Death of serum-free mouse embryo cells caused by epidermal growth factor deprivation

4-Hydroxyestradiol improves mouse embryo quality, epidermal growth factor-binding capability in vitro and implantation rates

Embryo implantation in the uterus is a critical step to achieve success following ART. Despite favorable uterine conditions, a great number of good quality embryos fail to implant, often for reasons that are unknown. Hence, improving the implantation potential of embryos is a subject of great interest. 4-Hydroxyestradiol (4-OH-E2), a metabolic product of estradiol produced by endometrial cells, plays a key role in endometrial-embryonic interactions that are necessary for implantation. Nonetheless, the effects of 4-OH-E2 on embryos obtained in vitro have not been yet described. This study was designed to determine whether culture media enriched in 4-OH-E2 could improve the quality and implantation rate of embryos obtained in vitro, using both in vitro and in vivo models. We also analyzed its effects on the epidermal growth factor (EGF)-binding capability of the embryos. Our results showed that the presence of 4-OH-E2 in the culture media of embryos during the morula to blastocyst transition increases embryo quality and attachment to endometrial cells in vitro. 4-OH-E2 can also improve viable pregnancy rates of mouse embryos produced in vitro, reaching success rates that are similar to those from embryos obtained directly from the uterus. 4-OH-E2 improved the embryos' ability to bind EGF, which could be responsible for the increased embryo implantation potential observed. Therefore, our results strongly suggest that 4-OH-E2 is a strong candidate molecule to supplement human IVF culture media in order to improve embryo implantation. However, further research is required before these findings can be translated with efficacy and safety to fertility clinics.

Serum Deprivation-Induced Human GM3 Synthase (hST3Gal V) Gene Expression Is Mediated by Runx2 in Human Osteoblastic MG-63 Cells

Serum deprivation (SD) is well known to induce G0/G1 cell cycle arrest and apoptosis in various cells. In the present study, we firstly found that SD could induce G1 arrest and the differentiation of human osteoblastic MG-63 cells, as evidenced by the increase of osteoblastic differentiation markers, such as bone morphogenetic protein-2 (BMP-2), osteocalcin and runt-related transcription factor 2 (Runx2). In parallel, gene expression of human GM3 synthase (hST3Gal V) catalyzing ganglioside GM3 biosynthesis was upregulated by SD in MG-63 cells. The 5′-flanking region of the hST3Gal V gene was functionally characterized to elucidate transcriptional regulation of hST3Gal V in SD-induced MG-63 cells. Promoter analysis using 5′-deletion constructs of the hST3Gal V gene demonstrated that the −432 to −177 region functions as the SD-inducible promoter. Site-directed mutagenesis revealed that the Runx2 binding sites located side-by-side at positions −232 and −222 are essential for the SD-induced expression of hST3Gal V in MG-63 cells. In addition, the chromatin immunoprecipitation assay also showed that Runx2 specifically binds to the hST3Gal V promoter region containing Runx2 binding sites. These results suggest that SD triggers upregulation of hST3Gal V gene expression through Runx2 activation by BMP signaling in MG-63 cells.

Combination effects of epidermal growth factor and glial cell line-derived neurotrophic factor on the in vitro developmental potential of porcine oocytes

The developmental potential of in vitro matured porcine oocytes is still lower than that of oocytes matured and fertilized in vivo. Major problems that account for the lower efficiency of in vitro production include the improper nuclear and cytoplasmic maturation of oocytes. With the aim of improving this issue, the single and combined effects of epidermal growth factor (EGF) and glial cell line-derived neurotrophic factor (GDNF) on oocyte developmental competence were investigated. Porcine cumulus-oocyte cell complexes (COCs) were matured in serum-free medium supplemented with EGF (0, 10 or 50 ng/ml) and/or GDNF (0, 10 or 50 ng/ml) for 44 h, and subsequently subjected to fertilization and cultured for 7 days in vitro. The in vitro-formed blastocysts derived from selected growth factor groups (i.e. EGF = 50 ng/ml; GDNF = 50 ng/ml; EGF = 50 ng/ml + GDNF = 50 ng/ml) were also used for mRNA expression analysis, or were subjected to Hoechst staining. The results showed that the addition of EGF and/or GDNF during oocyte maturation dose dependently enhanced oocyte developmental competence. Compared with the embryos obtained from control or single growth factor-treated oocytes, treatment with the combination of EGF and GDNF was shown to significantly improve oocyte competence in terms of blastocyst formation, blastocyst cell number and blastocyst hatching rate (P < 0.05), and also simultaneously induced the expression of BCL-xL and TERT and suppressed the expression of caspase-3 in resulting blastocysts (P < 0.05). These results suggest that both GDNF and EGF may play an important role in the regulation of porcine in vitro oocyte maturation and the combination of these growth factors could promote oocyte competency and blastocyst quality.

PDGF in gliomas: more than just a growth factor?

Platelet-derived growth factor B (PDGF-B) is a growth factor promoting and regulating cell migration, proliferation, and differentiation, involved in both developmental processes and in maintaining tissue homeostasis under strict regulation. What are the implications of prolonged or uncontrolled growth factor signaling in vivo, and when does a growth factor such as PDGF-B become an oncogene? Under experimental conditions, PDGF-B induces proliferation and causes tumor induction. It is not known whether these tumors are strictly a PDGF-B-driven proliferation of cells or associated with secondary genetic events such as acquired mutations or methylation-mediated gene silencing promoting neoplasia. If PDGF-B-driven tumorigenesis was only cellular proliferation, associated changes in gene expression would thus be correlated with proliferation and not associated with secondary events involved in tumorigenesis and neoplastic transformation such as cycle delay, DNA damage response, and cell death. Changes in gene expression might be expected to be reversible, as is PDGF-B-driven proliferation under normal circumstances. Since PDGF signaling is involved in oligodendrocyte progenitor cell differentiation and maintenance, it is likely that PDGF-B stimulates proliferation of a pool of cells with that phenotype, and inhibition of PDGF-B signaling would result in reduced expression of oligodendrocyte-associated genes. More importantly, inhibition of PDGF signaling would be expected to result in reversion of genes induced by PDGF-B accompanied by a decrease in proliferation. However, if PDGF-B-driven tumorigenesis is more than simply a proliferation of cells, inhibition of PDGF signaling may not reverse gene expression or halt proliferation. These fundamental questions concerning PDGF-B as a potential oncogene have not been resolved.

Viability and cell cycle analysis of equine fibroblasts cultured in vitro

This experiment aimed to study equine fibroblasts in culture analyzing and the cell cycle and viability of cells pre- and post-freezing. Skin fragments were obtained from 6 horses and cultured in DMEM high glucose + 10% FCS in 5% CO(2) until the beginning of confluence. Two passages were performed before freezing. Cells subjected to serum starvation (0.5% FCS) were analyzed for viability and cell cycle at 24, 48, 72, 96, 120, 144 and 168 h of culture. For the confluent groups, cells were analyzed at the moment they achieved confluence. Cellular viability was assisted with Hoescht 33342 and propidium iodide. The analysis of apoptosis/necrosis and cell cycle was performed using a flow cytometer (FACS Calibur BD((R))) after staining the cells with annexin V and propidium iodide. Both optical microscopy and flow cytometry confirmed that cellular viability was similar for serum starvation and confluent groups (average 84%). Similarly, both methods were efficient to synchronize the cell cycle before freezing. However, after thawing, serum starvation, for more than 24 h, was superior to culture for synchronizing cells in G0/G1 (69% x 90%). The results of this experiment indicate that equine fibroblasts can be efficiently cultured after thawing.

Mitogen limitation and bone morphogenetic protein-4 promote neurogenesis in SFME cells, an EGF-dependent neural stem cell line

Serum-free mouse embryo (SFME) cells are an epidermal growth factor (EGF)-dependent established line derived from brains of 16-d-old Balb/c mouse embryos. SFME cells grow indefinitely in serum-free medium without replicative senescence, chromosomal abnormalities, or malignant transformation. SFME cells express nestin, a neural stem cell marker, under serum-free conditions. Exposure to serum or transforming growth factor beta (TGF-beta) leads to a marked increase in differentiation toward the astrocytic lineage with expression of glial fibrillary acidic protein and other astrocyte markers. In this study, we show that treatment of SFME cells with bone morphogenetic protein-4 (BMP-4), another member of the TGF-beta family, led to differentiation toward a neuronal lineage under conditions of low mitogenic stimulation (0.5 ng/mL) by EGF and fibroblast growth factor. Maximum mitogenic stimulation with 50 ng/mL EGF blocked the BMP-4 effect on neuronal differentiation, but did not block TGF-beta-induced expression of markers of the astrocytic lineage. BMP-4 treatment also enhanced the activity of the neuron-specific enolase (NSE) promoter in SFME-NSE-lacZ cells that carry the gene for bacterial beta-galactosidase under the control of the NSE promoter. Extended BMP-4 treatment caused SFME cells to express a neuronal phenotype synthesizing gamma-aminobutyric acid. These results indicate that SFME cells have the capacity to generate both neurons and astrocytes in vitro, which resemble the behavior of EGF-dependent multipotential stem cells in the central nervous system, and establish a relationship between effects of BMP-4 and degree of mitogenic stimulation by other peptide growth factors.

Rabbit Oocyte Cytoplasm Supports Development of Nuclear Transfer Embryos Derived from the Somatic Cells of the Camel and Tibetan Antelope

This study was designed to examine the ability of rabbit metaphase II oocyte cytoplasm to support the development of interspecies nuclear transfer embryos reconstructed using donor nuclei from different species. Skin fibroblast cells from a camel and Tibetan antelope were used as donor nuclei. As a first step, we investigated the efficiency of different activation protocols by comparing the parthenogenetic development of rabbit oocytes. The protocol that yielded the highest blastocyst rate was used to activate the reconstructed embryos in nuclear transfer experiments. In addition, the effect of donor cell serum starvation on the development of the reconstructed embryo was also examined. More than half of the karyoplast-cytoplast couplets could be fused, and about one third of the reconstructed embryos were capable of completing first cleavage, regardless of the species of donor nuclei. Some of the cleaving reconstructed embryos were even capable of progressing further and developing to the blastocyst stage (1.4-8.7% for the Tibetan antelope and 0-7.5% for the camel, respectively). Our results suggest that the mechanisms regulating early embryo development may be conserved among mammalian species and some factors existing in rabbit oocyte cytoplasm for somatic nucleus reprogramming and dedifferentiation may not be species-specific. Rabbit oocyte cytoplasm can reprogram donor nuclei regardless of the origin of the nucleus and support in vitro development to an advanced stage.

Cell confluency is as efficient as serum starvation for inducing arrest in the G0/G1 phase of the cell cycle in granulosa and fibroblast cells of cattle

The cell cycle stage of donor cells is an important factor influencing developmental ability of nuclear transfer embryos. In the present experiment, cumulus and fibroblast cells of cattle were subjected to flow cytometric cell cycle analysis before being used in somatic cloning experiments. The following experimental groups were analyzed for each cell type: (1) actively dividing cells, (2) cells confluent for 4 days, (3) cells starved for 1, 2, 3 or 5 days. Using the propidium iodide flow cytometric assay, there were no significant differences (P > or = 0.05) in the percentage of cells in G0/G1 regardless of origin and type of cell, after confluency or serum starvation. Differences with the growing cells were found (P < or = 0.01). To determine what subset of cells in G0/G1 were in the G0 subphase of the cell cycle, an immunofluorescence analysis was conducted using monoclonal anti-PCNA antibodies in a FACS assay. There were not statistically significant differences in the percentage of cells that enter G0, between confluent and any starved group for either type of cells. Bovine fibroblast cells, confluent or serum starved for 3 days, were used in nuclear transfer experiments. A slight trend for a more desirable fusion rate in starved cells was detected, and embryo cleavage was greater in starved cells, however, in vitro development to blastocysts was similar between groups. Data indicate that prolonged culture of cells in the absence of serum does not imply a shift in the percentage of cells that enter G0/G1 or G0 alone, and that confluency is sufficient to induce quiescence. This finding can be beneficial in nuclear transfer programs, because there are negative effects such as apoptosis, associated with serum starvation.

Cell cycle synchronization of porcine fetal fibroblasts by serum deprivation initiates a nonconventional form of apoptosis

The success of somatic nuclear transfer depends upon the cell cycle stage of the donor nucleus and the recipient cytoplast. Recently, we established efficient cell cycle synchronization protocols for porcine fetal fibroblasts and found that serum withdrawal leads to cell death. Here, we examined whether the specific cell death induced by serum deprivation follows the conventional apoptotic pathway in porcine fibroblasts. Terminal deoxynucleotidyl transferase mediated dUTP nick end-labeling analysis revealed that serum deprivation induced DNA fragmentation in a concentration and time dependent manner. Semiquantitative RT-PCR and Western blotting revealed activation of cell death-related genes Bak and Bax of the Bcl-2 family. However, electrophoretic analysis of genomic DNA from serum deprived cells did not provide evidence for the internucleosomal DNA cleavage which is characteristic of conventional apoptosis. Thus, serum deprivation triggers initial steps in the apoptotic pathway, but does not lead to the typical oligonucleosome-sized DNA ladder. These findings contribute to a better understanding of apoptotic pathways and aid to define essential parameters of the donor nucleus for successful somatic cloning.

Inhibition of apoptosis by amphiregulin via an insulin-like growth factor-1 receptor-dependent pathway in non-small cell lung cancer cell lines

Several abnormalities in the insulin-like growth factor-1 (IGF1) and erbB receptors pathways stimulate the growth and survival of lung cancer cells, but their mechanisms of action and cooperation are poorly understood. In this report, we have identified a new mechanism of apoptosis inhibition by amphiregulin through an IGF1-dependent survival pathway in non-small cell lung cancer (NSCLC) cells: amphiregulin activates the IGF1 receptor that in turn induces the secretion of amphiregulin and IGF1. In the absence of serum, the NSCLC cell line H358 resists apoptosis and secretes factors protecting the NSCLC cell line H322 from serum deprivation apoptosis. IGF1 receptor inhibitor AG1024 as well as epidermal growth factor receptor inhibitors AG556 and ZD1839 restore apoptosis in H322 cells cultured in H358-conditioned medium. Accordingly, the anti-apoptotic activity of H358-conditioned medium is completely abolished after incubation with anti-amphiregulin neutralizing antibody and only partially with anti-IGF1 neutralizing antibody. H358-conditioned medium and amphiregulin induce IGF1 receptor phosphorylation in H322 cells, which is prevented by anti-amphiregulin neutralizing antibody but not by AG556 or ZD1839. H358 cells secrete a high level of amphiregulin that, in combination with IGF1, prevents serum deprivation apoptosis. Finally, IGF1 receptor inhibitor blocks amphiregulin and IGF1 release by H358 cells.

Transforming growth factor-alpha prevents detachment-induced inhibition of c-Src kinase activity, Bcl-XL down-regulation, and apoptosis of intestinal epithelial cells

Detachment of epithelial cells from the extracellular matrix (ECM) results in apoptosis, a phenomenon often referred to as anoikis. Acquisition of anoikis resistance is now thought to be a prerequisite for the progression of carcinomas. Colorectal cancer cells frequently secrete epidermal growth factor receptor (EGFR) ligands, which are known to have anti-apoptotic activity. However, whether these ligands have the ability to inhibit anoikis of intestinal epithelial cells is unclear, since at least in some cell types efficient EGFR signaling requires cell-ECM adhesion. Here we report that transforming growth factor-alpha (TGF-alpha), an EGFR ligand that is frequently secreted by colorectal cancer cells, strongly inhibits anoikis of the non-malignant rat intestinal epithelial cell lines, IEC-18 and RIE-1. TGF-alpha exerts its anti-anoikis effect by preventing detachment-induced inhibition of c-Src kinase activity. We also show that Fas activation, a molecular event known to play a critical role in anoikis, is not suppressed by TGF-alpha. On the other hand, this growth factor strongly inhibits the detachment-induced down-regulation of Bcl-X(L), another change that is involved in the induction of anoikis. We further demonstrate that this inhibition occurs in a c-Src-dependent manner. We conclude that TGF-alpha has the ability to suppress anoikis of intestinal epithelial cells, at least in part, by reverting the loss of c-Src activity and Bcl-X(L) expression induced by detachment from the ECM.

Implication of the small GTPase Rac1 in the apoptosis induced by UV in Rat-2 fibroblasts

Exposure of mammalian cells to ultraviolet (UV) light elicits a cellular response and also lead to apoptotic cell death. However, the role of Rac, a member of Rho family GTPases, in the UV-induced apoptosis has never been examined. In UV-irradiated Rat-2 fibroblasts, nuclear fragmentation began to be observed within 2 h and the total viability of Rat-2 cells were only about 15% at 6 h following by UV irradiation, whereas the total viability in Rat2-Rac(N17) cells stably expressing RacN17, a dominant negative Rac1 mutant, was almost close to 67%. Pretreatment with SB203580, a specific inhibitor of p38 kinase, likewise attenuated UV-induced cell death, but PD98059, a MEK inhibitor, did not. Thus, Rac1 and p38 kinase appear to be components in the apoptotic signaling pathway induced by UV irradiation in Rat-2 fibroblasts. In addition, our results show that p38 kinase stimulation by UV is dramatically inhibited by RacN17, suggesting that p38 kinase is situated downstream of Rac1 in the UV signaling to apoptosis.

Insulin-like growth factor I (IGF-I) protects cells from apoptosis by Alzheimer's V642I mutant amyloid precursor protein through IGF-I receptor in an IGF-binding protein-sensitive manner

It has been found that insulin-like growth factor I (IGF-I) exerts cytoprotection against Abeta amyloid-induced neuronal cell death. Deposits of Abeta amyloid are one of the pathological hallmarks of Alzheimer's disease (AD). Here, we examined whether IGF-I exerts protective activity against cell death induced by a familial AD (FAD)-linked mutant of amyloid precursor protein (APP), and we found that IGF-I protected cells from toxicity of FAD-associated V642I mutant of APP in multiple cell systems. IGFBP-3 blocked this action of IGF-I, but not of des(1-3)IGF-I, which was as active as IGF-I in the presence of IGFBP-3. The data also demonstrated that the IGF-I receptor (IGF-IR) mediates the protective activity of IGF-I. The antagonizing function of the IGF-I/IGF-IR system against V642I-APP, which is further antagonized by IGFBP-3, provides a molecular clue to the understanding of AD pathophysiology and to the establishment of potential therapy for AD.

Insulin-like growth factor I (IGF-I) protects cells from apoptosis by Alzheimer's V642I mutant amyloid precursor protein through IGF-I receptor in an IGF-binding protein-sensitive manner

It has been found that insulin-like growth factor I (IGF-I) exerts cytoprotection against Abeta amyloid-induced neuronal cell death. Deposits of Abeta amyloid are one of the pathological hallmarks of Alzheimer's disease (AD). Here, we examined whether IGF-I exerts protective activity against cell death induced by a familial AD (FAD)-linked mutant of amyloid precursor protein (APP), and we found that IGF-I protected cells from toxicity of FAD-associated V642I mutant of APP in multiple cell systems. IGFBP-3 blocked this action of IGF-I, but not of des(1-3)IGF-I, which was as active as IGF-I in the presence of IGFBP-3. The data also demonstrated that the IGF-I receptor (IGF-IR) mediates the protective activity of IGF-I. The antagonizing function of the IGF-I/IGF-IR system against V642I-APP, which is further antagonized by IGFBP-3, provides a molecular clue to the understanding of AD pathophysiology and to the establishment of potential therapy for AD.

Paracrine regulation of apoptosis by steroid hormones in the male and female reproductive system

In males, androgens are essential in maintaining the integrity of the prostate. Androgen-ablation induces apoptosis of the prostatic epithelium. In females, ovariectomy induces apoptosis in uterine epithelium while progesterone inhibits this process. The objective of this study was to determine whether androgen and progesterone inhibit apoptosis, respectively, in mouse prostatic and uterine epithelia via steroid receptors in the epithelium or in the stroma. To address this question, prostatic tissue recombinants were prepared with rat urogenital sinus mesenchyme plus bladder epithelium from wild-type or testicular feminization mutant (Tfm) mice. Thus, prostatic tissue was generated having androgen receptor (AR) in both epithelium and stroma or in the stroma only. Castration of hosts induced apoptosis in the AR-negative Tfm prostatic epithelium with an epithelial apoptotic index virtually identical to prostatic tissue recombinants containing wild-type epithelium. Moreover, this castration-induced prostatic epithelial apoptosis was blocked by testosterone and dihydrotestosterone in both wild-type and Tfm prostatic tissue recombinants. Likewise, uterine tissue recombinants were prepared in which epithelium and/or stroma was devoid of progesterone receptor (PR) by using uterine epithelium and stroma of wild-type and PR knockout mice. Progesterone inhibited uterine epithelial apoptosis only in tissue recombinants prepared with PR-positive stroma. The PR status of the epithelium did not affect epithelial apoptotic index. Therefore, the apoptosis in prostatic and uterine epithelia is regulated by androgen and progesterone via stromal AR and PR, respectively. In both cases, epithelial AR or PR is not required for hormonal regulation of epithelial apoptosis in prostatic and uterine epithelium.

Calcitonin potentiates oxygen-glucose deprivation-induced neuronal death

Calcitonin is a hormone that decreases plasma calcium through inhibition of osteolysis. It is used in the treatment of osteoporosis and other bone disorders. Salmon calcitonin is typically utilized in individuals for whom use of estrogen is contraindicated, for example, women at high risk for breast cancer. In addition to actions on bone, calcitonin may have effects on the central nervous system. Receptors for calcitonin are present on central neurons, and salmon calcitonin has been shown to alter neuronal activity. Since salmon calcitonin is used clinically, and it can have actions on neurons, the present studies were designed to determine whether salmon calcitonin could alter death of cortical neurons. The effects of salmon calcitonin on neuronal death induced by exposure of murine cortical cultures to serum deprivation, staurosporine, oxygen-glucose deprivation, kainate, and NMDA were tested. Salmon calcitonin had no effect on apoptotic cell death in cortical cultures. However, acute treatment with salmon calcitonin (1-1000 nM) caused significant potentiation of neuronal death induced by oxygen-glucose deprivation. Similarly, salmon calcitonin potentiated cell death induced by exposure to kainate. In contrast, it did not potentiate cell death induced by exposure to NMDA. In fact, addition of a high concentration (1000 nM) of salmon calcitonin attenuated NMDA toxicity. These results indicate that calcitonin is not a survival factor for cortical neurons; however, it can alter excitotoxic cell death. The most interesting, and disturbing, effect is the ability of low concentrations of salmon calcitonin to potentiate oxygen-glucose deprivation-induced cell death.

Rho family proteins modulate rapid apoptosis induced by cytotoxic T lymphocytes and Fas

Little is known about the role of Rho proteins in apoptosis produced by stimuli evolved specifically to produce apoptosis, such as granzymes from cytotoxic T lymphocytes (CTLs) and Fas. Here we demonstrate that all three Rho family members are involved in CTL- and Fas-induced killing. Dominant-negative mutants of each Rho family member and Clostridium difficile toxin B, an inhibitor of all family members, strongly inhibited the susceptibility of cells to CTL- and Fas-induced apoptosis. Fas-induced caspase-3 activation was inhibited by C. difficile toxin. Activated mutants of each GTPase increased susceptibility to apoptosis, and activation of Cdc42 increased within 5 min of Fas stimulation. In contrast, during the time required for CTL and Fas killing, no apoptosis was produced by dominant-negative or activated mutants or by C. difficile toxin alone. Inhibition of actin polymerization using latrunculin A reduced the ability of constitutively active GTPase mutants to stimulate apoptosis and blocked Fas-induced activation of caspase-3. Furthermore, the ability of Rac to enhance apoptosis was decreased by point mutations reported to block Rac induction of actin polymerization. Rho family proteins may regulate apoptosis through their effects on the actin cytoskeleton.

Multiple autocrine factors including an extracellular matrix protein are required for the proliferation and spreading of human colon carcinoma cells in vitro

The human colon carcinoma cell line LIM1215 proliferates and changes morphology (spread) in a cell density-dependent manner in response to epidermal growth factor (EGF). At high density, production of autocrine transforming growth factor-alpha enables the cells to proliferate and spread in the absence of exogenous EGF or serum. At low cell density (< 1 x 10(4)/cm2) EGF alone fails to elicit a mitogenic or morphological response and requires the presence of conditioned medium (derived from high cell density serum-free culture of the same cells) to exert its effects. This synergy between EGF and LIM1215 conditioned medium was investigated further. Using a low cell density assay and fractionated LIM1215 conditioned medium, we show that EGF-mediated mitogenic and morphological responses are separable. These responses are dependent on the synergistic action of a low molecular weight autocrine survival factor and an extracellular matrix-like spreading factor(s) secreted into the culture medium respectively. We find that under low cell density, serum-free conditions, EGF alone is insufficient to rescue LIM1215 from rapid apoptotic death. Catalase or LIM1215 autocrine survival factor prevent the death of LIM1215 cells and restore their proliferative (but not morphological) response to EGF, suggesting that cell death under these conditions may be the result of oxidative stress. Combination of EGF, partially purified autocrine survival and spreading factors induced proliferation and spreading of low density LIM1215 cells similar to that observed with EGF and unfractionated conditioned medium. GRGDS peptides strongly inhibited the spreading of LIM1215 cells in the presence of EGF and the partially purified autocrine spreading factor, demonstrating that integrin receptors are involved in the spreading process. Comparison of the spreading response of LIM1215 and Colo 526 cells on ASF and various adhesion proteins indicate that ASF is not collagen-I, collagen-IV, fibronectin or vitronectin. Taken together, these results support the concept that the autonomous growth of colon carcinoma cells in vitro is dependent on the synergistic interaction between several autocrine systems.

Simian virus 40 large T antigen J domain and Rb-binding motif are sufficient to block apoptosis induced by growth factor withdrawal in a neural stem cell line

Serum-free mouse embryo (SFME) cells are a neural stem cell line that is dependent upon epidermal growth factor (EGF) for survival. Removal of EGF results in the G1 arrest and apoptosis of SFME cells. We have shown that the expression of simian virus 40 large T antigen in SFME cells blocks apoptosis and allows cell survival and division in the absence of EGF. Therefore the presence of T antigen abrogates the EGF requirement. The steady-state levels of p53, p21, and mdm-2 do not increase as SFME cells undergo apoptosis upon EGF withdrawal. Furthermore, the amino-terminal 136 amino acids (N136) of T antigen are sufficient to block death and to promote proliferation in the absence of EGF, while the carboxy-terminal fragment (C251-708), which contains the p53 binding site, is unable to block death. Taken together, these data suggest that SFME cells deprived of EGF undergo p53-independent apoptosis. Mutations that disrupt either the J domain or Rb family binding abolish the ability of T antigen to block SFME cell apoptosis and to promote cell growth. We conclude that T antigen must act on one or more members of the Rb family to inhibit SFME cell apoptosis.

Growth arrest of melanoma cells is differentially regulated by contact inhibition and serum deprivation

Both growth-factor deprivation and contact inhibition suppress cell growth; however, the mechanisms by which they inhibit cell proliferation may not be identical. The function of antiproliferative genes and the induction of programmed cell death are among the potential differences between these growth-arrest mechanisms. Specifically, an inverse relation between the expression of cyclin-dependent kinase inhibitors (CDKIs) and the susceptibility to apoptosis has been reported. To test this relation, we examined the features of growth arrest in a canine melanoma cell line, TLM1. Both contact inhibition and serum deprivation halted cell-cycle progression of TLM1 cells in the G1 phase. Prolonged growth arrest of the cells without restimulation resulted in apoptosis; conversely, the cells reentered the cell cycle after release from contact inhibition or on restimulation with serum. Cell-to-cell contact, but not serum deprivation, led to the expression of p53 and p21/Waf-1. The expression of p21/Waf-1 did not prevent apoptosis. Moreover, the ectopic overexpression of CDKIs increased apoptosis. These results support the premise that growth arrest induced by contact inhibition and serum deprivation are mediated through distinct mechanisms. Furthermore, CDKIs are not universal inhibitors of apoptosis, and in some cases, they may initiate or enhance the apoptotic program.

EGF-related peptides are involved in the proliferation and survival of MDA-MB-468 human breast carcinoma cells

A majority of human breast carcinomas co-express the epidermal growth factor (EGF)-like peptides CRIPTO (CR), amphiregulin (AR) and transforming growth factor alpha (TGF-alpha). MDA-MB-468 breast carcinoma cells express CR, AR and TGFalpha, while SK-BR-3 cells express CR and TGF-alpha. Anti-sense phosphorothioate oligodeoxynucleotides (AS S-oligos) directed against either CR or TGF-alpha inhibit the proliferation of both cell lines. A 40-50% growth inhibition was observed at a 2-microM concentration of each AS S-oligo. Treatment with the AR AS S-oligo also resulted in a significant inhibition of MDA-MB-468 anchorage dependent growth (ADG). No significant growth inhibition was observed when MDA-MB-468 or SK-BR-3 cells were treated with a mis-sense S-oligo. The AS S-oligos inhibited the expression of AR, CR or TGF-alpha proteins and mRNAs, as assessed by immuno-cytochemistry and semi-quantitative RT-PCR. An additive growth-inhibitory effect was observed when MDA-MB-468 cells were treated with a combination of EGF-related AS S-oligos. Indeed, treatment of MDA-MB-468 cells with a combination of AR, CR and TGF-alpha AS S-oligos resulted in about 70% growth inhibition at a concentration of 0.7 microM each. Finally, treatment of MDA-MB-468 cells with a combination either of the 3 AS S-oligos or of an EGF receptor-blocking antibody (MAb 225) and either CR, AR or TGFalpha AS S-oligos resulted in a significant increase in DNA fragmentation. Our data suggest that the EGF-related peptides are involved in the proliferation and survival of breast carcinoma cells.

Retinoic acid-induced apoptosis is prevented by serum albumin and enhanced by Lipiodol in human hepatoma Hep3B cells

The effects of retinoic acid (RA) on the cell growth and viability of human hepatoma Hep3B cells were examined. We showed that removal of serum in the presence of RA results in cell death in a dose-dependent manner in human hepatoma Hep3B cells. Time-course cell death analysis showed that RA at a dose of 10 microM induces a rapid (48-72 h) fall in cell viability (>95%). The drug-induced cell death was RA-specific, since three RA analogs (retinol, retinal and retinol acetate) did not show any cytocidal activity at an equimolar dose. Fluorescence microscopy and DNA fragmentation analysis showed that Hep3B cells treated with RA underwent a death process highly reminiscent of apoptosis, with chromatin condensation, nuclear fragmentation and the presence of a 180-200 bp DNA fragment ladder. Additionally, we found that RA-induced apoptosis was reduced by 70-80% when the medium was supplemented with serum albumin (human and bovine) at a concentration of 0.05%. However, a variety of known growth factors were ineffective in preventing RA-induced apoptosis. Preincubating serum and serum albumin with Lipiodol restored the apoptotic effects of RA demonstrated in serum-free systems. These data suggest that the binding of RA by serum albumin may have reduced the bioavailability of RA, restricting its apoptotic effects on Hep3B cells. Blocking RA-albumin interactions with a lipid lymphographic contrast medium (Lipiodol) may improve the bioavailability of RA and significantly enhance its apoptotic effect on human hepatoma Hep3B cells.

Measurement of cell death

Apoptosis, or programmed cell death, is a physiological form of cell death that plays a critical role in the development and maintenance of multicellular organisms. Apoptosis is characterized based on morphological and biochemical criteria. Morphological characteristics include cell shrinkage, cytoplasmic condensation, chromatin segregation and condensation, membrane blebbing, and the formation of membrane-bound apoptotic bodies, whereas the biochemical hallmark of apoptosis is internucleosomal DNA cleavage into oligonucleosome-length fragments. A great deal of research is aimed at defining the molecular mechanisms that play a role in apoptosis. As one of the common end points of experiments related to apoptosis is in fact the death of the cell, it has become important to develop reliable assays to measure cell death that may be compared among the various systems being investigated. This chapter reviews many of the current methods used to measure apoptotic cell death and points out strengths and weaknesses of each approach with respect to the system being examined and the questions being asked. Traditional cell-based methods, including light and electron microscopy, vital dyes, and nuclear stains, are described. Biochemical methods such as DNA laddering, lactate dehydrogenase enzyme release, and MTT/XTT enzyme activity are described as well. Additionally, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling of DNA fragments (TUNEL) and in situ end labeling (ISEL) techniques are reviewed, which when used in conjunction with standard flow cytometric staining methods may yield informative data relating cell death to various cellular parameters, including cell cycle and cell phenotype. The use of one or more of the methods described in this chapter for measuring cell death should enable investigators to accurately assess apoptosis in the context of the various models being examined and help define causal relationships between the mechanisms that regulate apoptosis and the cell death event itself.

Apoptosis in the chick wing bud and the permanence of FGF-2 rescue

Two regions of programmed cell death that occur in the mesoderm of developing chick wing buds were studied in vitro. The opaque patch (OP) and posterior necrotic zone (PNZ) were examined for the presence of internucleosomal DNA degradation and for rescue by protein synthesis inhibition, two defining characteristics of apoptosis. Agarose gel electrophoresis showed that DNA from OP and PNZ tissue was cleaved into nucleosome size pieces and this cleavage was prevented by inhibition of protein synthesis with cycloheximide. Both regions showed rescue with cycloheximide as determined by the chromium release assay and examination of electron micrographs. Also, the permanence of basic fibroblast growth factor (EGF-2) rescue in the OP and NPZ was examined using the chromium release assay. While rescue in the OP was found to be permanent, rescue in the PNZ only delayed death while FGF-2 was present in the culture medium. This research shows that death in the OP and PNZ exhibits internucleosomal DNA fragmentation and is prevented by inhibition of protein synthesis with cycloheximide, biochemically characterizing this death as apoptosis. It also suggests that in vitro FGF-2 rescue is permanent in the OP but is merely a delay of cell death in the PNZ.

NGF exhibits a pro-apoptotic activity for human vascular smooth muscle cells that is inhibited by TGFbeta1

Apoptosis of vascular smooth muscle cells (SMCs) has been described in culture and also during remodelling of the artery following injury. However, the mediators that regulate apoptosis in SMCs are unknown. Because neurotrophins, a family of related polypeptide growth factors, including nerve growth factor (NGF) and its cognate receptor TrkA have been shown to be strongly expressed in atherosclerotic lesions, the present study was undertaken to evaluate in vitro, the activity of NGF with regard to apoptosis of confluent cultures of human aortic SMCs. We report here that NGF induced apoptosis of SMCs in a dose-dependent manner. This effect was detected from the concentration of 1 ng/ml and reached a maximum at 100 ng/ml. The concentration that induced a half-maximum effect was 8.8 ng/ml. The pro-apoptotic activity of NGF was time dependent and was significant after 3 h of incubation. The pro-apoptotic activity of NGF was blocked in a dose-dependent manner by K-252a, an inhibitor of TrkA tyrosine phosphorylation, suggesting that a NGF/TrkA signal transduction pathway could activate apoptotic cell death programs in human SMCs. Significantly, NGF-induced apoptosis was inhibited by wortmannin and PD 98059, showing that both PI3 kinase and MEK kinase were involved. At a NGF concentration that strongly induced apoptosis (100 ng/ml), TGFbeta1 which has been identified several times as a protective factor, dose dependently inhibited the pro-apoptotic effect of NGF. The IC50 value was 1.5 ng/ml. These results indicate that, at least in vitro, TGFbeta1 can inhibit the pro-apoptotic activity of NGF for SMCs therefore suggesting that TGFbeta1 has the capacity to diminish the deleterious consequences of an excitotoxic or ischemic injury that might occur during atherogenesis or following angioplasty.

Transneuronal regulation of ribosomes after blockade of ionotropic excitatory amino acid receptors

Elimination of auditory nerve activity results in death and atrophy of neurons in the cochlear nucleus, nucleus magnocellularis (NM), of the chick. One early event believed to lead to cell death and atrophy is the disruption of ribosomes in the NM neuron. A useful assay for visualizing these ribosomal changes is immunolabeling with the antibody Y10B, which recognizes ribosomal RNA. Activity-dependent changes in Y10B labeling have been observed both in vivo, after unilateral cochlea removal and in vitro after unilateral auditory nerve stimulation. Although it is clear that activity is crucial for maintaining ribosomal integrity, the identity of the important transynaptic signal(s) is not known. It is possible that this trophic signal is glutamate, the neurotransmitter release from the auditory nerve. The present study investigates the role of ionotropic glutamate receptors in the activity-dependent regulation of ribosomes, as measured by the Y10B immunoreactivity. Brain slices containing the auditory nerve and NM on both sides were obtained from hatchling chicks. The auditory nerve on one side of the slice was stimulated for 1 h. The slice was then processed for Y10B immunoreactivity. As expected, greater Y10B immunolabeling was observed on the stimulated side of the slice. Unexpectedly, however, this immunolabeling difference was still observed after blocking NMDA receptors (50 microM DL-APV), non-NMDA receptors (20 microM CNQX), or blocking both ionotropic receptor subtypes (APV and CNQX). This was true even though CNQX eliminated driven postsynaptic potentials. These data suggest that ionotropic glutamate receptors are not necessary for the activity-dependent regulation of ribosomes in NM neurons.

Prevention of growth arrest-induced cell death of vascular smooth muscle cells by a product of growth arrest-specific gene, gas6

We have purified Gas6 as a growth-potentiating factor for vascular smooth muscle cells (VSMCs) [Nakano, T. et al. (1995) J. Biol. Chem. 270, 5702-5705]. However, specific production of Gas6 in growth-arrested cells raises an intriguing question as to the physiological function of Gas6. In this study, we found that serum-starved VSMCs secreted some survival factors and depletion of the factors induced cell death of VSMCs. Finally, we demonstrated that cell death was prevented by the addition of Gas6, suggesting that one of the major biological activities of Gas6 is protection of growth-arrested VSMCs from death.

Apoptosis of human seminoma cells upon disruption of their microenvironment

One of the main obstacles encountered when trying to culture human seminoma (SE) cells in vitro is massive degeneration of the tumour cells. We investigated whether dissociation of tumour tissue, to obtain single-cell suspensions for in vitro culture, results in the onset of apoptosis. Using morphological analysis and in situ end labelling, less than 4% of apoptotic tumour cells were detected in intact tissue from 11 out of 14 SEs. In these 11 tumours, apoptosis-specific DNA ladders, indicative of internucleosomal double-strand DNA cleavage, were not detected on electrophoresis gels. In contrast, three SEs with over 12% of apoptotic tumour cells in the intact tissue and all analysed (pure) SE cell suspensions, obtained after mechanical dissociation of intact tumour tissue, showed DNA ladders. Flow cytometric analysis of end labelled SE suspensions showed DNA breaks in up to 85% of the tumour cells. As indicated by cell morphology and DNA degradation, SE cells appear to rapidly enter the apoptotic pathway upon mechanical disruption of their microenvironment. No expression of p53 and of the apoptosis-inhibitor bcl-2 was detectable in intact SE tissue or cell suspensions. Our data suggest that abrogation of apoptosis might be crucial to succeed in culturing human SE cells in vitro.

Antibodies specific for proteolyzed forms of protein kinase C alpha

The activation of protein kinase C (PKC) is irreversibly regulated by limited proteolysis catalyzed by a calcium-activated neutral cysteine protease, calpain. Calpain cleaves PKC alpha at specific sites in the hinge region between the catalytic and the regulatory domains of this kinase. Here we show a novel method for production of antibodies that bind specifically to the catalytic fragment of PKC alpha but not to the unproteolyzed protein. To detect proteolyzed PKC alpha 'cleavage site-directed antibodies,' which recognize amino-terminal regions in the nascent catalytic fragments and do not cross-react with the unproteolyzed enzymes, were raised using synthetic peptides corresponding to the amino-terminal sequences. The synthetic peptides used in this study were the sequences of human PKC alpha at the cleavage sites by m- and mu-types of calpains (LGPAGNKV and VISPSEDRKQPSNNLDRVKLT, respectively) and they are designated as CF alpha 2, CF alpha 4, in this order. Each synthetic peptide was injected into rabbit after conjugation with a carrier protein. The antibodies thus obtained (anti-CF alpha 2 or -CF alpha 4) specifically reacted with either the 46- or 45-kDa catalytic fragment of PKC alpha, respectively, whereas they did not cross-react with other fragments. Furthermore, the antibodies did not bind to the unproteolyzed enzyme nor fragments of PKC alpha obtained by treatment with other proteinases unless the fragment carried the same amino-terminal sequence. When human platelets were treated with calcium ionophore, the catalytic fragments of PKC alpha (45- and 46-kDa) were detected in the cytosol by immunoblotting with the antibodies. However, these antibodies did not bind unproteolyzed 80-kDa PKC alpha, although this form was dominant in the cytosol of the calcium ionophore-treated human platelets. In addition, the 45-kDa catalytic fragment of PKC alpha was detected in an apoptotic human fibroblast TIG-3 cells cultured in serum-free medium. Our method is applicable for analysis of proteolysis in various cellular states.

Cell death induced by beta-amyloid 1-40 in MES 23.5 hybrid clone: the role of nitric oxide and NMDA-gated channel activation leading to apoptosis

The molecular events associated with beta-amyloid-induced neuronal injury remain incompletely characterized. Using a substantia nigra/neuroblastoma hybrid cell line (MES 23.5) synthetic beta-amyloid 1-40 induced a time and dose-dependent apoptotic cell death which was characterized by cell shrinkage and fragmentation of DNA, and was inhibited by aurintricarboxylic acid (ATA), and cycloheximide (CHX). Following beta-amyloid 1-40 treatment, cyclic GMP, an index of NO synthesis, was increased in MES 23.5 cells. The NO scavenger hemoglobin, as well as the NO synthase inhibitors NG-monomethyl-L-arginine acetate (L-NMMA) and L-N5-(1-iminoethyl)ornithine hydrochloride (L-NI0) attenuated such increases. These same inhibitors and scavengers also significantly prevented cytotoxicity. beta-Amyloid also induced an early and transient increase in intracellular calcium as monitored with laser scanning confocal microscopy and Fluo-3 imaging. These induced calcium transients could be significantly blocked by the N-methyl-D-aspartic acid (NMDA) receptor antagonist MK-801. Pretreatment with MK-801 or removal of extracellular Ca2+ also reduced beta-amyloid-induced NO production and neurotoxicity. Furthermore, beta-amyloid neurotoxicity was greatly enhanced in the absence of Mg2+ or in the presence of glutamate or NMDA. These data suggest that beta-amyloid can lead to apoptotic cell death through a NO mediated process possibly triggered by Ca2+ entry through activated NMDA-gated channels.

Activity-dependent regulation of a ribosomal RNA epitope in the chick cochlear nucleus

Elimination of auditory nerve activity results in rapid metabolic changes, cell atrophy, and cell death in nucleus magnocellularis (NM), the cochlear nucleus of the chick. The transneuronal signals involved in the activity-dependent regulation of NM neurons are not well understood. One of the most rapid transneuronal effects is alteration in protein synthesis by NM neurons. Previous studies using an in vitro preparation of the brain stem auditory system suggested that up-regulation of protein synthesis in NM neurons requires the action of some trophic substance released by active auditory nerve fibers. Here, similar results were obtained when measuring changes in immunoreactivity using a monoclonal antibody (Y10B) that recognizes ribosomal RNA. This immunolabeling assay has advantages over the global protein synthesis assay in that it is not sensitive to possible changes in specific activity of the precursor pool or possible differences in the uptake of the labeled amino acids. Unilateral stimulation of the auditory nerve for 1 h resulted in greater immunolabeling of NM neurons on the stimulated side of the slice. This is consistent with previous in vivo results after unilateral deafferentation. Blockade of synaptic transmission by maintaining the slice in a low-Ca2+/high Mg2+ medium prevented the stimulation-induced difference in immunolabeling. Electrical stimulation of the postsynaptic NM neurons alone (antidromic stimulation, via electrical stimulation of NM neuron axons) did not result in greater immunolabeling. Rather, antidromically stimulated neurons tended to show lighter labeling. Thus, the transneuronal regulation of ribosomes in NM neurons appears to require some substance released from the active auditory nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

EGF causes hyperproliferation and apoptosis in T51B cells: involvement of high and low affinity EGFR binding sites

We have recently described an in vitro model for liver homeostasis which involves growing T51B rat liver epithelial cells with 1 nM epidermal growth factor (EGF). There is an initial period of hyperplasia, lasting about 3 days, which is followed by an increase in apoptosis. The cell density returns to around the confluent control level 5 days after EGF addition. The dose response of T51B cells to EGF shows three distinct growth patterns. We have carried out EGF binding studies that suggest that the occupancy of the low affinity binding site of the EGF receptor, is responsible for the hyperproliferation seen when the cells are grown with high doses of EGF. These studies also suggest that the apoptosis could be triggered by down-regulation of the receptor, in a manner analogous to the removal of a trophic hormone in other systems.

The role of DNA fragmentation in apoptosis

The formation of distinct DNA fragments of oligonucleosomal size (180-200 bp lengths) is a biochemical hallmark of apoptosis in many cells. Recent observations also suggest large DNA fragments and even single-strand cleavage events occur during cell death. These observations have raised many questions. What are the types of DNA cleavage observed during apoptosis? What are the nucleases involved? And what is the role of these nucleolytic events in apoptosis?

Inhibitors of free radical formation fail to attenuate direct beta-amyloid25-35 peptide-mediated neurotoxicity in rat hippocampal cultures

The direct neurotoxic action of the beta-amyloid protein, the major constituent of senile plaques, may represent the underlying cause of neuronal degeneration observed in Alzheimer's disease. The apoptotic-mediated neuronal death induced by beta-amyloid appears to reside in its ability to form Ca(2+)-permeable pores in neuronal membranes resulting in an excessive influx of Ca2+ and the induction of neurotoxic cascades. It is possible that during beta-amyloid exposure a Ca(2+)-mediated increase in free radical generation may exceed the defensive capacity of cells and thus lead to cell death. Consequently, in the present study we have investigated the effect of a panoply of antioxidants and inhibitors of free radical formation on the development of beta-amyloid neurotoxicity. Acute exposure of rat hippocampal neurons to "aged" beta-amyloid25-35 peptide (5-50 microM) induced a slow, concentration-dependent apoptotic neurotoxicity (25-85%) during a 6 day exposure. Co-incubation of cultures with beta-amyloid25-35 peptide (25 microM) and inhibitors of nitric oxide synthase and/or xanthine oxidase (NG-monomethyl-L-arginine [1 mM), N omega-nitro-L-arginine [1 mM], oxypurinol [100 microM], allopurinol [100 microM]), important mediators of nitric oxide, superoxide, and hydroxyl radical formation, did not attenuate beta-amyloid neurotoxicity. Similarly, a reduction in free radical generation by selective inhibition of phospholipase-A2 cyclooxygenase, and lipoxygenase activities with quinacrine (0.5 microM), indomethacin (50 microM), and nor-dihydroguaiaretic acid (0.5 microM), respectively, did not reduce the proclivity of beta-amyloid to induce cell death. Exposure of cultures to catalase (25 U/ml) and/or superoxide dismutase (10 U/ml) as well as the free radical scavengers vitamin E (100 microM), vitamin C (100 microM), glutathione (100 microM), L-cysteine (100 microM), N-acetyl-cysteine (100 microM), deferoxamine (5 microM), or haemoglobin (35 micrograms/ml) failed to attenuate the neurotoxic action of beta-amyloid. On the other hand, pre-treatment of cultures with subtoxic concentrations of beta-amyloid peptide significantly increased the vulnerability of neurons to H2O2 exposure and suggest that beta-amyloid peptide renders neurons more sensitive to free radical attack. However, a potential beta-amyloid-mediated increase in free radical formation is not a proximate cause of the neurotoxic mechanism of beta-amyloid in vitro.

Growth factors as survival factors: regulation of apoptosis

Apoptosis is now widely recognized as a common form of cell death and represents a mechanism of cell clearance in many physiological situations where deletion of cells is required. Peptide growth factors, initially characterised as stimulators of cell proliferation, have now been shown to inhibit death in many cell types. Deprivation of growth factors leads to the induction of apoptosis, i.e. condensation of chromatin and degradation in oligonucleosome-sized fragments, formation of plasma and nuclear membrane blebs and cell fragmentation into apoptotic bodies which can be taken up by neighbouring cells. Here we discuss the mechanism(s) by which growth factors may inhibit apoptosis.

Genetically engineering mammalian cell lines for increased viability and productivity

The generation of new host cell lines for the production of foreign proteins can be achieved by cell engineering. This approach can be used to enhance the cell's ability to produce proteins that are properly processed and secreted at elevated levels and consequently can increase the overall productivity of an expression system. One potential target for cell engineering is the modification of the cell's protein folding capacity. The appropriate folding, assembly, localization and secretion of newly synthesized proteins is dependent upon the action of a group of proteins known as molecular chaperones. Improving the host cell's chaperoning capacity might increase the yield of properly folded recombinant proteins by preventing the formation of insoluble aggregates. Another potentially beneficial cell engineering goal is the inhibition of physiological cell death. The productivity of genetically engineered cells is dependent upon the maintenance of high levels of cell viability throughout the bioprocess period. Fluctuations in a cell's environment can trigger a deliberate form of cell death known as apoptosis. The proteins that mediate this self-destruction are currently being characterized. Regulating the expression of these death genes by cellular engineering could limit the loss of productivity that results from the physiological death of the recombinant cell line.

Regulation of glial fibrillary acidic protein in serum-free mouse embryo (SFME) cells by leukemia inhibitory factor and related peptides

The serum-free mouse embryo (SFME) cell line, derived in serum-free medium from 16-day-old mouse embryos, exhibits unique properties. SFME cells grow indefinitely in culture without senescence, require epidermal growth factor (EGF) or fibroblast growth factor (FGF) for survival and are growth-inhibited by serum. The cell line expresses glial fibrillary acidic protein (GFAP) in response to transforming growth factor beta or serum and cells with similar properties can be isolated directly from brain. Culture of SFME cells with leukemia inhibitory factor (LIF), a peptide implicated in neural tissue development, also resulted in expression of GFAP. Other peptides that share signal transduction mechanisms with LIF--ciliary neurotropic factor, oncostatin M and interleukin-6--also caused expression of GFAP in these cells. These effects were inhibited by concentrations of EGF or FGF that promoted rapid cell growth.

Apoptosis is induced by beta-amyloid in cultured central nervous system neurons

The molecular mechanism responsible for the neurodegeneration in Alzheimer disease is not known; however, accumulating evidence suggests that beta-amyloid peptide (A beta P) contributes to this degeneration. We now report that synthetic A beta Ps trigger the degeneration of cultured neurons through activation of an apoptotic pathway. Neurons treated with A beta Ps exhibit morphological and biochemical characteristics of apoptosis, including membrane blebbing, compaction of nuclear chromatin, and internucleosomal DNA fragmentation. Aurintricarboxylic acid, an inhibitor of nucleases, prevents DNA fragmentation and delays cell death. Our in vitro results suggest that apoptosis may play a role in the neuronal loss associated with Alzheimer disease.

Cytokines and growth factors in implantation

A variety of cell types at the blastocyst implantation site produce cytokines and growth factors that could play an important role in the implantation process. Furthermore, receptors for cytokines and growth factors have been detected on embryonic and trophoblastic cells. The purpose of the article is to review the published literature on the effect of cytokines and growth factors on implantation events, and to present recent data from our laboratory on effects of growth factors and cytokines on mouse blastocyst implantation events in vitro.

Expression of a TGF beta regulated, brain-specific mRNA in serum-free mouse embryo (SFME) cells

The serum-free mouse embryo (SFME) cell line was isolated from 16-day-old Balb/c mouse embryos in medium in which the usual serum supplement to the culture medium was replaced by purified growth factors and other components. SFME is an unusual line that does not undergo senescence in vitro, maintains an apparently normal karyotype, and is growth inhibited by serum. Transforming growth factor beta (TGF beta) or calf serum induces expression of the astrocyte marker glial fibrillary acidic protein (GFAP) in these cells, and similar cells can be isolated directly from brain. By differential screening of a cDNA library derived from SFME cells, a calf serum- and TGF beta-regulated 8.5 kb mRNA was identified in SFME cells and the cDNA partially sequenced. This mRNA was detected only in RNA preparations from brain among a number of tissues examined, and may provide an additional marker of TGF beta-regulated differentiation in these cells.

A free-radical hypothesis for the instability and evolution of genotype and phenotype in vitro

It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., an in vitro evolution, which includes crisis, spontaneous transformation ('immortalization'), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by the in vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause of in vitro evolution. We propose an oxyradical hypothesis to explain each of the stages of in vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.

Nerve growth factor withdrawal-induced cell death in neuronal PC12 cells resembles that in sympathetic neurons

Previous studies have shown that in neuronal cells the developmental phenomenon of programmed cell death is an active process, requiring synthesis of both RNA and protein. This presumably reflects a requirement for novel gene products to effect cell death. It is shown here that the death of nerve growth factor-deprived neuronal PC12 cells occurs at the same rate as that of rat sympathetic neurons and, like rat sympathetic neurons, involves new transcription and translation. In nerve growth factor-deprived neuronal PC12 cells, a decline in metabolic activity, assessed by uptake of [3H]2-deoxyglucose, precedes the decline in cell number, assessed by counts of trypan blue-excluding cells. Both declines are prevented by actinomycin D and anisomycin. In contrast, the death of nonneuronal (chromaffin-like) PC12 cells is not inhibited by transcription or translation inhibitors and thus does not require new protein synthesis. DNA fragmentation by internucleosomal cleavage does not appear to be a consistent or significant aspect of cell death in sympathetic neurons, neuronal PC12 cells, or nonneuronal PC12 cells, notwithstanding that the putative nuclease inhibitor aurintricarboxylic acid protects sympathetic neurons, as well as neuronal and nonneuronal PC12 cells, from death induced by trophic factor removal. Both phenotypic classes of PC12 cells respond to aurintricarboxylic acid with similar dose-response characteristics. Our results indicate that programmed cell death in neuronal PC12 cells, but not in nonneuronal PC12 cells, resembles programmed cell death in sympathetic neurons in significant mechanistic aspects: time course, role of new protein synthesis, and lack of a significant degree of DNA fragmentation.

Induction of apoptosis by wild-type p53 in a human colon tumor-derived cell line

A wild-type p53 gene under control of the metallothionein MT-1 promoter was stably transfected into human colon tumor-derived cell line EB. Repeated inductions of the metallothionein wild-type p53 gene with zinc chloride results in progressive detachment of wild-type p53 cells grown on culture dishes. Examination at both the light and electron microscopic level revealed that cells expressing wild-type p53 developed morphological features of apoptosis. DNA from both attached and detached cells was degraded into a ladder of nucleosomal-sized fragments. Expression of wild-type p53 inhibited colony formation in soft agar and tumor formation in nude mice. Furthermore, established tumors in nude mice underwent regression if wild-type p53 expression was subsequently induced. Regressing tumors showed histological features of apoptosis. Thus, regression of these tumors was the result of apoptosis occurring in vivo. Apoptosis may be a normal part of the terminal differentiation program of colonic epithelial cells. Our results suggest that wild-type p53 could play a critical role in this process.

Modulation of tumor cell susceptibility to cytokine-induced cell death by hormones, growth factors, and cell density

The mechanisms controlling "spontaneous" cellular death rates in normal and tumorigenic tissues are largely unknown. An important parameter in this respect is the susceptibility of the target cell to induction of the lytic pathway by appropriate signals. In the present article it is demonstrated in a serum-free in vitro system that the susceptibility of human tumor cells (TC) to induction of lysis by cytokine signals generated during interaction of TC with elutriated human monocytes (MO) is a highly dynamic parameter subject to modulation by hormones, growth factors, and tumor cell density. It was found that growth stimulatory signals such as insulin, and especially epidermal growth factor (EGF), increase lytic susceptibility, whereas hydrocortisone, which does not exert significant growth modulatory effects in these examples, protects TC against the induction of lysis. Increasing TC density above confluence dramatically enhances lytic susceptibility, suggesting interactions between TC to be involved in the induction of their death. In conjunction with previous data demonstrating the insusceptibility of TC, which are forced out of the cell cycle into the quiescent state (G0), the hypothesis is put forward that growth stimulatory factors increase a TC's lytic susceptibility by preventing its transit from G1 to G0 in response to growth inhibitory signals generated during MO/TC interaction. The data support the concept that TC susceptibility to the induction of cell death is a consequence of simultaneously activated growth stimulatory and growth inhibitory signalling pathways.