A quantitative protein interaction network for the ErbB receptors using protein microarrays

Although epidermal growth factor receptor (EGFR; also called ErbB1) and its relatives initiate one of the most well-studied signalling networks, there is not yet a genome-wide view of even the earliest step in this pathway: recruitment of proteins to the activated receptors. Here we use protein microarrays comprising virtually every Src homology 2 (SH2) and phosphotyrosine binding (PTB) domain encoded in the human genome to measure the equilibrium dissociation constant of each domain for 61 peptides representing physiological sites of tyrosine phosphorylation on the four ErbB receptors. This involved 77,592 independent biochemical measurements and provided a quantitative protein interaction network that reveals many new interactions, including ones that fall outside of our current view of domain selectivity. By slicing through the network at different affinity thresholds, we found surprising differences between the receptors. Most notably, EGFR and ErbB2 become markedly more promiscuous as the threshold is lowered, whereas ErbB3 does not. Because EGFR and ErbB2 are overexpressed in many human cancers, our results suggest that the extent to which promiscuity changes with protein concentration may contribute to the oncogenic potential of receptor tyrosine kinases, and perhaps other signalling proteins as well.

Neutrophils Suppress Intraluminal NK Cell-Mediated Tumor Cell Clearance and Enhance Extravasation of Disseminated Carcinoma Cells

Immune cells promote the initial metastatic dissemination of carcinoma cells from primary tumors. In contrast to their well-studied functions in the initial stages of metastasis, the specific roles of immunocytes in facilitating progression through the critical later steps of the invasion-metastasis cascade remain poorly understood. Here, we define novel functions of neutrophils in promoting intraluminal survival and extravasation at sites of metastatic dissemination. We show that CD11b(+)/Ly6G(+) neutrophils enhance metastasis formation via two distinct mechanisms. First, neutrophils inhibit natural killer cell function, which leads to a significant increase in the intraluminal survival time of tumor cells. Thereafter, neutrophils operate to facilitate extravasation of tumor cells through the secretion of IL1β and matrix metalloproteinases. These results identify neutrophils as key regulators of intraluminal survival and extravasation through their cross-talk with host cells and disseminating carcinoma cells.

SIGNIFICANCE

This study provides important insights into the systemic contributions of neutrophils to cancer metastasis by identifying how neutrophils facilitate intermediate steps of the invasion-metastasis cascade. We demonstrate that neutrophils suppress natural killer cell activity and increase extravasation of tumor cells. Cancer Discov; 6(6); 630-49. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 561.

The systemic response to surgery triggers the outgrowth of distant immune-controlled tumors in mouse models of dormancy

Patients undergoing surgical resection of primary breast tumors confront a risk for metastatic recurrence that peaks sharply 12 to 18 months after surgery. The cause of early metastatic relapse in breast cancer has long been debated, with many ascribing these relapses to the natural progression of the disease. Others have proposed that some aspect of surgical tumor resection triggers the outgrowth of otherwise-dormant metastases, leading to the synchronous pattern of relapse. Clinical data cannot distinguish between these hypotheses, and previous experimental approaches have not provided clear answers. Such uncertainty hinders the development and application of therapeutic approaches that could potentially reduce early metastatic relapse. We describe an experimental model system that definitively links surgery and the subsequent wound-healing response to the outgrowth of tumor cells at distant anatomical sites. Specifically, we find that the systemic inflammatory response induced after surgery promotes the emergence of tumors whose growth was otherwise restricted by a tumor-specific T cell response. Furthermore, we demonstrate that perioperative anti-inflammatory treatment markedly reduces tumor outgrowth in this model, suggesting that similar approaches might substantially reduce early metastatic recurrence in breast cancer patients.

Functional genomic landscape of cancer-intrinsic evasion of killing by T cells

The genetic circuits that allow cancer cells to evade destruction by the host immune system remain poorly understood^1-3. Here, to identify a phenotypically robust core set of genes and pathways that enable cancer cells to evade killing mediated by cytotoxic T lymphocytes (CTLs), we performed genome-wide CRISPR screens across a panel of genetically diverse mouse cancer cell lines that were cultured in the presence of CTLs. We identify a core set of 182 genes across these mouse cancer models, the individual perturbation of which increases either the sensitivity or the resistance of cancer cells to CTL-mediated toxicity. Systematic exploration of our dataset using genetic co-similarity reveals the hierarchical and coordinated manner in which genes and pathways act in cancer cells to orchestrate their evasion of CTLs, and shows that discrete functional modules that control the interferon response and tumour necrosis factor (TNF)-induced cytotoxicity are dominant sub-phenotypes. Our data establish a central role for genes that were previously identified as negative regulators of the type-II interferon response (for example, Ptpn2, Socs1 and Adar1) in mediating CTL evasion, and show that the lipid-droplet-related gene Fitm2 is required for maintaining cell fitness after exposure to interferon-γ (IFNγ). In addition, we identify the autophagy pathway as a conserved mediator of the evasion of CTLs by cancer cells, and show that this pathway is required to resist cytotoxicity induced by the cytokines IFNγ and TNF. Through the mapping of cytokine- and CTL-based genetic interactions, together with in vivo CRISPR screens, we show how the pleiotropic effects of autophagy control cancer-cell-intrinsic evasion of killing by CTLs and we highlight the importance of these effects within the tumour microenvironment. Collectively, these data expand our knowledge of the genetic circuits that are involved in the evasion of the immune system by cancer cells, and highlight genetic interactions that contribute to phenotypes associated with escape from killing by CTLs.

Protein kinase C α is a central signaling node and therapeutic target for breast cancer stem cells

The epithelial-mesenchymal transition program becomes activated during malignant progression and can enrich for cancer stem cells (CSCs). We report that inhibition of protein kinase C α (PKCα) specifically targets CSCs but has little effect on non-CSCs. The formation of CSCs from non-stem cells involves a shift from EGFR to PDGFR signaling and results in the PKCα-dependent activation of FRA1. We identified an AP-1 molecular switch in which c-FOS and FRA1 are preferentially utilized in non-CSCs and CSCs, respectively. PKCα and FRA1 expression is associated with the aggressive triple-negative breast cancers, and the depletion of FRA1 results in a mesenchymal-epithelial transition. Hence, identifying molecular features that shift between cell states can be exploited to target signaling components critical to CSCs.

Activation of PKA leads to mesenchymal-to-epithelial transition and loss of tumor-initiating ability

The epithelial-to-mesenchymal transition enables carcinoma cells to acquire malignancy-associated traits and the properties of tumor-initiating cells (TICs). TICs have emerged in recent years as important targets for cancer therapy, owing to their ability to drive clinical relapse and enable metastasis. Here, we propose a strategy to eliminate mesenchymal TICs by inducing their conversion to more epithelial counterparts that have lost tumor-initiating ability. We report that increases in intracellular levels of the second messenger, adenosine 3',5'-monophosphate, and the subsequent activation of protein kinase A (PKA) induce a mesenchymal-to-epithelial transition (MET) in mesenchymal human mammary epithelial cells. PKA activation triggers epigenetic reprogramming of TICs by the histone demethylase PHF2, which promotes their differentiation and loss of tumor-initiating ability. This study provides proof-of-principle for inducing an MET as differentiation therapy for TICs and uncovers a role for PKA in enforcing and maintaining the epithelial state.

Combined modality program with possible organ preservation for invasive bladder carcinoma: results of RTOG protocol 85-12

PURPOSE

This Phase II study was designed to test the tolerance and effectiveness of concurrent cisplatin-radiotherapy in the treatment of invasive bladder cancer. Objectives were to determine toxicity, complete response rate, bladder preservation rate, and survival.

METHODS AND MATERIALS

Patients with invasive bladder cancer, clinical Stages T2-4, NO-2 or NX, MO were treated with pelvic radiotherapy 40 Gy in 4 weeks and cisplatin 100 mg/m2 on days 1 and 22. Complete responders were given an additional 24 Gy bladder boost plus a third dose of cisplatin; patients with residual tumor after 40 Gy were assigned radical cystectomy.

RESULTS

The complete remission rate following cisplatin and 40 Gy for evaluable cases was 31/47 (66%). Acute toxicity was acceptable with only two patients not completing induction therapy. Patients with poorly differentiated tumors were more likely to achieve complete remission. Of fully evaluable patients, 28/42 (67%) achieved complete remission with induction therapy, 11 remain continuously in remission, and eight have relapsed with bladder as the only site of failure. Five of these eight cases relapsed with noninvasive tumor. Of the 14 patients who failed to achieve complete remission, only three remain disease-free. Median survival is not reached, with 17/42 (19/48) deaths reported. Actuarial survival is 64% at 3 years.

CONCLUSION

This combined cisplatin-radiotherapy regimen was moderately well-tolerated and associated with tumor clearance in 66% of patients treated. Isolated bladder recurrences with invasive carcinoma are infrequent. Better definition of pretreatment selection criteria is needed if combined modality treatment is to achieve disease control and organ preservation for patients with bladder cancer.

Ca2+ uptake by cardiac sarcoplasmic reticulum from patients with idiopathic dilated cardiomyopathy

We measured Ca2+ uptake by sarcoplasmic reticulum prepared from left ventricular myocardium obtained from six nonfailing human hearts and nine excised hearts from patients with class IV idiopathic dilated cardiomyopathy. Ca2+ uptake had a Vmax of 593 +/- 82 nmol/mg-min, a K0.5 of 0.68 +/- 0.07 microM, and an nHill of 1.7 +/- 0.1 in the nonfailing hearts. The corresponding values in the excised failing hearts were 593 +/- 36 nmol/mg-min, 0.63 +/- 0.03 microM, and 1.6 +/- 0.1. The beta-receptor density in crude sarcolemma prepared from left ventricular myocardium was 110.0 +/- 15.3 fmol/mg in the unmatched donors and 52.1 +/- 4.5 fmol/mg in the excised failing hearts. These results suggest that abnormal Ca2+ handling in idiopathic dilated cardiomyopathy in humans is not the result of any intrinsic alteration of Ca2+ uptake by sarcoplasmic reticulum.

High- and low-affinity epidermal growth factor receptor-ligand interactions activate distinct signaling pathways

Signaling mediated by the Epidermal Growth Factor Receptor (EGFR) is crucial in normal development, and aberrant EGFR signaling has been implicated in a wide variety of cancers. Here we find that the high- and low-affinity interactions between EGFR and its ligands activate different signaling pathways. While high-affinity ligand binding is sufficient for activation of most canonical signaling pathways, low-affinity binding is required for the activation of the Signal transducers and activators of transcription (Stats) and Phospholipase C-gamma 1 (PLCγ1). As the Stat proteins are involved in many cellular responses including proliferation, migration and apoptosis, these results assign a function to low-affinity interactions that has been omitted from computational models of EGFR signaling. The existence of receptors with distinct signaling properties provides a way for EGFR to respond to different concentrations of the same ligand in qualitatively different ways.

Sarcoplasmic reticulum-associated cyclic adenosine 5'-monophosphate phosphodiesterase activity in normal and failing human hearts

Sarcoplasmic reticulum-associated cAMP phosphodiesterase activity was examined in microsomes prepared from the left ventricular myocardium of eight heart transplant recipients with end-stage idiopathic dilated cardiomyopathy and six unmatched organ donors with normal cardiac function. At cAMP concentrations less than or equal to 1.0 microM, sarcoplasmic reticulum-associated cAMP phosphodiesterase activity was functionally homogeneous. cAMP phosphodiesterase activity was inhibited competitively by cGMP (Ki = 0.031 +/- 0.008 microM) and the cilostamide derivative OPC 3911 (Ki = 0.018 +/- 0.004 microM), but was essentially insensitive to rolipram. Vmax and Km were 781.7 +/- 109.2 nmol/mg per min and 0.188 +/- 0.031 microM, respectively, in microsomes prepared from nonfailing hearts and 793.9 +/- 68.9 nmol/mg per min and 0.150 +/- 0.027 microM in microsomes prepared from failing hearts. Microsomes prepared from nonfailing and failing hearts did not differ with respect to either the ratio of cAMP phosphodiesterase activity to ATP-dependent Ca2+ accumulation activity or the sensitivity of cAMP phosphodiesterase activity to inhibition by OPC 3911. These data suggest that the diminished inotropic efficacy of phosphodiesterase inhibitors in failing human hearts does not result from changes in the level, kinetic properties, or pharmacologic sensitivity of sarcoplasmic reticulum-associated cAMP phosphodiesterase activity.

Phospholamban-mediated stimulation of Ca2+ uptake in sarcoplasmic reticulum from normal and failing hearts

Studies in animal models have suggested that alterations affecting phospholamban-mediated stimulation of Ca2+ uptake by sarcoplasmic reticulum are involved in the pathophysiology of heart disease. A monoclonal antibody that binds to phospholamban and stimulates Ca2+ uptake was used to characterize phospholamban-mediated effects in human cardiac sarcoplasmic reticulum and to compare these effects in tissue from normal and failing hearts. Stimulation of Ca2+ uptake by anti-phospholamban monoclonal antibody simulated the effect of phosphorylation of phospholamban by cAMP-dependent protein kinase. Binding of anti-phospholamban antibody reduced the K0.5 of the Ca2(+)-transporting ATPase from 0.53 microM [( Ca2+]) to 0.29 microM [( Ca2+]), without affecting Vmax or nHill. At 0.2 microM Ca2+, stimulation was 1.93-fold in sarcoplasmic reticulum prepared from normal human left ventricular myocardium and 1.94-fold in sarcoplasmic reticulum prepared from the left ventricular myocardium of patients with heart failure resulting from idiopathic dilated cardiomyopathy. Stimulation of Ca2+ uptake in canine cardiac sarcoplasmic reticulum under identical conditions was 1.89-fold. Phospholamban-mediated stimulation of Ca2+ uptake in human cardiac sarcoplasmic reticulum is thus comparable in magnitude to that observed in other species and results from an increase in the apparent affinity of the Ca2(+)-transporting ATPase for Ca2+. The pathogenesis of heart failure in idiopathic dilated cardiomyopathy does not, however, appear to involve intrinsic alterations of this mechanism.

Genome-wide CRISPR screen identifies PRC2 and KMT2D-COMPASS as regulators of distinct EMT trajectories that contribute differentially to metastasis

Epithelial-mesenchymal transition (EMT) programs operate within carcinoma cells, where they generate phenotypes associated with malignant progression. In their various manifestations, EMT programs enable epithelial cells to enter into a series of intermediate states arrayed along the E-M phenotypic spectrum. At present, we lack a coherent understanding of how carcinoma cells control their entrance into and continued residence in these various states, and which of these states favour the process of metastasis. Here we characterize a layer of EMT-regulating machinery that governs E-M plasticity (EMP). This machinery consists of two chromatin-modifying complexes, PRC2 and KMT2D-COMPASS, which operate as critical regulators to maintain a stable epithelial state. Interestingly, loss of these two complexes unlocks two distinct EMT trajectories. Dysfunction of PRC2, but not KMT2D-COMPASS, yields a quasi-mesenchymal state that is associated with highly metastatic capabilities and poor survival of patients with breast cancer, suggesting that great caution should be applied when PRC2 inhibitors are evaluated clinically in certain patient cohorts. These observations identify epigenetic factors that regulate EMP, determine specific intermediate EMT states and, as a direct consequence, govern the metastatic ability of carcinoma cells.

Treatment-related morbidity in phase III RTOG studies of extended-field irradiation for carcinoma of the prostate

The incidence, severity, time of onset, and clinical course of complications of treatment have been reviewed in the RTOG studies of extended field irradiation in carcinoma of the prostate. A total of 526 patients, entered between 1976 and 1980 and followed for a minimum of 18 months, comprised the study population. In most instances of treatment-related morbidity, the symptoms were recorded during the first several months to 1 year following completion of treatment. Late occurrences, however, were not uncommon in certain types of radiation-produced injuries, such as proctitis, hematuria, and urethral strictures. Resolution of symptoms has been observed in a large proportion of patients including those with late occurrences of treatment-related morbidity, although the probability and the pattern of resolution differed considerably from one type of morbidity to another. Symptoms of cystitis are more likely to abate than those of proctitis. In patients who develop symptoms of proctitis the probability of persistence of symptoms beyond the second year following occurrence has been estimated at 20%-30%. Hematuria and symptoms secondary to urethral strictures seem to be even more likely to recur or persist, while genital and leg edema remain chronic in the majority of patients.

The prognostic significance of race and survival from prostate cancer based on patients irradiated on Radiation Therapy Oncology Group protocols (1976-1985)

A number of studies have identified race as a prognostic factor for survival from prostate cancer. To evaluate the prognostic significance of race in a controlled setting, we evaluated 1294 patients treated on three prospective randomized trials conducted by the Radiation Therapy Oncology Group between 1976 to 1985. One-hundred and twenty (9%) of the patients were coded as black, while 1077 (83%) of the patients were coded as white. Protocol 7506 included 607 patients with clinical Stage T3-T4Nx or T1b-T2N1-2. Protocol 7706 included 484 patients with clinical Stage T1b or T2 who were node negative. Protocol 8307 included 203 Stage T2b-T4 patients with no lymph node involvement beyond the pelvis. Univariate and multivariate analyses were used to assess the possible independent significance of race and other prognostic factors, including Gleason score, serum acid phosphatase, nodal status, and hormonal status. Protocols 7706 and 8307 revealed that race was not of prognostic significance for disease-free or overall survival by either univariate or multivariate analysis. Univariate analysis of Protocol 7506 revealed that the median survival for blacks was somewhat shorter (5.4 years vs. 7.1 years, p = 0.02). This difference persisted after a multivariate analysis. A higher percentage of blacks treated on 7506 had an abnormally elevated serum acid phosphatase compared to whites (p = 0.006), and the time to distant failure tended to be shorter (p = 0.07). These findings suggest that blacks treated on 7506 may have had more extensive disease at presentation. Based on these prospective randomized trials, it is most likely that the lower survival noted for black Americans with prostate cancer reflects the tendency for blacks to present with more advanced disease. Differences in access to care, the quality of care received, and the impact of co-morbid conditions may explain the lower survival reported for black Americans elsewhere in the literature.

Superoxide mediates the toxicity of paraquat for Chinese hamster ovary cells

The roles of superoxide and H2O2 in the cytotoxicity of paraquat were assessed in Chinese hamster ovary cells. Neither catalase nor superoxide dismutase inhibited the loss of ability to form colonies when added to the medium. When introduced into the cells, superoxide dismutase but not catalase inhibited the toxicity of paraquat. That superoxide dismutase acted by its known catalytic action is shown by the loss of inhibition when the enzyme was inactivated by H2O2 before being introduced into the cells. The lack of inhibition by catalase, by dimethyl sulfoxide, and by desferoxamine suggests that the toxicity is not mediated by a reaction between H2O2 and superoxide to engender the hydroxyl radical. Exposure of Chinese hamster ovary cells to paraquat may be a suitable means to determine the effects of superoxide anion in cultured cells and the ways in which cells can resist this toxic action.

Cytosolic and sarcoplasmic reticulum-associated low Km, cGMP-inhibited cAMP phosphodiesterase in mammalian myocardium

The distribution and phosphoprotein band patterns of low Km, cGMP-inhibited cAMP phosphodiesterase (cGI PDE) activity were examined in cytosolic and microsomal fractions of human, canine, rabbit and guinea pig left ventricular myocardium following phosphorylation by cAMP-dependent protein kinase, immunoprecipitation with anti-cGI PDE antibodies and SDS-PAGE. The recovery of cGI PDE activity in cytosolic and microsomal fractions was comparable in all four species. Microsomal cGI PDE was comprised chiefly of a approximately 135 kDa phosphoprotein. Cytosolic cGI PDE was comprised solely of approximately 116 kDa and lower molecular weight phosphoproteins. The approximately 135 kDa phosphoprotein probably corresponds to the holoenzyme encoded by the recently cloned cDNA for human myocardial cGI PDE, whose predicted molecular weight is 126 kDa. The approximately 116 kDa phosphoprotein may result from deletion or removal of putative membrane-association domains from the N-terminal region of the holoenzyme. These results suggest that the cytosolic and sarcoplasmic reticulum-associated forms of mammalian myocardial cGI PDE are separate molecular species.

Molecular forms of acetylcholinesterase in two sublines of human erythroleukemia K562 cells. Sensitivity or resistance to phosphatidylinositol-specific phospholipase C and biosynthesis

Acetylcholinesterase (AChE) in K562 cells exists in two molecular forms. The major form, an amphiphilic dimer (G2a) which sediments at 5.3 S, and the minor form, an amphiphilic monomer (G1a) which sediments at 3.5 S. Extraction in the presence of the sulfhydryl alkylating agent N-ethylmaleimide was required to preserve the G2a form. In Triton X-100 extracts of the subline K562-243, phosphatidylinositol-specific phospholipase C (PtdIns-PLC) from Bacillus thuringiensis converted most of the G2a AChE into a hydrophilic dimer (G2h), indicating that the G2a form possessed a hydrophobic glycoinositol phospholipid that mediated its attachment to the membrane. Treatment of intact K562-243 cells with PtdIns-PLC released approximately 60% of the total AChE activity and provided an estimate of the externally exposed AChE. The direct conversion from an amphiphilic to a hydrophilic dimeric form by PtdIns-PLC was not obtained in extracts or intact cells of the subline K562-48. Instead, pretreatment with alkaline hydroxylamine was necessary to render the amphiphilic G2 form of this subline susceptible to digestion by the phospholipase. In this respect, the amphiphilic dimer of K562-48 AChE resembles the G2a form of human erythrocyte AChE, which is resistant to PtdIns-PLC because of the direct palmitoylation of an inositol hydroxyl group in the anchor [Roberts et al. (1988) J. Biol. Chem. 263, 18766-18775]. Release of this acyl chain by hydroxylamine renders the enzyme susceptible to PtdIns-PLC [Toutant et al. (1989) Eur. J. Biochem. 180, 503-508]. In both K562 sublines, sialidase decreased the migration of the G2a form but not of the G1a form of AChE. G1a forms thus appear to represent an intracellular pool of newly synthesized molecules residing in a compartment proximal to the trans-Golgi apparatus. The sialidase-resistant G1a molecules were also resistant to PtdIns-PLC digestion; possible explanations for this resistance are presented.

Folate binding protein from kidney brush border membranes contains components characteristic of a glycoinositol phospholipid anchor

A number of cell surface proteins have been shown to be anchored to the plasma membrane by a covalently attached glycoinositol phospholipid (GPL) in amide linkage to the C-terminus of the mature protein. We applied several criteria to establish that folate binding protein (FBP) in brush border membranes of rat kidney contains a GPL anchor. Brush border membranes were isolated and labeled with [3H]folate, and the complex of FBP and [3H]folate was shown to be released to the supernatant by incubation with purified bacterial phosphatidylinositol-specific phospholipase C (PIPLC) but not by incubation with a purified bacterial phosphatidylcholine-specific phospholipase C. The FBP-[3H]folate complex both in crude extracts and after FBP purification by ligand-directed affinity chromatography interacted with Triton X-114 micelles, and prior incubation with PIPLC prevented this detergent interaction. Individual residues characteristic of GPL anchors were found to be covalently associated with FBP following polyacrylamide gel electrophoresis in sodium dodecyl sulfate. These included glucosamine and ethanolamine, which were radiolabeled by reductive methylation and identified by chromatography on an amino acid analyzer, and inositol phosphate, which was inferred by Western blotting with an anti-CRD antisera. This antisera gave positive immunostaining only after FBP had been cleaved by PIPLC, a reliable diagnostic of a GPL anchor. The relationship between GPL-anchored FBP in biological membranes and soluble FBP in biological fluids also is discussed.

Eye patch treatment for the pain of corneal abrasion

The traditional use of patching and topical antibiotics in the treatment of corneal abrasion has recently been challenged, particularly after foreign body removal. In a prospective, controlled, randomized study of 33 patients treated in the emergency department for eye pain and corneal abrasion, we attempted to determine whether eye patching affected the pain of simple corneal abrasions. After fluorescein examination with magnification (x 5), a visual analog pain score was recorded and the patient was randomized to either the patched or nonpatched group. A standard analgesic was supplied, and all patients had follow-up at 24 hours, when repeat pain scores and analgesic use were recorded. The groups were compared by using the Wilcoxon's rank sum test, Student's t test, and analysis of covariance as required. There was no significant difference in the mean changes in pain scores between the patched and nonpatched groups. Analgesic use was also similar. We conclude that routine eye patching does not favorably affect the pain associated with the treatment of simple corneal abrasion.

Paraquat-resistant HeLa cells: increased cellular content of glutathione peroxidase

Paraquat-resistant HeLa cells were selected and characterized to determine the mechanism(s) of the toxic action of paraquat for cultured mammalian cells. From HeLa cells already selected for resistance to the toxicity of 40 microM paraquat more resistant cells were selected in 90 microM paraquat. In these more resistant cells (PQRHM90) one adaptation which occurred at the lesser concentration of paraquat, magnification of the cellular content of both the CuZn- and the Mn-containing superoxide dismutases, did not increase further. Instead, the cellular content of catalase and of glutathione peroxidase increased. The increased cellular content of glutathione peroxidase appeared more likely to have produced increased resistance to paraquat than did the augmented content of catalase because, after cultivation in the absence of paraquat, the cells retained both resistance to 90 microM paraquat and the increased content of glutathione peroxidase, while the content of catalase declined. The cellular content of reduced glutathione in the PQRHM90 cells grown in paraquat was diminished in comparison with that in the cells from which they derived. The data suggest that the PQRHM90 cells resisted the toxicity of paraquat by increasing the cellular activity of glutathione peroxidase as a means of detoxifying the H2O2 produced by paraquat.

Effect of ryanodine on sarcoplasmic reticulum Ca2+ accumulation in nonfailing and failing human myocardium

BACKGROUND

The purpose of this study was to determine whether abnormal Ca2+ release through ryanodine-sensitive Ca2+ channels in the sarcoplasmic reticulum might contribute to the abnormal [Ca2+]i homeostasis that has been described in failing human myocardium.

METHODS AND RESULTS

Occupancy of low-affinity ryanodine binding sites on ryanodine-sensitive Ca2+ channels stimulates oxalate-supported, ATP-dependent Ca2+ accumulation in sarcoplasmic reticulum-derived microsomes by inhibiting concurrent Ca2+ efflux through these channels. We examined the effects of 0.5 mmol/L ryanodine on 45Ca2+ accumulation in microsomes prepared from nonfailing (n = 8) and failing (n = 10) human left ventricular myocardium. In the absence of ryanodine, 45Ca2+ accumulation reached similar levels in microsomes from nonfailing and failing hearts. Incubation with 0.5 mmol/L ryanodine caused a 52.2 +/- 6.5% increase in peak 45Ca2+ accumulation in microsomes from nonfailing hearts and a 24.3 +/- 4.1% increase in microsomes from failing hearts. The density of high-affinity ryanodine binding sites and the inhibition of [3H]ryanodine dissociation from these sites by 0.1 mmol/L ryanodine were similar in microsomes from nonfailing and failing hearts.

CONCLUSIONS

These results, which demonstrate a diminished stimulation of Ca2+ accumulation by ryanodine in sarcoplasmic reticulum-derived microsomes from failing human myocardium that could be explained by an uncoupling of the occupancy of low-affinity ryanodine binding sites from the reduction in the open probability of these channels or by concurrent Ca2+ efflux through a ryanodine-insensitive mechanism, are evidence that increased efflux of Ca2+ from the sarcoplasmic reticulum may contribute to the abnormal [Ca2+]i homeostasis described in failing human myocardium.