Modulation of high voltage -activated calcium channels by phosphorylation

High voltage-activated (HVA) calcium channels from rat brain and rabbit heart are expressed in Xenopus laevis oocytes and their modulation by protein kinases studied. A subtype of the HVA calcium current expressed by rat brain RNA is potentiated by the phospholipid- and calcium-dependent protein kinase (PKC). The calcium channel clone $\alpha\sb{\rm1C}$ from rabbit heart is modulated by the cAMP-dependent protein kinase (PKA), and another factor present in the cytoplasm.^ The HVA calcium channels from rat brain do not belong to the L-type subclass since they are insensensitive to dihydropyridine (DHP) agonists and antagonists. The expressed currents do contain a N-type fraction which is identified by inactivation at depolarized potentials, and a P-type fraction as defined by blockade by the venom of the funnel web spider Agelenopsis Aperta. A non N-type fraction of this current is potentiated, by using phorbol esters to activate PKC. This residual fraction of current resembles the newly described Q-type channel from cerebellar granule cells in its biophysical properties, and potentiation by activation of PKC.^ The $\alpha\sb{\rm1C}$ clone from rabbit heart is expressed in oocytes and single-channel currents are measured using the cell-attached and cell-excised patch clamp technique. The single-channel current runs down within two minutes after patch excision into normal saline bath solution. The catalytic subunit of PKA + MgATP is capable of reversing this rundown for over 15 minutes. There also appears to be an additional factor present in the cytoplasm necessary for channel activity as revealed in experiments where PKA failed to prevent rundown.^ These data are important in that these types of channels are involved in synaptic transmission at many different types of synapses. The mammalian synapse is not accessible for these types of studies, however, the oocyte expression system allows access to HVA calcium channels for the study of their modulation by phosphorylation. ^

Modulation of cytochrome P450 enzyme activity and PAH -induced skin carcinogenesis by naturally occurring coumarins

The present study was designed to determine the potential anticarcinogenic activity of naturally occurring coumarins and their mechanism of action. The results indicated that several naturally occurring coumarins including bergamottin, coriandrin, imperatorin, isopimpinellin, and ostruthin, to which humans are routinely exposed in the diet, were effective inhibitors and/or inactivators of CYP1A1-mediated ethoxyresorufin-O-dealkylase (EROD) or CYP2B1-mediated pentoxyresorufin-O-dealkylase (PROD) in mouse liver microsomes. In addition, bergamottin and corandrin were also found to be inhibitors of purified human P450 1A1 in vitro. Further studies with coriandrin revealed that this compound was a mechanism-based inactivator of P450 1A1 and covalently bound to the P450 1A1 apoprotein. In cultured mouse keratinocytes, bergamottin and coriandrin effectively inhibited the B(a) P metabolism and significantly decreased covalent binding of B(a) P and DMBA to keratinocyte DNA and anti-diol-epoxide-DNA adducts derived from both B(a) P and DMBA in keratinocytes. The data from in vivo experiments showed that bergamottin and coriandrin were potent inhibitors of covalent binding of B (a) P to epidermal DNA and the formation of (+) anti BPDE-DNA adduct, whereas imperatorin and isopimpinellin were more potent inhibitors of covalent binding of DMBA to epidermal DNA. The ability of coumarins to inhibit covalent binding of B (a) P to DNA in mouse epidermis was positively correlated with their inhibitory effect P450 1A1 in vitro, while the inhibitory effect of coumarins on covalent binding of DMBA to epidermal DNA was positively correlated with their inhibitory effects on P450 2B1 and negatively to their inhibitory activity toward P450 1A1. The data from tumor experiments indicated that bergamottin, ostruthin, and coriandrin inhibited tumor initiation by B (a) P in a two-stage carcinogenesis protocol. Bergamottin was most effective in this regard and produced a dose dependent inhibition of papilloma formation in these experiments. In addition, imperatorin was an effective inhibitor of skin tumorigenesis induced by DMBA in SENCAR mouse skin using both a two-stage and a complete carcinogenesis protocol. At dose levels higher than those effective against DMBA, imperatorin also inhibited tumor initiation by B (a) P. The results to date demonstrate that several naturally occurring coumarins possess the ability to block tumor initiation and tumorigenesis by PAHs such as B (a) P and DMBA through inhibition of the P450s involved in the metabolic activation of these hydrocarbons. A working model for the involvement of specific P450s in the metabolic activation of these two PAHs was proposed. ^

Thermo -modulation of MuSVts110 splicing by inhibitory RNA sequences

Viral systems have contributed tremendously to the understanding of eukaryotic molecular biology. The proportional pattern of retroviral RNA expression offers many clues into the alternative splicing of cellular transcripts. The MuSVts110 virus presents an unusual expression system, where the mechanistic combination of RNA splicing and cellular transformation can be physiologically manipulated. Splicing of MuSVts110 pre-mRNA occurs inefficiently (30%-50%) at 33$\sp\circ$C or below and is subdued at 39$\sp\circ$C ($<$5%). Like most alternatively spliced cellular and retroviral transcripts, the MuSVts110 pre-mRNA contains cis-acting intron and exon sequences that attenuate splicing. These include a splicing inhibitory sequence at the 3$\prime$ end of the MuSVts110 v-mos exon, called the E2 Distal Element (E2DE), and a sub-optimal 3$\prime$ splice site. The E2DE directly inhibits MuSVts110 RNA splicing in a sequence-specific fashion at 39$\sp\circ$C but not at 28$\sp\circ$C, potentially through the association of cellular factors. Inefficient MuSVts110 splicing is pre-dominantly attributed to the utilization of multiple weak branchpoint sequences located between $-113$ and $-34$ nucleotides upstream of the 3$\prime$ splice site. The molecular control of MuSVts110 splicing, represented primarily by scattered multiple inefficient branchpoint sequences that are conditionally modulated by the E2DE at higher growth temperatures, is discussed. ^

Modulation of BCL-X$\sb{\rm L}$ is a critical determinant of c-myc induced apoptosis

The fine balance between proliferation and apoptosis plays a primary role in carcinogenesis. Proto-oncogenes that induce both proliferation and apoptosis provide a powerful inbuilt system to inhibit clonal expansion of cells with high proliferation rates. This provides a restraint to the development of neoplasms. C-myc expressing cells undergo apoptosis in low serum by an unknown mechanism. Several lines of evidence suggested that c-myc induces apoptosis by a transcriptional mechanism. However, the target genes of this program have not been fully defined. Protein synthesis inhibitors induce apoptosis in c-myc over-expressing cells at high serum levels suggesting that inhibition of synthesis of a survival factor may induce apoptosis. We show that the expression of c-myc directly correlates with an increase in the level of a survival protein, bcl-$\rm x\sb{L},$ and a decrease in the pro-apoptotic protein, bax, at both the protein and mRNA level. Furthermore, a significant decrease of the bcl-$\rm x\sb{L}$ protein levels is observed under low serum conditions. In order to investigate the mechanism of regulation of bcl-$\rm x\sb{L}$ and bax by c-myc, the bcl-x and bax promoters were cloned, sequenced and shown to contain c-myc binding sites. The chloramephenicol acetyl transferase (CAT) reporter assay was used to demonstrate activation of the bcl-x promoter by increasing levels of c-myc when co-transfected in COS cells. The bax promoter was also shown to be transrepressed in c-myc expressing cells. The role of bcl-$\rm x\sb{L}$ in apoptosis regulation in c-myc cell lines in normal and low serum was then investigated. Cells lines expressing c-myc and bcl-$\rm x\sb{L}$ were generated and were shown to be resistant to apoptosis induction in low serum. Furthermore, cell lines expressing c-myc, anti-sense bcl-$\rm x\sb{L}$ and $\beta$-galactosidase demonstrated significantly enhanced rates of apoptosis in high serum compared to c-myc Rat 1a cells. These findings suggest that c-myc activates a survival program involving bcl-$\rm x\sb{L}$ upregulation and bax downregulation. However, this survival signal is reduced under low serum conditions by the relative downregulation of bcl-$\rm x\sb{L}$ allowing for apoptosis to proceed. These data also directly demonstrates that downregulation in the level of bcl-$\rm x\sb{L}$ associated with low serum conditions is a critical determinant of c-myc induced apoptosis. ^

Modulation of replicative senescence of skeletal muscle satellite cells by insulin -like growth factor-I (IGF-I)

Growth and regeneration of postnatal skeletal muscle requires a population of mononuclear myogenic cells, called satellite cells to add/replace myonuclei, which are postmitotic. Wedged between the sarcolemma and the basal lamina of the skeletal muscle fiber, these cells function as the stem cells of mature muscle fibers. Like other normal diploid cells, satellite cells undergo cellular senescence. Investigations of aging in both rodents and humans have shown that satellite cell self-renewal capacity decreases with advanced age. As a consequence, this could be a potential reason for the characteristically observed age-associated loss in skeletal muscle mass (sarcopenia). This provided the rationale that any intervention that can further increase the proliferative capacity of these cells should potentially be able to either delay, or even prevent sarcopenia. ^ Using clonogenicity assays to determine a cell's proliferation potential, these studies have shown that IGF-I enhances the doubling potential of satellite cells from aged rodents. Using a transgenic model, where the mice express the IGF-I transgene specifically in their striated muscles, some of the underlying biochemical mechanisms for the observed increase in replicative life span were delineated. These studies have revealed that IGF-I activates the PI3/Akt pathway to mediate downregulation of p27KIP1, which consequently is associated with an increase in cyclin E-cdk2 kinase activity, phosphorylation of pRb, and upregulation of cyclin A protein. However, the beneficial effects of IGF-I on satellite cell proliferative potential appears to be limited as chronic overexpression of IGF-I in skeletal muscles did not protect against sarcopenia in 18-mo old mice, and was associated with an exhaustion of satellite cell replicative reserves. ^ These results have shown that replicative senescence can be modulated by environmental factors using skeletal muscle satellite cells as a model system. A better understanding of the molecular basis for enhancement of proliferative capacity by IGF-I will provide a rational basis for developing more effective counter-measures against physical frailty. However, the implications of these studies are that these beneficial effects of enhanced proliferative potential by IGF-I may only be over a short-term period, and other alternative approaches may need to be considered. ^

Defence chemistry modulation by light and temperature (results in 4 excel files, zipped)

The goals of this study were (1) to investigate whether Fucus vesiculosus regulates the production of its antifouling defence chemicals against microfoulers in response to light limitation and temperature shifts and (2) to investigate if different surface concentrations of defence compounds shape epibacterial communities. F. vesiculosus was incubated in indoor mesocosms at five different temperature conditions (5 to 25°C) and in outdoor mesocosms under six differently reduced sunlight conditions (0 to 100%), respectively. Algal surface concentrations of previously identified antifouling compounds - dimethylsulphopropionate (DMSP), fucoxanthin and proline - were determined and the bacterial community composition was characterized by in-depth sequencing of the 16S-rRNA gene. Altogether, the effect of different treatment levels upon defence compound concentrations was limited. Under all conditions DMSP alone appeared to be sufficiently concentrated to warrant for at least a partial inhibitory action against epibiotic bacteria of F. vesiculosus. In contrast, proline and fucoxanthin rarely reached the necessary concentration ranges for self-contained inhibition. Nonetheless, in both experiments along with the direct influence of temperature and light, all three compounds apparently affected (and thereby shaped) the overall bacterial community composition associated with F. vesiculosus since tendencies for insensitivity towards all three compounds were observed among bacterial taxa that typically dominate those communities. Given that the concentrations of at least one of the compounds (in most cases DMSP) were always high enough to inhibit bacterial settlement, we conclude that the capacity of F. vesiculosus for such defence will hardly be compromised by shading or warming to temperatures up to 25°C.

Soil water availability modulation over estimated relative yield losses in wheat (Triticum aestivum L.) due to ozone exposure

The approach developed by Fuhrer in 1995 to estimate wheat yield losses induced by ozone and modulated by the soil water content (SWC) was applied to the data on Catalonian wheat yields. The aim of our work was to apply this approach and adjust it to Mediterranean environmental conditions by means of the necessary corrections. The main objective pursued was to prove the importance of soil water availability in the estimation of relative wheat yield losses as a factor that modifies the effects of tropospheric ozone on wheat, and to develop the algorithms required for the estimation of relative yield losses, adapted to the Mediterranean environmental conditions. The results show that this is an easy way to estimate relative yield losses just using meteorological data, without using ozone fluxes, which are much more difficult to calculate. Soil water availability is very important as a modulating factor of the effects of ozone on wheat; when soil water availability decreases, almost twice the amount of accumulated exposure to ozone is required to induce the same percentage of yield loss as in years when soil water availability is high.

Modulation-Mode Assignment in SVD-Aided Downlink Multiuser MIMO-OFDM Systems

Multicarrier transmission such as OFDM (orthogonal frequency division multiplexing) is an established technique for radio transmission systems and it can be considered as a promising approach for next generation wireless systems. However, in order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this field, the combination of MIMO transmission and OFDM can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple users' scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user's channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput.

Modulation-mode assignment in SVD-assisted multiuser MIMO-OFDM systems

In order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this field, the combination of MIMO transmission and OFDM (orthogonal frequency division multiplexing) can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple users’ scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user’s channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier along with the appropriate allocation of the transmit power shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput.

Real Time FPGA Implementation of an Modulation Classifier for Electronic Warfare Applications

This paper presents an automatic modulation classifier for electronic warfare applications. It is a pattern recognition modulation classifier based on statistical features of the phase and instantaneous frequency. This classifier runs in a real time operation mode with sampling rates in excess of 1 Gsample/s. The hardware platform for this application is a Field Programmable Gate Array (FPGA). This AMC is subsidiary of a digital channelised receiver also implemented in the same platform.

Modulation-mode Assignment for SVD-assisted Multiuser MIMO Systems with Correlation.

Multiuser multiple-input multiple-output (MIMO) downlink (DL) transmission schemes experience both multiuser interference as well as inter-antenna interference. The singular value decomposition provides an appropriate mean to process channel information and allows us to take the individual user’s channel characteristics into account rather than treating all users channels jointly as in zero-forcing (ZF) multiuser transmission techniques. However, uncorrelated MIMO channels has attracted a lot of attention and reached a state of maturity. By contrast, the performance analysis in the presence of antenna fading correlation, which decreases the channel capacity, requires substantial further research. The joint optimization of the number of activated MIMO layers and the number of bits per symbol along with the appropriate allocation of the transmit power shows that not necessarily all user-specific MIMO layers has to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput.

Modulation-mode Assignment in SVD-assisted Multiuser MIMO-OFDM Systems

In order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this field, the combination of MIMO transmission and OFDM (orthogonal frequency division multiplexing) can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple users’ scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user’s channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier along with the appropriate allocation of the transmit power shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput

DCT Type-III for Multicarrier Modulation

In this paper we propose the use of Discrete Cosine Transform Type-III (DCT3) for multicarrier modulation. There are two DCT3 (even and odd) and, for each of them, we derive the expressions for both prefix and suffix to be appended into each data symbol to be transmitted. Moreover, DCT3 are closely related to the corresponding inverse DCT Type-II even and odd. Furthermore, we give explicit expressions for the 1-tap per subcarrier equalizers that must be implemented at the receiver to perform the channel equalization in the frequency-domain. As a result, the proposed DCT3-based multicarrier modulator can be used as an alternative to DFT-based systems to perform Orthogonal Frequency-Division Multiplexing or Discrete Multitone Modulation

Multiphase Buck Converter with Minimum Time Control Strategy for RF Envelope Modulation

Power amplifier supplied with constant supply voltage has very low efficiency in the transmitter. A DC-DC converter in series with a linear regulator can be used to obtain voltage modulation. Since this converter should be able to change the output voltage very fast, a multiphase buck converter with a minimum time control strategy is proposed. To modulate supply voltage of the envelope amplifier, the multiphase converter works with some particular duty cycle (i/n, i=1, 2 ... n, n is the number of phase) to generate discrete output voltages, and in these duty cycles the output current ripple can be completely cancelled. The transition times for the minimum time are pre-calculated and inserted in a look-up table. The theoretical background, the system model that is necessary in order to calculate the transition times and the experimental results obtained with a 4-phase buck prototype are given