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

Pharmacological Evidence That Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake Partly via an Increase in Intracellular cAMP Content in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1) isolated from the cellular slime mold Dictyostelium discoideum can inhibit mammalian calmodulin-dependent cAMP/cGMP phosphodiesterase (PDE1) in vitro. DIF-1 also promotes glucose uptake, at least in part, via a mitochondria- and AMPK-dependent pathway in mouse 3T3-L1 fibroblast cells, but the mechanism underlying this effect has not been fully elucidated. In this study, we investigated the effects of DIF-1 on intracellular cAMP and cGMP levels, as well as the effects that DIF-1 and several compounds that increase cAMP and cGMP levels have on glucose uptake in confluent 3T3-L1 cells. DIF-1 at 20 μM (a concentration that promotes glucose uptake) increased the level of intracellular cAMP by about 20% but did not affect the level of intracellular cGMP. Neither the PDE1 inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine at 10-200 μM nor the broad-range PDE inhibitor 3-isobutyl-1-methylxanthine at 40-400 μM had any marked effects on glucose uptake. The membrane-permeable cAMP analog 8-bromo-cAMP at 200-1000 μM significantly promoted glucose uptake (by 20-25%), whereas the membrane-permeable cGMP analog 8-bromo-cGMP at 3-100 μM did not affect glucose uptake. The adenylate cyclase activator forskolin at 1-10 μM promoted glucose uptake by 20-30%. Thus, DIF-1 may promote glucose uptake by 3T3-L1 cells, at least in part, via an increase in intracellular cAMP level.

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.

Polyketide synthase genes and the natural products potential of Dictyostelium discoideum

MOTIVATION

The genome of the social amoeba Dictyostelium discoideum contains an unusually large number of polyketide synthase (PKS) genes. An analysis of the genes is a first step towards understanding the biological roles of their products and exploiting novel products.

RESULTS

A total of 45 Type I iterative PKS genes were found, 5 of which are probably pseudogenes. Catalytic domains that are homologous with known PKS sequences as well as possible novel domains were identified. The genes often occurred in clusters of 2-5 genes, where members of the cluster had very similar sequences. The D.discoideum PKS genes formed a clade distinct from fungal and bacterial genes. All nine genes examined by RT-PCR were expressed, although at different developmental stages. The promoters of PKS genes were much more divergent than the structural genes, although we have identified motifs that are unique to some PKS gene promoters.

Anti-leukemic activities of Dictyostelium secondary metabolites: a novel aromatic metabolite, 4-methyl-5-n-pentylbenzene-1,3-diol, isolated from Dictyostelium mucoroides suppresses cell growth in human leukemia K562 and HL-60 cells

It has previously been shown that DIF-1, a differentiation-inducing factor of the cellular slime mold Dictyostelium discoideum, possesses antitumor activities in mammalian tumor cells and that neuronal differentiation of PC12 cells can be induced with furanodictines (FDs), aminosugar analogs found in D. discoideum, or dictyoglucosamines (DGs), N-acetyl glucosamine derivatives (DG-A from D. purpureum and DG-B from D. discoideum). Thus, cellular slime molds are attractive natural resources that may provide valuable lead compounds to be utilized in the field of pharmacology and medicine. In this study, we have isolated a novel aromatic compound, 4-methyl-5-n-pentylbenzene-1,3-diol (MPBD), from fruiting bodies of the cellular slime mold D. mucoroides and assessed the in vitro antiproliferative activities of MPBD, FDs, and DGs in human leukemia K562 and HL-60 cells. MPBD at 20-80 microM dose-dependently suppressed cell growth in both K562 and HL-60 cells. While FDs at 10-80 microM did not affect cell growth, DGs at 10-40 microM dose-dependently suppressed cell growth in the cells. Although we failed to find the roles of FDs and DGs in the original organisms, MPBD at 5-20 microM was found to promote stalk cell formation in D. discoideum. The present results indicate that MPBD, DGs or their derivatives may have therapeutic potential in the treatment of cancer and confirm our expectations regarding cellular slime molds as drug resources.

The distinct stage-specific effects of 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid on the activation of MAP kinase and Cdc2 kinase in Xenopus oocyte maturation

2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid (PACA), pharmacological inhibitor of phospholipase A(2) (PLA(2)), inhibits epinephrine-stimulated thromboxane production in human platelets. In this study, we investigated the effect of PACA on meiotic maturation individually in stages V and VI oocytes. PACA prevented the maturation in stage V but merely delayed the process in stage VI oocytes. This was associated with the strong inhibition of Mos synthesis at both stages. Besides, PACA-induced inhibition of MAPK activation was evident in stage V but not in stage VI oocytes. PACA also inhibited the activation of Cdc2 kinase (Cdc2) in stage V but merely delayed the process in stage VI oocytes. Furthermore, 5 microM and higher concentrations of PACA completely inhibited the activation of MAPK and Cdc2 only in stage V, not in stage VI, oocytes. Moreover, we propose PACA as a new tool for the study of Xenopus oocyte maturation, which can also play a unique role for the studies of the stage-specific activation of MAPK and Cdc2.

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.