Multiple activities of a novel substance, dictyopyrone C isolated from Dictyostelium discoideum, in cellular growth and differentiation

Natural Products from Social Amoebae

Natural products are invaluable sources of structural diversity and complexity ideally suited for the development of therapeutic agents. The search for novel bioactive molecules has prompted scientists to explore various ecological niches. Microorganisms have been shown to constitute such an important source. Despite their biosynthetic potential, social amoebae, that is, microorganisms with both a uni- and multicellular lifestyle, are underexplored regarding their secreted secondary metabolome. In this review, we present the structural diversity of amoebal natural products and discuss their biological functions as well as their total syntheses.

[Novel biologically active compounds isolated from unexploited organisms, cellular sime molds]

Cellular slime molds are thought to be excellent model organisms for the study of cell and developmental biology because of their simple pattern of development. However, there have been few reports on secondary metabolites of them. We have focused on the utility of cellular slime molds as novel resources for natural product chemistry, and have studied the diversity of secondary metabolites produced by them as well as their physiological and pharmacological activities. We have recently isolated many novel compounds from the fruiting bodies of various species of Dictyostelium cellular slime molds. Total syntheses and biological evaluation of these compounds have been carried out. It was shown that dictyopyrones and dictyomedins may regulate Dictyostelium development. Amino sugar derivatives such as furanodictines and dictyoglucosamines induced neuronal differentiation of rat PC-12 cells. In addition, brefelamide inhibited the cellular proliferation of 1321N1 human astrocytoma cells. These results show that cellular slime molds are promising sources in natural product chemistry.

GrlJ, a Dictyostelium GABAB-like receptor with roles in post-aggregation development

BACKGROUND

The G-protein-coupled receptor (GPCR) family represents the largest and most important group of targets for chemotherapeutics. They are extremely versatile receptors that transduce signals as diverse as biogenic amines, purins, odorants, ions and pheromones from the extracellular compartment to the interior via biochemical processes involving GTP-binding proteins. Until recently, the cyclic AMP receptors (cARs) were the only known G protein coupled receptors in Dictyostelium discoideum. The completed genome sequence revealed the presence of several families of GPCRs in Dictyostelium, among them members of the family 3 of GPCRs, the GABAB/glutamate like receptor family, which in higher eukaryotes is involved in neuronal signaling.

RESULTS

D. discoideum has seventeen Family 3 members of GPCRs, denoted GrlA through GrlR. Their transcripts are detected throughout development with increased levels during early and late development. We have examined here GrlJ. GFP-tagged GrlJ localises to the plasma-membrane and to internal membranes. Inactivation of the grlJ gene leads to precocious development, and the mutant completes development ~6 hours earlier. Alterations were also noted at the slug stage and in spore formation. grlJ- slugs were longer and broke apart several times on their way to culmination forming smaller but proportionate fruiting bodies. Spores from grlJ- fruiting bodies were malformed and less viable, although the spore differentiation factors were synthesized and sensed normally. Expression of a GFP-tagged full length GrlJ rescued the phenotype.

CONCLUSION

Our data suggest that GrlJ acts at several stages of Dictyostelium development and that it is a negative regulator in Dictyostelium development.

Isolation and synthesis of a new aromatic compound, brefelamide, from dictyostelium cellular slime molds and its inhibitory effect on the proliferation of astrocytoma cells

[structure: see text] We have explored the diversity of secondary metabolites produced by cellular slime molds to examine the possible use of such cellular slime molds as a resource for novel drug development. A new aromatic amide, brefelamide (1), was isolated from methanol extracts of the fruiting bodies of Dictyostelium brefeldianum and D. giganteum. The structure of 1 was determined by spectral means including EIMS and (1)H and (13)C NMR. The total synthesis of 1 was carried out to confirm the structure and obtain sufficient samples for performing biological evaluation. Interestingly, compound 1 inhibited the cellular proliferation of 1321N1 human astrocytoma cells.

Dictyopyrones, novel alpha-pyronoids isolated from Dictyostelium spp., promote stalk cell differentiation in Dictyostelium discoideum

Dictyopyrones A and B (DpnA and B), whose function(s) is not known, were isolated from fruiting bodies of Dictyostelium discoideum. In the present study, to assess their function(s), we examined the effects of Dpns on in vitro cell differentiation in D. discoideum monolayer cultures with cAMP. Dpns at 1-20 microM promoted stalk cell formation to some extent in the wild-type strain V12M2. Although Dpns by themselves could hardly induce stalk cell formation in a differentiation-inducing factor (DIF)-deficient strain HM44, both of them dose-dependently promoted DIF-1-dependent stalk cell formation in the strain. In the sporogenous strain HM18, Dpns at 1-20 microM suppressed spore formation and promoted stalk cell formation in a dose-dependent manner. Analogs of Dpns were less effective in affecting cell differentiation in both HM44 and HM18 cells, indicating that the activity of Dpns should be chemical structure specific. It was also shown that DpnA at 2-20 microM dose-dependently suppressed spore formation induced with 8-bromo cAMP and promoted stalk cell formation in V12M2 cells. Interestingly, it was shown by the use of RT-PCR that DpnA at 10 microM slightly promoted both prespore- and prestalk-specific gene expressions in an early phase of V12M2 and HM18 in vitro differentiation. The present results suggest that Dpns may have functions (1) to promote both prespore and prestalk cell differentiation in an early stage of development and (2) to suppress spore formation and promote stalk cell formation in a later stage of development in D. discoideum.

Structural requirements of dictyopyrones isolated from Dictyostelium spp. in the regulation of Dictyostelium development and in anti-leukemic activity

Cellular slime molds are fascinating to the field of developmental biology, and have long been used as excellent model organisms for the study of various aspects of multicellular development. We have recently isolated alpha-pyronoids, named dictyopyrones A-D (1-4), from various species of Dictyostelium cellular slime molds, and it was shown that compound 3 may regulate Dictyostelium development. In this study, we synthesized dictyopyrones A-D (1-4) and their analogues, investigated the physiological role of the molecules in cell growth and morphogenesis in D. discoideum, and further verified their effects on human leukemia K562 cells. Nitrogen-containing compounds 22 and 37 strongly inhibited cell growth in K562 leukemia cells, indicating that these compounds may be utilized as novel lead compounds for anti-leukemic agents.