Eric R. Gauthier

Rapid induction of the intrinsic apoptotic pathway by L‐glutamine starvation

While the amino acid L‐glutamine is known to play a role in the survival of several cell types, the underlying molecular mechanisms are still poorly defined. We show in this report that L‐glutamine starvation rapidly triggered apoptosis in Sp2/0‐Ag14 hybridoma cells. This process involved the activation of both caspases‐9 and ‐3, suggesting that L‐glutamine deprivation initiated an intrinsic apoptotic pathway in Sp2/0‐Ag14 cells. Supporting this idea, the cytosolic release of the mitochondrial proteins SMAC/DIABLO and cytochrome c (Cyt c) was observed, with an initial limited leakage occurring during the first 30 min of L‐glutamine deprivation, followed by a greater release after 60 min. The latter occurred simultaneously with the translocation of the pro‐apoptotic protein Bax to the mitochondria. Finally, a decline in XIAP levels and the activation of caspases‐3 and ‐9 were observed. Thus, L‐glutamine deprivation of Sp2/0‐Ag14 cells rapidly triggers intracellular events, which target the mitochondria, leading to the cytosolic release of apoptogenic factors, the activation of caspases‐9 and ‐3, and the commitment to the death program. This work introduces the Sp2/0Ag14 hybridoma as a unique model for the study of the molecular events underlying the pro‐survival function of L‐glutamine.

Rapid RNA isolation without the use of commercial kits: application to small tissue samples

Abstract We describe an adapted version of the Chomczynski and Sacchi [Anal Biochem (1987) 162:156–159] RNA isolation procedure that can be performed in less than 1 h on small (<15 mg) tissue samples, using commonly available reagents. Our modifications included: (1) one rather than two precipitation steps in the aqueous phase with 99% ethanol and (2) elimination of the 1-h incubation step at –20°C. Our adaptations resulted in RNA yield (μg/mg of tissue) and purity (260/280 nm ratios) comparable to those of the original procedure. Furthermore, the isolated RNA was successfully utilized in reverse transcriptase-polymerase chain reaction assays, suggesting that it was essentially free of carry-over contaminants that could inhibit enzymatic reactions. When tested on tissue sample sizes of 7–12 mg, our adapted procedure allowed the recovery of enough total RNA for use in techniques such as Northern blot analysis. Our modified technique is therefore an inexpensive alternative to commercially available kits when isolating good-quality RNA from very small tissue samples, such as those obtained from needle biopsies.

Prolongation of murine hybridoma cell survival in stationary batch culture by Bcl-xL expression.

While the ectopic expression of the anti-apoptoticprotein Bcl-2 has been shown to significantly increaseboth cell viability and antibody production in batchculture, some cell lines are refractory to thesemanipulations. For example, the NS/O and theP3x63Ag8.653 murine myelomas, which express highendogenous levels of the Bcl-2 homologue Bcl-xL, areboth resistant to the anti-apoptotic effect of Bcl-2.This indicates that, in these cells, Bcl-2 and Bcl-xLmay be functionally redundant. In order to define therole which Bcl-xL plays in hybridoma cultures, we usedthe Sp2/0-Ag14 cell line. This murine hybridomaexpresses low levels of Bcl-xL and is highly sensitiveto apoptosis induction by cycloheximide (CHX) and byamino acid depletion. Bcl-xL-transfected Sp2/0-Ag14cells were more resistant than the wild type and theplasmid-containing cells to apoptosis induced by CHXand by glutamine depletion. Moreover, when compared tothe vector-transfected control, Bcl-xL-Sp2/0 cellsexhibited a substantial increase in viability instationary batch culture. Interestingly, Sp2/0-Ag14cells overexpressing Bcl-xL showed a growth behaviourthat was similar to the parent myeloma cell lineP3x63Ag8.653. Our results suggest that Bcl-xLexpression levels are sufficient to account for therelative robustness of some hybridoma cell lines instationary batch cultures.

Induction of Cellular Necrosis by the Glutathione Peroxidase Mimetic Ebselen

The selenium‐based compound ebselen is a powerful antioxidant, a potent anti‐inflammatory agent and a potential neuroprotective compound. Several studies have demonstrated that part of the biological effect of ebselen is the result of the inhibition of apoptosis. We show in this report that ebselen induced the necrotic cell death of Sp2/0‐Ag14 hybridoma cells. This process was rapid, with over 90% of the cells being dead after a 2 h exposure to 50 μM ebselen. The toxic effect of ebselen could not be prevented by the caspase inhibitor Z‐VAD‐fmk but could be blocked with thiol‐containing compounds. Interestingly, ebselen addition completely prevented caspase activation in cycloheximide‐treated Sp2/O‐Ag14 cells, indicating that this antioxidant interferes with the apoptotic machinery. Our results indicate that some cell types are acutely sensitive to the toxic effect of ebselen, and that ebselen‐induced cell death interferes with apoptotic processes. These observations are of particular importance since ebselen is currently used in clinical trials for possible use as therapeutic agent for stroke. J. Cell. Biochem. 89: 203–211, 2003.

Protection of hybridoma cells against apoptosis by a loop domain-deficient Bcl-xL protein.

The ectopic expression of several members of the Bcl-2 family of anti-apoptotic proteins is a promising strategy to improve the viability of hybridoma cells in culture. However, the impact of post-translational modifications on the function of these proteins in murine hybridomas is unknown. To address this issue, the anti-apoptotic properties of a mutant of Bcl-xL devoid of the so-called “loop domain„ (Bcl-xL▵ 46-83) were investigated using the Sp2/ O-Ag14 hybridoma model. Clones of Sp2/ O-Ag14 cells expressing Bcl-xL▵ 46-83 exhibited resistance against L-glutamine deprivation to similar levels than cells expressing the wild type protein. In contrast, protection against the cytotoxic effects of cycloheximide (CHX) was highly dependent on the level of expression of the Bcl-xL▵ 46-83 mutant. Analysis of the growth behaviour of the transfected cells showed that Bcl-xL▵ 46-83 was superior to the wild type protein in prolonging Sp2/ O-Agl4 cell viability in stationary batch culture. Furthermore, the prolongation of cell viability in batch culture was directly proportional to the level of expression of the mutated protein. Our results indicate that removal of the loop domain improves the anti-apoptotic activity of Bcl-xL in hybridoma cells grown in stationary batch culture.

Peptabody-EGF: A novel apoptosis inducer targeting ErbB1 receptor overexpressing cancer cells

The epidermal growth factor receptor (EGFR) plays a central role in cell life by controlling processes such as growth or proliferation. This receptor is commonly overexpressed in a number of epithelial malignancies and its upregulation is often associated with an aggressive phenotype of the tumor. Thus, targeting of EGFR represents a very promising challenge in oncology, and antibodies raised against this receptor have been investigated as potential antitumor agents. Various putative mechanisms of action were proposed for such antibodies, including decreased proliferation, induction of apoptosis, stimulation of the immunological response against targeted cancer cells or combinations thereof. We report here the development of an alternative high affinity molecule that is directed against EGFR. Production of this pentameric protein, named peptabody‐EGF, includes expression in a bacterial expression system and subsequent refolding and multimerization of peptabody monomers. The protein complex contains 5 human EGF ligand domains, which confer specific binding towards the extracellular portion of EGFR. Receptor binding of the peptabody‐EGF had a strong antiproliferative effect on different cancer cell lines overexpressing EGFR. However, cells expressing constitutive levels of the target receptor were barely affected. Peptabody‐EGF treated cancer cells exhibited typical characteristics of apoptosis, which was found to be induced within 30 min after the addition of the peptabody‐EGF. In vitro experiments demonstrated a significantly higher binding activity for peptabody‐EGF than for the therapeutic monoclonal EGFR antibody Mab‐425. Furthermore, the antitumor action provoked by the peptabody‐EGF was greatly superior than antibody mediated effects when tested on EGFR overexpressing cancer cell lines. These findings suggest a potential application of this high affinity molecule as a novel tool for anti‐EGFR therapy.

Control of late apoptotic events by the p38 stress kinase in L-glutamine-deprived mouse hybridoma cells.

l‐Glutamine (Gln) starvation rapidly triggers apoptosis in Sp2/0‐Ag14 (Sp2/0) murine hybridoma cells. Here, we report on the role played by the stress‐activated kinase p38 mitogen‐activated protein kinase (MAPK) in this process. p38 activation was detected 2 h after Gln withdrawal and, although treatment with the p38 inhibitor SB203580 did not prevent caspase activation in Gln‐starved cells, it reduced the occurrence of both nuclear condensation/fragmentation and apoptotic body formation. Similarly, transfection of Sp2/0 cells with a dominant negative p38 MAPK reduced the incidence of nuclear pyknosis and apoptotic body formation following 2 h of Gln starvation. Gln withdrawal‐induced apoptosis was blocked by the overexpression of the anti‐apoptotic protein Bcl‐xL or by the caspase inhibitor Z‐VAD‐fmk. Interestingly, Bcl‐xL expression inhibited p38 activation, but Z‐VAD‐fmk treatment did not, indicating that activation of this MAPK occurs downstream of mitochondrial dysfunction and is independent of caspases. Moreover, the anti‐oxidant N‐acetyl‐l‐cysteine prevented p38 phosphorylation, showing that p38 activation is triggered by an oxidative stress. Altogether, our findings indicate that p38 MAPK does not contribute to the induction of apoptosis in Gln‐starved Sp2/0 cells. Rather, Gln withdrawal leads to mitochondrial dysfunction, causing an oxidative stress and p38 activation, the latter contributing to the formation of late morphological features of apoptotic Sp2/0 cells. Copyright

GADD153 expression does not necessarily correlate with changes in culture behavior of hybridoma cells

BackgroundThe acute sensitivity of some hybridoma cell lines to culture-related stresses severely limits their productivity. Recent developments in the characterization of the stress signals modulating the cellular phenotype revealed that the pro-apoptotic transcription factor Gadd153 could be used as a marker to facilitate the optimization of mammalian cell cultures. In this report, we analyzed the expression of Gadd153 in Sp2/0-Ag14 murine hybridoma cells grown in stationary batch culture and subjected to two different culture optimization paradigms: L-glutamine supplementation and ectopic expression of Bcl-xL, an anti-apoptotic gene.ResultsThe expression of Gadd153 was found to increase in Sp2/0-Ag14 cells in a manner which coincided with the decline in cell viability. L-glutamine supplementation prolonged Sp2/0-Ag14 cell survival and greatly suppressed Gadd153 expression both at the mRNA and protein level. However, Gadd153 levels remained low after L-glutamine supplementation even as cell viability declined. Bcl-xL overexpression also extended Sp2/0-Ag14 cell viability, initially delayed the induction of Gadd153, but did not prevent the increase in Gadd153 protein levels during the later phase of the culture, when cell viability was declining. Interestingly, L-glutamine supplementation prevented Gadd153 up-regulation in cells ectopically expressing Bcl-xL, but had no effect on cell viability.ConclusionThis study highlights important limitations to the use of Gadd153 as an indicator of cell stress in hybridoma cells.

Ammonium ions improve the survival of glutamine-starved hybridoma cells.

BackgroundAs a consequence of a reprogrammed metabolism, cancer cells are dependent on the amino acid l-glutamine for their survival, a phenomenon that currently forms the basis for the generation of new, cancer-specific therapies. In this paper, we report on the role which ammonium ions, a product of glutaminolysis, play on the survival of l-glutamine-deprived Sp2/0-Ag14 mouse hybridoma cells.ResultsThe supplementation of l-glutamine-starved Sp2/0-Ag14 cell cultures with either ammonium acetate or ammonium chloride resulted in a significant increase in viability. This effect did not depend on the ability of cells to synthesize l-glutamine, and was not affected by the co-supplementation with α-ketoglutarate. When we examined the effect of ammonium acetate and ammonium chloride on the induction of apoptosis by glutamine deprivation, we found that ammonium salts did not prevent caspase-3 activation or cytochrome c leakage, indicating that they did not act by modulating core apoptotic processes. However, both ammonium acetate and ammonium chloride caused a significant reduction in the number of l-glutamine-starved cells exhibiting apoptotic nuclear fragmentation and/or condensation.ConclusionAll together, our results show that ammonium ions promote the survival of l-glutamine-deprived Sp2/0-Ag14 cells and modulate late-apoptotic events. These findings highlight the complexity of the modulation of cell survival by l-glutamine, and suggest that targeting survival-signaling pathways modulated by ammonium ions should be examined as a potential anti-cancer strategy.

Inhibition of MCL-1 by obatoclax sensitizes Sp2/0-Ag14 hybridoma cells to glutamine deprivation-induced apoptosis

For several cancer cell types, the lack of an adequate supply of the amino acidl‐glutamine (Gln) triggers apoptosis, a phenomenon termed Gln addiction. In this report, we examined the role of the anti‐apoptotic proteins of the B‐cell lymphoma 2 (BCL‐2) protein family in the survival of Sp2/0‐Ag14 (Sp2/0) mouse hybridoma cells, a cell line that undergoes apoptosis within minutes of Gln deprivation. Western blot analysis revealed that myeloid cell leukaemia 1 (MCL‐1) was expressed at much higher levels than BCL‐2, B‐cell lymphoma extra‐large and BCL‐2‐like protein 2 making it the prominent pro‐survival BCL‐2 family member in this hybridoma. Gln deprivation triggered a progressive decrease in MCL‐1 protein levels, which coincided with the decrease in Sp2/0 cell survival. Moreover, Sp2/0 cells were much more sensitive to the broad Bcl‐2 homology domain‐3 (BH3) mimetic obatoclax (which targets MCL‐1) than to the more selective drug ABT‐737 (which does not target MCL‐1). Finally, we show that obatoclax sensitizes Sp2/0 cells to apoptosis following Gln starvation. All together, the data presented here reveal that modulation of the pro‐survival protein MCL‐1 is an important step in the sequence of events leading to the initiation of apoptosis in Gln‐starved Sp2/0 cells. Cancer cells require an adequate supply ofl‐glutamine for their survival. Using a mouse hybridoma cell line that is exquisitely sensitive to glutamine starvation, we show that the levels of the pro‐survival BCL‐2 family protein MCL‐1 decrease upon glutamine starvation in a manner that correlates with the loss of cell viability. Moreover, inhibiting MCL‐1 with the drug obatoclax sensitizes hybridoma cells to glutamine starvation. Thus, in some cancer cells, glutamine starvation triggers the inactivation of pro‐survival proteins. Our data suggest that the combined inhibition of glutamine biosynthesis pathways and BCL‐2 proteins may prove effective against some cancers. Copyright