Death domain mutagenesis of KILLER/DR5 reveals residues critical for apoptotic signaling.

The Fas/tumor necrosis factor (TNF)/TRAIL receptors signal death through a cytoplasmic death domain (DD) containing six alpha-helices with positively charged helix 2 interacting with negatively charged helix 3 of another DD. DD mutation occurs in head/neck and lung cancer (TRAIL receptor KILLER/DR5) and in lpr mice (Fas). We examined the apoptotic potential of known KILLER/DR5 lung tumor-derived mutants (n = 6) and DD mutants (n = 18) generated based on conservation with DR4, Fas, Fas-associated death domain (FADD), and tumor necrosis factor receptor 1 (TNFR1). With the exception of Arg-330 required in Fas or FADD for aggregation or for TNFR1 cytotoxicity, surprisingly major loss-of-function KILLER/DR5 alleles (W325A, L334A (lpr-like), I339A, and W360A) contained hydrophobic residues. Loss-of-function of I339A (highly conserved) has not been reported in DDs. Charged residue mutagenesis revealed the following points. 1) E326A, conserved in DR4, is dispensable for death; the homologous residue is positively charged in Fas, TNFR1, and FADD and is critical for DD interactions. 2) K331A, D336A, E338A, K340A, K343A, and D351A have partial loss-of-function suggesting multiple charges stabilize receptor-adapter interactions. Analysis of the tumor-derived KILLER/DR5 mutants revealed the following. 1) L334F has partial loss-of-function versus L334A, whereas E338K has major loss-of-function versus E338A, examples where alanine and tumor-specific substitutions have divergent phenotypes. 2) Unexpectedly, S324F, E326K, K386N, and D407Y have no loss-of-function with tumor-specific or alanine substitutions. Loss-of-function KILLER/DR5 mutants were deficient in recruitment of FADD and caspase 8 to TRAIL death-inducing signaling complexes. The results reveal determinants within KILLER/DR5 for death signaling and drug design.

Enhanced TRAIL sensitivity by p53 overexpression in human cancer but not normal cell lines.

The cytotoxic ligand TRAIL is a promising anti-cancer agent that is entering into clinical trials. We previously identified a major subgroup of TRAIL resistant cancer cell lines with absent, or reduced DR4 expression containing a K441R polymorphism or harboring elevated levels of the caspase activation inhibitor FLIP. In the present study, we explored the use of a gene therapeutic approach utilizing p53, delivered by an adenovirus-p53 (Ad-p53) vector, which directly controls expression of the TRAIL receptor KILLER/DR5 in a panel of 8 cell lines including normal and TRAIL sensitive or resistant cancers. The functional status of the delivered p53 was monitored by detection of induced p21WAF1 expression by immunocytochemistry. In normal cells, which are TRAIL resistant, TRAIL did not reduce cell viability over and above the effect of Ad-p53 alone. All cancer cell lines were sensitive to Ad-p53 and up-regulated expression of the TRAIL receptor KILLER/DR5. TRAIL-resistant cancer cells became more sensitive to TRAIL at low Ad-p53 multiplicities of infection but TRAIL resistance was not completely overcome in one TRAIL-resistant cell line probably because of a high level of expression of FLIP. The results reveal that Ad-p53 induces the TRAIL receptor KILLER/DR5 and, like radiation or chemotherapy may effectively reverse TRAIL resistance.

The caspase 9 inhibitor Z-LEHD-FMK protects human liver cells while permitting death of cancer cells exposed to tumor necrosis factor-related apoptosis-inducing ligand.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis of transformed and cancer cells but not of most normal cells. Recent studies have revealed an unforeseen toxicity of TRAIL toward normal human hepatocytes, thereby bringing into question the safety of systemic administration of TRAIL in humans with cancer. We found that SW480 colon adenocarcinoma, or H460 non-small cell lung cancer cell lines, which are sensitive to TRAIL, were not protected by the caspase 9 inhibitor Z-LEHD-FMK from TRAIL-induced apoptosis. However, a human colon cancer cell line HCT116 and a human embryonic kidney cell line 293, which are sensitive to TRAIL, were protected by Z-LEHD-FMK from TRAIL-mediated death. Both HCT116 and SW480 cells were protected from TRAIL by the caspase 8 inhibitor Z-IETD-FMK, dominant-negative FADD and cellular FLIP-s and interestingly both cell lines displayed caspase 9 cleavage to a similar extent after TRAIL exposure. We confirmed that normal human liver cells are sensitive to TRAIL. Moreover, we found that normal human liver cells could be protected from TRAIL-induced apoptosis by simultaneous exposure to Z-LEHD-FMK. A similar brief exposure to TRAIL plus Z-LEHD-FMK inhibited colony growth of SW480 but not HCT116 cells. Because some cancer cell lines are not protected from TRAIL-mediated killing by Z-LEHD-FMK, we believe that a brief period of caspase 9 inhibition during TRAIL administration may widen the therapeutic window and allow cancer cell killing while protecting normal liver cells. This strategy could be further developed in the effort to advance TRAIL into clinical trials.

Bax is a transcriptional target and mediator of c-myc-induced apoptosis.

The c-Myc oncoprotein is a transcription factor involved in cellular transformation as well as apoptotic cell death. We show here that over-expression of c-Myc delivered by an adenovirus vector up-regulates endogenous proapoptotic bax mRNA and protein expression in human cells. In contrast, the cytotoxic tumor necrosis factor-related apoptosis-inducing ligand induces cell death without up-regulating bax expression. c-Myc/Max heterodimers bind to canonical E-box elements located in the bax promoter region as demonstrated by electrophoretic mobility shift analysis and DNaseI foot-printing assays. Analysis of bax regulatory region mutants suggests a model involving myc-dependent activation as well as relief of repression through distinct E-box elements. c-Myc-null cells are deficient in bax-promoter activation as compared with wild-type c-Myc-expressing cells. Overexpression of c-Myc in serum-starved human or mouse embryonic cells leads to apoptosis which is significantly reduced in the presence of growth factor-containing serum. c-Myc-induced apoptosis appears to be deficient in bax-null as compared with bax-wild-type mouse embryonic fibroblasts. The results suggest that the cell death-promoting gene bax is directly downstream of c-Myc in a pathway leading to apoptosis.

Repression of BRCA1 through a feedback loop involving p53.

The BRCA1 and p53 tumor suppressors have been shown to interact and cooperate to activate transcription of p53-responsive genes. In this study, we show that BRCA1 is initially up-regulated, followed by a reduction to below basal levels in response to treatment with the DNA-damaging agents adriamycin and mitomycin C, and that the reduction of BRCA1 expression is dependent on the presence of wild-type p53. Elimination of p53 by expression of human papilloma virus E6 resulted in an inability to down-regulate BRCA1 in response to adriamycin. Ectopic expression of p53 resulted in a rapid decrease in BRCA1 protein and RNA levels and BRCA1 promoter-driven luciferase activity even in null p21 cells deficient in p53-dependent G(1) arrest. ATM(-)(/-) lymphoblastoid cells were deficient in their ability to reduce BRCA1 protein in response to DNA damage, whereas the wild-type counterparts reduced BRCA1 protein levels after exposure to adriamycin. These results, in conjunction with others, suggest a loop wherein BRCA1 initially participates in accumulation of p53 protein, whereas later p53 acts to reduce BRCA1 expression.

Homozygous deletion of the death receptor DR4 gene in a nasopharyngeal cancer cell line is associated with TRAIL resistance.

The family of tumor necrosis factor related apoptosis inducing ligand (TRAIL) receptors, including the pro-apoptotic DR4 and p53-regulated KILLER/DR5, as well as the decoys TRID and TRUNDD, are all located on human chromosome 8p21-22. This region of the genome is frequently altered in head and neck cancer. We previously reported that KILLER/DR5 can be mutationally inactivated in head and neck cancer. Here, we report that the FaDu nasopharyngeal cancer cell line contains an abnormal chromosome 8p21-22 region. In addition, there appears to be a homozygous deletion involving DR4 but not KILLER/DR5 in FaDu cells. The homozygous loss within the DR4 gene encompasses its death domain, which is required for apoptotic signaling. The deletion of DR4 in FaDu cells is associated with resistance to the cytotoxic effects of TRAIL. Re-introduction of wild-type DR4 leads to apoptosis and restores TRAIL sensitivity of FaDu cells. These observations suggest that the death inducing DR4 receptor gene may be a rare target for inactivation in human cancer and that DR4 loss may contribute to resistance to TRAIL therapy.

Chromosome and cell wall segregation in Streptococcus faecium ATCC 9790.

Segregation was studied by measuring the positions of autoradiographic grain clusters in chains formed from single cells containing on average less than one radiolabeled chromosome strand. The degree to which chromosomal and cell wall material cosegregated was quantified by using the methods of S. Cooper and M. Weinberger, dividing the number of chains labeled at the middle. This analysis indicated that in contrast to chromosomal segregation in Escherichia coli and, in some studies, to that in gram-positive rods, chromosomal segregation in Streptococcus faecium was slightly nonrandom and did not vary with growth rate. Results were not significantly affected by strand exchange. In contrast, labeled cell wall segregated predominantly nonrandomly.

Cell cycle changes in the buoyant density of exponential-phase cells of Streptococcus faecium.

Cell buoyant densities were determined by centrifugation in Percoll gradients containing exponential-phase cells of Streptococcus faecium ATCC 9790 grown at a mass doubling time of about 33 min. This bacterium showed the highest average density values (1.13 g/ml) measured to date for any eucaryotic or procaryotic organism. Fractions having the highest densities were enriched with cells that were in the process of dividing or had just divided. These high-density fractions were also enriched with cells that had newly initiated sites of cell wall growth. It appears that S. faecium shows minimum cell densities in the midportion of its cycle.

Autoradiographic studies of chromosome replication during the cell cycle of Streptococcus faecium.

Analysis of the distribution of autoradiographic grains around cells of Streptococcus faecium which had been either continuously or pulse-labeled with tritiated thymidine (mass doubling time, 90 min) showed a non-Poisson distribution even when the distribution of cell sizes in the populations studied was taken into account. These non-Poisson distributions of grains were assumed to reflect the discontinuous nature of chromosome replication. To study this discontinuous process further, we fitted an equation to the grain distribution observed for the pulse-labeled cells that assumed that in any population of cells there were subpopulations in which there were zero, one, or two replicating chromosomes. This analysis predicted an average time for chromosome replication and for the period between completion of rounds of chromosome replication and division of 55 and 43 min, respectively, which were in excellent agreement with estimates made by other techniques. The present investigation extended past studies in indicating that the initiation and completion of rounds of chromosome replication are poorly phased with increases in cell volume and that the amount of chromosome replication may be different in different cell halves.

Autoradiographic studies of the synthesis of RNA and protein as a function of cell volume in Streptococcus faecium.

Mid-exponential-phase cultures were either labeled continuously with tritiated leucine and uracil or pulse-labeled with tritiated leucine. The amount of leucine and uracil incorporated into protein or RNA per cell was determined by grain counts of autoradiographs of cells seen in electron micrographs; the volume of each cell was determined by three-dimensional reconstruction. The average number of autoradiographic grains around cells continuously labeled with uracil and leucine increased linearly with cell volume. In contrast, while the average grain count around cells pulse-labeled with leucine increased in a near-linear fashion over most of the volume classes, less than the expected number of grains were seen around cells in large- and small-size classes. The distribution of grains around cells from both the continuously and pulse-labeled populations could be fit at the 5% confidence level with a Poisson distribution modified to take into consideration the volume distribution of each population of cells analyzed. These findings suggested that large changes in the density of RNA and protein do not occur in most cells as they increase in size; however, there may be decreases in the rate of protein synthesis in some large and small cells. The decrease in the rate of protein synthesis appears consistent with the hypothesis that new sites of envelope growth must be introduced into cells that are close to the division event to restore rapid growth.

Inhibition of beta-lactam antibiotics at two different times in the cell cycle of Streptococcus faecium ATCC 9790.

Treatment of Streptococcus faecium ATCC 9790 with sublytic concentrations of beta-lactam antibiotics revealed two different division blocks in the cell division cycle. One block, induced by N-formimidoyl thienamycin and methicillin, occurred before the completion of chromosome replication, whereas the other, induced by cefoxitin and cephalothin, took place later in the cycle. In addition, these antibiotics gave rise to distinct morphological forms; the antibiotics acting at the earlier block point produced mainly "dumbbells," whereas those affecting the later time formed "lemons." When used in combination N-formimidoyl thienamycin and cefoxitin exerted synergistic killing on this strain. These data suggest that beta-lactam antibiotics have at least two sites of action in S. faecium.

Isolation of cilia from porcine tracheal epithelium and extraction of dynein arms.

Milligram amounts of mammalian ciliary axonemes were isolated from porcine tracheas. These were reactivated upon addition of ATP, indicating intact functional capability with a mean beat frequency at 37 degrees C of 8.2 Hz. Electron microscopy showed typical ultrastructure of the isolated demembranated axonemes. Electrophoresis into polyacrylamide gradient gels containing sodium dodecyl sulfate revealed reproducible protein profiles from ten different tracheal preparations. Four major protein bands were observed in the 300-330 K molecular weight region, as well as tubulin at 51-54K. Extraction of the isolated tracheal axonemes with 0.6M KCl removed the outer dynein arms seen in electron microscopic cross-section of axonemes, preferentially solubilized two of the high molecular weight proteins at 320 and 330 K, and resulted in a three- to four-fold increase in ATPase specific activity. Sedimentation of the dialyzed salt extract on a 5-30% sucrose density gradient and subsequent fractionation yielded two peaks of ATPase activity. The faster migrating, 19S major ATPase peak correlated with the 320 and 330 K proteins, and two other proteins at 81 and 67 K. The slower sedimenting, 12S minor ATPase peak corresponded to a 308 K protein and two smaller proteins at 33 and 48 K. Thus, the outer dynein arm of tracheal cilia appeared to be associated with at least two high molecular weight proteins. These results demonstrate that adequate quantities of functionally intact axonemes can be reproducibly isolated from porcine tracheas, allowing further fractionation and analysis of mammalian cilia.