying drugs able to improve cancer treatment.

p53 facilitates pRb cleavage in IL-3-deprived cells: novel pro-apoptotic activity of p53

In the interleukin-3 (IL-3)-dependent lymphoid cell line DA-1, functional p53 is required for efficient apoptosis in response to IL-3 withdrawal. Activation of p53 in these cells, by either DNA damage or p53 overexpression, results in a vital growth arrest in the presence of IL-3 and in accelerated apoptosis in its absence. Thus, IL-3 can control the choice between p53-dependent cell-cycle arrest and apoptosis. Here we report that the cross-talk between p53 and IL-3 involves joint control of pRb cleavage and degradation. Depletion of IL-3 results in caspase-mediated pRb cleavage, occurring preferentially within cells which express functional p53. Moreover, pRb can be cleaved efficiently by extracts prepared from DA-1 cells but not from their derivatives which lack p53 function. Inactivation of pRb through expression of the human papillomavirus (HPV) E7 oncogene overrides the effect of IL-3 in a p53-dependent manner. Our data suggest a novel role for p53 in the regulation of cell death and a novel mechanism for the cooperation between p53 and survival factor deprivation. Thus, p53 makes cells permissive to pRb cleavage, probably by controlling the potential activity of a pRb-cleaving caspase, whereas IL-3 withdrawal provides signals that turn on this potential activity and lead to the actual cleavage and subsequent degradation of pRb. Elimination of a presumptive anti-apoptotic effect of pRb may then facilitate conversion of p53-mediated growth arrest into apoptosis.

[Late effects of ionizing radiations on the bone marrow]

Bone marrow is a tissue with a high mitotic activity, and consequently exquisitely radiosensitive. The clinical effects of bone marrow irradiation and its ability of regeneration are related to the volume irradiated. Management of hematopoietic side effects of radiation include surveillance, antibiotics, blood products transfusion, and more scarcely hematopoietic growth factors, bone marrow transplantation and peripheral blood stem cells reinfusion.

Antitumor agent-induced apoptosis in myeloid leukemia cells: a controlled suicide

Traditional antitumor research has generally believed that the cytotoxicity of antitumor agents was directly correlated with the amount of drug-induced cellular lesions. Accordingly, oncologists have tried to improve anticancer agent/target interactions by increasing the intracellular dose of active effectors. However, a growing body of evidence stemming from both clinical and experimental observations, strongly suggests that similar anticancer-induced lesions may result in different cellular responses, greatly influencing cytotoxicity. For example, it has been shown that in some but not all cellular models, antitumor agents trigger apoptosis, an irreversible process which leads to a rapid and complete elimination of tumor cells. Several of these studies also demonstrated that apoptosis induced by antitumor agents is highly regulated by multiple signaling pathways which are themselves influenced by oncogenes, protein kinase activities, external stimuli and the oxidative balance. Therefore, it appears that cell death commitment is controlled by both external and internal factors which interfere downstream of drug- or ionizing radiation-target interaction. The characterization of these mediators may provide novel strategies for modulating intracellular signaling pathways in order to promote apoptosis in drug-resistant tumor cells.

Cytokine rescue of p53-dependent apoptosis and cell cycle arrest is mediated by distinct Jak kinase signaling pathways

Exposure of hematopoietic progenitors to gamma-irradiation (IR) induces p53-dependent apoptosis and a p53-independent G2/M cell cycle arrest. These responses to DNA-damage can be inhibited by treatment with cytokine growth factors. Here we report that gamma-IR-induced apoptosis and cell cycle arrest are suppressed by specific cytokines (e.g., erythropoietin and interleukin-3) and that activation of the Jak kinase is necessary and sufficient for these effects. Using myleoid cells expressing a series of erythropoietin receptor (EpoR) mutants, we have demonstrated that Jak kinase-dependent signals initiated from the membrane proximal domain of EpoR were sufficient to prevent IR-induced apoptotic cell death, but failed to prevent cell cycle arrest. Cell survival by Epo did not require activation of other known signaling pathways including PI-3 kinase, PLC-gamma, Ras or Stats. Signaling targets of Jak kinase pathways included members of the Bcl-2 family of anti-apoptotic proteins, and enforced expression of Bcl-2 or Bcl-xL was as effective as cytokine treatment in blocking IR-induced apoptosis but did not prevent growth arrest. A distinct signal derived from a membrane distal domain of EpoR is required to overcome growth arrest associated with DNA damage. These findings functionally link the Jak signaling pathway to suppression of p53-mediated cell death by cytokines and demonstrate that the apoptotic and growth arrest responses to DNA damage in hematopoietic cells are modulated by distinct, cytokine specific signal transduction pathways.

Anti-apoptotic signaling by a colony-stimulating factor-1 receptor/insulin receptor chimera with a juxtamembrane deletion

The intracellular mechanisms used by insulin and insulin-like growth factors to block programmed cell death are unknown. To identify receptor structures and signaling pathways essential for anti-apoptotic effects on cells, we have created a chimeric receptor (colony-stimulating factor-1 receptor/insulin receptor chimera (CSF1R/IR)) connecting the extracellular, ligand-binding domain of the colony-stimulating factor-1 (CSF-1) receptor to the transmembrane and cytoplasmic domains of the insulin receptor. Upon activation with CSF-1, the CSF1R/IR phosphorylates itself and intracellular substrates in a manner characteristic of normal insulin receptors. CSF-1 treatment protected cells expressing the CSF1R/IR from staurosporine-induced apoptosis. A chimeric receptor (CSF1R/IRDelta960) with a deletion of 12 amino acids from its juxtamembrane domain was constructed and expressed. CSF-1-treated cells expressing the CSF1R/IRDelta960 are unable to phosphorylate IRS-1 and Shc (Chaika, O. V., Chaika, N., Volle, D. J., Wilden, P. A. , Pirrucello, S. J., and Lewis, R. E. (1997) J. Biol. Chem. 272, 11968-11974). CSF-1 stimulated glucose uptake, mitogen-activated protein kinases, and IRS-1-associated phosphatidylinositol 3' kinase in cells expressing the CSF1R/IR but not in cells expressing the CSF1R/IRDelta960. Surprisingly, the CSF1R/IRDelta960 was as effective as the CSF1R/IR in mediating CSF-1 protection of cells from staurosporine-induced apoptosis. These observations indicate that the anti-apoptotic effects of the insulin receptor cytoplasmic domain can be mediated by signaling pathways distinct from those requiring IRS-1 and Shc.

The myeloma cell antigen syndecan-1 is lost by apoptotic myeloma cells

Syndecan-1 is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. It is expressed only on malignant plasma cells in bone marrow samples from patients with multiple myeloma (MM). Several reports have suggested that syndecan-1 was present only on a part of the myeloma cells. By using either IL-6-dependent myeloma cell lines or primary myeloma cells stained by annexin V, we report here that syndecan-1 was rapidly lost by myeloma cells undergoing apoptosis. In the same experimental conditions, expression of other cell membrane antigens such as CD38, HLA class-I or CD49d on apoptotic myeloma cells was not affected. In addition, we show that syndecan-1 loss was independent of activation of the gp130 IL-6 transducer. Dexamethasone induced a strong apoptosis of myeloma cells associated with the loss of syndecan-1. Finally, by using freshly-explanted tumoural samples, we show that syndecan-1 rapidly disappeared from myeloma cells in association with induction of apoptosis. In conclusion we showed that syndecan-1 is a marker for viable myeloma cells which is rapidly lost by apoptotic cells. These results emphasize the usefulness of anti-syndecan-1 antibodies to purge tumoural cells from haemopoietic grafts or to purify these cells for further manipulations for immuno or gene therapies.

Tacrolimus-induced apoptosis and its prevention by interleukins in mitogen-activated human peripheral-blood mononuclear cells

The present study demonstrated that tacrolimus (FK506) induced apoptosis in mitogen-activated human PBMCs and that several interleukins (ILs) prevented the apoptosis. Mitogen-activated PBMCs obtained from healthy subjects treated with 1 ng/ml of FK506 exhibited a DNA-ladder structure in agarose-gel electrophoresis. Moreover, in quantitative analysis of fragmented DNA using cell death detection ELISA, 1 ng/ml of FK506 induced maximal apoptotic induction, whereas > 10 ng/ml of glucocorticoids (GCs) or cyclosporine (CsA) was required to achieve maximal induction of apoptosis in PBMCs. FK506-induced apoptosis was efficiently attenuated by co-addition of ILs including IL-1beta (2 ng/ml), IL-2 (5 ng/ml) and IL-4 (40 ng/ml) into culture. The results showed that FK506 induces apoptosis in mitogen-activated PBMCs at concentrations which exhibited sufficient suppression of PBMC-blastogenesis. The data also suggested that cytokine networks including those via IL-1beta and IL-4 in addition to IL-2 prevent FK506-induced apoptosis.

Serum deprivation and protein synthesis inhibition induce two different apoptotic processes in N18 neuroblastoma cells

N18 are murine neuroblastoma cells that underwent cell death upon serum deprivation or inhibition of protein synthesis by means of cycloheximide (CHX). In both cases, an ultrastructural morphology and an internucleosomal pattern of DNA fragmentation typical of apoptosis were found. However, electron microscopy revealed abundant lipid vesicles in the cytoplasm of CHX-treated cells that were not found in their serum-deprived counterparts. In addition, when both types of apoptotic cells were compared by means of flow cytometry and chromatin staining with propidium iodide, the former showed consistently less fluorescence than the latter. Therefore, in N18 cells, both apoptotic processes seemed to differ at a structural level. At a functional level, we found that apoptosis was blocked by the protease inhibitor TLCK in CHX-treated but not in serum-deprived cells. On the other hand, we generated N18 clones that overexpressed Bcl-2 protein. After a period of 48 h we found that identical levels of Bcl-2 protein were able to block apoptosis in serum-deprived but not in CHX-treated cells. In conclusion, two different biochemical pathways leading to apoptosis seem to coexist in N18 neuroblastoma cells.

Apoptosis and cell culture technology

The importance of apoptosis in cell culture has now been widely recognised. Recent work has shown that this process is widely manifested during the in vitro cultivation of commercially important mammalian cell lines. In this review I summarise what is now known of the characteristics, significance and regulatory mechanisms of apoptosis. As the process of cell proliferation and cell death are now considered intimately related, particular attention is paid to highlight the progress and opportunities in the field of cell culture engineering. The strategies that have been undertaken to prevent the induction of apoptosis in cell culture and those which have been suggested as possibilities to improve culture productivity through the apoptosis route are discussed with given examples.

Interleukin-10 promotes activation-induced cell death of SLE lymphocytes mediated by Fas ligand

Immune function in SLE is paradoxically characterized by active T cell help for autoantibody production, along with impaired T cell proliferative and cytokine responses in vitro. To reconcile these observations, we investigated the possibility that the accelerated spontaneous cell death of SLE lymphocytes in vitro is caused by an activation-induced cell death process initiated in vivo. 27 SLE patients, three patients with systemic vasculitis, seven patients with arthritis, and 14 healthy subjects were studied. Patients with clinically active SLE or systemic vasculitis had accelerated spontaneous death of PBMC with features of apoptosis at day 5 of culture. A prominent role for IL-10 in the induction of apoptosis was observed, as neutralizing anti-IL-10 mAb markedly reduced cell death in the active SLE patients by 50%, from 22.3 +/- 5.2% to 11.2 +/- 2.8%, and the addition of IL-10 decreased viability in the active SLE group, but not in the control group, by 38%. In addition, apoptosis was shown to be actively induced through the Fas pathway. The potential clinical relevance of T cell apoptosis in active SLE is supported by the correlation of increased apoptosis and IL-10 levels in vitro with low lymphocyte counts in vivo. We conclude that the spontaneous cell death observed in vitro in lymphocytes from patients with SLE and other systemic autoimmune disorders results from in vivo T cell activation, is actively induced by IL-10 and Fas ligand, and reflects pathophysiologically important events in vivo. Activation-induced cell death in vivo provides a pathogenic link between the aberrant T helper cell activation and impaired T cell function that are characteristic features of the immune system of patients with SLE.

Interleukin 3-dependent survival by the Akt protein kinase

Interleukin 3 (IL-3)-dependent survival of hematopoietic cells is known to rely on the activity of multiple signaling pathways, including a pathway leading to activation of phosphoinositide 3-kinase (PI 3-kinase), and protein kinase Akt is a direct target of PI 3-kinase. We find that Akt kinase activity is rapidly induced by the cytokine IL-3, suggesting a role for Akt in PI 3-kinase-dependent signaling in hematopoetic cells. Dominant-negative mutants of Akt specifically block Akt activation by IL-3 and interfere with IL-3-dependent proliferation. Overexpression of Akt or oncogenic v-akt protects 32D cells from apoptosis induced by IL-3 withdrawal. Apoptosis after IL-3 withdrawal is accelerated by expression of dominant-negative mutants of Akt, indicating that a functional Akt signaling pathway is necessary for cell survival mediated by the cytokine IL-3. Thus Akt appears to be an important mediator of anti-apoptotic signaling in this system.

Apoptosis: clinical relevance and pharmacological manipulation

Apoptosis, often synonymously used with the term 'programmed cell death', is an active, genetically controlled process that removes unwanted or damaged cells. Suppression, overexpression or mutation of a number of genes which orchestrate the apoptotic process are associated with disease. The diseases in which apoptosis has been implicated can be grouped into 2 broad groups: those in which there is increased cell survival (i.e. associated with inhibition of apoptosis) and those in which there is excess cell death (where apoptosis is overactive). Diseases in which there is an excessive accumulation of cells include cancer, autoimmune disorders and viral infections. Deprivation of trophic factors is known to induce apoptosis in cells dependent on them for survival. This fact has been exploited in the use of antiandrogens or antiestrogens in the management of prostate or breast cancer. Haemopoietic growth factors like granulocyte-macrophage colony stimulating factor (GM-CSF) or interleukin-3 prevent apoptosis in target cells and modulation of levels of these factors has been tried in the prevention of chemotherapy-induced myelosuppression. Until recently, it was thought that cytotoxic drugs killed target cells directly by interfering with some life-maintaining function. However, of late, it has been shown that exposure to several cytotoxic drugs with disparate mechanisms of action induces apoptosis in both malignant and normal cells. Physiological regulation of cell death is essential for the removal of potentially autoreactive lymphocytes during development and the removal of excess cells after the completion of an immune response. Recent work has clearly demonstrated that dysregulation of apoptosis may underlie the pathogenesis of autoimmune diseases by allowing abnormal autoreactive lymphocytes to survive. AIDS and neurodegenerative disorders like Alzheimer's or Parkinson's disease represent the most widely studied group of disorders where an excess of apoptosis has been implicated. Amyotrophic lateral sclerosis, retinitis pigmentosa, epilepsy and alcoholic brain damage are other neurological disorders in which apoptosis has been implicated. Apoptosis has been reported to occur in conditions characterised by ischaemia, e.g. myocardial infarction and stroke. The liver is a site where apoptosis occurs normally. This process has also been implicated in a number of liver disorders including obstructive jaundice. Hepatic damage due to toxins and drugs is also associated with apoptosis in hepatocytes. Apoptosis has also been identified as a key phenomenon in some diseases of the kidney, i.e. polycystic kidney, as well as in disorders of the pancreas like alcohol-induced pancreatitis and diabetes.