Comparison of cellular responses to ionizing radiation in keratinocytes isolated from healthy donors and type II diabetes patients

PURPOSE

Due to the expanding repertoire of treatment devices that use radiation, the possibility of exposure to both low-dose and high-dose radiation continues to increase. Skin is the outermost part of the body and thus directly exposed to radiation-induced damage. In particular, the skin of diabetes patients is fragile and easily damaged by external stimuli, such as radiation. However, damage and cellular responses induced by ionizing irradiation in diabetic skin have not been explored in detail. In this study, we investigated the effects of several irradiation dose on normal keratinocytes and those from type II diabetes patients, with particular focus on DNA damage.

MATERIALS AND METHODS

Cellular responses to low-dose radiation (0.1 Gy) and high-dose radiation (0.5 and 2 Gy) were evaluated. Cell cycle analysis was conducted via flow cytometry and cell viability analyzed using the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay. Proteins related to the DNA damage response (DDR) and repair signaling pathways and apoptosis were detected via immunoblot analysis. Apoptosis and cell differentiation were additionally examined in 3D skin organoids using immunohistochemistry.

RESULTS

Compared to respective control groups, no significant changes were observed in cell cycle, DDR and repair mechanisms, cell survival, and differentiation in response to 0.1 Gy irradiation in both normal and diabetes type II keratinocytes. On the other hand, the cell cycle showed an increase in the G2/M phase in both cell types following exposure to 2 Gy irradiation. At radiation doses 2 Gy, activation of the DDR and repair signaling pathways, apoptosis, and cell differentiation were increased and viability was decreased in both cell types. Notably, these differences were more pronounced in normal than diabetes type II keratinocytes.

CONCLUSIONS

Normal keratinocytes respond more strongly to radiation-induced damage and recovery than diabetes type II keratinocytes.

Cyclin D1 promotes radioresistance through regulation of RAD51 in melanoma

Melanoma is a notoriously radioresistant type of skin cancer. Elucidation of the specific mechanisms underlying radioresistance is necessary to improve the clinical efficacy of radiation therapy. To identify the key factors contributing to radioresistance, five melanoma cell lines were selected for study and genes that were upregulated in relatively radioresistant melanomas compared with radiosensitive melanoma cells determined via RNA sequencing technology. In particular, we focused on cyclin D1 (CCND1), a well known cell cycle regulatory molecule. In radiosensitive melanoma, overexpression of cyclin D1 reduced apoptosis. In radioresistant melanoma cell lines, suppression of cyclin D1 with a specific inhibitor or siRNA increased apoptosis and decreased cell proliferation in 2D and 3D spheroid cultures. In addition, we observed increased expression of γ-H2AX, a molecular marker of DNA damage, even at a later time after γ-irradiation, under conditions of inhibition of cyclin D1, with a response pattern similar to that of radiosensitive SK-Mel5. In the same context, expression and nuclear foci formation of RAD51, a key enzyme for homologous recombination (HR), were reduced upon inhibition of cyclin D1. Downregulation of RAD51 also reduced cell survival to irradiation. Overall, suppression of cyclin D1 expression or function led to reduced radiation-induced DNA damage response (DDR) and triggered cell death. Our collective findings indicate that the presence of increased cyclin D1 potentially contributes to the development of radioresistance through effects on RAD51 in melanoma and could therefore serve as a therapeutic target for improving the efficacy of radiation therapy.

0790 The Clinical Significance of Hepcidin as a Predictive Value for Treatment Responses in Restless Legs Syndrome

Introduction

Restless legs syndrome (RLS) is a common sensory motor neurological disorder that is related to iron-dopamine dysregulation and immune system alteration. Hepcidin is the key regulatory hormone of systemic iron homeostasis and is related to inflammatory processes. We aimed to evaluate the clinical utility of hepcidin as a diagnostic biomarker and index of therapeutic responses in RLS patients after dopaminergic treatment.

Methods

Non-anemic and drug-naive RLS patients (n=18) and healthy controls (n=15) were enrolled. Hepcidin (pre-prohepcidin) and iron-related values in serum were measured upon the first visit in both groups and 12 weeks later after dopaminergic treatment in 12 RLS patients. Information about sociodemographic characteristics, sleep-related profiles, mood, and anxiety was obtained upon the first visit in all participants as well as after treatment in RLS patients.

Results

Hepcidin levels exhibited no significant differences between patients with drug-naïve RLS and healthy controls at a diagnosis (7.1 ± 2.4 vs. 7.0 ± 3.2 ng/ml, p = 0.978). Decreased hepcidin levels were significantly associated with decreased RLS severity (β = 0.002, 95% CI = 0.00−0.00, p = 0.005) and improved quality of life (β = 0.002, 95% CI = 0.00−7.01, p = 0.044) in a dose-dependent manner after 12 weeks of treatment with a dopamine agonist. This association was independent of age, sex, inflammatory markers, sleep quality, insomnia, daytime sleepiness, depression, and anxiety.

Conclusion

This study demonstrates a role of hepcidin as a predictor of therapeutic responses in RLS patients.

Support

This work was supported by the Korea Health technology R&D Project through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, South Korea [grant number HI17C2072].

Integrin αvβ3-Akt signalling plays a role in radioresistance of melanoma

Melanoma is a deadly type of skin cancer that is particularly difficult to treat owing to its resistance to radiation therapy. Here, we attempted to determine the key proteins responsible for melanoma radioresistance, with the aim of improving disease response to radiation therapy. Two melanoma cell lines, SK-Mel5 and SK-Mel28, with different radiosensitivities were analysed via RNA-Seq (Quant-Seq) and target proteins with higher abundance in the more radioresistant cell line, SK-Mel28, identified. Among these proteins, integrin αvβ3, a well-known molecule in cell adhesion, was selected for analysis. Treatment of SK-Mel28 cells with cilengitide, an integrin αvβ3 inhibitor, as well as γ-irradiation resulted in more significant cell death than γ-irradiation alone. In addition, Akt, a downstream signal transducer of integrin αvβ3, showed high basic activation in SK-Mel28 and was significantly decreased upon co-treatment with cilengitide and γ-irradiation. MK-2206, an Akt inhibitor, exerted similar effects on the SK-Mel28 cell line following γ-irradiation. Our results collectively demonstrate that the integrin αvβ3-Akt signalling pathway contributes to radioresistance in SK-Mel28 cells, which may be manipulated to improve therapeutic options for melanoma.

The NLRP3 inflammasome: role in airway inflammation

Asthma is characterized by airway inflammation, airway hyperresponsiveness and airway remodelling. Uncontrolled airway inflammation or repeated asthma exacerbations can lead to airway remodelling, which cannot be reversed by current pharmacological treatment, and consequently lead to decline in lung function. Thus, it is critical to understand airway inflammation in asthma and infectious exacerbation. The inflammasome has emerged as playing a key role in innate immunity and inflammation. Upon ligand sensing, inflammasome components assemble and self-oligomerize, leading to caspase-1 activation and maturation of pro-IL-1β and pro-IL-18 into bioactive cytokines. These bioactive cytokines then play a pivotal role in the initiation and amplification of inflammatory processes. In addition to facilitating the proteolytic activation of IL-1β and IL-18, inflammasomes also participate in cell death through caspase-1-mediated pyroptosis. In this review, we describe the structure and function of the inflammasome and provide an overview of our current understanding of role of the inflammasome in airway inflammation. We focus on nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome as it is the best-characterized subtype shown expressed in airway and considered to play a key role in chronic airway diseases such as asthma.

Prediction of tumor necrosis fraction using combined volumetric and metabolic indices derived from FDG-PET/CT in osteosarcoma patients receiving neoadjuvant chemotherapy

10539

Background: Maximum standardized uptake values (mSUV) might not reliably reflect the chemotherapy response in osteosarcoma especially when treatment response within tumors is heterogenous. The purpose of this study was to compare the usefulnesses of various FDG PET/CT indices for predicting tumor response to neoadjuvant chemotherapy and to identify the most appropriate one in osteosarcoma. Methods: Thirteen patients with primary osteosarcoma (age 14±2.9 yrs, ranged 10–19 yrs) that had undergone FDG PET/CT scans before and after neoadjuvant chemotherapy were enrolled. The authors measured mSUV, metabolic tumor volumes (MTV), and total lesion glycolysis (TLG) in each PET/CT scan. MTVs were calculated by summing voxels with SUV greater than 1.5, 2, 2.5 and 3.0, and with % mSUV greater than 20%, 25%, 30% and 35%. Histopathologic necrosis fractions were compared with the above-mentioned PET/CT parameters and their pre- to post-treatment ratios (MTV ratio, rMTV; mSUV ratio, rSUV; TLG ratio, rTLG). Results: Histopathologic necrosis fractions ranged from 3% to 99% (62.2%±37.7%). rMTV and rTLG values were found to be correlated with histopathologic necrosis fractions (R2=0.45–0.65, p<0.05), whereas, mSUV and MR image volumes (MRV), both before and after treatment, rSUV values, and rMRV values were not. With regard to rMTV and rTLG values obtained using various MTV criteria, the highest correlation was observed for a rTLG value of 2.5 mg/ml (R2=0.65, p=0.001). Five patients were classified as responders and 8 as poor-responders to neoadjuvant chemotherapy defined as those with chemotherapy-induced necrosis fractions of ≥90% and <90%, respectively. The rSUVs of responders and poor-responders were not different, but rMTV and rTLG values showed a trend toward difference, although statistically not significant (p=0.110 and 0.106, respectively). The sensitivity and specificity of rTLG were 100% and 62.5%, respectively, at an SUV cut-off of 0.13. Conclusions: In our osteosarcoma patient population, TLG and MTV, which represent combined metabolic and volumetric indices, were found to predict tumor response better than pre- or post-treatment mSUV or rSUV.

No significant financial relationships to disclose.

Effective mass anisotropy of gamma electrons in GaAs/AlGaAs quantum wells

Resonant magnetotunneling in GaAs/Al(0.28)Ga0.72As double barrier structures is used to demonstrate that the effective mass of confined Gamma conduction electrons becomes anisotropic when an electric field is applied perpendicular to the interfaces. Although several authors have previously reported Gamma-related optical anisotropy, this is the first example of a corresponding electrical anisotropy. The results are explained using a quantum mechanical model involving interface band mixing that contains additional features not found in the optical case.

Developmentally dynamic histone acetylation pattern of a tissue-specific chromatin domain

We have defined the histone acetylation pattern of the endogenous murine beta-globin domain, which contains the erythroidspecific beta-globin genes. The beta-globin locus control region (LCR) and transcriptionally active promoters were enriched in acetylated histones in fetal liver relative to fetal brain, whereas the inactive promoters were hypoacetylated. In contrast, the LCR and both active and inactive promoters were hyperacetylated in yolk sac. Hypersensitive site two of the LCR was also hyperacetylated in murine embryonic stem cells, whereas beta-globin promoters were hypoacetylated. Thus, the acetylation pattern varied at different developmental stages. Histone deacetylase inhibition selectively increased acetylation at a hypoacetylated promoter in fetal liver, suggesting that active deacetylation contributes to silencing of promoters. We propose that dynamic histone acetylation and deacetylation play an important role in the developmental control of beta-globin gene expression.

Bypassing the kinetic trap of serpin protein folding by loop extension

The native form of some proteins such as strained plasma serpins (serine protease inhibitors) and the spring-loaded viral membrane fusion proteins are in a metastable state. The metastable native form is thought to be a folding intermediate in which conversion into the most stable state is blocked by a very high kinetic barrier. In an effort to understand how the spontaneous conversion of the metastable native form into the most stable state is prevented, we designed mutations of alpha1-antitrypsin, a prototype serpin, which can bypass the folding barrier. Extending the reactive center loop of alpha1-antitrypsin converts the molecule into a more stable state. Remarkably, a 30-residue loop extension allows conversion into an extremely stable state, which is comparable to the relaxed cleaved form. Biochemical data strongly suggest that the strain release is due to the insertion of the reactive center loop into the major beta-sheet, A sheet, as in the known stable conformations of serpins. Our results clearly show that extending the reactive center loop is sufficient to bypass the folding barrier of alpha1-antitrypsin and suggest that the constrain held by polypeptide connection prevents the conversion of the native form into the lowest energy state.

Distribution of the native strain in human alpha 1-antitrypsin and its association with protease inhibitor function

Serine protease inhibitors (serpins) are metastable in their native state. This strain, which is released upon binding to target proteases, is essential for the inhibitory activity of serpins. To understand the structural basis of the native strain, we previously characterized stabilizing mutations of alpha(1)-antitrypsin, a prototypical inhibitory serpin, in regions such as the hydrophobic core. The present study evaluates the effects of single point mutations throughout the molecule on stability and protease inhibitory activity. We identified stabilizing mutations in most secondary structures, suggesting that the native strain is distributed throughout the molecule. Examination of the substitution patterns and the structures of the mutation sites revealed surface hydrophobic pockets as a component of the native strain in alpha(1)-antitrypsin, in addition to the previously identified unusual interactions such as side chain overpacking and cavities. Interestingly, many of the stabilizing substitutions did not affect the inhibitory activity significantly. Those that affected the activity were confined in the regions that are mobilized during the complex formation with a target enzyme. The results of our study should be useful for designing proteins with strain and for regulating the stability and functions of serpins.

Role of Lys335 in the metastability and function of inhibitory serpins

The native form of inhibitory serpins (serine protease inhibitors) is not in the thermodynamically most stable state but in a metastable state, which is critical to inhibitory functions. To understand structural basis and functional roles of the native metastability of inhibitory serpins, we have been characterizing stabilizing mutations of human alpha1-antitrypsin, a prototype inhibitory serpin. One of the sites that has been shown to be critical in stability and inhibitory activity of alpha1-antitrypsin is Lys335. In the present study, detailed roles of this lysine were analyzed by assessing the effects of 13 different amino acid substitutions. Results suggest that size and architect of the side chains at the 335 site determine the metastability of alpha1-antitrypsin. Moreover, factors such as polarity and flexibility of the side chain at this site, in addition to the metastability, seem to be critical for the inhibitory activity. Substitutions of the lysine at equivalent positions in two other inhibitory serpins, human alpha1-antichymotrypsin and human antithrombin III, also increased stability and decreased inhibitory activity toward alpha-chymotrypsin and thrombin, respectively. These results and characteristics of lysine side chain, such as flexibility, polarity, and the energetic cost upon burial, suggest that this lysine is one of the structural designs in regulating metastability and function of inhibitory serpins in general.

Metastability in the inhibitory mechanism of human alpha1-antitrypsin

Metastability of the native form of proteins has been recognized as a mechanism of biological regulation. The energy-loaded structure of the fusion protein of influenza virus and the strained native structure of serpins (serine protease inhibitors) are typical examples. To understand the structural basis and functional role of the native metastability of inhibitory serpins, we characterized stabilizing mutations of alpha1-antitrypsin in a region presumably involved in complex formation with a target protease. We found various unfavorable interactions such as overpacking of side chains, polar-nonpolar interactions, and cavities as the structural basis of the native metastability. For several stabilizing mutations, there was a concomitant decrease in the inhibitory activity. Remarkably, some substitutions at Lys-335 increased the stability over 6 kcal mol-1 with simultaneous loss of activity over 30% toward porcine pancreatic elastase. Considering the location and energetic cost of Lys-335, we propose that this lysine plays a pivotal role in conformational switch during complex formation. Our current results are quite contradictory to those of previously reported hydrophobic core mutations, which increased the stability up to 9 kcal mol-1 without any significant loss of activity. It appears that the local strain of inhibitory serpins is critical for the inhibitory activity.

LlaFI, a type III restriction and modification system in Lactococcus lactis

We describe a type III restriction and modification (R/M) system, LlaFI, in Lactococcus lactis. LlaFI is encoded by a 12-kb native plasmid, pND801, harbored in L. lactis LL42-1. Sequencing revealed two adjacent open reading frames (ORFs). One ORF encodes a 680-amino-acid polypeptide, and this ORF is followed by a second ORF which encodes an 873-amino-acid polypeptide. The two ORFs appear to be organized in an operon. A homology search revealed that the two ORFs exhibited significant similarity to type III restriction (Res) and modification (Mod) subunits. The complete amino acid sequence of the Mod subunit of LlaFI was aligned with the amino acid sequences of four previously described type III methyltransferases. Both the N-terminal regions and the C-terminal regions of the Mod proteins are conserved, while the central regions are more variable. An S-adenosyl methionine (Ado-Met) binding motif (present in all adenine methyltransferases) was found in the N-terminal region of the Mod protein. The seven conserved helicase motifs found in the previously described type III R/M systems were found at the same relative positions in the LlaFI Res sequence. LlaFI has cofactor requirements for activity that are characteristic of the previously described type III enzymes. ATP and Mg2+ are required for endonucleolytic activity; however, the activity is not strictly dependent on the presence of Ado-Met but is stimulated by it. To our knowledge, this is the first type III R/M system that has been characterized not just in lactic acid bacteria but also in gram-positive bacteria.

Characterization of a human alpha1-antitrypsin variant that is as stable as ovalbumin

The metastability of inhibitory serpins (serine proteinase inhibitors) is thought to play a key role in the facile conformational switch and the insertion of the reactive center loop into the central beta-sheet, A-sheet, during the formation of a stable complex between a serpin and its target proteinase. We have examined the folding and inhibitory activity of a very stable variant of human alpha1-antitrypsin, a prototype inhibitory serpin. A combination of seven stabilizing single amino acid substitutions of alpha1-antitrypsin, designated Multi-7, increased the midpoint of the unfolding transition to almost that of ovalbumin, a non-inhibitory but more stable serpin. Compared with the wild-type alpha1-antitrypsin, Multi-7 retarded the opening of A-sheet significantly, as revealed by the retarded unfolding and latency conversion of the native state. Surprisingly, Multi-7 alpha1-antitrypsin could form a stable complex with a target elastase with the same kinetic parameters and the stoichiometry of inhibition as the wild type, indicating that enhanced A-sheet closure conferred by Multi-7 does not affect the complex formation. It may be that the stability increase of Multi-7 alpha1-antitrypsin is not sufficient to influence the rate of loop insertion during the complex formation.

The sapA promoter from Streptomyces coelicolor requires activation sites and initiator-like sequences but No -10 or -35 sequences

The Streptomyces coelicolor sapA gene encodes a spore coat protein. The sapA promoter is regulated developmentally, with maximal expression occurring in aerial hyphae at a late stage of colonial development. The DNA sequences upstream from the transcription start point do not appear to fall into a previously described promoter class. One (or more) putative activation site, required for full activity, is eliminated when 5' deletions extend to between -178 and -72 bases upstream from the transcription start point. In addition, a downstream activation site is destroyed by removing sequences between positions +40 and +120, relative to the transcription start point, in the absence of an intact upstream region. However, temporal regulation of transcription initiation over the course of the life cycle is maintained faithfully in the absence of these elements, even in the smallest 18-bp sapAp fragment containing sequences from positions -8 to +10. Site-specific mutations around the transcriptional start points shift the timing of sapA expression to an earlier stage in the developmental cycle. These results sugges that a novel mechanism may be involved in Streptomyces late gene expression.

Tn4556 and luciferase: synergistic tools for visualizing transcription in Streptomyces

Progress in understanding genetic regulatory controls in the Actinomycetes has been rate limited by the properties of in vivo transcriptional probes. We have developed a set of plasmid- and transposon-based promoter-probe vectors that employ the Vibrio harveyi luciferase-encoding luxAB cassette as a reporter of transcription. The primary advantages of luciferase (Lux) over other reporter gene products are: (i) unsurpassed sensitivity; (ii) utility during stationary-phase gene expression; and (iii) the ability to localize promoter activity spatially within developing colonies. We have used these vectors to screen for Streptomyces coelicolor promoters that exhibit developmental phenotypes or that are induced by various environmental stimuli. The plasmid-based probes have proved invaluable for identifying cis- and trans-acting elements that are required for stationary-phase expression of the S. coelicolor sapA gene. A collection of novel bld and whi insertion mutants has been obtained by use of the Lux-encoding transposon, Tn5353.

Construction and application of plasmid- and transposon-based promoter-probe vectors for Streptomyces spp. that employ a Vibrio harveyi luciferase reporter cassette

Several versatile promoter-probe vectors have been constructed for Streptomyces strains which utilize the production of blue-green light as a measure of transcription activity. Three plasmid vectors (two high and one low copy number) and two transposons are described. The multicopy plasmids pRS1106 and pRS1108 contain a transcription terminator and multiple-cloning polylinker upstream of promoterless luciferase (lux) and neomycin resistance reporter genes. Plasmid pHI90 is similar in structure to the pRS vectors except that its single copy number is an advantage for regulation studies or situations in which overexpression is otherwise toxic to the cell. The two transposons carry a promoterless lux cassette cloned such that transposition into a target DNA and fusion to the target's transcription unit occur simultaneously. Tn5351 was created by inserting the luciferase genes near the right end of the viomycin resistance transposon Tn4563. Tn5353 carries the luciferase genes near the right end of a neomycin resistance transposon derived from Tn4556. The size of Tn5353 was minimized by deleting nonessential transposon sequences, making this element small enough to be cloned into phi C31 bacteriophages for efficient transposon delivery to target cells of Streptomyces strains. The two Tnlux transposons have been used to generate Streptomyces coelicolor morphological mutants and to monitor transcription from chromosomal promoters during development.

Oxygen-dependent inactivation of ribulose 1,5-bisphosphate carboxylase/oxygenase in crude extracts of Rhodospirillum rubrum and establishment of a model inactivation system with purified enzyme

Ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBPC/O) was inactivated in crude extracts of Rhodospirillum rubrum under atmospheric levels of oxygen; no inactivation occurred under an atmosphere of argon. RuBP carboxylase activity did not decrease in dialyzed extracts, indicating that a dialyzable factor was required for inactivation. The inactivation was inhibited by catalase. Purified RuBPC/O is relatively oxygen stable, as no loss of activity was observed after 4 h under an oxygen atmosphere. The aerobic inactivation catalyzed by endogenous factors in crude extracts was mimicked by using a model system containing purified enzyme, ascorbate, and FeSO4 or FeCl3. Dithiothreitol was found to substitute for ascorbate in the model system. Preincubation of the purified enzyme with RuBP led to enhanced inactivation, whereas Mg2+ and HCO3- significantly protected against inactivation. Unlike the inactivation catalyzed by endogenous factors from extracts of R. rubrum, inactivation in the model system was not inhibited by catalase. It is proposed that ascorbate and iron, in the presence of oxygen, generate a reactive oxygen species which reacts with a residue at the activation site, rendering the enzyme inactive.