Molecular Forces Governing the Biological Function of Per-Arnt-Sim-B (PAS-B) Domains: A Comparative Computational Study

Per-Arnt-Sim (PAS) domains are evolutionarily-conserved regions found in proteins in all living systems, involved in transcriptional regulation and the response to hypoxic and xenobiotic stress. Despite having low primary sequence similarity, they show an impressively high structural conservation. Nonetheless, understanding the underlying mechanisms that drive the biological function of the PAS domains remains elusive. In this work, we used molecular dynamics simulations and bioinformatics tools in order the investigate the molecular characteristics that govern the intrinsic dynamics of five PAS-B domains (human AhR receptor, NCOA1, HIF1α, and HIF2α transcription factors, and Drosophila Suzukii (D. Suzukii) juvenile hormone receptor JHR). First, we investigated the effects of different length of N and C terminal regions of the AhR PAS-B domain, showing that truncation of those segments directly affects structural stability and aggregation propensity of the domain. Secondly, using the recently annotated PAS-B located in the methoprene-tolerant protein/juvenile hormone receptor (JHR) from D. Suzukii, we have shown that the mutation of the highly conserved “gatekeeper” tyrosine to phenylalanine (Y322F) does not affect the stability of the domain. Finally, we investigated possible redox-regulation of the AhR PAS-B domain by focusing on the cysteinome residues within PAS-B domains. The cysteines in AhR PAS-B are directly regulating the dynamics of the small molecule ligand-gating loop (residues 305 to 326). In conclusion, we comprehensibly described several molecular features governing the behaviour of PAS-B domains in solution, which may lead to a better understanding of the forces driving their biological functions.

Increase in longevity and amelioration of pesticide toxicity by natural levels of dietary phytochemicals in the honey bee, Apis mellifera

For the past decade, migratory beekeepers who provide honey bees for pollination services have experienced substantial colony losses on a recurring basis that have been attributed in part to exposure to insecticides, fungicides, or their combinations applied to crops. The phytochemicals p-coumaric acid and quercetin, which occur naturally in a wide variety of bee foods, including beebread and many types of honey, can enhance adult bee longevity and reduce the toxicity of certain pesticides. How variation in concentrations of natural dietary constituents affects interactions with xenobiotics, including synthetic pesticides, encountered in agroecosystems remains an open question. We tested the effects of these two phytochemicals at a range of natural concentrations on impacts of consuming propiconazole and chlorantraniliprole, a triazole fungicide and an insecticide frequently applied as a tank mix to almond trees during bloom in California’s Central Valley. Propiconazole, even at low field concentrations, significantly reduced survival and longevity when consumed by adult bees in a sugar-based diet. The effects of propiconazole in combination with chlorantraniliprole enhanced mortality risk. The detrimental effects of the two pesticides were for the most part reduced when either or both of the phytochemicals were present in the diet. These findings suggest that honey bees may depend on non-nutritive but physiologically active phytochemical components of their natural foods for ameliorating xenobiotic stress, although only over a certain range of concentrations; particularly at the high end of the natural range, certain combinations can incur additive toxicity. Thus, efforts to develop nectar or pollen substitutes with phytochemicals to boost insecticide tolerance or immunity or to evaluate toxicity of pesticides to pollinators should take concentration-dependent effects of phytochemicals into consideration.

Balancing selection maintains ancient genetic diversity in C. elegans

Summary paragraphThe mating system of a species profoundly influences its evolutionary trajectory1–3. Across diverse taxa, selfing species have evolved independently from outcrossing species thousands of times4. The transition from outcrossing to selfing significantly decreases the effective population size, effective recombination rate, and heterozygosity within a species5. These changes lead to a reduction in the genetic diversity, and therefore adaptive potential, by intensifying the effects of random genetic drift and linked selection6,7. Selfing has evolved at least three times independently in the nematode genus Caenorhabditis8, including in the model organism Caenorhabditis elegans, and all three selfing species show substantially reduced genetic diversity relative to outcrossing species8,9. Selfing and outcrossing Caenorhabditis species are often found in the same niches, but we still do not know how selfing species with limited genetic diversity can adapt to and inhabit these same diverse environments. Here, we discovered previously uncharacterized levels and patterns of genetic diversity by examining the whole-genome sequences from 609 wild C. elegans strains isolated worldwide. We found that genetic variation is concentrated in punctuated hyper-divergent regions that cover 20% of the C. elegans reference genome. These regions are enriched in environmental response genes that mediate sensory perception, pathogen response, and xenobiotic stress. Population genomic evidence suggests that these regions have been maintained by balancing selection. Using long-read genome assemblies for 15 wild isolates, we found that hyper-divergent haplotypes contain unique sets of genes and show levels of divergence comparable to that found between Caenorhabditis species that diverged millions of years ago. Taken together, these results suggest that ancient genetic diversity present in the outcrossing ancestor of C. elegans has been maintained by long-term balancing selection since the evolution of selfing. These results provide an example for how species can avoid the evolutionary “dead end” associated with selfing by maintaining ancestral genetic diversity.

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)–Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

NHR-8 regulated P-glycoproteins uncouple xenobiotic stress resistance from longevity in chemosensory C. elegans mutants

Longevity is often associated with stress resistance, but whether they are causally linked is incompletely understood. Here we investigate chemosensory defective Caenorhabditis elegans mutants that are long-lived and stress resistant. We find that mutants in the intraflagellar transport protein gene osm-3 were significantly protected from tunicamycin-induced ER stress. While osm-3 lifespan extension is dependent on the key longevity factor DAF-16/FOXO, tunicamycin resistance was not. osm-3 mutants are protected from bacterial pathogens, which is pmk-1 p38 MAP kinase dependent while TM resistance was pmk-1 independent. Inhibition of P-glycoproteins with verapamil suppressed tunicamycin resistance and expression of P-glycoprotein xenobiotic detoxification genes was elevated in osm-3 mutants. The nuclear hormone receptor nhr-8 was necessary and sufficient to regulate P-glycoproteins and tunicamycin resistance in a cholesterol-dependent fashion. We thus identify a cell-nonautonomous regulation of xenobiotic detoxification and show that separate pathways are engaged to mediate longevity, pathogen resistance, and xenobiotic detoxification in osm-3 mutants.

OZONE THERAPY: MECHANISMS OF ACTION, RECENT LITERATURE AND NEWLY DISCOVERED BIOCHEMICAL PATHWAYS

Ozone therapy is widely used in many countries since many years. Recently, the increasing widespread of this complementary therapy has been accomplished by an increased number of basic and clinic papers published on international journals. This lecture will deal on the first approach by a pharmacological point of view in the aim to characterize the mechanisms activated at sub-cellular level by ozone when used for medical and beauty application at low graded doses. The first theory was based upon the fact that the exposure to low, non-toxic, ozone concentrations could increase the efficacy of the endogenous antioxidant system by increasing the production or the activity of some enzymes exerting a key role in the mitochondrial respiratory chain. Many of the basic mechanisms of the ozone action are now well outlined. In addition, the modulation of interleukins productions and of some biochemical pathways related to inflammation and pain, indicates the rationale of its use in many pathological conditions related to pain, inflammation and age disorders. We also discuss on the mode of action of ozone that, with an hormetic mechanism, appear to be more similar to xenobiotic stress model than a pure pharmacological action. Indeed, our recent work in vivo on patients treated with major autohemo therapy (MAH) demonstrated the increase of Nrf2 level (P