IL-15 improves skeletal muscle oxidative metabolism and glucose uptake in association with increased respiratory chain supercomplex formation and AMPK pathway activation.

BACKGROUND: IL-15 is believed to play a role in the beneficial impact of exercise on muscle energy metabolism. However, previous studies have generally used supraphysiological levels of IL-15 that do not represent contraction-induced IL-15 secretion. METHODS: L6 myotubes were treated acutely (3 h) and chronically (48 h) with concentrations of IL-15 mimicking circulating (1-10 pg/ml) and muscle interstitial (100 pg/ml -20 ng/ml) IL-15 levels with the aim to better understand its autocrine/paracrine role on muscle glucose uptake and mitochondrial function. RESULTS: Acute exposure to IL-15 levels representing muscle interstitial IL-15 increased basal glucose uptake without affecting insulin sensitivity. This was accompanied by increased mitochondrial oxidative functions in association with increased AMPK pathway and formation of complex III-containing supercomplexes. Conversely, chronic IL-15 exposure resulted in a biphasic effect on mitochondrial oxidative functions and ETC supercomplex formation was increased with low IL-15 levels but decreased with higher IL-15 concentrations. The AMPK pathway was activated only by high levels of chronic IL-15 treatment. Similar results were obtained in skeletal muscle from muscle-specific IL-15 overexpressing mice that show very high circulating IL-15 levels. CONCLUSIONS: Acute IL-15 treatment that mimics local IL-15 concentrations enhances muscle glucose uptake and mitochondrial oxidative functions. That mitochondria respond differently to different levels of IL-15 during chronic treatments indicates that IL-15 might activate two different pathways in muscle depending on IL-15 concentrations. GENERAL SIGNIFICANCE: Our results suggest that IL-15 may act in an autocrine/paracrine fashion and be, at least in part, involved in the positive effect of exercise on muscle energy metabolism.

SirT1-null mice develop tumors at normal rates but are poorly protected by resveratrol.

The function of the class III histone deacetylase, Sir2, in promoting lifespan extension is well established in small model organisms. By analogy, SirT1, the mammalian orthologue of Sir2, is a candidate gene to slow down aging and forestall the onset of age-associated diseases. We have used SirT1-null mice to study the function of SirT1 in susceptibility to tumorigenesis. The number of intestinal polyps induced in mice carrying the Apc(min) mutation was unaffected by the SirT1 genotype although the average polyp size was slightly smaller in the SirT1-null animals. Similarly, the presence or absence of SirT1 had no effect on incidence and tumor load of skin papillomas induced by the classical two-stage carcinogenesis protocol. We found that resveratrol topically applied to the skin profoundly reduced tumorigenesis. This chemoprotective effect was significantly reduced but not ablated in SirT1-null mice, suggesting that part of the protection afforded by resveratrol requires the SirT1-encoded protein. Thus, our results suggest that SirT1 does not behave like a classical tumor-suppressor gene but the antitumor activity of resveratrol is mediated at least in part by SirT1.

Dietary lipids alter the effect of steroids on the transport of fructose following intestinal resection in rats.

BACKGROUND: Glucocorticosteroids alter intestinal morphology and transport. We tested the hypothesis that the desired intestinal adaptive response following intestinal resection may be enhanced further by the locally active steroid budesonide, and by feeding a saturated as compared with a polyunsaturated fatty acid diet. METHODS: An in-vitro uptake method was used to assess intestinal fructose uptake by rats of semisynthetic diets enriched in saturated or polyunsaturated fatty acids, and injected with budesonide or control solution. RESULTS: Budesonide increased ileal fructose uptake in chow and PUFA-fed animals, but reduced jejunal fructose uptake in rats fed SFA. GLUT5 and GLUT2 protein and mRNA did not correlate with changes in fructose uptake. Steroids reduced jejunal proglucagon expression in animals fed chow. Animals fed SFA and given budesonide had a reduction in jejunal ODC mRNA compared with those fed PUFA or chow. CONCLUSIONS: (1) budesonide increases ileal fructose uptake following intestinal resection, and this beneficial effect is prevented by feeding SFA rather than PUFA; (2) fructose uptake does not correlate with GLUT5 and GLUT2 protein and mRNA; (3) ODC and proglucagon may be involved in this adaptive response.

Effects of breakfast meal composition on second meal metabolic responses in adults with Type 2 diabetes mellitus.

OBJECTIVE: We tested the relative importance of a low-glycemic response versus a high glycemic response breakfast meal on postprandial serum glucose, insulin and free fatty acid (FFA) responses after consumption of a standardized mid-day meal in adult individuals with Type 2 diabetes mellitus (DM). DESIGN: Following an overnight fast of 8-10 h, a randomized crossover intervention using control and test meals was conducted over a 3-week-period. A fasting baseline measurement and postprandial measurements at various time intervals after the breakfast and mid-day meal were taken. SUBJECTS: Forty-five Type 2 DM subjects completed the requirements and were included in the study results. INTERVENTIONS: Two different breakfast meals were administered during the intervention: (A) a high glycemic load breakfast meal consisting of farina (kJ 1833; carbohydrate (CHO) 78 g and psylium soluble fiber 0 g), (B) a low-glycemic load breakfast meal consisting of a fiber-loop cereal (kJ 1515; CHO 62 g and psyllium soluble fiber 6.6 g). A standardized lunch was provided approximately 4 h after breakfast. Blood plasma concentrations and area under the curve (AUC) values for glucose, insulin and FFA were measured in response to the breakfast and mid-day lunch. Statistical analyses were performed using SAS software (8.02). Comparisons between diets were based on adjusted Bonferroni t-tests. RESULTS: In post-breakfast analyses, Breakfast B had significantly lower area under the curve (AUC) values for plasma glucose and insulin compared to Breakfast A (P<0.05) (95% confidence level). The AUC values for FFA were higher for Breakfast B than for Breakfast A (P<0.05) (95% confidence level). Post-lunch analyses indicated similar glucose responses for the two breakfast types. Insulin AUC values for Breakfasts B were significantly lower than Breakfast A (P<0.05) (95% confidence level). The AUC values for FFA were unaffected by breakfast type. CONCLUSIONS: These data indicate that ingesting a low-glycemic load meal containing psyllium soluble fiber at breakfast significantly improves the breakfast postprandial glycemic, insulinemic and FFA responses in adults with Type 2 DM. These data revealed no residual postprandial effect of the psyllium soluble fiber breakfast meal beyond the second meal consumed. Thus, there was no evidence of an improvement postprandially in the glycemic, insulinemic and FFA responses after the consumption of the lunch meal.

The Sirt1 deacetylase modulates the insulin-like growth factor signaling pathway in mammals.

The lifespan of the nematode, Caenorhabditis elegans, can be extended by mutations affecting components of the insulin-like growth factor (IGF) signaling cascade or by overexpression of SIR2, an NAD+-dependent protein deacetylase. The mammalian homologue of SIR2, Sirt1, has been shown to modulate the activity of FoxO, a transcription factor that is downstream of the IGF signaling system. These results suggest that Sirt1 ought to affect the IGF pathway. We report here evidence that this is the case in mice. The loss of Sirt1 protein in mice results in increased expression of the IGF binding protein IGFBP1, a secreted modulator of IGF function. A number of the anatomical characteristics of Sirt1-null mice closely resemble those of transgenic mice overexpressing IGFBP1. Our data suggest that Sirt1 is part of a regulatory loop that limits the production of IGFBP1 thereby modulating IGF signaling.

The effects of fiber enrichment of pasta and fat content on gastric emptying, GLP-1, glucose, and insulin responses to a meal.

OBJECTIVE: To assess whether the addition of viscous fiber at an amount recommended by the US FDA to allow a 'low saturated fat, cholesterol, soluble fiber and coronary heart disease', health claim label on a food package (1.7 g psyllium) and/or fat (30 g sunflower oil and 3 g sodium propionate) to a pasta meal would affect gastric emptying, postprandial glucose, insulin and GLP-1 concentrations. DESIGN: Ten subjects participated in a two-by-two single blind randomized crossover study. Four meals containing 50 g of available carbohydrate were consumed: pasta with or without psyllium enrichment served with a tomato sauce with (520 kcal per meal) and without (240 kcal per meal) fat. Blood samples were taken for 240 min following the meal and all subjects consumed a buffet meal at the end of the study. Gastric emptying was measured using the paracetamol absorption test. Blood was analysed for glucose, insulin, GLP-1. Visual analog scales were used to record feelings of hunger, pleasantness and nausea. RESULTS: The psyllium-enriched pasta had no significant effect on gastric emptying or the incremental area under the curve (IAUC) for GLP-1, insulin or glucose compared with the control pasta. The addition of polyunsaturated fat and sodium propionate significantly increased the IAUC for GLP-1 (P<0.001), delaying gastric emptying (P<0.002), and decreasing glucose (P<0.002). CONCLUSIONS: A dose of 1.7 g psyllium did not evoke measurable effects on gastric emptying, postprandial GLP-1, insulin or glucose metabolism. However the addition of 30 g of oil and 3 g of sodium propionate to the pasta did reduce gastric emptying, increase GLP-1 and reduce glucose and insulin concentrations. While this short-term study may have implications in terms of reducing the risk of diabetes and improving coronary risk factor profiles the long term effects of these nutrients need to be studied.

The locally acting glucocorticosteroid budesonide enhances intestinal sugar uptake following intestinal resection in rats.

BACKGROUND AND AIMS: Locally and systemically acting corticosteroids alter the morphology and transport function of the intestine. This study was undertaken to assess the effect of budesonide, prednisone, and dexamethasone on sugar uptake. METHODS: Adult male Sprague Dawley rats underwent transection or resection of 50% of the middle portion of the small intestine, and in vitro uptake of sugars was measured. RESULTS: The 50% enterectomy did not alter jejunal or ileal uptake of glucose or fructose. Prednisone had no effect on the uptake of glucose or fructose in resected animals. In contrast, in resected rats budesonide increased by over 120% the value of the jejunal maximal transport rate for the uptake of glucose, and increased by over 150% ileal uptake of fructose. Protein abundance and mRNA expression of the sodium dependent glucose transporter in brush border membrane (SGLT1), sodium independent fructose transporter in the brush border membrane (GLUT5), sodium independent glucose and fructose transporter in the basolateral and brush border membranes (GLUT2), and Na(+)/K(+) ATPase alpha1 and beta1 did not explain the enhancing effect of budesonide on glucose or fructose uptake. Budesonide, prednisone, and dexamethasone reduced jejunal expression of the early response gene c-jun. In resected animals, expression of the mRNA of ornithine decarboxylase (ODC) in the jejunum was reduced, and corticosteroids reduced jejunal expression of the mRNA of proglucagon. CONCLUSIONS: These data suggest that the influence of corticosteroids on sugar uptake in resected animals may be achieved by post translational processes involving signalling with c-jun, ODC, and proglucagon, or other as yet unknown signals. It remains to be determined whether budesonide may be useful to stimulate the absorption of sugars following intestinal resection in humans.

Intestinal resection- and steroid-associated alterations in gene expression were not accompanied by changes in lipid uptake.

BACKGROUND/AIMS: Glucocorticosteroids alter the morphology and transport function of the intestine of adult rats. This study was undertaken to assess the possible effect on intestinal lipid uptake of the locally acting steroid budesonide, or the systemically active prednisone or dexamethasone. METHODS: Sprague-Dawley rats underwent intestinal transection or 50% intestinal resection. Budesonide, prednisone, dexamethasone, or control vehicle was given for 2 weeks from the time of surgery. Uptake was measured using ring uptake technique. RESULTS: Resection had no effect on the mRNA expression for the early response genes, for proglucagon, or for the ileal lipid binding protein (ILBP), but was associated with reduced jejunal ornithine decarboxylase (ODC) mRNA and with reduced jejunal mRNA for the liver fatty acid binding protein (L-FABP). All three steroids reduced jejunal mRNA for proglucagon and c-jun, and did not affect the mRNA for L-FABP or for ILBP. These resection- and steroid-associated changes in gene expression were not associated with alterations in the intestinal uptake of long chain fatty acids or cholesterol. CONCLUSIONS: The resection-associated alterations in the RNA expression of ODC and L-FABP and the steroid-associated changes in mRNA expression of c-jun and proglucagon were not accompanied by variations in lipid uptake.

Dietary lipids alter the effect of steroids on the uptake of lipids following intestinal resection in rats.

Steroids alter the transport function of the intestine. This study was undertaken to assess the effect of glucocorticosteroids on lipid uptake in rats fed either a saturated (SFA) or a polyunsaturated fatty acid (PUFA) diet. Sprague-Dawley rats underwent transection or 50% resection of the small intestine. The steroids had no effect on the uptake of lipids. However, resection decreased the jejunal uptake of palmitic acid in animals fed SFA and increased the jejunal uptake of palmitic and linoleic acids in those fed PUFA. In animals undergoing intestinal resection, fed SFA, and given control vehicle, there was a reduction in jejunal proglucagon mRNA expression as compared to those fed chow or PUFA. Ornithine decarboxylase (ODC) mRNA expression in the jejunum of resected animals was reduced. In summary, dietary lipids modify the uptake of lipids in resected animals and ODC and proglucagon may be involved in this adaptive response.

Reexpression of a cluster of silenced transgenes is associated with their rearrangement.

Irreversible inactivation or silencing of tumor suppressor genes occurs frequently in the development of cancer. A similar process of silencing can occur after the integration of transfected or microinjected genes into the genomes of recipient cells. The inactivation of transfected genes seems particularly efficient in cells with stem cell characteristics. We have been studying the inactivation of genes transfected into cultured P19 embryonal carcinoma cells and found that the CpG-rich sequence comprising the coding region of the lacZ reporter gene becomes extensively methylated after integration into the genome. 5-Aza-2'-deoxycytidine (5AdC), an inhibitor of DNA methylation, induced the reexpression of silent transgenes in one clone of P19 cells studied in detail. However, the reexpressed genes remained heavily methylated over the lacZ coding sequence. We used pulsed-field gel electrophoresis to analyze the structure of the transgenic locus in the parental and in 5AdC-treated cells and found that, in each of the cells reexpressing the transgene, the cluster of transgenes had been rearranged. Each clone had undergone a different rearrangement that appeared to involve recombination within the tandemly repeated copies of the transgene. Our data seem consistent with the idea that 5AdC induces efficient DNA recombination between tandemly repeated genes and that the reexpression of silenced genes induced by 5AdC might be triggered by the chromatin reorganization at the site of DNA recombination.

Candidate foods in the Asia-Pacific region for cardiovascular protection: relevance of grains and grain-based foods to coronary heart disease.

This review elucidates the importance of healthy dietary and lifestyle habits to reduce morbidity and mortality associated with coronary heart disease (CHD), stroke and cardiovascular diseases. Given published evidence of the poor compliance, increased cost, and decreased benefit/risk ratios of medical therapies, individuals (and populations) are encouraged to adopt healthy life habits. The three most atherogenic dietary risk factors are saturated fat, cholesterol and obesity. Dietary patterns associated with the consumption of grains and grain-based foods predict risk of CHD independently of other life habits. Epidemiological and intervention studies elucidating the strong protective associations of grains, cereal fibers and anti-oxidant vitamins on CHD are reviewed. In summary, the consumption of grains and grain-based cereals is repeatedly associated with the ingestion of many nutrients, e.g., dietary fiber and anti-oxidants, that alter energy balance and nutrient intakes to positively affect cardiovascular health, especially when combined with healthy life habits,

Identification of XAF1 as an antagonist of XIAP anti-Caspase activity.

The inhibitors of apoptosis (IAPs) suppress apoptosis through the inhibition of the caspase cascade and thus are key proteins in the control of cell death. Here we have isolated the protein XIAP-associated factor 1 (XAF1) on the basis of its ability to bind XIAP, a member of the IAP family. XIAP suppresses caspase activation and cell death in vitro, and XAF1 antagonizes these XIAP activities. Expression of XAF1 triggers a redistribution of XIAP from the cytosol to the nucleus. XAF1 is ubiquitously expressed in normal tissues, but is present at low or undetectable levels in many different cancer cell lines. Loss of control over apoptotic signalling is now recognized as a critical event in the development of cancer. Our results indicate that XAF1 may be important in mediating the apoptosis resistance of cancer cells.

Comparison of high- and low-glycemic-index breakfast cereals with monounsaturated fat in the long-term dietary management of type 2 diabetes.

BACKGROUND: Results of 6-wk studies suggest that high-carbohydrate diets are deleterious for people with type 2 diabetes. OBJECTIVE: Our objective was to see whether long-term replacement of dietary monounsaturated fatty acids (MUFAs) with carbohydrate from breakfast cereals with either a high or a low glycemic index (GI) affected blood glucose and lipids in subjects with type 2 diabetes. DESIGN: Subjects with type 2 diabetes (n = 91) were randomly assigned to receive approximately 10% of energy from a low-GI breakfast cereal, a high-GI cereal, or oil or margarine containing MUFA for 6 mo. Eating breakfast cereal was prohibited for subjects in the MUFA group. RESULTS: Seventy-two subjects completed the trial. The subjects who received cereals consumed approximately 10% more energy from carbohydrate than did the subjects in the MUFA group. Changes in glycated hemoglobin, body weight, and fasting cholesterol and triacylglycerol did not differ significantly among groups. HDL cholesterol increased by approximately 10% in the MUFA group compared with subjects who consumed either high- or low-GI cereals (P = 0.002). The ratio of total to HDL cholesterol was higher in the subjects who consumed the high-GI cereal than in the MUFA group at 3 mo but not at 6 mo (diet x time interaction, P = 0.041). During 8-h metabolic profiles, mean plasma insulin was higher and mean free fatty acids were lower in the 2 cereal groups than in the MUFA group (P < 0.05). CONCLUSIONS: A 10% increase in carbohydrate intake associated with breakfast cereal consumption had no deleterious effects on glycemic control or blood lipids over 6 mo in subjects with type 2 diabetes. The increase in plasma insulin and the reduction in free fatty acids associated with higher carbohydrate intake may reduce the rate of progression of diabetes.

Ontogeny of intestinal nutrient transport.

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be lifesaving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.

MAN1, an inner nuclear membrane protein that shares the LEM domain with lamina-associated polypeptide 2 and emerin.

The "MAN antigens" are polypeptides recognized by autoantibodies from a patient with a collagen vascular disease and localized to the nuclear envelope. We now show that one of the human MAN antigens termed MAN1 is a 82.3-kDa protein with an amino-terminal domain followed by two hydrophobic segments and a carboxyl-terminal tail. The MAN1 gene contains seven protein-coding exons and is assigned to human chromosome 12q14. Its mRNA is approximately 5.5 kilobases and is detected in several different cell types that were examined. Cell extraction experiments show that MAN1 is an integral membrane protein. When expressed in transfected cells, MAN1 is exclusively targeted to the nuclear envelope, consistent with an inner nuclear membrane localization. Protein sequence analysis reveals that MAN1 shares a conserved globular domain of approximately 40 amino acids, which we term the LEM module, with inner nuclear membrane proteins lamina-associated polypeptide 2 and emerin. The LEM module is also present in two proteins of Caenorhabditis elegans. These results show that MAN1 is an integral protein of the inner nuclear membrane that shares the LEM module with other proteins of this subcellular localization.

Luminal amino acids acutely decrease intestinal mucosal protein synthesis and protease mRNA in piglets.

Because parenteral feeding is associated with negative N balance and reduced rates of protein synthesis in intestinal mucosa, we hypothesized that luminal exposure to specific amino acids or energy fuels would stimulate intestinal protein synthesis. We studied the acute effects of luminal nutrients on mucosal protein synthesis in the absence of systemic influences. Multiple jejunal segments constructed in piglets deprived of food overnight (n = 6) were randomly assigned to luminal perfusion with saline, 30 mmol/L amino acid mixture with or without 50 mmol/L glucose, or 30 mmol/L glutamine for 90 min. Protein synthesis was then measured by luminal perfusion with L-[2,6-(3)H]-phenylalanine. Energy substrates (glucose, short-chain fatty acids or beta-hydroxybutyrate) had no effect on mucosal protein synthesis. Relative to saline, a 30 mmol/L amino acid mixture or 30 mmol/L glutamine suppressed mucosal protein synthesis by 20-25% (P < 0.05). On the basis of these surprising results, we speculated that a coordinate reduction of proteolytic processes would be required to maintain positive intestinal N balance. Although intestinal protein catabolism cannot be assessed directly, the 30 mmol/L amino acid mixture acutely suppressed mucosal levels of mRNA encoding ubiquitin, 14-kDa ubiquitin conjugating enzyme and the C9 subunit of the proteasome by 20-30% (P < 0.05), demonstrating the sensitivity of components of the ATP-ubiquitin proteolytic pathway to acute regulation by nutrients. The suppression of protein synthesis by luminal amino acids in the absorptive state might lower intestinal utilization of amino acids to ensure efficient allocation of absorbed nutrients to nonintestinal tissues.

Cell-cell interaction modulates myoD-induced skeletal myogenesis of pluripotent P19 cells in vitro.

P19 embryonal carcinoma cells can be induced to differentiate in culture to develop into a wide variety of cell types that include skeletal muscle. Skeletal myogenesis is controlled by transcription factors of the bHLH class, such as myoD. Expression of myoD from transfected genes did not induce significant amounts of myogenesis in P19 cells and it was possible to establish lines of undifferentiated P19[myoD] cells that express high levels of myoD mRNA. These P19[myoD] cells remained undifferentiated when cultured on solid surfaces but when allowed to aggregate, P19[myoD] cells differentiated efficiently into skeletal muscle. Aggregation did not increase the amount of myoD mRNA or the amount of myoD protein in P19[myoD] cells. The myoD protein was present in the nucleus in cells grown as attached or aggregated cultures and, in both culture conditions, the myoD protein was associated with transcription factors of the E2A family and was able to bind DNA at E-box sequences. Thus, the aggregation-induced myogenesis of P19[myoD] cells occurs in the absence of change in the myoD protein, suggesting that the cell-cell contact achieved in aggregates may result in the induction of an activity that increases accessibility of the myoD transcription factor to muscle-specific genes in chromatin.

DNA methylation pattern of a tandemly repeated LacZ transgene indicates that most copies are silent.

The Pgk-1,2-lacZ transgene consists of the ubiquitously-expressed Pgk-1 promoter driving expression of the E. coli lacZ reporter gene. We studied the expression of this transgene in a mouse strain carrying 8-9 tandem copies of this construct. When inherited through the male germ line, the transgene was expressed in all tissues examined but when inherited through the female germ line, the transgene became irreversibly inactivated. The lacZ region is a CpG-rich island that was essentially entirely methylated in all copies of the silent, maternally-inherited transgene. At the active transgenic locus, all but one of the copies were entirely methylated. This one unmethylated copy was adjacent to the cellular DNA and was presumed to be the expressed transgene copy. These results suggest that the tandem repeats of transgenes become silenced by a mechanism associated with DNAmethylation and that proximity to the cellular genome may be important in maintaining expression against the spread of inactivation from the adjacent silent transgenes.

Characterization of transgenic mice with targeted disruption of the catalytic domain of the double-stranded RNA-dependent protein kinase, PKR.

The interferon-inducible, double-stranded RNA-dependent protein kinase PKR has been implicated in anti-viral, anti-tumor, and apoptotic responses. Others have attempted to examine the requirement of PKR in these roles by targeted disruption at the amino terminal-encoding region of the Pkr gene. By using a strategy that aims at disruption of the catalytic domain of PKR, we have generated mice that are genetically ablated for functional PKR. Similar to the other mouse model of Pkr disruption, we have observed no consequences of loss of PKR on tumor suppression. Anti-viral response to influenza and vaccinia also appeared to be normal in mice and in cells lacking PKR. Cytokine signaling in the type I interferon pathway is normal but may be compromised in the erythropoietin pathway in erythroid bone marrow precursors. Contrary to the amino-terminal targeted Pkr mouse, tumor necrosis factor alpha-induced apoptosis and the anti-viral apoptosis response to influenza is not impaired in catalytic domain-targeted Pkr-null cells. The observation of intact eukaryotic initiation factor-2alpha phosphorylation in these Pkr-null cells provides proof of rescue by another eukaryotic initiation factor-2alpha kinase(s).