Differentiation-inducing factor from the slime mould Dictyostelium discoideum and its analogues. Synthesis, structure and biological activity

Derivatives of Differentiation-Inducing Factor 1 Differentially Control Chemotaxis and Stalk Cell Differentiation in Dictyostelium discoideum

Differentiation-inducing factors 1 and 2 (DIF-1 and DIF-2) are small lipophilic signal molecules that induce stalk cell differentiation but differentially modulate chemotaxis toward cAMP in the cellular slime mold Dictyostelium discoideum; DIF-1 suppresses chemotactic cell movement in shallow cAMP gradients, whereas DIF-2 promotes it. The receptor(s) for DIF-1 and DIF-2 have not yet been identified. We examined the effects of nine derivatives of DIF-1 on chemotactic cell movement toward cAMP and compared their chemotaxis-modulating activity and stalk cell differentiation-inducing activity in wild-type and mutant strains. The DIF derivatives differentially affected chemotaxis and stalk cell differentiation; for example, TM-DIF-1 suppressed chemotaxis and showed poor stalk-inducing activity, DIF-1(3M) suppressed chemotaxis and showed strong stalk-inducing activity, and TH-DIF-1 promoted chemotaxis. These results suggest that DIF-1 and DIF-2 have at least three receptors: one for stalk cell induction and two for chemotaxis modulation. In addition, our results show that the DIF derivatives can be used to analyze the DIF-signaling pathways in D. discoideum.

Dictyostelium: An Important Source of Structural and Functional Diversity in Drug Discovery

The cellular slime mold Dictyostelium discoideum is an excellent model organism for the study of cell and developmental biology because of its simple life cycle and ease of use. Recent findings suggest that Dictyostelium and possibly other genera of cellular slime molds, are potential sources of novel lead compounds for pharmacological and medical research. In this review, we present supporting evidence that cellular slime molds are an untapped source of lead compounds by examining the discovery and functions of polyketide differentiation-inducing factor-1, a compound that was originally isolated as an inducer of stalk-cell differentiation in D. discoideum and, together with its derivatives, is now a promising lead compound for drug discovery in several areas. We also review other novel compounds, including secondary metabolites, that have been isolated from cellular slime molds.

An individual-level selection model for the apparent altruism exhibited by cellular slime moulds

In Dictyostelium discoideum, cells that become part of the stalk or basal disc display behaviour that can be interpreted as altruistic. Atzmony et al. (Curr Sci 72:142-145, 1997) had hypothesised that this behaviour could be the outcome of an adaptive strategy based on differing intrinsic quality as reflected by phenotypes that indicate differences in potential for survival and reproduction, followed by intercellular competition among amoebae of differing qualities. Low-quality amoebae would have a poor chance of succeeding in the competition to form spores; they could enhance their chances of survival by adopting a presumptive stalk strategy. Here we extend the hypothesis by making use of recent findings. Our approach is based on the view that an evolutionary explanation for the apparent altruism of stalk cells in D. discoideum must apply broadly to other cellular slime moulds (CSMs) that exhibit stalk cell death. Further, it must be capable of being modified to cover social behaviour in CSMs with an extracellular stalk, as well as in sorocarpic amoebae whose stalk cells are viable. With regard to D. discoideum, we suggest that (a) differentiation-inducing factor, thought of as a signal that inhibits amoebae from forming spores and induces them to differentiate into basal disc cells, is better viewed as a mediator of competition among post-aggregation amoebae and (b) the products of the 'recognition genes', tgrB and tgrC, allow an amoeba to assess its quality relative to that of its neighbours and move to a position within the aggregate that optimises its reproductive fitness. From this perspective, all cells behave in a manner that is 'selfish' rather than 'altruistic', albeit with different expectations of success.

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.

Evidence that differentiation-inducing factor-1 controls chemotaxis and cell differentiation, at least in part, via mitochondria in D. discoideum

Differentiation-inducing factor-1 [1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one (DIF-1)] is an important regulator of cell differentiation and chemotaxis in the development of the cellular slime mold Dictyostelium discoideum However, the entire signaling pathways downstream of DIF-1 remain to be elucidated. To characterize DIF-1 and its potential receptor(s), we synthesized two fluorescent derivatives of DIF-1, boron-dipyrromethene (BODIPY)-conjugated DIF-1 (DIF-1-BODIPY) and nitrobenzoxadiazole (NBD)-conjugated DIF-1 (DIF-1-NBD), and investigated their biological activities and cellular localization. DIF-1-BODIPY (5 µM) and DIF-1 (2 nM) induced stalk cell differentiation in the DIF-deficient strain HM44 in the presence of cyclic adenosine monosphosphate (cAMP), whereas DIF-1-NBD (5 µM) hardly induced stalk cell differentiation under the same conditions. Microscopic analyses revealed that the biologically active derivative, DIF-1-BODIPY, was incorporated by stalk cells at late stages of differentiation and was localized to mitochondria. The mitochondrial uncouplers carbonyl cyanide m-chlorophenylhydrazone (CCCP), at 25-50 nM, and dinitrophenol (DNP), at 2.5-5 µM, induced partial stalk cell differentiation in HM44 in the presence of cAMP. DIF-1-BODIPY (1-2 µM) and DIF-1 (10 nM), as well as CCCP and DNP, suppressed chemotaxis in the wild-type strain Ax2 in shallow cAMP gradients. These results suggest that DIF-1-BODIPY and DIF-1 induce stalk cell differentiation and modulate chemotaxis, at least in part, by disturbing mitochondrial activity.

A polycystin-type transient receptor potential (Trp) channel that is activated by ATP

ATP and ADP are ancient extra-cellular signalling molecules that in Dictyostelium amoebae cause rapid, transient increases in cytosolic calcium due to an influx through the plasma membrane. This response is independent of hetero-trimeric G-proteins, the putative IP3 receptor IplA and all P2X channels. We show, unexpectedly, that it is abolished in mutants of the polycystin-type transient receptor potential channel, TrpP. Responses to the chemoattractants cyclic-AMP and folic acid are unaffected in TrpP mutants. We report that the DIF morphogens, cyclic-di-GMP, GABA, glutamate and adenosine all induce strong cytoplasmic calcium responses, likewise independently of TrpP. Thus, TrpP is dedicated to purinergic signalling. ATP treatment causes cell blebbing within seconds but this does not require TrpP, implicating a separate purinergic receptor. We could detect no effect of ATP on chemotaxis and TrpP mutants grow, chemotax and develop almost normally in standard conditions. No gating ligand is known for the human homologue of TrpP, polycystin-2, which causes polycystic kidney disease. Our results now show that TrpP mediates purinergic signalling in Dictyostelium and is directly or indirectly gated by ATP.

Summary: We show that a Trp channel related to the mammalian polycystin channel, rather than a P2X receptor, is responsible for the purinergic stimulation of cytosolic calcium levels in Dictyostelium cells.

Glutathione S-transferase 4 is a putative DIF-binding protein that regulates the size of fruiting bodies in Dictyostelium discoideum

In the development of the cellular slime mold Dictyostelium discoideum, two chlorinated compounds, the differentiation-inducing factors DIF-1 and DIF-2, play important roles in the regulation of both cell differentiation and chemotactic cell movement. However, the receptors of DIFs and the components of DIF signaling systems have not previously been elucidated. To identify the receptors for DIF-1 and DIF-2, we here performed DIF-conjugated affinity gel chromatography and liquid chromatography-tandem mass spectrometry and identified the glutathione S-transferase GST4 as a major DIF-binding protein. Knockout and overexpression mutants of gst4 (gst4^- and gst4^OE, respectively) formed fruiting bodies, but the fruiting bodies of gst4^- cells were smaller than those of wild-type Ax2 cells, and those of gst4^OE cells were larger than those of Ax2 cells. Both chemotaxis regulation and in vitro stalk cell formation by DIFs in the gst4 mutants were similar to those of Ax2 cells. These results suggest that GST4 is a DIF-binding protein that regulates the sizes of cell aggregates and fruiting bodies in D. discoideum.

Differentiation-inducing factor 2 modulates chemotaxis via the histidine kinase DhkC-dependent pathway in Dictyostelium discoideum

Differentiation-inducing factor 1(DIF-1) and DIF-2 are signaling molecules that control chemotaxis in Dictyostelium discoideum. Whereas DIF-1 suppresses chemotaxis in shallow cAMP gradients, DIF-2 enhances chemotaxis under the same conditions via a phosphodiesterase, response regulator A (RegA), which is a part of the DhkC-RdeA-RegA two-component signaling system. In this study, to investigate the mechanism of the chemotaxis regulation by DIF-2, we examined the effects of DIF-2 (and DIF-1) on chemotaxis in rdeA(-) and dhkC(-) mutant strains. In the parental wild-type strains, chemotactic cell movement was suppressed with DIF-1 and enhanced with DIF-2 in shallow cAMP gradients. In contrast, in both rdeA(-) and dhkC(-) strains, chemotaxis was suppressed with DIF-1 but unaffected by DIF-2. The results suggest that DIF-2 modulates chemotaxis via the DhkC-RdeA-RegA signaling system.

Derivatives of Dictyostelium differentiation-inducing factors inhibit lysophosphatidic acid-stimulated migration of murine osteosarcoma LM8 cells

Osteosarcoma is a common metastatic bone cancer that predominantly develops in children and adolescents. Metastatic osteosarcoma remains associated with a poor prognosis; therefore, more effective anti-metastatic drugs are needed. Differentiation-inducing factor-1 (DIF-1), -2, and -3 are novel lead anti-tumor agents that were originally isolated from the cellular slime mold Dictyostelium discoideum. Here we investigated the effects of a panel of DIF derivatives on lysophosphatidic acid (LPA)-induced migration of mouse osteosarcoma LM8 cells by using a Boyden chamber assay. Some DIF derivatives such as Br-DIF-1, DIF-3(+2), and Bu-DIF-3 (5-20 μM) dose-dependently suppressed LPA-induced cell migration with associated IC50 values of 5.5, 4.6, and 4.2 μM, respectively. On the other hand, the IC50 values of Br-DIF-1, DIF-3(+2), and Bu-DIF-3 versus cell proliferation were 18.5, 7.2, and 2.0 μM, respectively, in LM8 cells, and >20, 14.8, and 4.3 μM, respectively, in mouse 3T3-L1 fibroblasts (non-transformed). Together, our results demonstrate that Br-DIF-1 in particular may be a valuable tool for the analysis of cancer cell migration, and that DIF derivatives such as DIF-3(+2) and Bu-DIF-3 are promising lead anti-tumor agents for the development of therapies that suppress osteosarcoma cell proliferation, migration, and metastasis.

DIF-1 inhibits tumor growth in vivo reducing phosphorylation of GSK-3β and expressions of cyclin D1 and TCF7L2 in cancer model mice

We reported that differentiation-inducing factor-1 (DIF-1), synthesized by Dictyostelium discoideum, inhibited proliferation of various tumor cell lines in vitro by suppressing the Wnt/β-catenin signaling pathway. However, it remained unexplored whether DIF-1 also inhibits tumor growth in vivo. In the present study, therefore, we examined in-vivo effects of DIF-1 using three cancer models: Mutyh-deficient mice with oxidative stress-induced intestinal tumors and nude mice xenografted with the human colon cancer cell line HCT-116 and cervical cancer cell line HeLa. In exploration for an appropriate route of administration, we found that orally administered DIF-1 was absorbed through the digestive tract to elevate its blood concentration to levels enough to suppress tumor cell proliferation. Repeated oral administration of DIF-1 markedly reduced the number and size of intestinal tumors that developed in Mutyh-deficient mice, reducing the phosphorylation level of GSK-3β Ser(9) and the expression levels of early growth response-1 (Egr-1), transcription factor 7-like 2 (TCF7L2) and cyclin D1. DIF-1 also inhibited the growth of HCT-116- and HeLa-xenograft tumors together with decreasing phosphorylation level of GSK-3β Ser(9), although it was not statistically significant in HeLa-xenograft tumors. DIF-1 also suppressed the expressions of Egr-1, TCF7L2 and cyclin D1 in HCT-116-xenograft tumors and those of β-catenin, TCF7L2 and cyclin D1 in HeLa-xenograft tumors. This is the first report to show that DIF-1 inhibits tumor growth in vivo, consistent with its in-vitro action, suggesting that this compound may have potential as a novel anti-tumor agent.

Novel chlorinated dibenzofurans isolated from the cellular slime mold, Polysphondylium filamentosum, and their biological activities

Cellular slime molds are expected to have the huge potential for producing secondary metabolites including polyketides, and we have studied the diversity of secondary metabolites of cellular slime molds for their potential utilization as new biological resources for natural product chemistry. From the methanol extract of fruiting bodies of Polysphondylium filamentosum, we obtained new chlorinated benzofurans Pf-1 (4) and Pf-2 (5) which display multiple biological activities; these include stalk cell differentiation-inducing activity in the well-studied cellular slime mold, Dictyostelium discoideum, and inhibitory activities on cell proliferation in mammalian cells and gene expression in Drosophila melanogaster.

Identification of a eukaryotic reductive dechlorinase and characterization of its mechanism of action on its natural substrate

Chlorinated compounds are important environmental pollutants whose biodegradation may be limited by inefficient dechlorinating enzymes. Dictyostelium amoebae produce a chlorinated alkyl phenone called DIF which induces stalk cell differentiation during their multicellular development. Here we describe the identification of DIF dechlorinase. DIF dechlorinase is active when expressed in bacteria, and activity is lost from Dictyostelium cells when its gene, drcA, is knocked out. It has a K_m for DIF of 88 nM and K_cat of 6.7 s⁻¹. DrcA is related to glutathione S-transferases, but with a key asparagine-to-cysteine substitution in the catalytic pocket. When this change is reversed, the enzyme reverts to a glutathione S-transferase, thus suggesting a catalytic mechanism. DrcA offers new possibilities for the rational design of bioremediation strategies.

Control of prestalk-cell differentiation by transcription factors

Transcriptional control of developmental genes is important for cell differentiation and pattern formation. Developing Dictyostelium discoideum cells form a multicellular structure in which individual cells differentiate into either stalk cells or spores. This simplicity makes the organism an attractive model for studying fundamental problems in developmental biology. However, the morphogenetic process of forming a stalked fruiting body conceals a certain degree of complexity. This is reflected in the presence of multiple prestalk subtypes that have individual roles to generate the fruiting body. This review describes recent advances in understanding the molecular mechanisms, mediated by transcription factors that generate prestalk-cell heterogeneity.

Evolution of cooperation and control of cheating in a social microbe

Much of what we know about the evolution of altruism comes from animals. Here, we show that studying a microbe has yielded unique insights, particularly in understanding how social cheaters are controlled. The social stage of Dictylostelium discoideum occurs when the amoebae run out of their bacterial prey and aggregate into a multicellular, motile slug. This slug forms a fruiting body in which about a fifth of cells die to form a stalk that supports the remaining cells as they form hardy dispersal-ready spores. Because this social stage forms from aggregation, it is analogous to a social group, or a chimeric multicellular organism, and is vulnerable to internal conflict. Advances in cell labeling, microscopy, single-gene knockouts, and genomics, as well as the results of decades of study of D. discoideum as a model for development, allow us to explore the genetic basis of social contests and control of cheaters in unprecedented detail. Cheaters are limited from exploiting other clones by high relatedness, kin discrimination, pleiotropy, noble resistance, and lottery-like role assignment. The active nature of these limits is reflected in the elevated rates of change in social genes compared with nonsocial genes. Despite control of cheaters, some conflict is still expressed in chimeras, with slower movement of slugs, slightly decreased investment in stalk compared with spore cells, and differential contributions to stalk and spores. D. discoideum is rapidly becoming a model system of choice for molecular studies of social evolution.

On the paradigm of altruistic suicide in the unicellular world

Altruistic suicide is best known in the context of programmed cell death (PCD) in multicellular individuals, which is understood as an adaptive process that contributes to the development and functionality of the organism. After the realization that PCD-like processes can also be induced in single-celled lineages, the paradigm of altruistic cell death has been extended to include these active cell death processes in unicellular organisms. Here, we critically evaluate the current conceptual framework and the experimental data used to support the notion of altruistic suicide in unicellular lineages, and propose new perspectives. We argue that importing the paradigm of altruistic cell death from multicellular organisms to explain active death in unicellular lineages has the potential to limit the types of questions we ask, thus biasing our understanding of the nature, origin, and maintenance of this trait. We also emphasize the need to distinguish between the benefits and the adaptive role of a trait. Lastly, we provide an alternative framework that allows for the possibility that active death in single-celled organisms is a maladaptive trait maintained as a byproduct of selection on pro-survival functions, but that could-under conditions in which kin/group selection can act-be co-opted into an altruistic trait.

Anti-angiogenic effects of differentiation-inducing factor-1 involving VEGFR-2 expression inhibition independent of the Wnt/β-catenin signaling pathway

BACKGROUND

Differentiation-inducing factor-1 (DIF-1) is a putative morphogen that induces cell differentiation in Dictyostelium discoideum. DIF-1 inhibits proliferation of various mammalian tumor cells by suppressing the canonical Wnt/β-catenin signaling pathway. To assess the potential of a novel cancer chemotherapy based on the pharmacological effect of DIF-1, we investigated whether DIF-1 exhibits anti-angiogenic effects in vitro and in vivo.

RESULTS

DIF-1 not only inhibited the proliferation of human umbilical vein endothelial cells (HUVECs) by restricting cell cycle in the G0/G1 phase and degrading cyclin D1, but also inhibited the ability of HUVECs to form capillaries and migrate. Moreover, DIF-1 suppressed VEGF- and cancer cell-induced neovascularization in Matrigel plugs injected subcutaneously to murine flank. Subsequently, we attempted to identify the mechanism behind the anti-angiogenic effects of DIF-1. We showed that DIF-1 strongly decreased vascular endothelial growth factor receptor-2 (VEGFR-2) expression in HUVECs by inhibiting the promoter activity of human VEGFR-2 gene, though it was not caused by inhibition of the Wnt/β-catenin signaling pathway.

CONCLUSION

These results suggested that DIF-1 inhibits angiogenesis both in vitro and in vivo, and reduction of VEGFR-2 expression is involved in the mechanism. A novel anti-cancer drug that inhibits neovascularization and tumor growth may be developed by successful elucidation of the target molecules for DIF-1 in the future.

A flavin-dependent halogenase catalyzes the chlorination step in the biosynthesis of Dictyostelium differentiation-inducing factor 1

Differentiation-inducing factor 1 (DIF-1) is a polyketide-derived morphogen which drives stalk cell formation in the developmental cycle of Dictyostelium discoideum. Previous experiments demonstrated that the biosynthetic pathway proceeds via dichlorination of the precursor molecule THPH, but the enzyme responsible for this transformation has eluded characterization. Our recent studies on prokaryotic flavin-dependent halogenases and insights from the sequenced Dd genome led us to a candidate gene for this transformation. In this work, we present in vivo and in vitro evidence that chlA from Dd encodes a flavin-dependent halogenase capable of catalyzing both chlorinations in the biosynthesis of DIF-1. The results provide in vitro characterization of a eukaryotic oxygen-dependent halogenase and demonstrate a broad reach in biology for this molecular tailoring strategy, notably its involvement in the differentiation program of a social amoeba.

Dictyostelium differentiation-inducing factor-1 binds to mitochondrial malate dehydrogenase and inhibits its activity

We have reported that the differentiation-inducing factors (DIFs) DIF-1 and DIF-3, morphogens secreted from Dictyostelium discoideum, inhibit proliferation of several cancer cells via suppression of the Wnt/beta-catenin signaling pathway. However, the target molecules of DIFs involved in the anti-proliferative effects are still unknown. In the present study, DIF-1-tethered resins were synthesized to explore the target molecules of DIFs, and mitochondrial malate dehydrogenase (mMDH) was identified as one of the target molecules. In the in vitro assay, DIF-1 and other analogs including 2-MIDIF-1, DIF-3, and 6-MIDIF-3 were found to be capable of binding to mMDH but not to cytoplasmic MDH. However, only DIF-1 and 2-MIDIF-1 inhibited the enzymatic activity of mMDH. The effects of DIF analogs on ATP content and cell proliferation were then analyzed using HeLa cells. DIF-1 and 2-MIDIF-1 were found to lower the ATP content and both chemicals inhibited HeLa cell proliferation, suggesting that inhibition of mMDH activity affected cell energy production, probably leading to the inhibition of proliferation. These results suggest that the inhibition of mMDH activity by DIF-1 and 2-MIDIF-1 could be one of the mechanisms to induce anti-proliferative effects, independent of the inhibition of the Wnt/beta-catenin signaling pathway.

Differentiation-inducing factor-1 and -2 function also as modulators for Dictyostelium chemotaxis

BACKGROUND

In the early stages of development of the cellular slime mold Dictyostelium discoideum, chemotaxis toward cAMP plays a pivotal role in organizing discrete cells into a multicellular structure. In this process, a series of signaling molecules, such as G-protein-coupled cell surface receptors for cAMP, phosphatidylinositol metabolites, and cyclic nucleotides, function as the signal transducers for controlling dynamics of cytoskeleton. Differentiation-inducing factor-1 and -2 (DIF-1 and DIF-2) were originally identified as the factors (chlorinated alkylphenones) that induce Dictyostelium stalk cell differentiation, but it remained unknown whether the DIFs had any other physiologic functions.

METHODOLOGY/PRINCIPAL FINDINGS

To further elucidate the functions of DIFs, in the present study we investigated their effects on chemotaxis under various conditions. Quite interestingly, in shallow cAMP gradients, DIF-1 suppressed chemotaxis whereas DIF-2 promoted it greatly. Analyses with various mutants revealed that DIF-1 may inhibit chemotaxis, at least in part, via GbpB (a phosphodiesterase) and a decrease in the intracellular cGMP concentration ([cGMP](i)). DIF-2, by contrast, may enhance chemotaxis, at least in part, via RegA (another phosphodiesterase) and an increase in [cGMP](i). Using null mutants for DimA and DimB, the transcription factors that are required for DIF-dependent prestalk differentiation, we also showed that the mechanisms for the modulation of chemotaxis by DIFs differ from those for the induction of cell differentiation by DIFs, at least in part.

CONCLUSIONS/SIGNIFICANCE

Our findings indicate that DIF-1 and DIF-2 function as negative and positive modulators for Dictyostelium chemotaxis, respectively. To our knowledge, this is the first report in any organism of physiologic modulators (small molecules) for chemotaxis having differentiation-inducing activity.

Use of the Dictyostelium stalk cell assay to monitor GSK-3 regulation

GSK-3 activity mediates cAMP repression of stalk induction of cells in low-density monolayer culture. The lower the GSK-3 activity the greater the percentage of stalk cells formed. This protocol describes a robust and quantitative method utilizing an adapted stalk cell monolayer assay to measure GSK-3 activation.

Biological activities of novel derivatives of DIF-1 isolated from Dictyostelium

The differentiation-inducing factor-1 (DIF-1) is a lipophilic signal molecule (chlorinated alkylphenone) that induces stalk cell differentiation in the cellular slime mold Dictyostelium discoideum. In addition, DIF-1 and its derivatives have been shown to possess anti-leukemic activity and glucose consumption-promoting activity in vitro in mammalian cells. In this study, to assess the chemical structure-effect relationship of DIF-1, we synthesized eight derivatives of DIF-1 and investigated their stalk cell-inducing activity in Dictyostelium cells and pharmacological activities in mammalian cells. Of the derivatives, two amide derivatives of DIF-1, whose hydrophobic indexes are close to that of DIF-1, induced stalk cell differentiation as strongly as DIF-1 in Dictyostelium cells. It was also found that some derivatives suppressed cell growth in human K562 leukemia cells and promoted glucose consumption in mouse 3T3-L1 cells. These results give us valuable information as to the chemical structure-effect relationship of DIF-1.

Exploitation of the derivatives of Dictyostelium differentiation-inducing factor-1, which promote glucose consumption in mammalian cells

AIMS

The differentiation-inducing factor-1 (DIF-1) is a signal molecule that induces stalk cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has also been shown to possess pharmacological activities, such as the suppression of tumor cell growth and the promotion of glucose uptake in non-transformed mammalian cells. In this study, we tried to develop compounds that possess weaker anti-tumor activity and stronger glucose uptake-promoting activity than DIF-1.

MAIN METHODS

We investigated the in vitro effects of 12 derivatives of DIF-1 on glucose consumption in mouse 3T3-L1 cells and on cell growth in K562 human leukemia cells. We also examined the effect of a good compound on the blood glucose concentration in KK-Ay diabetic mice.

KEY FINDINGS

We found that some derivatives at 20 microM promoted glucose consumption more than twice as fast as the control. Of the derivatives, a compound named DIF-1(3M), which has a weaker anti-leukemic effect than DIF-1, promoted glucose consumption as strongly as DIF-1 in confluent 3T3-L1 cells. While DIF-1 at 20 microM was inhibitory to the cell growth of 3T3-L1, DIF-1(3M) at 20 microM exhibited no inhibitory effect on the growing cells. We also found that DIF-1(3M) injected (10-12.5 mg/kg body weight) intraperitoneally in mice tended to lower the blood glucose concentration.

SIGNIFICANCE

The present results open the possibility for the development of new agents that possess strong glucose-uptake-promoting activity but little anti-tumor activity and may have therapeutic potential for the treatment of diabetes and/or obesity.

Aromatic polyketides from marine algicolous fungi

The investigation of the marine-derived fungi Acremonium sp. and Nodulisporium sp. led to the isolation of the new natural products acremonisol A ( 1) and (3 R)-7-hydroxy-5-methylmellein ( 2). Both fungi are endophytes of marine algae. Compounds 1 and 2 are biosynthetically related by both being aromatic pentaketides belonging to the dihydroisocoumarins. All structures were elucidated by extensive spectroscopic measurements.

Dictyostelium development: a prototypic Wnt pathway?

Although Wnt signaling is ubiquitous within the animal phylogenetic group, it is unclear how it evolved. Genes related to the components of Wnt pathway are found in other eukaryotes and one of the most studied of these non-metazoan organisms is the social amoeba Dictyostelium discoideum. This organism contains the enzyme GSK-3 and a beta -catenin homolog, Aardvark (Aar). Both are required to regulate pattern formation during multi-cellular stages of Dictyostelium development. Aar is also required for formation of adherens junctions, as seen in animals. Finally, analysis of the completed Dictyostelium genome shows there to be 16 Frizzled (Fz) gene homologs. This chapter discusses Dictyostelium development and the role of these proteins.

A new environmentally resistant cell type from Dictyostelium

This paper describes the serendipitous discovery and first characterization of a new resistant cell type from Dictyostelium, for which the name aspidocyte (from aspis: Greek for shield) is proposed. These cells are induced from amoebae by a range of toxins including heavy metals and antibiotics, and were first detected by their striking resistance to detergent lysis. Aspidocytes are separate, rounded or irregular-shaped cells, which are immotile but remain fully viable; once the toxic stress is removed, they revert to amoeboid cells within an hour. Induction takes a few hours and is completely blocked by the protein synthesis inhibitor cycloheximide. Aspidocytes lack a cell wall and their resistance to detergent lysis is active, requiring continued energy metabolism, and may be assisted by a complete cessation of endocytosis, as measured by uptake of the dye FM1-43. Microarray analysis shows that aspidocytes have a distinct pattern of gene expression, with a number of genes up-regulated that are predicted to be involved in lipid metabolism. Aspidocytes were initially detected in a hypersensitive mutant, in which the AMP deaminase gene is disrupted, suggesting that the inductive pathway involves AMP levels or metabolism. Since aspidocytes can also be induced from wild-type cells and are much more resistant than amoebae to a membrane-disrupting antibiotic, it is possible that they are an adaptation allowing Dictyostelium cells to survive a sudden onslaught of toxins in the wild.

Involvement of GSK-3beta and DYRK1B in differentiation-inducing factor-3-induced phosphorylation of cyclin D1 in HeLa cells

Differentiation-inducing factors (DIFs) are putative morphogens that induce cell differentiation in Dictyostelium discoideum. We previously reported that DIF-3 activates glycogen synthase kinase-3beta (GSK-3beta), resulting in the degradation of cyclin D1 in HeLa cells. In this study, we investigated the effect of DIF-3 on cyclin D1 mutants (R29Q, L32A, T286A, T288A, and T286A/T288A) to clarify the precise mechanisms by which DIF-3 degrades cyclin D1 in HeLa cells. We revealed that T286A, T288A, and T286A/T288A mutants were resistant to DIF-3-induced degradation compared with wild-type cyclin D1, indicating that the phosphorylation of Thr(286) and Thr(288) were critical for cyclin D1 degradation induced by DIF-3. Indeed, DIF-3 markedly elevated the phosphorylation level of cyclin D1, and mutations introduced to Thr(286) and/or Thr(288) prevented the phosphorylation induced by DIF-3. Depletion of endogenous GSK-3beta and dual-specificity tyrosine phosphorylation regulated kinase 1B (DYRK1B) by RNA interference attenuated the DIF-3-induced cyclin D1 phosphorylation and degradation. The effect of DIF-3 on DYRK1B activity was examined and we found that DIF-3 also activated this kinase. Further, we found that not only GSK-3beta but also DYRK1B modulates cyclin D1 subcellular localization by the phosphorylation of Thr(288). These results suggest that DIF-3 induces degradation of cyclin D1 through the GSK-3beta- and DYRK1B-mediated threonine phosphorylation in HeLa cells.

Biosynthesis of Dictyostelium discoideum differentiation-inducing factor by a hybrid type I fatty acid-type III polyketide synthase

Differentiation-inducing factors (DIFs) are well known to modulate formation of distinct communal cell types from identical Dictyostelium discoideum amoebas, but DIF biosynthesis remains obscure. We report complimentary in vivo and in vitro experiments identifying one of two approximately 3,000-residue D. discoideum proteins, termed 'steely', as responsible for biosynthesis of the DIF acylphloroglucinol scaffold. Steely proteins possess six catalytic domains homologous to metazoan type I fatty acid synthases (FASs) but feature an iterative type III polyketide synthase (PKS) in place of the expected FAS C-terminal thioesterase used to off load fatty acid products. This new domain arrangement likely facilitates covalent transfer of steely N-terminal acyl products directly to the C-terminal type III PKS active sites, which catalyze both iterative polyketide extension and cyclization. The crystal structure of a steely C-terminal domain confirms conservation of the homodimeric type III PKS fold. These findings suggest new bioengineering strategies for expanding the scope of fatty acid and polyketide biosynthesis.

Differentiation-inducing factor-1 alters canonical Wnt signaling and suppresses alkaline phosphatase expression in osteoblast-like cell lines

Because DIF-1 has been shown to affect Wnt/beta-catenin signaling pathway, the effects of DIF-1 on osteoblast-like cell lines, SaOS-2 and MC3T3-E1, were examined. We found that DIF-1 inhibited this pathway, resulting in the suppression of ALP promoter activity through the TCF/LEF binding site.

INTRODUCTION

Differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium, inhibits cell proliferation and induces cell differentiation in several mammalian cells. Previous studies showed that DIF-1 activated glycogen synthase kinase-3beta, suggesting that this chemical could affect the Wnt/beta-catenin signaling pathway. This pathway has been shown to be involved in bone biology.

MATERIALS AND METHODS

We studied the effects of DIF-1 on SaOS-2 and MC3T3-E1, osteosarcoma cell lines widely used as a model system for ostoblastic cells and murine osteoblast-like cell line, respectively. Reporter gene assays were also carried out to examine the effect of DIF-1 on the Wnt/beta-catenin signaling pathway.

RESULTS

DIF-1 inhibited SaOS-2 proliferation and reduced alkaline phosphatase (ALP) activity in a concentration- and a time-dependent manner. The expression of ALP was markedly suppressed by DIF-1-treatment in protein and mRNA levels. DIF-1 also suppressed the expression of other osteoblast differentiation markers, including core binding factor alpha1, type I collagen, and osteocalcin, in protein and mRNA levels and inhibited osteoblast-mediated mineralization. Subsequently, we examined the effect of DIF-1 on the Wnt/beta-catenin signaling pathway. We found that DIF-1 suppressed the expression of beta-catenin protein and the activity of the reporter gene containing T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) consensus binding sites. We examined the effect of DIF-1 on a reporter gene driven by the human ALP promoter and found that DIF-1 significantly reduced the ALP reporter gene activity through the TCF/LEF binding site (-1023/-1017 bp). Furthermore, the effect of DIF-1 on MC3T3-E1, a murine osteoblast-like cell line, was examined, and it was found that DIF-1 suppressed ALP mRNA expression by the reduction of the ALP reporter gene activity through the TCF/LEF binding site.

CONCLUSIONS

Our data suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of ALP promoter activity. To our knowledge, this is the first report to analyze the role of the TCF/LEF binding site (-1023/-1017 bp) of the ALP gene promoter in osteoblast-like cell lines.

Differentiation-inducing factor-1 suppresses gene expression of cyclin D1 in tumor cells

To determine the mechanism by which differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium discoideum, inhibits tumor cell proliferation, we examined the effect of DIF-1 on the gene expression of cyclin D1. DIF-1 strongly reduced the expression of cyclin D1 mRNA and correspondingly decreased the amount of beta-catenin in HeLa cells and squamous cell carcinoma cells. DIF-1 activated glycogen synthase kinase-3beta (GSK-3beta) and inhibition of GSK-3beta attenuated the DIF-1-induced beta-catenin degradation, indicating the involvement of GSK-3beta in this effect. Moreover, DIF-1 reduced the activities of T-cell factor (TCF)/lymphoid enhancer factor (LEF) reporter plasmid and a reporter gene driven by the human cyclin D1 promoter. Eliminating the TCF/LEF consensus site from the cyclin D1 promoter diminished the effect of DIF-1. These results suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of cyclin D1 promoter activity.

Structural requirements of Dictyostelium differentiation-inducing factors for their stalk-cell-inducing activity in Dictyostelium cells and anti-proliferative activity in K562 human leukemic cells

The differentiation-inducing factor-1 (DIF-1) is a lipophilic signal molecule (chlorinated alkylphenone) that induces stalk-cell differentiation in the cellular slime mould Dictyostelium discoideum. It has also been shown that DIF-1 and its derivative (DIF-3) suppress cell growth in mammalian tumor cells. In the present study, in order to assess the chemical structure-effect relationship of DIF derivatives and to develop useful agents for the study of both Dictyostelium development and cancer biology, we synthesized 28 analogues of DIF-1 and DIF-3 and investigated their stalk-cell-inducing activity in Dictyostelium HM44 cells (mutant strain) and anti-proliferative activity in human leukemia K562 cells. HM44 cells are defective in endogenous DIF-1 production and should be suitable for the assay for stalk-cell-inducing activity of DIF analogues. DIF-1 and some of its derivatives at nanomolar levels were good stalk-cell inducers in HM44 cells, whereas DIF-3 and some DIF-3 derivatives at micromolar levels were potent anti-proliferative agents in K562 cells. We also tried to search for antagonistic molecules against DIF-1 and DIF-3 but failed to find such molecules from the analogues used here. The present findings would give us hints for identifying the target molecule(s) of DIFs and also for developing novel anti-cancer drugs.

Novel development rescuing factors (DRFs) secreted by the developing Dictyostelium cells, that are involved in the restoration of a mutant lacking MAP-kinase ERK2

We found novel development rescuing factors (DRFs) secreted from developing Dictyostelium cells, by using a mutant (erkB-) which is missing MAP-kinase ERK2 as a test strain for bioassay. The mutant erkB- fails to undergo multicellular morphogenesis due to impaired cAMP signaling. However, such developmental defect can be restored by the presence of low-molecular weight DRFs that are secreted from developing wild-type cells. We previously showed that DIF-1 (Differentiation-Inducing Factor 1 for stalk cells) possesses this activity, indicating a newly discovered role of DIF-1. Surprisingly, however, the mutant dmtA-, which is incapable of DIF-1 synthesis still exerts a strong inducing activity of the multicellular morphogenesis of erkB-. After analysis of HPLC fractions of conditioned media prepared from both wild type Ax2 and dmtA- strains revealed that both strains secrete at least two novel DRF activities with DIF-like mobility. However, these activities were not derived from other DIFs such as DIF-2 and DIF-3. Identification of these DRFs found in this study would provide insight into the mechanism by which the development of the erkB- mutant is restored and how these factors act in the normal development of Dictyostelium.

Calmodulin-dependent cyclic nucleotide phosphodiesterase (PDE1) is a pharmacological target of differentiation-inducing factor-1, an antitumor agent isolated from Dictyostelium

The differentiation-inducing factor-1 (DIF-1) isolated from Dictyostelium discoideum is a potent antiproliferative agent that induces growth arrest and differentiation in mammalian cells in vitro. However, the specific target molecule(s) of DIF-1 has not been identified. In this study, we have tried to identify the target molecule(s) of DIF-1 in mammalian cells, examining the effects of DIF-1 and its analogs on the activity of some candidate enzymes. DIF-1 at 10-40 micro M dose-dependently suppressed cell growth and increased the intracellular cyclic AMP concentration in K562 leukemia cells. It was then found that DIF-1 at 0.5-20 micro M inhibited the calmodulin (CaM)-dependent cyclic nucleotide phosphodiesterase (PDE1) in vitro in a dose-dependent manner. Kinetic analysis revealed that DIF-1 acted as a competitive inhibitor of PDE1 versus the substrate cyclic AMP. Because DIF-1 did not significantly affect the activity of other PDEs or CaM-dependent enzymes and, in addition, an isomer of DIF-1 was a less potent inhibitor, we have concluded that PDE1 is a pharmacological and specific target of DIF-1.

Differentiation-inducing factor-1-induced growth arrest of K562 leukemia cells involves the reduction of ERK1/2 activity

The differentiation-inducing factor-1 (DIF-1) is a signal molecule that induces stalk cell differentiation in the cellular slime mold Dictyostelium discoideum. In addition, DIF-1 is a potent antileukemic agent that induces growth arrest in K562 cells. In this study, we investigated the mechanism of action of DIF-1 in K562 cells in the light of cell-cycle regulators such as cyclins, retinoblastoma protein (pRb), and the mitogen-activated protein kinase (MAPK) family. DIF-1 down-regulated cyclins D/E and a phosphorylated form of pRb (p-pRb), and thereby induced G(1) arrest of the cell cycle. DIF-1 inactivated the extracellular signal-regulated kinase (ERK) in a biphasic manner but did not affect the c-Jun N-terminal kinase (JNK) or p38 MAPK. The MEK (MAPK kinase) inhibitor, U0126, which has been shown to induce growth arrest, inactivated ERK and down-regulated cyclins D and E. Although DIF-1 activated the phosphatidylinositol 3-kinase (PI-3K)/Akt pathway, neither wortmannin nor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002; PI-3K inhibitors) cancelled DIF-1-induced growth arrest. The present results suggest that ERK inactivation may be involved in DIF-1-induced growth arrest and that PI-3K activity is not required for DIF-1-induced growth arrest in K562 cells.

Polypropionate lactones of deoxysugars glycosides from slime mold Lycogala epidendrum

Two novel polypropionate lactone glycosides (1 and 2, i.e. lycogalinosides A and B) were isolated from the slime mold Lycogala epidendrum. Their structures, including the absolute configurations of the hydroxyl and methyls groups, were determined by means of extensive spectroscopic data such as mass, IR, UV, and 1D and 2D NMR spectra and chemical degradation followed by spectroscopic and chromatographic analysis. Compounds 1 and 2 are unique in structure containing a 2-deoxy-alpha-L-fucopyranosyl-(1-4)-6-deoxy-beta-D-gulopyranosyl unit and a beta-D-olivopyranosyl-(1-4)-beta-D-fucopyranosyl unit, respectively, and showed growth inhibitory activities against Gram-positive bacteria.

DIF-1, an anti-tumor substance found in Dictyostelium discoideum, inhibits progesterone-induced oocyte maturation in Xenopus laevis

Differentiation-inducing factor-1 (DIF-1; 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one) is a putative morphogen that induces stalk-cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has previously been shown to suppress cell growth in mammalian cells. In this study, we examined the effects of DIF-1 on the progesterone-induced germinal vesicle breakdown in Xenopus laevis, which is thought to be mediated by a decrease in intracellular cAMP and the subsequent activation of mitogen-activated protein kinase (MAPK) and maturation-promoting factor, a complex of cdc2 and cyclin B, which regulates germinal vesicle breakdown. DIF-1 at 10-40 microM inhibited progesterone-induced germinal vesicle breakdown in de-folliculated oocytes in a dose-dependent manner. Progesterone-induced cdc2 activation, MAPK activation, and c-Mos accumulation were inhibited by DIF-1. Furthermore, DIF-1 was found to inhibit the progesterone-induced cAMP decrease in the oocytes. These results indicate that DIF-1 inhibits progesterone-induced germinal vesicle breakdown possibly by blocking the progesterone-induced decrease in [cAMP](i) and the subsequent events in Xenopus oocytes.

Cross-induction of cell types in Dictyostelium: evidence that DIF-1 is made by prespore cells

To investigate how cell type proportions are regulated during Dictyostelium development, we have attempted to find out which cell type produces DIF-1, a diffusible signal molecule inducing the differentiation of prestalk-O cells. DIF-1 is a chlorinated alkyl phenone that is synthesized from a C12 polyketide precursor by chlorination and methylation, with the final step catalysed by the dmtA methyltransferase. All our evidence points to the prespore cells as the major source of DIF-1. (1) dmtA mRNA and enzyme activity are greatly enriched in prespore compared with prestalk cells. The chlorinating activity is also somewhat prespore-enriched. (2) Expression of dmtA is induced by cyclic-AMP and this induction is inhibited by DIF-1. This regulatory behaviour is characteristic of prespore products. (3) Short-term labelling experiments, using the polyketide precursor, show that purified prespore cells produce DIF-1 at more than 20 times the rate of prestalk cells. (4) Although DIF-1 has little effect on its own synthesis in short-term labelling experiments, in long-term experiments, using 36Cl– as label, it is strongly inhibitory (IC50 about 5 nM), presumably because it represses expression of dmtA; this is again consistent with DIF-1 production by prespore cells. Inhibition takes about 1 hour to become effective.

We propose that prespore cells cross-induce the differentiation of prestalk-O cells by making DIF-1, and that this is one of the regulatory loops that sets the proportion of prespore-to-prestalk cells in the aggregate.

The role of DIF-1 signaling in Dictyostelium development

We have constructed a mutant blocked in the biosynthesis of DIF-1, a chlorinated signal molecule proposed to induce differentiation of both major prestalk cell types formed during Dictyostelium development. Surprisingly, the mutant still forms slugs retaining one prestalk cell type, the pstA cells, and can form mature stalk cells. However, the other major prestalk cell type, the pstO cells, is missing. Normal pstO cell differentiation and their patterning in the slug are restored by development on a uniform concentration of DIF-1. We conclude that pstO and pstA cells are in fact induced by separate signals and that DIF-1 is the pstO inducer. Positional information, in the form of DIF-1 gradients, is evidently not required for pstO cell induction.

A novel role of differentiation-inducing factor-1 in Dictyostelium development, assessed by the restoration of a developmental defect in a mutant lacking mitogen-activated protein kinase ERK2

It has been previously reported that the differentiating wild-type cells of Dictyostelium discoideum secrete a diffusible factor or factors that are able to rescue the developmental defect in the mutant lacking extracellular signal-regulated kinase 2 (ERK2), encoded by the gene erkB. In the present study, it is demonstrated that differentiation-inducing factor-1 (DIF-1) for stalk cells can mimic the role of the factor(s) and the mechanism of the action of DIF-1 in the erkB null mutant is also discussed. The mutant usually never forms multicellular aggregates, because of its defect in cyclic adenosine monophosphate (cAMP) signaling. In the presence of 100 nM DIF-1, however, the mutant cells formed tiny slugs, which eventually developed into small fruiting bodies. In contrast, DIF-1 never rescued the developmental arrest of other Dictyostelium mutants lacking adenylyl cyclase A (ACA), cAMP receptors cAR1 and cAR3, heterotrimeric G-protein, the cytosolic regulator of ACA, or the catalytic subunit of cAMP-dependent protein kinase (PKA-C). Most importantly, it was found that DIF-1 did not affect the cellular cAMP level, but rather elevated the transcriptional level of pka during the development of erkB null cells. These results suggest that DIF-1 may rescue the developmental defect in erkB null cells via the increase in PKA activity, thus giving the first conclusive evidence that DIF-1 plays a crucial role in the early events of Dictyostelium development as well as in prestalk and stalk cell induction.

DIF signalling and cell fate

The DIFs are a family of secreted chlorinated molecules that control cell fate during development of Dictyostelium cells in culture and probably during normal development too. They induce stalk cell differentiation and suppress spore cell formation. The biosynthetic and inactivation pathways of DIF-1 (the major bioactivity) have been worked out. DIF-1 is probably synthesised in prespore cells and inactivated in prestalk cells, by dechlorination. Thus, each cell type tends to alter DIF-1 level so as to favour differentiation of the other cell type. This relationship leads to a model for cell-type proportioning during normal development.

Signalling pathways that direct prestalk and stalk cell differentiation in Dictyostelium

Prestalk cell differentiation in Dictyostelium is induced by DIF and two DIF-induced genes, ecmA and ecmB, have revealed the existence of multiple prestalk and stalk cell sub-types. These different sub-types are defined by the pattern of expression of subfragments derived from the ecmA and ecmB promoters. These markers have been utilised in three ways; for fate mapping in vivo, to investigate the molecular mechanisms underlying DIF signalling and to explore the relative requirement for DIF and other signalling molecules for prestalk and stalk cell differentiation in vitro. The heterogeneity of the prestalk and stalk populations seems to be reflected in differences in the cell signalling pathways that they utilise.

The putative morphogen, DIF-1, of Dictyostelium discoideum activates Akt/PKB in human leukemia K562 cells

The differentiation-inducing factor-1 (DIF-1) is a putative morphogen that induces stalk-cell formation in the lower eukaryote Dictyostelium discoideum. This molecule has been shown to inhibit cell growth and induce erythroid differentiation in human leukemia K562 cells. In the present study, to clarify the mechanism of the actions of DIF-1, we examined the effect of DIF-1 on Akt/protein kinase B (PKB) in K562 cells. Akt/PKB is a serine/threonine kinase that plays a pivotal role in the regulation of cell survival and differentiation in a variety of cells. A nonphosphorylated (inactive) form of Akt/PKB was ordinarily expressed in K562 cells. However, Akt/PKB was phosphorylated and potently activated within several hours of incubation with 5-30 microM DIF-1, and this activation was inhibited by wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-kinase). Calcium-increasing agents thapsigargin and A23187 also activated Akt/PKB slightly, which was inhibited by wortmannin. By contrast, calcium-reducing agents TMB-8 and EGTA together with A23187 inhibited the DIF-1-induced activation of Akt/PKB. PMA (PKC activator) also activated Akt/PKB but this activation was not inhibited by wortmannin. DIF-1 exhibited no marked effect on the activation of PKCalpha, beta, and gamma, which were activated by PMA. These results indicate that DIF-1 activates Akt/PKB possibly via cytosolic calcium and subsequent activation of PI3-kinase and also that PMA activates Akt/PKB in a PI3-kinase-independent manner.

Effects of differentiation-inducing factors of Dictyostelium discoideum on human leukemia K562 cells: DIF-3 is the most potent anti-leukemic agent

DIF-1 (differentiation-inducing factor-1; 1-(3,5-dichloro-2, 6-dihydroxy-4-methoxyphenyl)hexan-1-one) is a putative morphogen that induces stalk cell formation in the cellular slime mold, Dictyostelium discoideum. It has been previously reported that DIF-1 exhibits anti-tumor activity in mammalian cells. In this study, we examined the effects of six DIF analogues on DNA synthesis, cell growth, erythroid differentiation, and cytosolic free calcium concentration ([Ca2+]i) in human leukemia K562 cells. The DIF analogues used here were DIF-1, DIF-2 (which has pentanone in place of hexanone), DIF-3 (dechlorinated form of DIF-1), 2-MIDIF-1 (2-methoxy isomer of DIF-1), DMPH (dechlorinated form of DIF-3), and THPH (4-hydroxy substitution of DMPH). DIF-3 proved to be the most potent anti-leukemic agent among them, and the order of potency for causing growth inhibition, erythroid induction, and increases in [Ca2+]iTHPH in all the categories tested. The present results suggest new routes for the development of more potent and effective anti-tumor agents.

The biosynthesis of differentiation-inducing factor, a chlorinated signal molecule regulating Dictyostelium development

Differentiation-inducing factor (DIF)-1 is a chlorinated alkyl phenone released by developing Dictyostelium amoebae, which induces them to differentiate into stalk cells. A biosynthetic pathway for DIF-1 is proposed from labeling, inhibitor, and enzymological experiments. Cells incorporate 36Cl- into DIF-1 during development, showing that the chlorine atoms originate from chloride ions; peak incorporation is at the first finger stage. DIF-1 synthesis can be blocked by cerulenin, a polyketide synthase inhibitor, suggesting that it is made from a polyketide. This is most likely the C12 polyketide (2,4,6-trihydroxyphenyl)-1-hexan-1-one (THPH). Feeding experiments confirm that living cells can convert THPH to DIF-1. Conversion requires both chlorination and methylation of THPH, and enzymatic activities able to do this exist in cell lysates. The chlorinating activity, assayed using 36Cl-, is stimulated by H2O2 and requires both soluble and particulate components. It is specific for THPH and does not use this compound after O-methylation. The methyltransferase is soluble, uses S-adenosyl-L-methionine as a co-substrate, has a Km for dichloro-THPH of about 1.1 microM, and strongly prefers this substrate to close analogues. Both chlorinating and methyltransferase activities increase in development in parallel with DIF-1 production, and both are greatly reduced in a mutant strain that makes little DIF-1. It is proposed that DIF-1 is made by the initial assembly of a C12 polyketide skeleton, which is then chlorinated and methylated.