Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis

Erythropoiesis involves a dynamic process that begins with committed erythroid burst forming units (BFU-Es) followed by rapidly dividing erythroid colony ...

Northwestern University

Three new natural compounds, striguellolide A (1), striguellol A (2) and striguellone A (6), together with three known ones, 3,4-trans-dihydroxy-6-methoxy-2,2-dimethylchroman (3), 3-hydroxy-6- methoxy-2,2-dimethylchroman-4-one (4) and 3-hydroxy-6- methoxy-2,2-dimethylchroman (5), were isolated from the agar cultures of the edible fungal strain Lentinus striguellus. Their structures were elucidated by spectroscopic and mass spectrometric analyses, including 1D-, 2D-NMR and HR-ESI-Q-TOF-MS, and chemical reactions. Striguellone A showed cytotoxicity against HeLa cells by MTT assay and was found to be an activator of apoptosis, assessed by morphological observation and cell cycle analysis using the flow cytometer.

Isolation, structure elucidation and apoptosis-inducing activity of new compounds from the edible fungus Lentinus striguellus.

Mycoepoxydiene (MED) is a polyketide isolated from a marine fungus associated with mangrove forests. It contains an oxygen-bridged cyclooctadiene core and an α,β-unsaturated δ-lactone moiety. MED induced the reorganization of cytoskeleton in actively growing HeLa cells by promoting formation of actin stress fiber and inhibiting polymerization of tubulin. MED could induce cell cycle arrest at G2/M in HeLa cells. MED-associated apoptosis was characterized by the formation of fragmented nuclei, PARP cleavage, cytochrome c release, activation of caspase-3, and an increased proportion of sub-G1 cells. Additionally, MED activated MAPK pathways. Interestingly, the time of JNK, p38, and Bcl-2 activation did not correlate with the release of cytochrome c. This study is the first report demonstrating the action mechanism of MED against tumor cell growth. These results provide the potential of MED as a novel low toxic antitumor agent.

Mycoepoxydiene, a fungal polyketide, induces cell cycle arrest at the G2/M phase and apoptosis in HeLa cells.

AMP-activated protein kinase (AMPK) plays a key role in maintaining intracellular and whole-body energy homeostasis. Activation of AMPK has been shown to ameliorate the symptoms of metabolic diseases, such as type 2 diabetes and obesity. Here we show that gambogic acid (GB), a known antitumor agent, activates AMPK by increasing the phosphorylation of AMPKα and its downstream substrate ACC in various cell lines. Further study revealed that GB stimulated AMPK activity independent of upstream kinases. Moreover, the AMPK inhibitor, compound C, has no effects on the GB-induced AMPK activation. We also found that GB promptly increased intracellular ROS level, and antioxidants attenuated the ROS production. Interestingly, only the thiol antioxidants significantly abolished GB-enhanced AMPK activation. In addition, analysis of binding and dissociation kinetics indicated that GB bound to the AMPKα subunit. Collectively, these results suggest that GB may be a novel direct activator of AMPK.

Gambogic acid activates AMP-activated protein kinase in mammalian cells.

Mycoepoxydiene (MED) is a cytotoxic polyketide that is isolated from the marine fungal strain Diaporthe sp. HLY-1, which is associated with mangroves; however, the mechanism of action of MED remains unknown. Here, we report the molecular mechanisms of apoptosis activation and growth inhibition induced by MED in MCF-7 cells. The present results show that MED induces DNA damage through the production of reactive oxygen species (ROS), which resulted in the phosphorylation of H2AX and the activation of the Ataxia telangiectasia mutated kinase (ATM) and p53 signaling pathways. In addition, MED increases the accumulation of IκBα and enhances the association between IKKγ and Hsp27 via the activation of Hsp27, which eventually resulted in the inhibition of TNF-α-induced NF-κB transactivation. Therefore, we conclude that MED inhibits MCF-7 cells by simultaneously activating p53 to induce apoptosis and suppressing NF-κB to disrupt cell proliferation. Because small molecules having both of these effects are rare, further exploration of MED as an antitumor lead compound is needed.

Mycoepoxydiene, a fungal polyketide inhibits MCF-7 cells through simultaneously targeting p53 and NF-κB pathways.

A novel series of p-terphenyl derivatives (1-4, 1a-4a) was successfully synthesized and their in vitro anticancer activities were evaluated. Compound 1, showing the best antiproliferative activity with IC50<1 μM against MDA-MB-435 cells, was further investigated. Compound 1 brought about a remarkable accumulation of MDA-MB-435 cells in G2/M phase prior to the induction of apoptosis. Further antitumor mechanism study indicated that compound 1, which inhibited the enzyme activity of Topo I and Topo IIα by interfering predominantly with the enzyme, could be topoisomerase suppressors instead of poisons. We conclude that compound 1 represents a novel class of Topo catalytic suppressors for developing new chemotherapeutic agents.

A novel p-terphenyl derivative inducing cell-cycle arrest and apoptosis in MDA-MB-435 cells through topoisomerase inhibition.

Differentiation of erythroblasts to mature red blood cells involves dynamic changes of the membrane and cytoskeleton networks that are not fully characterized. Using a mouse fetal liver erythroblast culture system and a targeted shRNA functional screening strategy, we identified a critical role of pleckstrin-2 in actin dynamics and protection of early stage terminal erythroblasts from oxidative damage. Knockdown of pleckstrin-2 in the early stage of terminal erythropoiesis disrupted the actin cytoskeleton and led to differentiation inhibition and apoptosis. This pro-survival and differentiation function of pleckstrin-2 was mediated through its interaction with cofilin, by preventing cofilin's mitochondrial entry when the intracellular level of reactive oxygen species was higher in the early stage of terminal erythropoiesis. Treatment of the cells with a scavenger of reactive oxygen species rescued cofilin's mitochondrial entry and differentiation inhibition induced by pleckstrin-2 knockdown. In contrast, pleckstrin-2 knockdown in late stage terminal erythroblasts had no effect on survival or differentiation but blocked enucleation due to disorganized actin cytoskeleton. Thus, our study identified a dual function of pleckstrin-2 in the early and late stages of terminal erythropoiesis through its regulations of actin dynamics and cofilin's mitochondrial localization, which reflects intracellular level of reactive oxygen species in different developmental stages.

Targeted shRNA screening identified critical roles of pleckstrin-2 in erythropoiesis.

The myelodysplastic syndromes (MDSs) include a spectrum of stem cell malignancies characterized by an increased risk of developing acute myeloid leukemia. Heterozygous loss of chromosome 5q (del[5q]) is the most common cytogenetic abnormality in MDS. DIAPH1 is localized to 5q31 and encodes one of the formin proteins, mDia1, which is involved in linear actin polymerization. Mice with mDia1 deficiency develop hematologic features with age mimicking human myeloid neoplasm, but its role in the pathogenesis of MDS is unclear. Here we report that mDia1 heterozygous and knockout mice develop MDS phenotypes with age. In these mice, CD14 was aberrantly overexpressed on granulocytes in a cell-autonomous manner, leading to a hypersensitive innate immune response to lipopolysaccharide (LPS) stimuli through CD14/Toll-like receptor 4 signaling. Chronic stimulation with LPS accelerated the development of MDS in mDia1 heterozygous and knockout mice that can be rescued by lenalidomide. Similar findings of CD14 overexpression were observed on the bone marrow granulocytes of del(5q) MDS patients. Mechanistically, mDia1 deficiency led to a downregulation of membrane-associated genes and a specific upregulation of CD14 messenger RNA in granulocytes, but not in other lineages. These results underscore the significance of mDia1 heterozygosity in deregulated innate immune responses in del(5q) MDS.

Baobing Zhao

Department of Pathology

Northwestern University

Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis

Baobing Zhao

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Pathology

Northwestern University

Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis

Department of Pathology