Interactions between the yeast mitochondrial and nuclear genomes: isogenic suppressive and hypersuppressive petites differ in their resistance to the alkaloid lycorine

Insight to the antifungal properties of Amaryllidaceae constituents

BACKGROUND

Fungal pathogenesis continues to be a burden to healthcare structures in both developed and developing nations. The gradual and irreversible loss of efficacies of existing antifungal medicines as well as the emergence of drug-resistant strains have contributed largely to this scenario. There is therefore a pressing need for new drugs from diverse structural backgrounds with improved potencies and novel modes of action to fortify or replace contemporary antifungal schedules.

AIM

Alkaloids of the plant family Amaryllidaceae exhibit good growth inhibitory activities against several fungal pathogens. This review focuses on the mechanistic aspects of these antifungal activities. It achieves this by highlighting the molecular targets as well as structural features of Amaryllidaceae constituents which serve to enhance such action.

METHODS

During the information gathering stage extensive use was made of the three database platforms; Google Scholar, SciFinder and Scopus. In most instances articles were accessed directly from journals licensed to the University of KwaZulu-Natal. In the absence of such proprietary agreements the respective corresponding authors were approached directly for copies of papers.

RESULTS

Although several classes of molecules from the Amaryllidaceae have been probed for their antifungal effects, it is the key constituents lycorine and narciclasine which have together afforded the most profound mechanistic insights. These may be summarized as follows: (i) effects on the fungal cell wall and cell membrane; (ii) effects on morphology such as budding and hyphal growth; (iii) effects on fungal organelles such as ribosomes; (iv) effects on macromolecules such as DNA, RNA and proteins and; (v) identification of the active sites for these constituents.

CONCLUSION

The key feature in the antifungal effects of Amaryllidaceae alkaloids is the inhibition of protein synthesis. This involved the inhibition of peptide bond formation by binding to yeast ribosomes via the 60S subunit. Related effects involved the inhibition of both DNA and RNA synthesis. These adverse effects were reflected morphologically on both the fungal cell wall and cell membrane. Such observations should prove useful in the chemotherapeutic arena should efforts shift towards the development of a clinical candidate.

Lycorine: A prospective natural lead for anticancer drug discovery

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Outline of the anticancer properties and associated molecular mechanism mediated by lycorine.

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Comprehensive analysis of the structure activity relationship associated with anticancer activity of lycorine.

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Summary of the pharmacological aspects and implications for future directions with this compound.

Nature is the most abundant source for novel drug discovery. Lycorine is a natural alkaloid with immense therapeutic potential. Lycorine is active in a very low concentration and with high specificity against a number of cancers both in vivo and in vitro and against various drug-resistant cancer cells. This review summarized the therapeutic effect and the anticancer mechanisms of lycorine. At the same time, we have discussed the pharmacology and comparative structure-activity relationship for the anticancer activity of this compound. The researches outlined in this paper serve as a foundation to explain lycorine as an important lead compound for new generation anticancer drug design and provide the principle for the development of biological strategies to utilize lycorine in the treatment of cancers.

Ty1 transposition induced by carcinogens in Saccharomyces cerevisiae yeast depends on mitochondrial function

The transposition of the Ty mobile genetic element of Saccharomyces cerevisiae is induced by carcinogens. While the molecular background of spontaneous Ty1 transposition is well understood, the detailed mechanism of carcinogen induced Ty1 transposition is not clear. We found that mitochondrial functions participate in the Ty induced transposition induced by carcinogens. Contrary to the parental rho(+) cells rho(-) mutants (spontaneous or induced by ethidium bromide) do not increase the rate of Ty1 transposition upon treatment with carcinogens. Preliminary results strongly suggest that the absence of oxidative phosphorylation in rho(-) mutants is the reason for the inhibited Ty transposition. The lack of carcinogen induced Ty1 transposition in rho(-) cells is not specific for a particular carcinogen and represents a general feature of different carcinogenic substances inducing rho(-). It is concluded that carcinogen induced Ty1 transposition depends on the functional state of mitochondria and cannot take place in cells with compromised mitochondrial function (rho(-)).

Chemical and biological aspects of Narcissus alkaloids

This chapter discusses the chemical and biological aspects of Narcissus alkaloids. Numerous alkaloids have been isolated from Narcissus speciesasaresult of the continuing search for novel alkaloids with pharmacological activity in the Amaryllidaceae family. The alkaloids isolated from this genus, classified in relation to the different skeleton types. The different Narcissus wild species and intersectional hybrids, grouped into subgenera and sections, with their corresponding alkaloids, arranged according to their ring system are listed. The biosynthetic pathways of Narcissus alkaloids includes: (1) enzymatic preparation of the precursors, (2) primary cyclization mechanisms, (3) enzymatic preparation of intermediates, (4) secondary cyclization, diversification, and restructuring. The chapter discusses proton nuclear magnetic resonance (1H NMR), carbon nuclear magnetic resonance (13C NMR), and mass spectrometry (MS) for Narcissus alkaloids. A list of the different Narcissus alkaloids, their spectroscopic properties, and literature with the most recent spectroscopic data is given. Several Narcissus extracts shows the following activities: antiviral, prophage induction, antibacterial, antifungal, antimalarial, insecticidal, cytotoxic, antitumor, antimitotic, antiplatelet, hypotensive, emetic, acetylcholine esterase inhibitory, antifertility, antinociceptive, chronotropic, pheromone, plant growth inhibitor, and allelopathic.

Interaction between yeast mitochondrial and nuclear genomes: null alleles of RTG genes affect resistance to the alkaloid lycorine in rho0 petites of Saccharomyces cerevisiae

Some nuclear genes in Saccharomyces cerevisiae (S. cerevisiae) respond to signals from the mitochondria in a process called by Butow (Cell Death Differ. 9 (2002) 1043-1045) retrograde regulation. Expression of these genes is activated in cells lacking mitochondrial function by involvement of RTG1, RTG2 and RTG3 genes whose protein products bind to "R-boxes" in the promoter region; RTG2p is a cytoplasmic protein. Since S. cerevisiae rho0 strains, lacking the entire mitochondrial genome, are resistant to lycorine, an alkaloid extracted from Amaryllis plants, it could be hypothesized that in rho0 cells the dysfunctional mitochondrial status stimulates overexpression of nuclear genes very likely involved in both nuclear and mitochondrial DNA replication. In this report we show that the resistance of rho0 cells to lycorine is affected by the deletion of RTG genes.

Hyper-expression of small nucleolar RNAs (snoRNAs) in female inflorescences of hazelnut (Corylus avellana L.) supports rRNA aggregation in vitro

Under certain in vitro (salt and temperature) conditions rRNA aggregation occurs in female inflorescences but not in leaves or pollen RNA preparations from hazelnut (Corylus avellana L.), a species of economic interest. This paper describes experiments addressing an explanation of this phenomenon. The experiments demonstrate that: (i) trans-acting factors induce rRNA aggregate formation in female inflorescences RNA preparations; (ii) these factors support aggregation also of heterologous rRNA; (iii) aggregation is a function of temperature pre-treatment of rRNA and not of source 18S rRNA; (iv) the factors inducing rRNA aggregates are sensitive to RNase; (v) antisense small nucleolar RNAs (snoRNAs) participate in rRNA aggregate formation. snoRNAs are involved in pre-rRNA spacer cleavages, and are required for the two most common types of rRNA modifications: 2'-O-ribose methylation and pseudouridylation. Even though it is questionable whether rRNA aggregation really happens in female inflorescence in vivo, the phenomenon observed in vitro may reflect the abundance of snoRNAs in these reproductive structures. In fact the level of accumulation of three tested snoRNAs, R1, U14 and U3, is much higher in female inflorescence than in leaves or pollen of hazelnut. This finding opens the possibility of studying the role of snoRNAs in tissue development in plants.

Use of lycorine and DAPI staining in Saccharomyces cerevisiae to differentiate between rho0 and rho- cells in a cce1/delta cce1 nuclear background

In the yeast Saccharomyces cerevisiae, mutants are viable with large deletions (rho-), or even complete loss of the mitochondrial genome (rho0). One class of rho- mutants, which is called hypersuppressive, is characterised by a high transmission of the mutated mitochondrial genome to the diploid progeny when mated to a wild-type (rho+) haploid. The nuclear gene CCE1 encodes a cruciform cutting endonuclease, which is located in the mitochondrion and is responsible for the highly biased transmission of the hypersuppressive rho- genome. CCE1 is a Holliday junction specific endonuclease that resolves recombination intermediates in mitochondrial DNA. The cleavage activity shows a strong preference for cutting after a 5'-CT dinucleotide. In the absence of the CCE1 gene product, the mitochondrial genomes remain interconnected and have difficulty segregating to the daughter cells. As a consequence, there is an increase in the fraction of daughter cells that are rho0. In this paper we demonstrate the usefulness of lycorine, together with staining by 4',6-diamidino-2-phenylindole (DAPI), to assay for the mitotic stability of a variety of mitochondrial genomes. We have found that rho+ and rho- strains that contain CT sequences produce a large fraction of rho0 progeny in the absence of CCE1 activity. Only those rho- mitochondrial genomes lacking the CT recognition sequence are unaffected by the cce1 allele.

Purification of the alkaloid lycorine and simultaneous analysis of ascorbic acid and lycorine by micellar electrokinetic capillary chromatography

The pyrrolophenanthridine alkaloid lycorine has frequently been used as a specific inhibitor to help elucidate the function of ascorbic acid (vitamin C) in a wide range of biological processes. It was recently reported that this function can be exercised by inhibiting the activity of L-galactono-1,4-lactone dehydrogenase, the terminal enzyme of ascorbic acid biosynthesis, although working with the purified enzyme, we have been unable to repeat this result. Here, we present a procedure for the purification and analysis of lycorine by high-performance liquid chromatography from two Crinum species and describe for the first time a method that allows the simultaneous analysis of ascorbic acid and lycorine in tissue extracts of Crinum asiaticum by micellar electrokinetic chromatography.

Complete absence of mitochondrial DNA in the petite-negative yeast Schizosaccharomyces pombe leads to resistance towards the alkaloid lycorine

The petite-positive yeast Saccharomyces cerevisiae can be efficiently and completely converted to respiratory-deficient cytoplasmic petite mutants by intercalating drugs. Rho0 petites from Schizosaccharomyces pombe could only be obtained in strains carrying a nuclear mutation. In this paper we report the efficient isolation of rho0 mutants in a Sch. pombe strain containing a mitochondrial mutator mutation. We also show that the alkaloid lycorine is able to differentiate between cells containing defective mitochondrial DNA (mit-) and those lacking mitochondrial DNA completely (rho0). Rho0 cells are resistant to the alkaloid whereas mit- and wild-type cells show the same sensitivity.