Quantitative correlation between the residual activity of β-hexosaminidase A and arylsulfatase A and the severity of the resulting lysosomal storage disease

A previously suggested model for the correlation between residual activity of a lysosomal enzyme and the turnover rate of its substrate(s) has been extended to a discussion of substrate accumulation rates in individual cells and whole organs. With these considerations, much of the observed variability in age of onset and clinical phenotype, as well as the phenomenon of pseudo-deficiency, can be understood as the consequences of small differences in the residual activity of the affected enzyme. In order to experimentally verify the basic assumptions on which this model rests, studies were performed in cell culture. The radiolabeled substrates ganglioside GM2 and sulfatide were added to cultures of skin fibroblasts with different activities of beta-hexosaminidase A or arylsulfatase A, respectively, and their uptake and turnover measured. In both series of experiments, the correlation between residual enzyme activity and the turnover rate of the substrate was essentially as predicted: degradation increased steeply with residual activity, to reach the control level at a residual activity of approximately 10-15% of normal. All cells with an activity above this critical threshold had a normal turnover. Comparison of the results of these feeding studies with the clinical status of the donor of each cell line basically confirmed our notions but also revealed the limitations of the cell culture approach.

Circadian rhythm in membrane conductance expressed in isolated neurons

Although isolated neurons can generate rhythmic activity, they have not yet been shown to generate rhythms with a period in the circadian range (near 24 hours). The eye of the mollusk Bulla gouldiana expresses a circadian rhythm in optic nerve impulses that is generated by electrically coupled cells known as basal retinal neurons (BRNs). Daily fluctuations in the membrane potential of the BRNs appear to be driven by a rhythm in membrane conductance. Isolated BRNs exhibited spontaneous conductance changes similar to those observed in the intact retina. Membrane conductance was high in the late subjective night and decreased approximately twofold near projected dawn during at least two circadian cycles in culture. The persistence of daily conductance changes in isolated BRNs indicates that individual neurons can function as circadian pacemakers.

Differential expression of peroxisome proliferator-activated receptor subtypes during the differentiation of human keratinocytes

The expression of mRNA encoding peroxisome proliferator-activated receptor (PPAR) subtypes in human keratinocytes was determined by semiquantitative reverse transcriptase-polymerase chain reaction. When normal human keratinocytes were induced to differentiate by shifting the culture medium to high Ca2+ concentration, the expression of PPAR-alpha and -gamma mRNA was increased, whereas that of PPAR-delta remained unchanged. At the protein level, the expression of PPAR in cultured human keratinocytes was demonstrated by a DNA mobility shift assay and the functionality of the receptor subtypes was assessed by transactivation experiments. In epidermis reconstructed in vitro, the level of PPAR-alpha and -gamma mRNA was also associated with keratinocyte differentiation. In lesional compared with nonlesional psoriatic epidermis, the expression of PPAR-alpha and -gamma mRNA was reduced, indicating that these two subtypes are tightly linked to the epidermal differentiation process.

Farm exposure and time trends in early childhood may influence DNA methylation in genes related to asthma and allergy

BACKGROUND

Genetic susceptibility and environmental influences are important contributors to the development of asthma and atopic diseases. Epigenetic mechanisms may facilitate gene by environment interactions in these diseases.

METHODS

We studied the rural birth cohort PASTURE (Protection against allergy: study in rural environments) to investigate (a) whether epigenetic patterns in asthma candidate genes are influenced by farm exposure in general, (b) change over the first years of life, and (c) whether these changes may contribute to the development of asthma. DNA was extracted from cord blood and whole blood collected at the age of 4.5 years in 46 samples per time point. DNA methylation in 23 regions in ten candidate genes (ORMDL1, ORMDL2, ORMDL3, CHI3L1, RAD50, IL13, IL4, STAT6, FOXP3, and RUNX3) was assessed by pyrosequencing, and differences between strata were analyzed by nonparametric Wilcoxon-Mann-Whitney tests.

RESULTS

In cord blood, regions in ORMDL1 and STAT6 were hypomethylated in DNA from farmers' as compared to nonfarmers' children, while regions in RAD50 and IL13 were hypermethylated (lowest P-value (STAT6) = 0.001). Changes in methylation over time occurred in 15 gene regions (lowest P-value (IL13) = 1.57*10(-8)). Interestingly, these differences clustered in the genes highly associated with asthma (ORMDL family) and IgE regulation (RAD50, IL13, and IL4), but not in the T-regulatory genes (FOXP3, RUNX3).

CONCLUSIONS

In this first pilot study, DNA methylation patterns change significantly in early childhood in specific asthma- and allergy-related genes in peripheral blood cells, and early exposure to farm environment seems to influence methylation patterns in distinct genes.

Molecular anatomy of the neuro-immune connection

Light microscopic immunohistochemistry was employed to elucidate and compare the presence, distribution, and coexistence of various peptides, neuroendocrine markers and enzymes of the catecholamine pathway in nerves supplying lymphoid tissues in a variety of mammalian species. All lymphoid organs and tissues receive innervation by fibers containing dopamine-beta-hydroxylase and/or tyrosine hydroxylase, neural markers like protein gene product 9.5, synaptophysin and neurofilament and a varied spectrum of peptides. The prominent peptides were tachykinins (substance P, neurokinin A), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal polypeptide/peptide histidine isoleucine (VIP/PHI). Opioid innervation was variable. Double immunofluorescence revealed coexistence of tachykinins and CGRP and of tyrosine hydroxylase and NPY. A minor proportion of fibers showed coexistence of NPY and tachykinins and of VIP/PHI and tachykinins. The possible importance of the complex peptidergic innervation of lymphoid tissues in inflammation, allergy, inflammatory pain and psycho-neuro-immuno-endocrine network function is discussed. A special immunomodulatory role of the sensory neurons is suggested.

Sequential gene disruption in Candida albicans by FLP-mediated site-specific recombination

The genetic manipulation of the human fungal pathogen Candida albicans is difficult because of its diploid genome, the lack of a known sexual phase and its unusual codon usage. We devised a new method for sequential gene disruption in C. albicans that is based on the repeated use of the URA3 marker for selection of transformants and its subsequent deletion by FLP-mediated, site-specific recombination. A cassette was constructed that, in addition to the URA3 selection marker, contained an inducible SAP2P-FLP fusion and was flanked by direct repeats of the minimal FLP recognition site (FRT). This URA3 flipper cassette was used to generate homozygous C. albicans mutants disrupted for both alleles of either the CDR4 gene, encoding an ABC transporter, or the MDR1 gene, encoding a membrane transport protein of the major facilitator superfamily. After insertion of the URA3 flipper into the first copy of the target gene, the whole cassette could be efficiently excised by induced FLP-mediated recombination, leaving one FRT site in the disrupted allele of the target gene. The URA3 flipper was then used for another round of mutagenesis to disrupt the second allele. Deletion of the cassette from primary and secondary transformants occurred exclusively by intrachromosomal recombination of the FRT sites flanking the URA3 flipper, whereas interchromosomal recombination between FRT sites on the homologous chromosomes was never observed. This new gene disruption strategy facilitates the generation of specific, homozygous C. albicans mutants as it eliminates the need for a negative selection scheme for marker deletion and minimizes the risk of mitotic recombination in sequential disruption experiments.

Targeted gene disruption in Candida albicans wild-type strains: the role of the MDR1 gene in fluconazole resistance of clinical Candida albicans isolates

Resistance of the pathogenic yeast Candida albicans to the antifungal agent fluconazole is often caused by active drug efflux out of the cells. In clinical C. albicans strains, fluconazole resistance frequently correlates with constitutive activation of the MDR1 gene, encoding a membrane transport protein of the major facilitator superfamily that is not expressed detectably in fluconazole-susceptible isolates. However, the molecular changes causing MDR1 activation have not yet been elucidated, and direct proof for MDR1 expression being the cause of drug resistance in clinical C. albicans strains is lacking as a result of difficulties in the genetic manipulation of C. albicans wild-type strains. We have developed a new strategy for sequential gene disruption in C. albicans wild-type strains that is based on the repeated use of a dominant selection marker conferring resistance against mycophenolic acid upon transformants and its subsequent excision from the genome by FLP-mediated, site-specific recombination (MPAR-flipping). This mutagenesis strategy was used to generate homozygous mdr1/mdr1 mutants from two fluconazole-resistant clinical C. albicans isolates in which drug resistance correlated with stable, constitutive MDR1 activation. In both cases, disruption of the MDR1 gene resulted in enhanced susceptibility of the mutants against fluconazole, providing the first direct genetic proof that MDR1 mediates fluconazole resistance in clinical C. albicans strains. The new gene disruption strategy allows the generation of specific knock-out mutations in any C. albicans wild-type strain and therefore opens completely novel approaches for studying this most important human pathogenic fungus at the molecular level.

Synthesis and cytotoxic and antitumor activity of esters in the 1,2-dihydroxy-1,2-dihydroacronycine series

Seven 1,2-dihydroxy-1,2-dihydroacronycine and 1,2-dihydroxy-1,2-dihydro-6-demethoxyacronycine esters and diesters were synthesized via osmic oxidation of acronycine or 6-demethoxyacronycine followed by acylation. The 6-demethoxyacronycine derivatives were found to be inactive, whereas in contrast, all of the acronycine derivatives were more potent than acronycine itself when tested against L1210 cells in vitro. Four selected acronycine derivatives (17,19, 21, and 22) were evaluated in vivo against murine P388 leukemia and colon 38 adenocarcinoma implanted in mice. All compounds were markedly active against P388 at doses 4-16-fold lower than acronycine itself. Against the colon 38 adenocarcinoma, the three compounds 17, 21, and 22 were highly efficient. 1,2-Diacetoxy-1,2-dihydroacronycine (17) was the most active, all the treated mice being tumor-free on day 23.

Host-induced, stage-specific virulence gene activation in Candida albicans during infection

An understanding of the complex interactions between pathogenic microbes and their host must include the identification of gene expression patterns during infection. To detect the activation of virulence genes in the opportunistic fungal pathogen Candida albicans in vivo by host signals, we devised a reporter system that is based on FLP-mediated genetic recombination. The FLP gene, encoding the site-specific recombinase FLP, was genetically modified for expression in C. albicans and fused to the promoter of the SAP2 gene that codes for one of the secreted aspartic proteinases, which are putative virulence factors of C. albicans. The SAP2P-FLP fusion was integrated into one of the SAP2 alleles in a strain that contained a deletable marker that conferred resistance to mycophenolic acid and was flanked by direct repeats of the FLP recognition target (FRT). Using this reporter system, a transient gene induction could be monitored at the level of single cells by the mycophenolic acid-sensitive phenotype of the colonies generated from such cells after FLP-mediated marker excision. In two mouse models of disseminated candidiasis, SAP2 expression was not observed in the initial phase of infection, but the SAP2 gene was strongly induced after dissemination into deep organs. In contrast, in a mouse model of oesophageal candidiasis in which dissemination into internal organs did not occur, no SAP2 expression was detected at any time. Our results support a role of the SAP2 gene in the late stages of an infection, after fungal spread into deep tissue. This new in vivo expression technology (IVET) for a human fungal pathogen allows the detection of virulence gene induction at different stages of an infection, and therefore provides clues about the role of these genes in the disease process.

High density of FOXP3-positive T cells infiltrating colorectal cancers with microsatellite instability

High-level microsatellite instability (MSI-H) in colorectal cancer accounts for about 12% of colorectal cancers and is typically associated with a dense infiltration with cytotoxic CD8-positive lymphocytes. The role of regulatory T cells that may interfere with the host's antitumoural immune response in MSI-H colorectal cancers has not been analysed yet. Using an antibody directed against the regulatory T-cell marker transcription factor forkhead box P3 (FOXP3), regulatory T cells were examined in 70 colorectal cancers with known MSI status (MSI-H, n=37; microsatellite stable, n=33). In MSI-H colorectal cancers, we found a significantly higher intraepithelial infiltration with FOXP3-positive cells (median: 8.5 cells per 0.25 mm²vs 3.1 cells per 0.25 mm² in microsatellite stable, P<0.001), and a significantly elevated ratio of intraepithelial to stromal infiltration (0.05 vs 0.01 in microsatellite stable, P<0.001). CD8-positive cell counts were related positively to the number of FOXP3-positive cells (Spearman's ρ=0.56 and 0.55, respectively). Our results show that the elevated number of CD8-positive lymphocytes found in MSI-H colorectal cancers is paralleled by an enhanced infiltration with CD8-negative FOXP3-positive cells. These data suggest that FOXP3-positive cells may play a role in the regulation of the immune response directed against MSI-H colorectal cancers at the primary tumour site.

Synthesis, structure-affinity relationships, and biological activities of ligands binding to retinoic acid receptor subtypes

The retinoic acid receptors (RARs) transduce retinoid dependant gene regulation, and many biological effects of retinoids are mediated through binding and activation of three closely related receptor subtypes (RAR alpha, RAR beta, and RAR gamma). In order to investigate the role of receptor subtypes, we have carried out a chemical synthesis program to seek selective retinoids for these receptors. We measured receptor binding affinity using recombinant RAR alpha, -beta, and -gamma proteins and assessed cellular differentiating activity in F9 murine teratocarcinoma cells (F9 cells). This research has identified the 4-substituted-3-(1-adamantyl)phenyl moiety as a new pharmacophore which can replace the beta-cyclogeranylidene ring of the naturally occurring all-trans-retinoic acid. Two chemical series derived from the general structures 6-(3-tertioalkylphenyl)-2-naphthoic acid (series I) and 4-[(E)-2-(3-tertioalkylphenyl)propenyl]benzoic acid (series II) were developed. In particular, we have obtained the RAR gamma selective derivatives 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthoic acid (7) [Ki(RAR alpha) = 6500 nM, Ki(RAR beta) = 2480 nM, Ki(RAR gamma) = 77 nM] and 4-[(E)-2-[3-(1-adamantyl)-4-hydroxyphenyl]propenyl]benzoic acid (19) [Ki(RAR alpha) = 1,144 nM, Ki(RAR beta) = 1245 nM, Ki(RAR gamma) = 53 nM]. In series I, the presence of a phenol group, irrespective of the nature of tertioalkyl group, imparted at least partial RAR gamma selectivity, whereas in series II, the presence of both adamantyl and phenol groups is needed to confer RAR gamma selectivity. The RAR gamma selective ligands induce differentiation in F9 cells (7, AC50 = 33 nM; 19, AC50 = 66 nM). From series I, a mixed RAR beta-gamma agonist with potent cellular differentiating activity was selected for development as a topical antiacne agent, 6-[3-(1-adamantyl)-4-methoxyphenyl]-2-naphthoic acid (5, CD 271) [Ki(RAR alpha) = 1100 nM, Ki-(RAR beta) = 34 nM, Ki(RAR gamma) = 130 nM, AC50(F9) = 37 nM]. Finally, from series II, we have obtained a weak antagonist in the F9 cellular differentiation assay, 4-[(E)-2-(3-tert-butyl-4-hydroxyphenyl)propenyl]benzoic acid (15, IC50 = 700 nM).

Peroxisome proliferator-activated receptor-alpha enhances lipid metabolism in a skin equivalent model

Peroxisome proliferator-activated receptors are involved in certain cell types such as adipocytes and hepatocytes, in the control of several pathways of lipid synthesis or catabolism by regulating the gene expression level of key lipid metabolizing enzymes. As the epidermis exhibits an extensive lipid metabolism necessary for the establishment of the barrier function, we have examined the role of peroxisome proliferator-activated receptor-alpha activation in this process. Living skin equivalents were treated with Wy 14,643, a selective peroxisome proliferator- activated receptor-alpha ligand, which enhanced greatly the synthesis of membrane coating granules, the organelles specialized in the processing of stratum corneum lipids. Also, the overall stratum corneum neutral lipid content assessed by Oil red O staining was increased. A detailed analysis of the lipid species present in the reconstructed epidermis showed that peroxisome proliferator-activated receptor-alpha activation increased the synthesis of ceramides and cholesterol derivatives, thought to be essential structural components of the permeability barrier. A synergistic effect was observed on lipid synthesis when peroxisome proliferator-activated receptor-alpha and retinoid X receptor were simultaneously activated by selective ligands. Furthermore, activation of peroxisome proliferator-activated receptor-alpha led to increased mRNA expression of several key enzymes of ceramide and cholesterol metabolism. An increase of serine-palmitoyl transferase and of beta-glucocerebrosidase enzymatic activity was also demonstrated. Altogether, these results show that peroxisome proliferator-activated receptor-alpha is a key transcription factor involved in the control of the epidermal lipid barrier.

Selective deficits in the circadian light response in mice lacking PACAP

Previous studies indicate that light information reaches the suprachiasmatic nucleus through a subpopulation of retinal ganglion cells that contain both glutamate and pituitary adenylyl cyclase-activating peptide (PACAP). Although the role of glutamate in this pathway has been well studied, the involvement of PACAP and its receptors is only beginning to be understood. To investigate the functions of PACAP in vivo, we developed a mouse model in which the gene coding for PACAP was disrupted by targeted homologous recombination. RIA was used to confirm a lack of detectable PACAP protein in these mice. PACAP-deficient mice exhibited significant impairment in the magnitude of the response to brief light exposures with both light-induced phase delays and advances of the circadian system impacted. This mutation equally impacted phase shifts induced by bright and dim light exposure. Despite these effects on phase shifting, the loss of PACAP had only limited effects on the generation of circadian oscillations, as measured by rhythms in wheel-running activity. Unlike melanopsin-deficient mice, the mice lacking PACAP exhibited no loss of function in the direct light-induced inhibition of locomotor activity, i.e., masking. Finally, the PACAP-deficient mice exhibited normal phase shifts in response to exposure to discrete dark treatments. The results reported here show that the loss of PACAP produced selective deficits in the light response of the circadian system.

Morphological and biochemical characterization of the cornified envelopes from human epidermal keratinocytes of different origin

The formation of a cornified envelope (CE) is a major event in the terminal differentiation of epidermal cells. Nomarski contrast microscopy of the envelopes purified from different sources reveals the existence of two major, but morphologically distinct classes: the very irregularily shaped fragile type CEf, and the polygonal rigid type CEr. Human keratinocytes in submerged culture are only able to produce type CEf. Specimens from healthy human epidermis contain largely type CEr. Psoriatic scales from different patients show both types in varying proportions. Tape stripping of normal epidermis reveals that type CEf is present in the lowermost layers of the stratum corneum and type CEr is present in the upper layers, indicating that the two types represent a different stage of maturation. Cyanogen bromide peptide mapping of electrophoretically purified envelopes reveals striking differences between cultured keratinocytes, normal epidermis, and psoriatic scales but also slight interindividual variations. This variability supports the view that the molecular CE composition is not strictly determined. On the other hand, no difference could be detected in the peptide maps of CEf and CEr obtained after tape stripping from the same healthy volunteer indicating that CE maturation within the stratum corneum does not involve the provision of qualitatively new proteins.

Expression of a chromosomally integrated, single-copy GFP gene in Candida albicans, and its use as a reporter of gene regulation

Genetically engineered versions of the GFP gene, which encodes the green fluorescent protein of Aequorea victoria, were placed under the control of the constitutively active Candida albicans ACT1 promoter and integrated in single copy into the genome of this pathogenic yeast. Integrative transformants in which one of the two ACT1 alleles had been replaced by a GFP gene exhibited a homogeneous, constitutive fluorescent phenotype. Cells expressing GFP with the wild-type chromophore exhibited very weak fluorescence compared to those GFP proteins with the S65T or S65A, V68L, S72A (GFPmut2) chromophore mutations. Substitution of the CTG codon, which specifies serine instead of leucine in C. albicans, by TTG was absolutely necessary for GFP expression. Although GFP mRNA levels in cells containing a GFP gene with the CTG codon were comparable to those of transformants containing GFP with the TTG substitution, only the latter produced GFP protein, as detected by Western blotting, suggesting that the frequent failure to express heterologous genes in C. albicans is principally due to the noncanonical codon usage. Transformants expressing the modified GFP gene from the promoter of the SAP2 gene, which encodes one of the secreted acid proteinases of C. albicans, showed fluorescence only under conditions which promote proteinase expression, thereby demonstrating the utility of stable, chromosomally integrated GFP reporter genes for the study of gene activation in C. albicans.

Localization of bullous pemphigoid antigen (BPA) in isolated human keratinocytes

In early studies, the bullous pemphigoid antigen (BPA) has been localized extracellularly in the lamina lucida in the basement membrane zone. However, trypsin-dissociated basal cells can be tagged with bullous pemphigoid sera (BPS). By immunofluorescence, BPA appears located at the dermal pole of basal cells (BC). This may indicate that when BC are separated from the underlying matrix molecules, chunks of BPA remain attached to them. In the present study, fresh crude initial suspensions (CIS) of epidermal cells were prepared by trypsin-EDTA dissociation. The cells were smeared and air-dried. Polar fluorescent cells (i.e., BC) amounted to 42% +/- 7%. CIS were then passed through a fluorescence-activated cell sorter (FACS). In the fluorescent-positive fractions selected by FACS, 34% +/- 7% only of the BC were present. FACS-negative cell fractions were smeared on glass slides, air-dried, and restained with BPS + fluorescein isothiocyanate; 66% +/- 10% of BC were present in these fractions. This is evidence that trypsin-isolated BC comprise two subpopulations: one with BPA directly accessible, the other not. Viability tests and tissue culture studies indicated that the FACS-positive cell fractions were not viable. BPA was extracted from CIS, FACS-positive, and FACS-negative fractions and immunoblotted against BPS. Identical blots were found. FACS-negative cell fractions were treated with heparitinase, nitrous acid, methanol-chloroform, or EDTA without modifying the number of reacting cells. When BC were treated with Triton X-100 or permeabilized by successive freezings and thawings, the number of positive cells became comparable to those obtained by air-drying smears. Finally, BPA was localized on the intracellular part of hemidesmosomes of BC by immunoelectron microscopy. To see whether BPA was also present extracellularly, suction blisters were raised in minipigs and BPS injected into the blister cavity. BPA was found attached to all cells of the cellular roof but not to the dermal base of the blisters. When pieces of skin kept overnight in cold trypsin were reacted with BPS, BPA was found on both sides (epidermal and dermal) of the split. It is concluded that BPA has two localizations: one extracellular, essentially labile which accumulates at the dermal-epidermal junction; the other essentially stable which remains on the intracellular part of basal cell hemidesmosomes and which can be detected after permeabilization of the cells.

Pharmacology and chemistry of adapalene

BACKGROUND

Retinoid research in the field of dermatology has been influenced by the clinical success of topical tretinoin and oral isotretinoin in the treatment of acne, and by the discovery of high-affinity binding proteins for retinoic acid mediating its action and interaction with other vitamins and hormones.

OBJECTIVE

We sought molecules with an optimal balance between stability, efficacy, and local tolerance for topical acne therapy.

METHODS

In vitro and in vivo bioassay systems were used to test the ability of retinoids to modulate cell proliferation and differentiation. In addition, antiinflammatory properties were assessed. Binding and transactivation assays were used to compare affinities and transcriptional activities of adapalene and tretinoin for the nuclear transcription factors, retinoic acid receptors (RARs).

RESULTS AND CONCLUSION

Adapalene is a stable naphthoic acid derivative with potent retinoid pharmacology, controlling cell proliferation and differentiation. In addition it has significant antiinflammatory action. The nuclear gene transcription factors RAR beta and RAR gamma mediate the retinoid activity of adapalene.

Regulation of vascular endothelial growth factor expression in human keratinocytes by retinoids

Vascular endothelial growth factor (VEGF) is overexpressed in hyperproliferative diseases, such as psoriasis and cancers, which are characterized by increased angiogenesis. Experimentally, VEGF overexpression can be induced by the treatment of cell cultures and biological tissues with phorbol esters, such as 12-O-tetradecanoylphorbol-13-acetate (TPA). Using normal human keratinocytes in conventional cultures and skin grafted onto nude mice in vivo, we show that retinoids can inhibit TPA-mediated VEGF gene induction at the transcriptional level. Because retinoids are biologically active either by interacting with the nuclear retinoic acid receptors or by interfering with the activator protein 1 (AP1) transcription factor, we studied the effect of the retinoic acid derivative CD 2409, which exhibits strong anti-AP1 activity but does not bind to the known retinoic acid receptors in vitro. The results demonstrate that the inhibition of VEGF expression by retinoids only depends on their anti-AP1 activity and does not require gene transactivation via retinoic acid response elements. Because the VEGF promoter contains four potential AP1 binding sites, we used different promoter constructs to identify the functional site responsible for TPA induction and retinoid inhibition. This site turned out to be localized at position -621 of the 5' flanking region of the VEGF gene.

Activation of the multiple drug resistance gene MDR1 in fluconazole-resistant, clinical Candida albicans strains is caused by mutations in a trans-regulatory factor

Resistance of Candida albicans against the widely used antifungal agent fluconazole is often due to active drug efflux from the cells. In many fluconazole-resistant C. albicans isolates the reduced intracellular drug accumulation correlates with constitutive strong expression of the MDR1 gene, encoding a membrane transport protein of the major facilitator superfamily that is not detectably expressed in vitro in fluconazole-susceptible isolates. To elucidate the molecular changes responsible for MDR1 activation, two pairs of matched fluconazole-susceptible and resistant isolates in which drug resistance coincided with stable MDR1 activation were analyzed. Sequence analysis of the MDR1 regulatory region did not reveal any promoter mutations in the resistant isolates that might account for the altered expression of the gene. To test for a possible involvement of trans-regulatory factors, a GFP reporter gene was placed under the control of the MDR1 promoter from the fluconazole-susceptible C. albicans strain CAI4, which does not express the MDR1 gene in vitro. This MDR1P-GFP fusion was integrated into the genome of the clinical C. albicans isolates with the help of the dominant selection marker MPA(R) developed for the transformation of C. albicans wild-type strains. Integration was targeted to an ectopic locus such that no recombination between the heterologous and resident MDR1 promoters occurred. The transformants of the two resistant isolates exhibited a fluorescent phenotype, whereas transformants of the corresponding susceptible isolates did not express the GFP gene. These results demonstrate that the MDR1 promoter was activated by a trans-regulatory factor that was mutated in fluconazole-resistant isolates, resulting in deregulated, constitutive MDR1 expression.

Induction of apoptosis by retinoids and retinoic acid receptor gamma-selective compounds in mouse thymocytes through a novel apoptosis pathway

Retinoic acids are morphogenic signaling molecules that are derived from vitamin A and involved in a variety of tissue functions. Two groups of their nuclear receptors have been identified: retinoic acid receptors (RARs) and retinoic acid X receptors (RXRs). All-trans retinoic acid is the high affinity ligand for RARs, and 9-cis retinoic acid also binds to RXRs with high affinity. In cells at high concentrations, all-trans retinoic acid can be converted to 9-cis retinoic acid via unknown mechanisms. It was previously shown that retinoic acids prevents activation-induced death of thymocytes. Here, we report that both all-trans and 9-cis retinoic acid induce apoptosis of mouse thymocytes and purified CD4+CD8+ cells in ex vivo cultures, with 9-cis retinoic acid being 50 times more effective. The induction of apoptosis by retinoic acids is mediated by RARgamma because (a) the phenomenon can be reproduced only by RARgamma-selective retinoic acid analogs, (b) the cell death induced by either retinoic acids or RARgamma analogs can be inhibited by RARgamma-specific antagonists, and (c) CD4+CD8+ thymocytes express RARgamma. In vivo administration of an RARgamma analog resulted in thymus involution with the concomitant activation of the apoptosis-related endonuclease and induction of tissue transglutaminase. The RARgamma pathway of apoptosis is RNA and protein synthesis dependent, affects the CD4+CD8+ double positive thymocytes, and can be inhibited by the addition of either Ca2+ chelators or protease inhibitors. Using various RAR- and RXR-specific analogs and antagonists, it was demonstrated that stimulation of RAR alpha inhibits the RARgamma-specific death pathway (which explains the lack of apoptosis stimulatory effects of all-trans retinoic acid at physiological concentrations) and that costimulation of the RXR receptors (in the case of 9-cis retinoic acid) can neutralize this inhibitory effect. It is suggested that formation of 9-cis retinoic acid may be a critical element in regulating both the positive selection and the "default cell death pathway" of thymocytes.

Demystifying chromosome preparation and the implications for the concept of chromosome condensation during mitosis

The processes taking place during routine chromosome preparation are not well understood. In this study, the morphological changes in amniotic fluid cells, blood lymphocytes, and bone marrow cells in the metaphase stage were examined under an inverted microscope during chromosome preparation. The putative processes that occur during chromosome preparation were simulated in suspension, and the cells were treated with different mixtures of hypotonic solution, fixative, methanol, acetic acid, and water. Evaporation of the fixative was performed under normal atmospheric conditions and under vacuum at different levels of humidity. Freeze fracture electron microscopy was used to analyze the effects of fixative on the cell membrane. Confocal microscopic analysis was used to investigate three-dimensionally the effects of hypotonic treatment on the positions of chromosomes in fixed mitotic lymphocytes. Chromosome preparation-induced changes in the lengths of single chromosomes were also investigated. The results show that chromosome spreading involves significant water-induced swelling of mitotic cells during evaporation of the fixative from the slide, which is a prerequisite for chromosomal elongation, the production of metaphase spreads for chromosome analysis, and the appearance of Giemsa banding patterns. Hypotonic treatment is essential for well-spread metaphase chromosomes because it moves the chromosomes from a central to a more peripheral position in the cell, where they can be stretched more effectively during mitotic swelling. Like mitotic cells, isolated single chromosomes also have their own potential to swell and lengthen during chromosome preparation. We hypothesize that chromosome preparation leads to a genome-wide chromosomal region-specific opening of chromatin structures as GTG-light bands and sub-bands. Living cells may possess a similar mechanism, which is used only to open single chromatin structures to facilitate transcription. We propose the concept of chromosomal region-specific protein swelling.

Pharmacology of adapalene

Adapalene, a synthetic retinoid, is a new drug proposed for the treatment of acne patients. Studies on the in vitro and in vivo pharmacology of adapalene have shown that it is very active on cell and tissue proliferation and differentiation. Furthermore, adapalene has anti-inflammatory potential as determined by its anti-AP1 activity. Adapalene interacts selectively with the nuclear receptors RAR beta and RAR gamma, and its activity on proliferation and differentiation can be blocked by a RAR beta-gamma antagonist. Because RAR beta is not expressed in human keratinocytes, the effect of adapalene on the major cell type of the epidermis is certainly mediated by its interaction with RAR gamma. The unique pharmacological properties of adapalene may explain why, when compared to tretinoin, it has an improved therapeutic ratio due to its better tolerance.