Factors of skin ageing share common mechanisms

Ageing has been defined as the accumulation of molecular modifications which manifest as macroscopic clinical changes. Human skin, unique among mammalians insofar as it is deprived of fur, is particularly sensitive to environmental stress. Major environmental factors have been recognized to induce modifications of the morphological and biophysical properties of the skin. Metabolites from ingested or inhaled substances do affect skin, which is also sensitive to endogenous hormone levels. Factors as diverse as ultraviolet radiation, atmospheric pollution, wounds, infections, traumatisms, anoxya, cigarette smoke, and hormonal status have a role in increasing the rate of accumulation of molecular modifications and have thus been termed 'factors of ageing'. All these factors share as a common feature, the capability to directly or indirectly induce one of the steps of the micro-inflammatory cycle, which includes the expression of ICAM-1 in endothelial cells. This triggers a process leading to the accumulation of damages in the skin resulting in skin ageing since ICAM-1 expression provokes recruitment and diapedesis of circulating immune cells, which digest the extracellular matrix (ECM) by secreting collagenases, myeloperoxidases and reactive oxygen species. The activation of these lytic processes provokes random damage to resident cells, which in turn secrete prostaglandines and leukotrienes. These signaling molecules induce the degranulation of resident mast cells which release the autacoid histamine and the cytokine TNF-alpha thus activating endothelial cells lining adjacent capillaries which release P-selectin and synthesize ICAM-1. This closes a self-maintained micro-inflammatory cycle, which results in the accumulation of ECM damage, i.e. skin aging. In this paper we review the evidence that two factors able to induce macroscopical and molecular modifications in the skin, protein glycation and stretch, activate the micro-inflammatory cycle. We further present evidence that three additional factors, two external factors (electromagnetic fields and psychological stressors) and one internal factor (neuropeptides) also activate the micro-inflammatory cycles and may therefore be considered as factors of skin ageing.

Cultured cells as a model system for the study of UV-induced cytotoxicity

In vivo, UV radiation induces a series of morphological and ultrastructural alterations in human epidermis. These and other changes eventually lead to well described pathological modifications including erythema and cancer. Morphological alterations are easier to detect in cultured cells, such as human keratinocytes or other epithelial cells. One can use different intensities of different radiation types (UV-A, -B and -C) and expose cell monolayers to different doses. In these experimental conditions it is possible to evaluate radiation risks and to provide additional information thanks to the reproducibility and the enormous amplification of the phenomena normally occurring in vivo. Alterations observed in structural studies can be summarized as the succession of the following events: (i) cell retraction with loss of cell-cell interactions; (ii) surface blebbing; and eventually (iii) cell death. Cytoskeletal components play a key role in this cascade. Morphogenesis of these changes can be ascribed to oxidative modifications due to reactive oxygen species formation following radiation that can modify both cell membrane and cytoskeleton. The use of in vitro systems can be of great relevance in the understanding of the pathogenetic mechanisms of UV radiation changes and to determine possible drugs capable of counteracting UV-mediated subcellular pathology.

Individual variations in the correlation between erythemal threshold, UV-induced DNA damage and sun-burn cell formation

A linear correlation between erythema intensity and DNA damage upon exposure to UV has not been firmly established. Many of the deleterious effects of UV exposure do occur after exposure to suberythemal doses. After DNA damage, cells undergo DNA repair. It is commonly accepted that when the burden of damage is beyond the repair capacities, the cell undergoes programmed cell death or apoptosis. The aim of this study is to quantify the amount of UV-induced DNA damage (estimated via the measurement of DNA repair or unscheduled DNA synthesis or UDS) and cellular damage (estimated via the determination of the density of sunburn cells or SBC). If DNA damage and erythema are correlated, similar intensity of UDS and similar density of SBC should be found in volunteers irradiated with a UV dose equal to two minimal erythema doses (MED). Our results show that in 15 different individuals the same relative dose (2 MEDs) provokes UDS values, which vary within a factor of 4. An even larger variability affects SBC counts after the same relative dose. When DNA damage or SBC are plotted versus the absolute dose (i.e. the dose expressed in J/m(2)), there is a rough correlation (with several exceptions) between dose and extent of UDS and SBC counts. It seems possible to divide the volunteers into two subpopulations with different susceptibilities to UV damage. It is well known that UDS and SBC measurements are often affected by large experimental indeterminacy, yet, the analysis of our results makes it plausible to suggest that for the triggering of erythema, a common threshold value for DNA damage or for SBC count are not to be found. In conclusion, the erythema response seems to be loosely correlated with DNA damage. This suggests that the protection offered by the sunscreens against DNA damage, the molecular basis of UV-induced mutagenesis, might not be related to the sun protection factor (SPF) indicated on the label of sunscreens, which is evaluated using the erythema as an endpoint.

Optimizing the energy status of skin cells during solar radiation

Ionizing- and ultraviolet-radiation cause cell damage or death by directly altering DNA and protein structures and by production of reactive oxygen species (ROS) and reactive carbonyl species (RCS). These processes disrupt cellular energy metabolism at multiple levels. The formation of DNA strand breaks activates signaling pathways that consume NAD, which can lead to the depletion of cellular ATP. Poly(ADP)-ribose polymerase (PARP-1) is the enzyme responsible for much of the NAD degradation following DNA damage, although numerous other PARPs have been discovered recently that await functional characterization. Studies on mouse epidermis in vivo and on human cells in culture have shown that UV-B radiation provokes the transient degradation of NAD and the synthesis of ADP-ribose polymers by PARP-1. This enzyme functions as a component of a DNA damage surveillance network in eukaryotic cells to determine the fate of cells following genotoxic stress. Additionally, the activation of PARP-1 results in the activation of a nuclear proteasome that degrades damaged nuclear proteins including histones. Identifying approaches to optimize these responses while maintaining the energy status of cells is likely to be very important in minimizing the deleterious effects of solar radiation on skin.

Aging of human skin: review of a mechanistic model and first experimental data

The physical, chemical, and biochemical factors that accelerate skin aging have been proposed to activate a self-maintained microinflammatory process, one of the expected end results of which is an imbalance in the turnover of macromolecules in the dermis. Surface peroxides are recognized as controllable factors of skin aging, and their accumulation is attributed to environmentally induced impairment of defense enzymes. Topical application of antioxidants decreases the rate at which skin elasticity and skin thickness are modified.

Vitamin E prevents UVB-induced cell blebbing and cell death in A431 epidermoid cells

Cultured A431 epidermoid cells exposed to UVB (120-2400 J/m2) develop numerous blebs on their surface, detach from the plastic dish, and undergo injury and death. Numerous detached cells display fragmented nuclei, typical of apoptotic cells. Since bleb formation also occurs after oxidative stress it was assumed that the morphological variations observed are the consequence of free radical-mediated insult. In order to test this hypothesis, the antioxidant alpha-tocopherol (vitamin E) was added to cell cultures at different times, before or after irradiation. The results indicate that vitamin E inhibits UVB-induced surface blebbing as well as cell detachment from the substrate. Moreover, vitamin E is most effective in stimulating cell recovery when it is added after the end of UVB irradiation. Finally, vitamin E treatment also seems to reduce the fraction of cells undergoing death (probably those which will undergo apoptosis) after exposure to UVB radiation.

Both UVA and UVB induce cytoskeleton-dependent surface blebbing in epidermoid cells

Data on the morphological changes induced by UVA or UVB irradiation of A431 epidermoid cells in culture are presented. After irradiation with different doses of UVB (120-2400 J m-2) or UVA (10(4)-10(5) J m-2), the membrane and cytoskeleton of these cells were analysed by immunofluorescence and scanning electron microscopy at different times after exposure (0-48 h). Both UVA and UVB alter microtubules and microfilaments and surface blebs are formed after UV irradiation. In particular, UVB induces multiple small blebs on the cells, while UVA induces one single large bleb on each cell. Since cytoskeletal damage and surface blebbing of this type are also induced by oxidative stress, these results add to the body of evidence indicating that UV radiation is capable of pro-oxidant behaviour. Specifically, the morphological changes described in this paper are reminiscent of the modifications which accompany epidermal keratinocytes during their transformation to sunburn cells after UV irradiation. The physiological implications of these findings are discussed.

Modulation by L-histidine of H2O2-mediated damage of cellular and isolated DNA

The mechanism by which L-histidine modulates H2O2-induced damage to DNA has been investigated by alkaline and neutral gel electrophoresis of cellular DNA, by measuring the conversion of purified supercoiled DNA to its relaxed and linear forms and by the ESR spin-trapping technique. L-Histidine greatly increased the amount of H2O2-mediated DNA single-strand breaks. DNA double-strand breaks were produced only in cells exposed to H2O2 and L-histidine. The addition of a cell permeable chelator such as o-phenanthroline (unlike EDTA, DTPA and desferrioxamine) prevented both DNA single- and double-strand breakage induced by H2O2 plus L-histidine. In vitro, the profile of the dose-response curve for the ferrous iron-mediated, H2O2-dependent DNA nicking was modified by the addition of L-histidine. At low H2O2 concentrations, corresponding to the maximum extent of DNA cleavage, L-histidine was protective. At higher H2O2 concentrations L-histidine enhanced the formation of DNA single-stand breaks and produced DNA double-strand breaks. The increase in H2O2-mediated DNA nicking by L-histidine depended on the L-histidine:Fe(II) ratio, the maximal rate occurring at a molar ratio of 10(3):1 and being independent of the concentration of DNA. Thus, it appeared that intracellular iron mediated both DNA single- and double-strand breaks induced by H2O2 plus L-histidine. Results of ESR experiments seemed to rule out the involvement of the hydroxyl radical by itself in DNA cleavage mediated by the L-histidine:Fe(II):H2O2 system.

Protonation of the imidazole ring prevents the modulation by histidine of oxidative DNA degradation

When supercoiled DNA is incubated with Fe(II) at pH 7 in the presence of hydrogen peroxide, the rate of nicking first increases with increasing H2O2 concentration to reach a maximum, then decreases and eventually increases again. When 0.1 mM histidine is added at neutral pH at low H2O2 concentration (< 3 mM), it hinders the nicking of DNA; when it is added at high H2O2 concentrations (> 10 mM), it enhances the rate of nicking. When similar experiments are performed at slightly acidic pH (4.5) the biphasic behavior is maintained, independent of the presence of histidine. One can conclude that the protonation of imidazole (pK = 5.9) abolishes the capability of histidine to modulate the oxidative degradation of DNA. Results of electron spin resonance experiments suggest that at low H2O2 concentration, the protective effect of histidine could be the consequence of its capability to bind OH. radicals.

L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity: relationships between DNA single/double strand breakage and cell killing

Results presented in this study demonstrate an association between the L-Histidine-mediated enhancement of H2O2-induced cytotoxicity and the formation of DNA double strand breakage (DSB), whereas no relationship exists between the increased cytotoxic response and DNA single strand breakage (SSB). Indeed, the higher lethality and the production of DNA DSB occurred in oxidatively-injured cells regardless of whether the exposure to L-Histidine was performed before or during challenge with the oxidant. In fact, the increased level of DNA SSB detected in cells simultaneously exposed to the oxidant and the amino acid was not observed in cells pre-treated with L-Histidine and then challenged with hydrogen peroxide. Further experiments have demonstrated an association between the kinetics of DNA DSB formation and the enhancement of the cytotoxic response. In conclusion, intracellular L-Histidine seems to mediate the formation of DNA DSB and the increased growth-inhibitory response elicited by the oxidant. In addition, these results suggest that the enhancement of DNA SSB is produced by the extracellular/plasma membrane fraction of the amino acid and not causally related to the L-Histidine-mediated increase of the growth-inhibitory response to H2O2-treated cells.

Differential effects of histidine on hydrogen peroxide-induced bacterial killing and DNA nicking in vitro

The hydrogen peroxide dose-response curves for Escherichia coli killing and DNA nicking in vitro display remarkably similar bimodal patterns. The concentrations of the oxidant resulting in maximum mode one killing, however, exceeds by two orders of magnitude those resulting in the mode one DNA nicking response. Addition of histidine differentially affects the experimental curves describing the dose-dependency for bacterial killing and DNA damage in vitro. Indeed, the lethal effect elicited by the oxidant in the presence of the amino acid is strictly concentration-dependent and thus the inactivation curve loses its bimodal character. In marked contrast, histidine abolishes DNA damage generated by low concentrations of hydrogen peroxide (< 100 microM) in the in vitro system (the mode one DNA nicking response) but greatly increases DNA damage produced by concentrations of the oxidant higher than 1 mM (the mode two DNA nicking response). Experimental results also suggest that treatment of covalently closed circular double-stranded super-coiled DNA with hydrogen peroxide, in the presence of both histidine and iron, may result in the formation of DNA double strand breakage, a type of lesion which is not efficiently produced by the oxidant in the absence of the amino acid. Taken together, the above results indicate that histidine differentially affects the in vitro DNA cleavage and E. coli lethality induced by hydrogen peroxide and suggest that different molecular events mediate mode one DNA nicking in vitro and mode one killing of bacterial cells.

DNA nicking by ultraviolet radiation is enhanced in the presence of iron and of oxygen

Double-stranded covalently closed circular supercoiled DNA (ccc DNA) from plasmid pUK 9 was irradiated in vitro at defined wavelengths in the UV region (290, 313 and 365 nm). The nicking was monitored by electrophoresis on agarose gels, ethidium staining and densitometric quantitation of supercoiled and relaxed moieties. At the explored wavelengths, the dose required for introducing one nick per million phosphodiester bonds diminishes with increased concentration of added ferric iron, whereas the effect of cupric iron is practically negligible. Adding metal chelators or bubbling argon prior to the irradiation results in a dramatic increase in the dose required for introducing one nick per million phosphodiester bonds. Taken together, these results seem to indicate that iron and oxygen play a role as cofactors in the UV-induced nicking of ccc DNA in vitro.

Modulation of DNA breakage induced via the Fenton reaction

The conversion of the covalently closed circular double-stranded supercoiled DNA (pBR322) to a relaxed circle was used to investigate DNA nicking induced by Fe2+ and H2O2. In our experimental conditions of ionic strength (150 mM NaCl), pH = 7 and temperature (37 degrees C), the dose-response curve for the ferrous iron mediated H2O2 dependent DNA nicking is peculiar. For a fixed concentration of ferrous iron (2 microM), the concentration of H2O2 producing a maximum extent of DNA nicking was about 10-30 microM. The DNA single-strand breakage decreased with an increase of H2O2 concentration. We have investigated the effects of several factors such as the nature of the buffer, ionic strength, temperature and pH. Buffer components leading to the autoxidation of ferrous iron to ferric iron (phosphate) or to the scavenging of reactive oxygen species (Tris) greatly alter the dose-response curve. The H2O2 concentrations required for producing the maximum extent of DNA single-strand breaks at 4 degrees C and 56 degrees C were respectively 30 microM and 3 microM. At pH = 10, the pattern of the dose-response curve was totally different. The data showed that the peculiar dose-response curve for the ferrous iron mediated H2O2 dependent DNA nicking greatly depended on the experimental conditions.

L-glutamine prevents the L-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity

Results presented in this study demonstrate that L-glutamine, a competitive inhibitor of L-histidine uptake, inhibits in a concentration-dependent fashion the L-histidine-mediated enhancement of H2O2-induced cytotoxicity. L-Glutamine also prevents the induction of DNA double strand breaks (DSB) but does not affect the enhancing effect of L-histidine on DNA single strand break induction by H2O2. Taken together, these data demonstrate that L-histidine, in order to allow the formation of DNA double strand breakage and increase the toxicity elicited by the oxidant, has to enter the cell. In addition, these results indicate that the enhancement of DNA single strand breakage is a consequence of the action of the amino acid at the extracellular level and/or outer surface of the plasma membrane and does not appear related to the mechanism whereby L-histidine increases the cytotoxic response to H2O2. The latter mechanism very likely involves the formation of DNA DSB.

Effects of L-histidine on hydrogen peroxide-induced DNA damage and cytotoxicity in cultured mammalian cells

L-Histidine markedly increased the growth- and DNA synthesis-inhibitory effects elicited by hydrogen peroxide in cultured Chinese hamster ovary cells. DNA single-strand breakage was also higher in the presence of the amino acid and, in addition, these breaks were characterized by a slower rate of repair, compared with that of the breaks generated by the oxidant alone. In the presence of L-histidine, hydrogen peroxide also produced DNA double-strand breakage, a lesion that cannot be detected in cells treated with even exceedingly high concentrations of the oxidant alone. Data reported herein suggest that the L-histidine-mediated increase of the cytotoxic response of cultured Chinese hamster ovary cells to hydrogen peroxide may be at least partially dependent on the formation of DNA double-strand breaks.

Enhancement of oxidative DNA degradation by histidine: the role of stereochemical parameters

The nicking of supercoiled DNA by H2O2 and ferrous iron has been studied in a variety of environmental conditions. The replicative form of phage fd DNA (fd RF DNA) was used for investigating the phenomenon. The rate of nicking was measured in 10 mM NaCl. The addition of 1 mM Tris-HCl buffer (pH 7.5) slowed down the rate of nicking, the addition of 0.1 mM histidine enhanced it. The simultaneous presence of 1 mM Tris-HCl buffer and of 0.1 mM histidine further enhanced the rate of nicking of fd RF DNA. Increasing the concentration of NaCl dramatically reduced the rate of the reaction. The degradation of fd RF DNA was determined as a function of the concentration of histidine (0-5 mM): the rate increases with concentration, reaches a maximum and then decreases. In the presence of histidine, increasing the concentration of Tris leads to a similar phenomenon. In the absence of histidine, Tris always quenches the degradation of DNA. Electron spin resonance measurements failed to detect an enhancement of the signal characteristic for the hydroxyl radical when histidine was added to the solution containing hydrogen peroxide and ferrous iron. When the nicking of DNA is achieved via the process of auto-oxidation of ferrous iron (i.e., in the absence of added H2O2), histidine only reduces the rate of reaction in a dose-dependent manner, in the explored range of concentrations. In the presence of H2O2 and ferrous iron, histidine enhances the rate of nicking of double-stranded DNA in its supercoiled as well as in its relaxed state, but fails to modify the rate of nicking of fd DNA when it is in its vegetative, single-stranded form.

The role of extracellular medium components and specific amino acids in the cytotoxic response of Escherichia coli and Chinese hamster ovary cells to hydrogen peroxide

A concentration of H2O2 resulting in mode one killing of Escherichia coli is more toxic when exposure to the oxidant is performed in complete medium (K medium), as compared to a saline (M9 salts). Inorganic salts (MgSO4 and CaCl2), thiamine or glucose, when added separately, or combined, to M9 salts had no effect on the cytotoxic response to H2O2. In contrast, the lethality of the oxidant was highly dependent on the presence of the amino acids in the incubation medium. The addition of glucose further enhanced this response. Among the seventeen amino acids which are present in the complete amino acid mixture, only two, i.e. L-histidine and L-cystine, were found to increase the toxicity of H2O2. Again, glucose augmented this response. The effect of these amino acids on the growth inhibitory action of hydrogen peroxide was also tested in Chinese Hamster Ovary cells. It was found that L-histidine was capable of increasing the toxicity of the oxidant whereas all the other amino acids did not affect the toxicity of the oxidant. Glucose only slightly augmented this effect of L-histidine. DNA single strand breakage produced by H2O2 was increased by L-histidine and was not significantly modified by the other amino acids. DNA double strand breakage was also shown to occur in cells exposed to H2O2-L-histidine, and this effect was independent on the presence of glucose. These results demonstrate that the cytotoxic response of bacterial and mammalian cells to challenge with H2O2 is highly dependent on the composition of the extracellular milieu.(ABSTRACT TRUNCATED AT 250 WORDS)

Unscheduled DNA synthesis: a quantitative indicator of residual immunodetectable pyrimidine dimers in human fibroblasts after ultraviolet-B irradiation

We have addressed the question whether the level of UV-B induced DNA damage can be accurately assessed by the measurement of the rate of unscheduled DNA synthesis (UDS). Cultured human fibroblasts were irradiated with UV radiation at 290, 313 or 365 nm. The LD50 was 85 J/m2 at 290 nm, 4500 J/m2 at 313 nm, and 70 kJ/m2 at 365 nm. The analysis of UDS measurements indicate complete arrest of repair processes within 24 h after irradiation, irrespective of the dose (in the range 10-60 J/m2 at 290 nm, and 250-1000 J/m2 at 313 nm). Irradiation at 365 nm failed to yield detectable evidence of UDS. Incubation of irradiated cells with an antiserum directed against both 6-4 type and cyclobutane-type pyrimidine dimers shows a clear parallelism between the disappearance of the antibody-binding determinants and the variation of the rate of UDS vs time after the end of the irradiation. Thus it is concluded that in UV-B irradiated normal cultured human fibroblasts, the lack of UDS reflects the absence of immunodetectable pyrimidine dimers.

Specific mRNAs accumulate in long-wavelength UV-irradiated mouse epidermis

Total RNA from hairless mice epidermis was analysed by RNA-DNA hybridization on slot blots at various times following irradiation with long-wavelength UV light (UV-B or UV-B plus UV-A). Densitometric scanning of the autoradiographies indicates that the amount of RNA which hybridizes with an Ha-ras DNA probe remains constant for up to 72 h after irradiation. The amount of the transcript which hybridizes to a c-fos DNA probe increases dose dependently from 15 min to 2 h after irradiation. RNA which hybridizes to a tubulin DNA probe accumulates in parallel with the increase in mitotic index associated with the radiation-induced hyperplasia.

Heat shock mRNA in mouse epidermis after UV irradiation

Total RNA from murine epidermis was extracted at different times after irradiation with erythemogenic doses of ultraviolet light (UVB or UVB/UVA) and hybridized to a DNA probe from the gene of a heat shock protein (hsp 70). An intense and transitory enrichment in RNA molecules hybridizing to the DNA probe was found between 15 and 120 min after irradiation, followed by a return to control levels over the next 70 h. Dose-response analysis indicates that 30 min after the irradiation, the relative amount of RNA hybridizing to the hsp 70 DNA probe increases with the dose (within the range explored: 0-180 mJ/cm2) up to values greater than 5 times the control.

Histidine modulates the clastogenic effect of oxidative stress

The kinetics of the formation of single-strand breaks induced by H2O2 in DNA is more rapid in Eagle's Modified Minimal Essential Medium (MEM) than in phosphate-buffered saline (PBS). Among the components of MEM, we found that histidine increases the rate of degradation of DNA by H2O2 in PBS dose-dependently. In hamster lung fibroblasts histidine increases the cytotoxicity of H2O2, as well as the number of sister-chromatid exchanges and the frequency of micronuclei induced by hydrogen peroxide.

Nicotinamide adenosine dinucleotide level in dimethylsulfate-treated or UV-irradiated mouse epidermis

The level of nicotinamide adenosine dinucleotide (NAD) has been determined in the epidermis of 30 mice. Its value is 0.63 +/- 0.15 microgram/mg protein. Upon treatment with dimethylsulfate (DMS), the level of NAD drops in a dose-dependent fashion. This diminution is reversible when low doses of DMS are used. Upon irradiation with ultraviolet light, the level of NAD drops in the irradiated epidermis, the threshold of saturation being below 1200 J/m2. There is also a drop in the level of NAD in the epidermis protected against irradiation with a black rubber sheet.

Effect of UV irradiation at defined wavelengths on the tertiary structure of double-stranded covalently closed circular DNA

Double-stranded, covalently closed, supercoiled circular DNA from phage fd (replicative form) was irradiated with increasing doses of UV light at 254 nm, 290 nm, 313 nm and 365 nm, and subjected to electrophoresis on agarose slab gels. Increasing the doses of UV light at 254 and 290 nm promotes a smooth reduction in the electrophoretic mobility of the sample, as would be expected if the major effect of light at these two wavelengths were to induce the formation of photoproducts leading to the unwinding of the double strand. At high doses, UV light at 290 nm introduces single-strand breaks (1.2 kJ m-2 per nick per million phosphodiester bonds). UV light at 313 nm promotes an abrupt change in the electrophoretic mobility, as would be expected if the effect of this wavelength were to induce single-strand breaks, leading to the transformation of the supercoiled molecules in their relaxed form (23 kJ m-2 in order to introduce one nick per million phosphodiester bonds). UV light at 365 nm also promotes single-strand breaks in DNA (140 kJ m-2 per nick per million phosphodiester bonds).

Onc-gene expression in hyperplasia induced by tape stripping or by topical application of TPA

Guinea-pig ears were treated topically with 20 nmol of 12-O-tetradecanoyl phorbol-13-acetate, or deprived of their horny layer by nine successive strippings. At different times after the treatment, the animals were sacrificed, the epidermis removed from the ears, and the RNA from the epidermis purified and analysed by dot-blot hybridization in order to assess and determine the amount of RNA able to hybridize to each one of the 18 onc-gene DNA probes. The following probes were used: v-src, v-fps, v-yes, v-ros, v-myc, c-myc, v-erb AB, v-myb, v-mos, v-Ha-ras, v-Ki-ras, v-abl, v-fos, v-fes, v-fms, c-sis, B-lym, v-raf. At 0 h, expression of B-lym and of myc and fos is seen. ErbAB mRNA is detected between 10 min and 4 h after stripping, as well as after TPA application. B-lym mRNA is detected for up to 36 h after stripping and for up to 8 h after TPA application. C-myc mRNa is detected for up to 36 h after tape stripping, but only for the first hour after TPA application. RNA complementary to the other onc probes was not detected, and synthesis of RNA complementary to an actin DNA probe was observed for 8 h after TPA application.

Ellipticines: correlation between in vitro DNA intercalation and physiological properties?

The in vitro DNA-intercalator ellipticine and five of its derivatives have been investigated for some of their physiological effects on several Escherichia coli strains. The highly water-soluble, quaternarized derivatives of ellipticine have no bactericidal effect and do not induce the synthesis of rec A protein. Ellipticine itself, as well as the derivatives obtained by adding an amino or an hydroxyl substituent in position 9, promotes the induction of rec A protein and is cytostatic on some bacterial strains. The non-intercalating brominated derivative is a strong bactericidal agent, which apparently promotes the lysis of the bacteria. At low concentrations, it slightly induces the synthesis of rec A protein. We conclude that there is no correlation at all between the physiological properties of the ellipticines and their physico-chemical behavior in vitro.

Survival and induction of recA protein in mitomycin C-treated Escherichia coli rec, lex, or uvr strains

The capability to synthesize recA protein has been tested for Escherichia coli treated with mitomycin C. recA protein was assayed using an immunoradiometric assay (Paoletti, C., Salles, B., and Giacomoni, P. U. (1982) Biochimie 64, 239-246). Mitomycin C-treated wild type E. coli can express recA gene in a similar quantitative fashion, independently of the growth media used in this work; glucose did not inhibit induction of recA protein in cells growing in synthetic media. Wild type E. coli recovering from energy starvation displays a similar qualitative capability to induce the synthesis of recA protein independently of the stage of growth at which the cells are treated with the drug. At midexponential phase, the cells appear to have an enhanced capability to synthesize recA protein. The relationship between survival and capability to synthesize recA protein was explored for E. coli lex, rec, and/or uvr mutants, after treatment with mitomycin C. A good correlation was found, except for a recB mutant and for an ethidium-sensitive strain, both able to produce as much recA protein as the wild type but 100-fold more sensitive to the drug. A similarly satisfactory correlation was found when plotting the survival after UV irradiation versus the capability of synthetizing recA protein with the exception of an uvrA strain and of a lexA strain.

Induction by mitomycin C of recA protein synthesis in bacteria and spheroplasts

The effect of mitomycin C on the synthesis of recA protein in Escherichia coli has been analyzed in a variety of conditions, using an immunoradiometric assay (Paoletti, C., Salles, B., and Giacomoni, P. U. (1982) Biochimie 64, 239-246). In exponentially growing cultures of E. coli AB 1157, the addition of mitomycin C (5 micrograms/ml) promotes a 15-fold increase of the content of recA protein with respect to the basal level. Kinetic analysis of this induction shows that the maximum is reached 60 to 90 min after the addition of the drug and then the level decreases. In an uvrA mutant treated with mitomycin C the level of recA protein reaches a maximum within an hour and afterwards it does not decrease. Treatment of exponentially growing cells with EDTA and lysozyme induces a 3-fold increase of recA protein content, in comparison to the basal level. When such spheroplasts are added with mitomycin or nalidixic acid, a striking increase of the recA protein content in the spheroplast suspension is observed, which tends to level off an hour and a half after the addition of the drugs. The maximum level of recA protein content is five times the level measured after lysozyme treatment, i.e. 15 times the basal level in exponentially growing cells.

Effects of the positively regulating product of gene 28 of the B. subtilis phage SPO1 on in vitro transcription

Some of the properties of the RNA polymerase purified from SPO1-infected Bacillus subtilis have been compared with the properties of RNA polymerase from uninfected cells (core + sigma). The two enzymes synthetize RNA from nonoverlapping regions on SPO1 DNA, and they lead to the retention of different restriction fragments of SPO1 DNA on cellulose-nitrate filters. The action of the positively regulating product of gene 28 of SPO1 (gp 28) has been analyzed. The isolated gp 28 has been shown to be unable to increase the dissociation rate of core + sigma from SPP1 DNA, while it efficiently blocks the initiation of RNA synthesis if it is added to performed complexes between core + sigma and SPP1 DNA in 0.2 M NaCl.

Purification and DNA-binding properties of RNA polymerase from Bacillus subtilis

Four RNA-polymerizing activities having different subunit composition can be purified from uninfected and from SPO1-infected Bacillus subtilis. Lysozyme and sodium deoxycholate are used for lysing the cells. Polymin P is used for precipitating nucleic acids and DEAE-cellulose chromatography allows separation of enzymatic activity from the residual Polymin P. After these common steps, one can purify core + sigma + delta by chromatography on single-stranded DNA-agarose followed by gel filtration while pure core + sigma can be obtained by chromatography on double-stranded DNA cellulose. Core + delta is obtained by high-salt sucrose/glycerol gradient centrifugation. The host enzyme modified by the product of gene 28 of phage SPO1 can be purified from SPO1 infected cells by chromatography on DNA cellulose (or CNA agarose) followed by chromatography on phosphocellulose. The pH and salt dependance of the initial rate of RNA synthesis of core + sigma has been investigated using SPO1 and SPP1 DNA as templates. The optimum pH for the initial rate of transcription is 8.2 at 30 degrees C in 50 mM N,N-bis(2-hydroxyethyl)glycine buffer, and the optimum Na+ concentration is between 0.1 and 0.15 M. The kinetics of formation and of dissociation of non-filterable complexes between SPP1 DNA and core + sigma have been analyzed at different cationic concentrations. The value of the rate constant of dissociation in 0.1 M NaCl at 30 degrees C is kd = 2.16 x 10(-4) S-1. The value of the rate constant of association, under the same conditions, is ka = 5.5 x 10(8) M-1 S-1; this value is compatible with a diffusion-controlled reaction for promoter selection.

Protein . nucleic-acid reaction kinetics. Theoretical analysis of the binding reaction between DNA and RNA polymerase

This paper presents methods developed in order to analyze experimental results concerning the binding of Escherichia coli DNA-dependent RNA polymerase to DNA at high and at low DNA concentrations, using the filter retention assay. The basis hypotheses, under which the mathematical expressions for describing the kinetics of binding are derived, are as follows. (a) At low DNA concentration: equivalence and independence of the specific binding sites; first-order dependence of the binding reaction on both DNA and protein concentration. (b) At high DNA concentration: equivalence and independence of the non-specific binding sites; no direct transfer or one-dimensional sliding of the protein along the DNA. Comparison between theoretical predictions and experimental results at high DNA concentration will allow one to determine the relative value of the rates of binding of RNA polymerase to different promoters (between 1 and 2 in T5 DNA). Binding experiments performed at low DNA concentration are reported in this paper: these results and the analysis which is reported allow one to determine the value of the rate constant of formation of non-filterable complexes for the system fd DNA (replicative form) . RNA-polymerase (kappa a = 3.3 X 10(8) M-1 s-1 in 0.1 M NaCl, 0.01 M MgCl2).

Electron microscopy analysis of the interaction between Escherichia coli DNA-dependent RNA polymerase and the replicative form of phage fd DNA. 1. Mapping of the binding sites

The interaction of Escherichia coli DNA-dependent RNA polymerase (EC 2.7.7.6) with the replicative form of the DNA from the filamentous coliphage fd cleaved by the restriction endonuclease HindII has been studied by electron microscopy at low and high ionic strength. In the presence of ATP or GTP, and heparin, RNA polymerase binds to fd replicative-form DNA at a few specific sites which have been mapped. The map was oriented so that transcription is from right to left. Three main GTP initiator sites are found at 15%, 82% and 94% of the genome length. One main ATP initiator site is found which cannot be mapped with the same accuracy, and which is localized between 38% and 50%. In the absence of initiator triphosphates and heparin, the binding of the enzyme to fd DNA is much more heterogeneous and therefore the mapping is more difficult. Nevertheless it seems that the preferential binding regions correspond to the specific sites mapped in the presence of GTP or ATP. The mean number of polymerase molecules bound to DNA as a function of the molecular ratio enzyme to DNA present in the mixture has been determined. From these results a binding isotherm can be obtained. The apparent equilibrium constant (K approximately 10(9) M-1) which is derived certainly represents an under-estimated value, as discussed.

Electron microscopy analysis of the interaction between Escherichia coli DNA-dependent RNA polymerase and the replicative form of phage fd DNA. 2. Analysis of the dissociation kinetics

The kinetics of dissociation of the fd DNA - RNA-polymerase complex has been analyzed. Heparin was added to a solution of the enzyme - DNA complex in order to trap free polymerases. At different times after, samples were taken and analyzed by electron microscopy to determine the mean number of enzymes bound per DNA molecule. Unexpectedly, the measured dissociation is not a first-order reaction. The apparent rate constant increases with heparin concentration in the range between 0.001 and 2 mg/ml. These results strongly suggest the existence of a direct transfer process of RNA polymerase to heparin, bypassing the rate-limiting step of dissociation of the enzyme - DNA complex to free enzyme. Theoretical analysis of the direct-transfer model shows that the rate constant of dissociation should level off at high heparin concentrations: measurements of the residual transcription activity show that this is the case. From these experiments, the equilibrium constant of the DNA - RNA-polymerase complex can be determined. The value K = 10(12) M-1 which is obtained solves a striking paradox which existed because measurements performed in other laboratories indicated K = 10(14) M-1, which is greater than the equilibrium constant of the lac-repressor - lac-operator complex (=10(13) M-1).

Escherichia coli RNA-polymerase binding sites on DNA are only 14 base pairs long and are located between sequences that are very rich in AplusT

E. coli DNA-dependent RNA-polymerase binding sites on DNAs of T5, T7, and lambda coliphages have been isolated according to three different methods in order to analyze the binding sites themselves as well as the nearest neighboring regions. It is shown that the binding sites are regions that are rather rich in G+C, are about 14 base pairs long and are located between DNA sequences highly enriched in A+T. The biological implications of this result are discussed.