The psychosocial work environment among educators during the COVID-19 pandemic

BACKGROUND

The education sector has been heavily impacted by COVID-19. While the impact on school-aged children has received much attention, less attention has focused on the experiences of educators.

AIMS

To compare various dimensions of the psychosocial work environment and health outcomes between educators engaged in online learning to those engaged in in-person learning in the Canadian province of Ontario.

METHODS

Responses from 5438 educators engaged in either online or in-person learning were collected between 23 November and 21 December 2020; three months after the start of the 2020/21 academic year in September 2020. Psychosocial outcomes included quantitative demands, work pace, predictability, role conflicts, and social support from supervisors and co-workers; assessed using an abbreviated version of the Copenhagen Psychosocial Questionnaire. Secondary outcomes included burnout and sleep troubles. Ordinary Least-Squares regression models examined adjusted mean differences in the levels of outcomes for respondents in in-person versus online learning, after adjustment for a variety of covariates.

RESULTS

Compared to respondents engaged in in-person learning, respondents engaged in online learning reported less predictability, higher role conflicts and less support from supervisors and co-workers. Statistically significant differences in work pace, burnout and sleep troubles were also observed across learning modes, although these differences did not exceed previously suggested thresholds for minimum important differences.

CONCLUSIONS

Important differences in the psychosocial work environment were observed between respondents engaged in in-person learning versus online learning. Addressing these differences is required, given the potential continued importance of online learning within the context of the COVID-19 pandemic and beyond.

Regulation of liver subcellular architecture controls metabolic homeostasis

Cells display complex intracellular organization by compartmentalization of metabolic processes into organelles, yet the resolution of these structures in the native tissue context and their functional consequences are not well understood. Here we resolved the three-dimensional structural organization of organelles in large (more than 2.8 × 10⁵ µm³) volumes of intact liver tissue (15 partial or full hepatocytes per condition) at high resolution (8 nm isotropic pixel size) using enhanced focused ion beam scanning electron microscopy^1,2 imaging followed by deep-learning-based automated image segmentation and 3D reconstruction. We also performed a comparative analysis of subcellular structures in liver tissue of lean and obese mice and found substantial alterations, particularly in hepatic endoplasmic reticulum (ER), which undergoes massive structural reorganization characterized by marked disorganization of stacks of ER sheets³ and predominance of ER tubules. Finally, we demonstrated the functional importance of these structural changes by monitoring the effects of experimental recovery of the subcellular organization on cellular and systemic metabolism. We conclude that the hepatic subcellular organization of the ER architecture are highly dynamic, integrated with the metabolic state and critical for adaptive homeostasis and tissue health.

Aberrant Ca2+ signaling by IP3Rs in adipocytes links inflammation to metabolic dysregulation in obesity

Chronic metabolic inflammation is a key feature of obesity, insulin resistance, and diabetes. Here, we showed that altered regulation of the Ca²⁺ channel inositol trisphosphate receptor (IP₃R) was an adipocyte-intrinsic event involved in the emergence and propagation of inflammatory signaling and the resulting insulin resistance. Inflammation induced by cytokine exposure in vitro or by obesity in vivo led to increases in the abundance and activity of IP₃Rs and in the phosphorylation of the Ca²⁺-dependent kinase CaMKII in adipocytes in a manner dependent on the kinase JNK. In mice, adipocyte-specific loss of IP₃R1/2 protected against adipose tissue inflammation and insulin resistance, despite the mice exhibiting substantial diet-induced weight gain. Thus, this work suggests that increased IP₃R activity is a key link between obesity, inflammation, and insulin resistance. These data also suggest that approaches to target IP₃R-mediated Ca²⁺ homeostasis in adipocytes may offer new therapeutic opportunities against metabolic diseases, especially because GWAS studies also implicate this locus in human obesity.

Adipocytes promote interleukin-18 binding to its receptors during abdominal aortic aneurysm formation in mice

AIMS

Obesity is a risk factor of abdominal aortic aneurysm (AAA). Inflammatory cytokine interleukin-18 (IL18) has two receptors: IL18 receptor (IL18r) and Na-Cl co-transporter (NCC). In human and mouse AAA lesions, IL18 colocalizes to its receptors at regions rich in adipocytes, suggesting a role of adipocytes in promoting IL18 actions in AAA development.

METHODS AND RESULTS

We localized both IL18r and NCC in human and mouse AAA lesions. Murine AAA development required both receptors. In mouse AAA lesions, IL18 binding to these receptors increased at regions enriched in adipocytes or adjacent to perivascular adipose tissue. 3T3-L1 adipocytes enhanced IL18 binding to macrophages, aortic smooth muscle cells (SMCs), and endothelial cells by inducing the expression of both IL18 receptors on these cells. Adipocytes also enhanced IL18r and IL18 expression from T cells and macrophages, AAA-pertinent protease expression from macrophages, and SMC apoptosis. Perivascular implantation of adipose tissue from either diet-induced obese mice or lean mice but not that from leptin-deficient ob/ob mice exacerbated AAA development in recipient mice. Further experiments established an essential role of adipocyte leptin and fatty acid-binding protein 4 (FABP4) in promoting IL18 binding to macrophages and possibly other inflammatory and vascular cells by inducing their expression of IL18, IL18r, and NCC.

CONCLUSION

Interleukin-18 uses both IL18r and NCC to promote AAA formation. Lesion adipocyte and perivascular adipose tissue contribute to AAA pathogenesis by releasing leptin and FABP4 that induce IL18, IL18r, and NCC expression and promote IL18 actions.

Uncoupling of Metabolic Health from Longevity through Genetic Alteration of Adipose Tissue Lipid-Binding Proteins

Deterioration of metabolic health is a hallmark of aging and generally assumed to be detrimental to longevity. Exposure to a high-calorie diet impairs metabolism and accelerates aging; conversely, calorie restriction (CR) prevents age-related metabolic diseases and extends lifespan. However, it is unclear whether preservation of metabolic health is sufficient to extend lifespan. We utilized a genetic mouse model lacking Fabp4/5 that confers protection against metabolic diseases and shares molecular and lipidomic features with CR to address this question. Fabp-deficient mice exhibit extended metabolic healthspan, with protection against insulin resistance and glucose intolerance, inflammation, deterioration of adipose tissue integrity, and fatty liver disease. Surprisingly, however, Fabp-deficient mice did not exhibit any extension of lifespan. These data indicate that extension of metabolic healthspan in the absence of CR can be uncoupled from lifespan, indicating the potential for independent drivers of these pathways, at least in laboratory mice.

Increased oxidative phosphorylation in response to acute and chronic DNA damage

Accumulation of DNA damage is intricately linked to aging, aging-related diseases and progeroid syndromes such as Cockayne syndrome (CS). Free radicals from endogenous oxidative energy metabolism can damage DNA, however the potential of acute or chronic DNA damage to modulate cellular and/or organismal energy metabolism remains largely unexplored. We modeled chronic endogenous genotoxic stress using a DNA repair-deficient Csa^-/-|Xpa^-/- mouse model of CS. Exogenous genotoxic stress was modeled in mice in vivo and primary cells in vitro treated with different genotoxins giving rise to diverse spectrums of lesions, including ultraviolet radiation, intrastrand crosslinking agents and ionizing radiation. Both chronic endogenous and acute exogenous genotoxic stress increased mitochondrial fatty acid oxidation (FAO) on the organismal level, manifested by increased oxygen consumption, reduced respiratory exchange ratio, progressive adipose loss and increased FAO in tissues ex vivo. In multiple primary cell types, the metabolic response to different genotoxins manifested as a cell-autonomous increase in oxidative phosphorylation (OXPHOS) subsequent to a transient decline in steady-state NAD+ and ATP levels, and required the DNA damage sensor PARP-1 and energy-sensing kinase AMPK. We conclude that increased FAO/OXPHOS is a general, beneficial, adaptive response to DNA damage on cellular and organismal levels, illustrating a fundamental link between genotoxic stress and energy metabolism driven by the energetic cost of DNA damage. Our study points to therapeutic opportunities to mitigate detrimental effects of DNA damage on primary cells in the context of radio/chemotherapy or progeroid syndromes.

Deficiency of FcϵR1 Increases Body Weight Gain but Improves Glucose Tolerance in Diet-Induced Obese Mice

Prior studies demonstrated increased plasma IgE in diabetic patients, but the direct participation of IgE in diabetes or obesity remains unknown. This study found that plasma IgE levels correlated inversely with body weight, body mass index, and body fat mass among a population of randomly selected obese women. IgE receptor FcϵR1-deficient (Fcer1a(-/-)) mice and diet-induced obesity (DIO) mice demonstrated that FcϵR1 deficiency in DIO mice increased food intake, reduced energy expenditure, and increased body weight gain but improved glucose tolerance and glucose-induced insulin secretion. White adipose tissue from Fcer1a(-/-) mice showed an increased expression of phospho-AKT, CCAAT/enhancer binding protein-α, peroxisome proliferator-activated receptor-γ, glucose transporter-4 (Glut4), and B-cell lymphoma 2 (Bcl2) but reduced uncoupling protein 1 (UCP1) and phosphorylated c-Jun N-terminal kinase (JNK) expression, tissue macrophage accumulation, and apoptosis, suggesting that IgE reduces adipogenesis and glucose uptake but induces energy expenditure, adipocyte apoptosis, and white adipose tissue inflammation. In 3T3-L1 cells, IgE inhibited the expression of CCAAT/enhancer binding protein-α and peroxisome proliferator-activated receptor-γ, and preadipocyte adipogenesis and induced adipocyte apoptosis. IgE reduced the 3T3-L1 cell expression of Glut4, phospho-AKT, and glucose uptake, which concurred with improved glucose tolerance in Fcer1a(-/-) mice. This study established two novel pathways of IgE in reducing body weight gain in DIO mice by suppressing adipogenesis and inducing adipocyte apoptosis while worsening glucose tolerance by reducing Glut4 expression, glucose uptake, and insulin secretion.

Chronic enrichment of hepatic endoplasmic reticulum-mitochondria contact leads to mitochondrial dysfunction in obesity

Proper function of the endoplasmic reticulum (ER) and mitochondria is crucial for cellular homeostasis, and dysfunction at either site has been linked to pathophysiological states, including metabolic diseases. Although the ER and mitochondria play distinct cellular roles, these organelles also form physical interactions with each other at sites defined as mitochondria-associated ER membranes (MAMs), which are essential for calcium, lipid and metabolite exchange. Here we show that in the liver, obesity leads to a marked reorganization of MAMs resulting in mitochondrial calcium overload, compromised mitochondrial oxidative capacity and augmented oxidative stress. Experimental induction of ER-mitochondria interactions results in oxidative stress and impaired metabolic homeostasis, whereas downregulation of PACS-2 or IP3R1, proteins important for ER-mitochondria tethering or calcium transport, respectively, improves mitochondrial oxidative capacity and glucose metabolism in obese animals. These findings establish excessive ER-mitochondrial coupling as an essential component of organelle dysfunction in obesity that may contribute to the development of metabolic pathologies such as insulin resistance and diabetes.

A diurnal serum lipid integrates hepatic lipogenesis and peripheral fatty acid use

Food intake increases the activity of hepatic de novo lipogenesis, which mediates the conversion of glucose to fats for storage or utilization. In mice, this program follows a circadian rhythm that peaks with nocturnal feeding^1,2 and is repressed by Rev-erbα/β and an HDAC3-containing complex^3–5 during the day. The transcriptional activators controlling rhythmic lipid synthesis in the dark cycle remain poorly defined. Disturbances in hepatic lipogenesis are also associated with systemic metabolic phenotypes^6–8, suggesting that lipogenesis in the liver communicates with peripheral tissues to control energy substrate homeostasis. Here we identify a PPARδ-dependent de novo lipogenic pathway in the liver that modulates fat utilization by muscle via a circulating lipid. The nuclear receptor PPARδ controls diurnal expression of lipogenic genes in the dark/feeding cycle. Liver-specific PPARδ activation increases, while hepatocyte-Ppard deletion reduces, muscle fatty acid (FA) uptake. Unbiased metabolite profiling identifies PC(18:0/18:1), or 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), as a serum lipid regulated by diurnal hepatic PPARδ activity. PC(18:0/18:1) reduces postprandial lipid levels and increases FA utilization through muscle PPARα. High fat feeding diminishes rhythmic production of PC(18:0/18:1), whereas PC(18:0/18:1) administration in db/db mice improves metabolic homeostasis. These findings reveal an integrated regulatory circuit coupling lipid synthesis in the liver to energy utilization in muscle by coordinating the activity of two closely related nuclear receptors. These data implicate alterations in diurnal hepatic PPARδ-PC(18:0/18:1) signaling in metabolic disorders including obesity.

Adipocyte lipid chaperone AP2 is a secreted adipokine regulating hepatic glucose production

Proper control of hepatic glucose production is central to whole-body glucose homeostasis, and its disruption plays a major role in diabetes. Here, we demonstrate that although established as an intracellular lipid chaperone, aP2 is in fact actively secreted from adipocytes to control liver glucose metabolism. Secretion of aP2 from adipocytes is regulated by fasting- and lipolysis-related signals, and circulating aP2 levels are markedly elevated in mouse and human obesity. Recombinant aP2 stimulates glucose production and gluconeogenic activity in primary hepatocytes in vitro and in lean mice in vivo. In contrast, neutralization of secreted aP2 reduces glucose production and corrects the diabetic phenotype of obese mice. Hyperinsulinemic-euglycemic and pancreatic clamp studies upon aP2 administration or neutralization demonstrated actions of aP2 in liver. We conclude that aP2 is an adipokine linking adipocytes to hepatic glucose production and that neutralizing secreted aP2 may represent an effective therapeutic strategy against diabetes.

Direct control of hepatic glucose production by interleukin-13 in mice

Hyperglycemia is a result of impaired insulin action on glucose production and disposal, and a major target of antidiabetic therapies. The study of insulin-independent regulatory mechanisms of glucose metabolism may identify new strategies to lower blood sugar levels. Here we demonstrate an unexpected metabolic function for IL-13 in the control of hepatic glucose production. IL-13 is a Th2 cytokine known to mediate macrophage alternative activation. Genetic ablation of Il-13 in mice (Il-13-/-) resulted in hyperglycemia, which progressed to hepatic insulin resistance and systemic metabolic dysfunction. In Il-13-/- mice, upregulation of enzymes involved in hepatic gluconeogenesis was a primary event leading to dysregulated glucose metabolism. IL-13 inhibited transcription of gluconeogenic genes by acting directly on hepatocytes through Stat3, a noncanonical downstream effector. Consequently, the ability of IL-13 to suppress glucose production was abolished in liver cells lacking Stat3 or IL-13 receptor α1 (Il-13rα1), which suggests that the IL-13Rα1/Stat3 axis directs IL-13 signaling toward metabolic responses. These findings extend the implication of a Th1/Th2 paradigm in metabolic homeostasis beyond inflammation to direct control of glucose metabolism and suggest that the IL-13/Stat3 pathway may serve as a therapeutic target for glycemic control in insulin resistance and type 2 diabetes.

Deletion of the κ genes from mouse hybridomas established with NS-1 myelomas

Monoclonal antibodies (mAbs) of the IgG class produced by mouse hybridomas raised with NS-1 myelomas have been shown to contain two types of immunoglobulin light (κ) chains derived from the myelomas and antigen-stimulated spleen lymphocytes, and the hybridomas produce three mAb species with light chain heterogeneity (Abe and Inouye, 1993). In the present study, 9 hybridoma lines secreting homogeneous mAbs have been isolated from 63 lines cloned from an established hybridoma line producing three mAbs. They secrete homogeneous mAbs containing light chains derived from either myeloma or spleen cells. They contain either κ gene derived from the respective cells, and the other gene was deleted during the cultivation. The deletion frequency of the κ gene of myelomas is 3 times higher than that of spleen cells, although 80-85% of hybridomas reach the stable state containing both κ genes.

PKR is required for NLRP3 inflammasome activation and HMGB1 release (114.7)

The NLR family pyrin domain-containing 3 (NLRP3) inflammasome, an intracellular oligomeric protein complex, regulates release of caspase-1 activation-dependent cytokines, including IL-1β, IL-18, and high-mobility group box 1 (HMGB1). During the course of studying HMGB1 release mechanisms from macrophages, we unexpectedly observed that double-stranded RNA dependent protein kinase (PKR) is required for NLRP3 inflammasome activation. PKR inactivation by genetic deletion or pharmacological inhibition blocked NLRP3 inflammasome activation in response to double-stranded RNA, ATP, monosodium urate, adjuvant aluminum, and live E coli. Overexpression of PKR significantly enhanced the reconstituted NLRP3 inflammasome-induced caspase-1 activation and IL-1β maturation; whereas blocking PKR significantly inhibited the reconstituted NLRP3 inflammasome activation. PKR physically interacts with NLRP3, and PKR autophosphorylation is required for efficient PKR and NLRP3 interaction. Importantly, PKR autophosphorylation in a cell free system with recombinant NLRP3, ASC and pro-casapse-1 reconstitutes inflammasome activity. Together, these results indicate that PKR is required for inflammasome activation, and that it should be possible to target this molecule to inhibit inflammasome activity during inflammation.

Identification of the 30K protein of TMV by immunoprecipitation with antibodies directed against a synthetic peptide

A synthetic hexadecapeptide corresponding to the predicted C-terminal sequence of the 30K protein of TMV has been coupled to bovine serum albumin and used to raise antibodies in rabbits. The resulting antiserum reacted with the 30K protein translated in vitro. We report the use of this antiserum in the first detection of the 30K protein in vivo, in TMV-infected tobacco protoplasts. Several proteins, the so called family of 30K-related peptides, were immunoprecipitated among in vitro translation products, but only the 30K protein was immunoprecipitated from TMV-infected protoplasts.

TLR4 links innate immunity and fatty acid-induced insulin resistance

TLR4 is the receptor for LPS and plays a critical role in innate immunity. Stimulation of TLR4 activates proinflammatory pathways and induces cytokine expression in a variety of cell types. Inflammatory pathways are activated in tissues of obese animals and humans and play an important role in obesity-associated insulin resistance. Here we show that nutritional fatty acids, whose circulating levels are often increased in obesity, activate TLR4 signaling in adipocytes and macrophages and that the capacity of fatty acids to induce inflammatory signaling in adipose cells or tissue and macrophages is blunted in the absence of TLR4. Moreover, mice lacking TLR4 are substantially protected from the ability of systemic lipid infusion to (a) suppress insulin signaling in muscle and (b) reduce insulin-mediated changes in systemic glucose metabolism. Finally, female C57BL/6 mice lacking TLR4 have increased obesity but are partially protected against high fat diet-induced insulin resistance, possibly due to reduced inflammatory gene expression in liver and fat. Taken together, these data suggest that TLR4 is a molecular link among nutrition, lipids, and inflammation and that the innate immune system participates in the regulation of energy balance and insulin resistance in response to changes in the nutritional environment.

Distribution, structure, organ-specific expression, and phylogenic analysis of the pathogenesis-related protein-3 chitinase gene family in rice (Oryza sativaL.)

Rice (Oryza sativa L.) pathogenesis-related (PR)-3 chitinases, like other PR proteins, are each coded by one of the genes of a multigene family in the plant genome. We assembled the database information about rice PR-3 chitinase sequences. A total of 12 PR-3 chitinase loci (Cht1 to Cht12) were found deployed in the rice genome. Some of the loci were occupied by 2 or more alleles. For all the loci expect Cht4, Cht5, Cht6, and Cht11, the amino acid sequence was polymorphic between japonica and indica varieties of rice, but glutamic acid acting as a catalytic residue was completely conserved in all the loci expect Cht7. All the genes except Cht7, which was not tested in this study, were transcripted in some organs (leaf, sheath, root, and meristem) of rice plants. These results suggest that chitinase proteins encoded by the genes at these loci have important biological effects, at least antifungal activities, on rice plants. We also proposed a new classification of rice PR-3 chitinases based on their domain structures. This classification was consistent with the results of phylogenetic analysis of rice chitinases.Key words: allelic relationship, classification, organ-specific expression, PR-3 chitinase, rice (Oryza sativa L.).

Overexpression of suppressor of cytokine signaling 3 in adipose tissue causes local but not systemic insulin resistance

In adipocytes, suppressor of cytokine signaling (SOCS)3 deficiency increases insulin-stimulated insulin receptor substrate (IRS)-1 and -2 phosphorylation, IRS-associated phosphatidylinositol 3 kinase activity, and insulin-stimulated glucose uptake. Moreover, SOCS3 is required for tumor necrosis factor-alpha full inhibition of insulin-stimulated IRS-1 and -2 phosphorylation, phosphatidylinositol 3 kinase activity, and glucose uptake. Whether SOCS3 also inhibits adipocyte insulin signaling in vivo and whether this action further affects systemic insulin sensitivity is not clear. We therefore generated a transgenic mouse (aP2-SOCS3 mouse) overexpressing SOCS3 in adipose tissue. Overexpression of SOCS3 in adipocytes decreases IRS1 protein levels and subsequent insulin-stimulated IRS-1 and -2 phosphorylation, decreases p85 binding to IRS-1, and leads to decreased insulin-stimulated glucose uptake in adipocytes. This impaired insulin signaling in adipose tissue of aP2-SOCS3 mice causes decreased lipogenesis and blocks insulin's antilipolytic action. However, because of decreased energy partitioning in adipose tissue, aP2-SOCS3 mice are resistant to diet-induced obesity and are protected against systemic insulin resistance caused by a high-fat diet. Therefore, overexpression of SOCS3 in adipocytes causes local adipocyte insulin resistance, but it is not sufficient to cause systemic insulin resistance.

Practical application of mammalian cytochrome P450

Heterologous expression systems play an important role in the analysis of structure-function relationships of mammalian P450s. In addition, these expression systems allow practical application of mammalian P450s. Genetically engineered fused enzymes between mammalian P450 and yeast NADPH-P450 reductase have possible applications in bioconversion processes. Combined use of techniques reported thus far could produce steroid hormones in the recombinant yeast cells harboring four P450 species, CYP11A1, CYP17A1, CYP21B1 and CYP11B1. In an Escherichia coli expression system, the technology of the construction of the mitochondrial P450 electron transport chain has been established. The recombinant E. coli cells expressing CYP27B1, adrenodoxin and NADPH-adrenodoxin reductase would be applicable to a bioconversion process to produce 1alpha,25-dihydroxyvitamin D3. We also demonstrated the usefulness of heterologous expression systems for human liver microsomal P450s for the prediction of drug metabolism in the human body. Microsomal fractions prepared from recombinant yeast, insect and mammalian cells are commercially available and play an important role in preclinical drug development. Application of mammalian P450 to bioremediation with genetic engineering has also been developed. Thus, mammalian P450s appear to have great potential for a wide range of practical applications.

Hyperglycemia does not increase basal hypothalamo-pituitary-adrenal activity in diabetes but it does impair the HPA response to insulin-induced hypoglycemia

Recently, we established that hypothalamo-pituitary-adrenal (HPA) and counterregulatory responses to insulin-induced hypoglycemia were impaired in uncontrolled streptozotocin (STZ)-diabetic (65 mg/kg) rats and insulin treatment restored most of these responses. In the current study, we used phloridzin to determine whether the restoration of blood glucose alone was sufficient to normalize HPA function in diabetes. Normal, diabetic, insulin-treated, and phloridzin-treated diabetic rats were either killed after 8 days or subjected to a hypoglycemic (40 mg/dl) glucose clamp. Basal: Elevated basal ACTH and corticosterone in STZ rats were normalized with insulin but not phloridzin. Increases in hypothalamic corticotrophin-releasing hormone (CRH) and inhibitory hippocampal mineralocorticoid receptor (MR) mRNA with STZ diabetes were not restored with either insulin or phloridzin treatments. Hypoglycemia: In response to hypoglycemia, rises in plasma ACTH and corticosterone were significantly lower in diabetic rats compared with controls. Insulin and phloridzin restored both ACTH and corticosterone responses in diabetic animals. Hypothalamic CRH mRNA and pituitary pro-opiomelanocortin mRNA expression increased following 2 h of hypoglycemia in normal, insulin-treated, and phloridzin-treated diabetic rats but not in untreated diabetic rats. Arginine vasopressin mRNA was unaltered by hypoglycemia in all groups. Interestingly, hypoglycemia decreased hippocampal MR mRNA in control, insulin-, and phloridzin-treated diabetic rats but not uncontrolled diabetic rats, whereas glucocorticoid receptor mRNA was not altered by hypoglycemia. In conclusion, despite elevated basal HPA activity, HPA responses to hypoglycemia were markedly reduced in uncontrolled diabetes. We speculate that defects in the CRH response may be related to a defective MR response. It is intriguing that phloridzin did not restore basal HPA activity but it restored the HPA response to hypoglycemia, suggesting that defects in basal HPA function in diabetes are due to insulin deficiency, but impaired responsiveness to hypoglycemia appears to stem from chronic hyperglycemia.

Mutational effect for stability in a conserved region of thermolysin

AIMS

To investigate the mutational effect for the stability of thermolysin (TLN) in conserved regions.

METHODS AND RESULTS

Mutational effects for stability at autodegradation sites of TLN in conserved region were studied. The bands of mutant TLN (34 kDa) on SDS-PAGE were decreased. However, those of mutant TLN cultivated with CaCl2 recovered to the same level as WT TLN. Dialysis study shows that these mutant TLN require more calcium ions than WT TLN.

CONCLUSIONS

From these results, calcium affinity of mutant TLN in the conserved regions seem to become weak, subsequently mutant TLN were easily autodegraded in the case of low concentration of CaCl2.

SIGNIFICANCE AND IMPACT OF THE STUDY

The autodegradation sites located in conserved regions of bacilli neutral proteases are important for the tertiary structure formation concerning the stability of the protein.

Insulin alone increases hypothalamo-pituitary-adrenal activity, and diabetes lowers peak stress responses

Diabetes is associated with increased basal hypothalamo-pituitary-adrenal (HPA) activity and impaired stress responsiveness. Previously, we demonstrated that the HPA response to hypoglycemia is significantly impaired in diabetic rats. In this study our goals were to 1) differentiate between the effects of hyperinsulinemia and those of hypoglycemia per se, and 2) establish whether diabetes lowers peak stress responses. Normal and streptozotocin-diabetic rats were subjected to hyperinsulinemic-euglycemic glucose clamps to evaluate central and peripheral responses. These were compared with peak ACTH and corticosterone responses to restraint and hypoglycemia. Hyperinsulinemia increased CRH and vasopressin mRNA, and plasma ACTH and corticosterone in normal and diabetic rats. In normal animals, insulin-induced activation of ACTH and corticosterone was lower than the responses during either restraint or hypoglycemia. In contrast, ACTH and corticosterone activation in diabetic rats was similar with all three stressors. Pituitary-adrenal axis activation in diabetic animals was also much lower compared with that in normal controls. The response to hyperinsulinemia (euglycemia) was associated with increases in glucocorticoid receptor mRNA in the anterior pituitary and paraventricular nucleus. Hippocampal mineralocorticoid receptor mRNA expression was increased in normal, but not in diabetic, animals. We speculate that the ability to appropriately match the HPA response to the potency of a stressor is related to the ability to alter hippocampal mineralocorticoid receptor expression. In diabetes, this ability is impaired; hence, maximal HPA activation is greatly diminished. This is a novel observation that may have important implications in the treatment of impaired counterregulatory mechanisms in human diabetes.

Partial leptin restoration increases hypothalamic-pituitary-adrenal activity while diminishing weight loss and hyperphagia in streptozotocin diabetic rats

Chronic leptin administration at pharmacologic doses normalizes food intake and body weight in streptozotocin (STZ)-diabetic rats. We examined the metabolic effects of acute partial physiological leptin restoration in STZ-diabetic rats by using subcutaneous osmotic mini pumps. Groups: (1) Rats infused with vehicle (DV); (2) rats infused with recombinant murine methionine leptin (DL) at 4.5 microg . (kg body weight . d)(-1); (3)pair-fed rats (DP) given a food ration matching that consumed by the DL group. A fourth group of nondiabetic, normal (N) rats was also studied to assess normal metabolic efficiency, hypothalamic-pituitary-adrenal (HPA) activity and sympathoadrenal activity. Following leptin infusion, food consumption by DL rats was significantly lower than in DV rats. Paradoxically, despite a similar food intake to that of the DP group, which demonstrated a 40% reduction in body mass, DL rats increased their initial body weight by approximately 20% (P < .05). Plasma corticosterone and ACTH concentrations were elevated by 2-fold to 3-fold in DL versus N, DP, and DV rats. In the pars distalis, glucocorticoid receptor (GR) mRNA levels were significantly higher in DL and DP rats compared with N and DV rats. Our results suggest that partial restoration of physiologic leptin: (1) successfully reduces hyperphagia while allowing body weight gain in STZ-diabetic rats; (2) increases corticosterone levels in STZ-diabetic rats, which may in turn counteract the anorexic effects of diabetes; and (3) is associated with increased pituitary GR mRNA levels, despite elevated corticosterone levels, suggesting that leptin may interfere with the negative feedback regulation of the HPA axis.

Bacillus thuringiensis serovar shandongiensis strain 89-T-34-22 produces multiple cytotoxic proteins with similar molecular masses against human cancer cells

AIMS

To prove that Bacillus thuringiensis serovar shandongiensis strain 89-T-34-22 produces several novel cytotoxic proteins against human leukaemic T cells.

METHODS AND RESULTS

Parasporal inclusion protein was solubilized and processed by proteinase K and was separated by anion-exchange chromatography. Cytopathic effects of each fraction against MOLT-4 and Jurkat cells were monitored.

CONCLUSIONS

Existence of at least two novel cytotoxic proteins was suggested and N-terminal sequences of the newly identified proteins were determined to be QSTTDVIREY and X (Y or I) (P or I) NLANELA (X indicates uncertain amino acids). Molecular masses of the two proteins were approx. 27-28 kDa.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, we demonstrated that the strain 89-T-34-22 produces at least two novel cytotoxic proteins with similar molecular masses against human cancer cells. This is the first strain of B. thuringiensis which produces multiple cytotoxic proteins against human cancer cells.

Diabetes and the hypothalamo-pituitary-adrenal (HPA) axis

Patients and animals with poorly controlled or uncontrolled diabetes present with diurnal hypersecretion of glucocorticoids and altered regulation of the hypothalamo-pituitary-adrenocortical (HPA) axis. Although some of these changes are reversed with insulin replacement therapy, neuroendocrine function is not always restored to normal, even with rigorous glycemic control. In addition, stress responsiveness is also impaired in diabetes and this has important implications in the way patients with diabetes cope with many stress challenges, including the metabolic challenge of insulin-induced hypoglycemia. HPA dysregulation in diabetes appears to involve complex interactions between impaired glucocorticoid negative feedback sensitivity and factors such as hypoinsulinemia, hyperglycemia and/or hypoleptinemia, that may increase central drive of the axis. This review examines some of the evidence indicating hyperactivation of the HPA axis in patients with diabetes. Using the streptozotocin-diabetic rat as a model of type-1 diabetes, we will focus on elucidating some of the mechanisms underlying HPA dysregulation in diabetes. Hyperactivation of the HPA axis in diabetes is associated with increased expression of hypothalamic corticotrophin-releasing hormone (CRH) mRNA and hippocampal mineralocorticoid receptor (MR) mRNA. Although insulin replacement restores ACTH and corticosterone levels to normal, likely through glucocorticoid-mediated suppression of ACTH secretion, CRH and MR mRNA expression remain elevated. A better understanding of these mechanisms may be important in developing new treatment modalities for patients with diabetes mellitus.

Mechanisms of impaired hypothalamic-pituitary-adrenal (HPA) function in diabetes: reduced counterregulatory responsiveness to hypoglycaemia

In summary, our data suggest that in uncontrolled diabetes, increased HPA activity is caused by increased central drive at or above the level of the PVN. Insulin treatment only restores HPA activity at and below the pituitary level, presumably by GC-mediated suppression of ACTH secretion. We hypothesize that the defective HPA response to hypoglycaemia is at least in part due to a lack of a decrease in MR mRNA in response to hypoglycaemia, and diminished sensitivity of the pituitary and adrenal gland to stimulation. Interestingly, insulin treatment restores the HPA response, but not the defective epinephrine response. Therefore, defective epinephrine responses are not linked to defective HPA responses. Similarly, antecedent hypoglycaemia specifically impairs epinephrine responses, but not HPA responses to hypoglycaemia. These studies have revealed some of the mechanisms of impaired HPA function in diabetes and its impaired responsiveness to hypoglycaemia. Further investigations are essential for understanding poor counterregulation in insulin-treated diabetes and may lead to new strategies for preventing hypoglycaemia.

Effects of recurrent hyperinsulinemia with and without hypoglycemia on counterregulation in diabetic rats

To understand the mechanisms whereby recurrent hypoglycemia increases the risk of subsequent hypoglycemia, it was necessary to differentiate the effects of recurrent hyperinsulinemia from those of hyperinsulinemic hypoglycemia. We examined basal and hypoglycemic endocrine function in normal rats, streptozotocin-diabetic controls, and diabetic rats exposed to 4 days of 2 episodes/day of hyperinsulinemic hypoglycemia (DH) or hyperinsulinemic hyperglycemia (DI). DH and DI rats differentiated the effects of hyperinsulinemia from those of hypoglycemia. In diabetic controls, basal plasma ACTH tended to be increased, and plasma corticosterone, plasma somatostatin, and pancreatic prosomatostatin and proglucagon mRNA were increased (P < 0.05) vs. normal rats. These parameters were normalized in DH and DI rats. In diabetic controls, glucagon, epinephrine, norepinephrine, corticosterone, and peak glucose production responses to hypoglycemia were reduced (P < 0.05) vs. normal rats. In DI rats, epinephrine responses were normalized. Conversely, DH rats displayed marked further impairment of epinephrine and glucose production responses and increased peripheral insulin sensitivity (P < 0.05 vs. diabetic controls). Both insulin regimens partially normalized glucagon and fully normalized norepinephrine and corticosterone responses. In summary, recurrent hyperinsulinemia in diabetic rats normalized most pituitary-adrenal, sympathoadrenal, and pancreatic parameters. However, concurrent hypoglycemia further impaired epinephrine and glucose production responses and increased insulin sensitivity. We conclude that 1) recurrent hypoglycemia may increase the risk of subsequent hypoglycemia by increasing insulin sensitivity, and 2) epinephrine counterregulation is particularly sensitive to impairment by recurrent hypoglycemia.

Diabetes impairs hypothalamo-pituitary-adrenal (HPA) responses to hypoglycemia, and insulin treatment normalizes HPA but not epinephrine responses

We recently established that in addition to plasma adrenocorticotrophic hormone (ACTH) and corticosterone, hypothalamic corticotrophin-releasing hormone (CRH) mRNA and hippocampal type 1 glucocorticoid receptor (GR1) mRNA were also upregulated in uncontrolled streptozotocin-induced diabetes. In the current study, control, diabetic, and insulin-treated diabetic rats underwent a hyperinsulinemic-hypoglycemic glucose clamp to evaluate central mechanisms of hypothalamo-pituitary-adrenal (HPA) and counterregulatory responses to insulin-induced hypoglycemia. Increases in plasma ACTH, corticosterone, and epinephrine were significantly lower in diabetic rats versus controls. Insulin treatment restored ACTH and corticosterone but not epinephrine responses to hypoglycemia in diabetic rats. Glucagon and norepinephrine responses to hypoglycemia were not affected by diabetes or insulin treatment. In response to hypoglycemia, hypothalamic CRH mRNA and pituitary proopiomelanocortin mRNA expression increased in control and insulin-treated but not in untreated diabetic rats. Arginine vasopressin mRNA was unaltered by hypoglycemia in all groups. Interestingly, hypoglycemia decreased hippocampal GR1 mRNA expression in control and insulin-treated diabetic rats but not in diabetic rats. In contrast, type 2 glucocortoid receptor (GR2) mRNA was not altered by hypoglycemia. In conclusion, despite increased basal HPA activity, HPA responses to hypoglycemia were markedly reduced in uncontrolled diabetes. We speculate that the defect in CRH response could be related to the defective GR1 response. It is intriguing that insulin treatment restored the HPA response to hypoglycemia but, surprisingly, not the deficient epinephrine response. This is important because during severe hypoglycemia, epinephrine is an important counterregulatory hormone.

Hyperactivation of the hypothalamo-pituitary-adrenocortical axis in streptozotocin-diabetes is associated with reduced stress responsiveness and decreased pituitary and adrenal sensitivity

Although increased hypothalamo-pituitary-adrenocortical (HPA) activity has been reported in diabetic patients, the mechanisms underlying hyperactivation are still unclear. We investigated whether alterations in pituitary, adrenal and/or glucocorticoid negative feedback sensitivity in diabetes are responsible for 1) the impaired HPA response to stress and 2) basal hyperactivation of the HPA axis. Normal control, untreated streptozotocin-diabetic and insulin-treated diabetic rats were chronically catheterized. Eight days following surgery, pituitary-adrenal function was monitored throughout the day. Stress responsiveness was evaluated using 20 min of restraint on d 10. Thereafter, the rats were treated with CRH (0.5 microg/kg), ACTH(1-24) (75ng/kg) or dexamethasone (25 microg/kg) iv on d 12, 14, and 16 to evaluate pituitary, adrenal and glucocorticoid feedback sensitivity, respectively. Plasma ACTH and corticosterone (B) concentrations in untreated diabetic rats were significantly higher at 0800 h, but no different at 1300 h or 1800 h. Insulin treatment of diabetic rats normalized ACTH and B concentrations at 0800 h. The pituitary-adrenal response to restraint was greatly diminished in untreated diabetic rats, whereas insulin treatment partially restored this response in diabetic rats. Administration of CRH and ACTH revealed reduced pituitary and adrenal sensitivity in untreated diabetic animals compared with both control and insulin-treated diabetic animals. The dexamethasone suppression test indicated decreased glucocorticoid negative feedback sensitivity in diabetic rats, which was restored with insulin treatment. In conclusion, these studies demonstrate that: 1) impaired stress responsiveness of the diabetic HPA axis involves both decreased pituitary and adrenal sensitivity; and 2) basal hyperactivation of the diabetic HPA axis in the morning is due, in part, to decreased glucocorticoid negative feedback sensitivity.

Enzymatic studies on the key enzymes of vitamin D metabolism; 1 alpha-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24)

The key enzymes of vitamin D3 metabolism, renal 25-hydroxyvitamin D3 1 alpha-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24) were expressed in Escherichia coli, and their enzymatic properties were revealed. As expected, mouse CYP27B1 and human CYP27B1 showed the 1 alpha-hydroxylation of 25-hydroxyvitamin D3 with the Michaelis constant, Km, value of 2.7 microM. Unexpectedly, both mouse CYP27B1 and human CYP27B1 showed greater Vmax/Km values toward 24,25-dihydroxyvitamin D3 than 25-hydroxyvitamin D3, suggesting that 24, 25-dihydroxyvitamin D3 is a better substrate than 25-hydroxyvitamin D3 for both CYP27B1. Enzymatic studies on substrate specificity of CYP27B1 revealed that 25-hydroxyl group of vitamin D3 was essential for the 1 alpha-hydroxylase activity, and 24-hydroxyl group enhanced the activity, but, 23-hydroxyl group greatly reduced the activity. On rat CYP24, it was demonstrated that CYP24 catalyzed four-step monooxygenation towards 25-hydroxyvitamin D3. Furthermore, in vivo and in vitro metabolic studies on 1 alpha,25-dihydroxyvitamin D3 clearly indicated that CYP24 catalyzed six-step monooxygenation to convert 1 alpha,25-dihydroxyvitamin D3 into calcitroic acid which is known as a final metabolite of 1 alpha,25-dihydroxyvitamin D3 for excretion in bile. These results strongly suggest that CYP24 is highly responsible for the metabolism of both 25-hydroxyvitamin D3 and 1 alpha,25-dihydroxyvitamin D3. In addition, we have succeeded in the construction of mitochondrial P450 electron transport chain consisting of ADR, ADX and each of CYP27B1 and CYP24 in E. coli cells. The coexpression system with CYP27B1 might be useful as a bioreactor to produce 1 alpha,25-dihydroxyvitamin D3. In contrast, the coexpression system with CYP24 would be applied to metabolic studies of vitamin D analogs used as drugs.

Effects of cobalt-substitution of the active zinc ion in thermolysin on its activity and active-site microenvironment

Thermolysin is remarkably activated in the presence of high concentrations (1-5 M) of neutral salts [Inouye, K. (1992) J. Biochem. 112, 335-340]. The activity is enhanced 13-15 times with 4 M NaCl at pH 7.0 and 25 degrees C. Substitution of the active site zinc with other transition metals alters the activity of thermolysin [Holmquist, B. and Vallee, B.L. (1974) J. Biol. Chem. 249, 4601-4607]. Cobalt is the most effective among the transition metals and doubles the activity toward N-[3-(2-furyl)acryloyl]-glycyl-L-leucine amide. In this study, the effect of NaCl on the activity of cobalt-substituted thermolysin was examined. Cobalt-substituted thermolysin, with 2.8-fold increased activity compared with the native enzyme, is further activated by the addition of NaCl in an exponential fashion, and the activity is enhanced 13-15 times at 4 M NaCl. The effects of cobalt-substitution and the addition of salt are independent of each other. The activity of cobalt-substituted thermolysin, expressed as k(cat)/K(m), is pH-dependent and controlled by at least two ionizing residues with pK(a) values of 6.0 and 7.8, the acidic pK(a) being slightly higher compared to 5.6 of the native enzyme. These pK(a) values remain constant in the presence of 4 M NaCl, indicating that the electrostatic environment of cobalt-substituted thermolysin is more stable than that of the native enzyme, the acidic pK(a) of which shifts remarkably from 5.6 to 6.7 at 4 M NaCl. Zincov, a competitive inhibitor, binds more tightly to the cobalt-substituted than to native thermolysin at pH 4.9-9.0, probably because of its preference for cobalt in the fivefold coordination. The cobalt substitution has been shown to be a favorable tool with which to explore the active-site microenvironment of thermolysin.

Structure-function analysis of CYP27B1 and CYP27A1. Studies on mutants from patients with vitamin D-dependent rickets type I (VDDR-I) and cerebrotendinous xanthomatosis (CTX)

We have determined eight types of missense mutants of CYP27B1 from Japanese vitamin D-dependent rickets type I (VDDR-I) patients [Kitanaka, S., Takeyama, K., Murayama, A., Sato, T., Okumura, K., Nogami, M., Hasegawa, Y., Niimi, H., Yanagisawa, J., Tanaka, T. & Kato, S. (1998) New England J. Med., 338, 653-661 and Kitanaka, S., Murayama, A., Sakaki, T., Inouye, K., Seino, Y., Fukumoto, S., Shima, M., Yukizane, S., Takayanagi, M., Niimi, H., Takeyama, K. & Kato, S. (1999) J. Clin. Endocrine Metab., 84, 4111-4117]. None of the CYP27B1 mutants showed 1alpha-hydroxylase activity towards 25-hydroxyvitamin D3. Thus, it was assumed that the mutated amino-acid residues play important roles in the 1alpha-hydroxylase activity, such as substrate binding, activation of molecular oxygen, interaction with adrenodoxin, and folding of the cytochrome P450 structure. To examine our hypothesis, we generated various mutants of CYP27B1 and studied their enzymatic properties. In addition, the corresponding mutations were introduced to CYP27A1, which belongs to the same family as CYP27B1. As CYP27A1 showed much higher expression level than CYP27B1 in Escherichia coli, further analysis including heme-binding and substrate-binding was performed with CYP27A1 in place of CYP27B1. Western blot analysis, spectral analysis including reduced CO-difference spectra and substrate-induced difference spectra, and enzymatic analysis of the mutant CYP27A1 gave information on the structure-function relationships of both CYP27A1 and CYP27B1. Although the sequence alignment suggested that Arg107, Gly125, and Pro497 of CYP27B1 might be involved in substrate binding, the experimental data strongly suggested that mutations of these amino-acid residues destroyed the tertiary structure of the substrate-heme pocket. It was also suggested that Arg389 and Arg453 of CYP27B1 were involved in heme-propionate binding, and Asp164 stabilized the four-helix bundle consisting of D, E, I and J helices, possibly by forming a salt bridge. Thr321 was found to be responsible for the activation of molecular oxygen.

Involvement of B-Raf in Ras-induced Raf-1 activation

The mechanism of Ras-induced Raf-1 activation is not fully understood. Previously, we identified a 400-kDa protein complex as a Ras-dependent Raf-1 activator. In this study, we identified B-Raf as a component of this complex. B-Raf was concentrated during the purification of the activator. Immunodepletion of B-Raf abolished the effect of the activator on Raf-1. Furthermore, B-Raf and Ras-activated Raf-1 co-operatively, when co-transfected into human embryonic kidney 293 cells. On the other hand, Ras-dependent extracellular signal-regulated kinase/mitogen-activated protein kinase kinase stimulator (a complex of B-Raf and 14-3-3) failed to activate Raf-1 in our cell-free system. These results suggest that B-Raf is an essential component of the Ras-dependent Raf-1 activator.

Molecular regulation of the hypothalamo-pituitary-adrenal axis in streptozotocin-induced diabetes: effects of insulin treatment

Increased hypothalamo-pituitary-adrenocortical (HPA) activity in diabetes is likely important in the development of some pathologies associated with the disorder. We hypothesized that central regulation of HPA activity differs among normal, streptozotocin (STZ)-diabetic, and insulin-treated diabetic rats. Blood glucose, ACTH, and corticosterone were elevated, 8 d after inducing diabetes. Insulin treatment normalized these parameters. Plasma norepinephrine was similar in all groups, but epinephrine was lower in STZ-diabetic and higher in insulin-treated rats vs. normals. Increased ACTH with diabetes corresponded with increased hypothalamic CRH mRNA, but no change in pituitary POMC mRNA. With insulin-treatment, CRH mRNA remained elevated, and POMC mRNA was unaltered. Hippocampal MR mRNA expression was dramatically increased with diabetes and, moreover, was not normalized by insulin. No differences in GR mRNA were detected between normal and STZ-diabetic rats. However, insulin treatment increased GR mRNA levels in the paraventricular nucleus and pituitary. We postulate that, in STZ-diabetes: 1) increased HPA activity is caused by increased central drive at and/or above the level of the paraventricular nucleus and is associated with decreased epinephrine; and 2) normalized pituitary-adrenal activity with insulin may be caused by the compensatory increase in GR mRNA allowing glucocorticoid-mediated suppression of ACTH secretion despite the residual increase in central HPA activity. Thus, insulin apparently restored HPA activity at and below the pituitary but, surprisingly, not above it.

Effects of antecedent hypoglycemia, hyperinsulinemia, and excess corticosterone on hypoglycemic counterregulation

This study aimed to differentiate the effects of repeated antecedent hypoglycemia, antecedent marked hyperinsulinemia, and antecedent increases in corticosterone on counterregulation to subsequent hypoglycemia in normal rats. Specifically, we examined whether exposure to hyperinsulinemia or elevated corticosterone per se could impair subsequent counterregulation. Four groups of male Sprague-Dawley rats were used: 1) normal controls (N) had 4 days of sham antecedent treatment; 2) an antecedent hypoglycemia group (AH) had 7 episodes of hyperinsulinemic hypoglycemia over 4 days; 3) an antecedent hyperinsulinemia group (AE) had 7 episodes of hyperinsulinemic euglycemia; and 4) an antecedent corticosterone group (AC) had 7 episodes of intravenous corticosterone to simulate the hypoglycemic corticosterone levels in AH rats. On day 5, hyperinsulinemic euglycemic-hypoglycemic clamps were performed. Epinephrine responses to hypoglycemia were impaired (P < 0.05 vs. N) after antecedent hypoglycemia and hyperinsulinemia. This correlated with diminished (P < 0.05 vs. N) absolute glucose production responses in AH rats and diminished incremental glucose production responses in AE rats. Paradoxically, norepinephrine responses were increased (P < 0.05 vs. N) after antecedent hypoglycemia. Glucagon and corticosterone responses were unaffected by antecedent hypoglycemia and hyperinsulinemia. In AC rats, incremental but not absolute glucose production responses were decreased (P < 0.05 vs. N). However, neuroendocrine counterregulation was unaltered. We conclude that both antecedent hypoglycemia and hyperinsulinemia impair epinephrine and glucose production responses to subsequent hypoglycemia, suggesting that severe recurrent hyperinsulinemia may contribute to the development of hypoglycemia-associated autonomic failure.

Myosin II-dependent cylindrical protrusions induced by quinine inDictyostelium: antagonizing effects of actin polymerization at the leading edge

We found that amoeboid cells of Dictyostelium are induced by a millimolar concentration of quinine to form a rapidly elongating, cylindrical protrusion, which often led to sustained locomotion of the cells. Formation of the protrusion was initiated by fusion of a contractile vacuole with the cell membrane. During protrusion extension, a patch of the contractile vacuole membrane stayed undiffused on the leading edge of the protrusion for over 30 seconds. Protrusion formation was not inhibited by high osmolarity of the external medium (at least up to 400 mosM). By contrast, mutant cells lacking myosin II (mhc− cells) failed to extend protrusions upon exposure to quinine. When GFP-myosin-expressing cells were exposed to quinine, GFP-myosin was accumulated in the cell periphery forming a layer under the cell membrane, but a newly formed protrusion was initially devoid of a GFP-myosin layer, which gradually formed and extended from the base of the protrusion. F-actin was absent in the leading front of the protrusion during the period of its rapid elongation, and the formation of a layer of F-actin in the front was closely correlated with its slowing-down or retraction. Periodical or continuous detachment of the F-actin layer from the apical membrane of the protrusion, accompanied by a transient increase in the elongation speed at the site of detachment, was observed in some of the protrusions. The detached F-actin layers, which formed a spiral layer of F-actin in the case of continuous detachment, moved in the opposite direction of protrusion elongation. In the presence of both cytochalasin A and quinine, the protrusions formed were not cylindrical but spherical, which swallowed up the entire cellular contents. The estimated bulk flux into the expanding spherical protrusions of such cells was four-times higher than the flux into the elongating cylindrical protrusions of the cells treated with quinine alone. These results indicate that the force responsible for the quinine-induced protrusion is mainly due to contraction of the cell body, which requires normal myosin II functions, while actin polymerization is important in restricting the direction of its expansion. We will discuss the possible significance of tail contraction in cell movement in the multicellular phase of Dictyostelium development, where cell locomotion similar to that induced by quinine is often observed without quinine treatment, and in protrusion elongation in general.

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Pepsin digestion of a mouse monoclonal antibody of IgG1 class formed F(ab')(2) fragments in which the light chains as well as the heavy chains were truncated

In the preparation of F(ab')(2) fragments of monoclonal antibodies (mAbs) of IgG class, heavy (H) chains are truncated by pepsin and light (L) chains are remained intact. However, F(ab')(2) fragments formed by pepsin-digestion of a mouse mAb PM373, which was of the IgG1 class and raised against human prostate specific antigen (PSA), indicated that the L chains of 31 kDa were cleaved into 23-kDa fragments as well as the cleavage of H chains of 50 kDa into 28-kDa fragments. On the other hand, F(ab')(2) fragments formed by digesting the mAb by cathepsin D showed that the L chains were intact and the H chains were truncated. The immunoreactivities against PSA of the F(ab')(2) fragments containing the intact L chains and those containing the truncated L chains were almost the same as that of the parental mAb, suggesting that the truncation of the L chains does not affect the interaction of the mAb with its specific antigen.

Interactions of human matrix metalloproteinase 7 (matrilysin) with the inhibitors thiorphan and R-94138

The effects of the metalloproteinase inhibitors thiorphan and R-94138 on the matrilysin-catalyzed hydrolysis of (7-methoxycoumarin-4-yl)acetyl-L-Pro-L-Leu-Gly-L-Leu-[N(3)-(2,4-dinitrophenyl)-L-2,3-diamino-propionyl]-L-Ala-L-Arg-NH(2) [MOCAc-PLGL(Dpa)AR] were examined. The inhibitor constants (K(i)) of thiorphan and R-94138 for matrilysin at pH 7.5, 25 degrees C were determined to be 11.2 and 7.65 microM, respectively. From the temperature dependence of the K(i) values at pH 7.5, the standard enthalpy change (Delta H degrees ') values for the binding of matrilysin with thiorphan and R-94138 were determined to be -(18.2 +/- 0.9) and (1.65 +/- 1.07) kJ x mol(-1), respectively. The binding of matrilysin to thiorphan is exothermic and the free energy change in the complex formation depends mainly on the change in enthalpy, while the binding to R-94138 is endothermic and typically entropy-driven. Hydrophobic interactions are suggested to contribute significantly to the binding of matrilysin to R-94138 as well as to the substrate. The pH dependence of the K(i) value suggests that at least two ionizing groups with pK(a) values of 4.5 and 9.1--9.3 are involved in the binding. The matrilysin activity is regulated by ionizing groups with pK(a) values of 4.3 and 9.6. Both inhibition and hydrolysis are suggested to be controlled by the same residues in matrilysin, most likely Glu 198 and Tyr 219, respectively.