Influence of GPRC5A-Regulated ABCB1 Expression on Lung Adenocarcinoma Proliferation.

Objective Aberrant expression of ATP binding cassette subfamily B member 1 (ABCB1) plays a key role in several cancers. However, influence of G protein coupled receptor family C group 5 type A (GPRC5A)-regulated ABCB1 expression on lung adenocarcinoma proliferation remains unclear. Therefore, this study investigated the effect of GPRC5A regulated ABCB1 expression on the proliferation of lung adenocarcinoma. Methods ABCB1 expressions in lung adenocarcinoma cell lines, human lung adenocarcinoma tissues, and tracheal epithelial cells and lung tissues of GPRC5A knockout mice and wild-type mice were analyzed with RT-PCR, Western blot, or immunohistochemical analysis. Cell counting kit-8 assay was performed to analyze the sensitivity of tracheal epithelial cells from GPRC5A knockout mice to chemotherapeutic agents. Subcutaneous tumor formation assay was performed to confirm whether down-regulation of ABCB1 could inhibit the proliferation of lung adenocarcinoma in vivo. To verify the potential regulatory relationship between GPRC5A and ABCB1, immunofluorescence and immunoprecipitation assays were performed. Results ABCB1 expression was up-regulated in lung adenocarcinoma cell lines and human lung adenocarcinoma tissues. ABCB1 expression in the tracheal epithelial cells and lung tissues of GPRC5Adeficient mice was higher than that in the wild type mice. Tracheal epithelial cells of GPRC5A knockout mice were much more sensitive to tariquidar and doxorubicin than those of GPRC5A wild type mice. Accordingly, 28 days after injection of the transplanted cells, the volume and weight of lung tumor in ABCB1knockout cell-transplanted GPRC5A-/-C57BL/6 mice were significantly smaller than those in wild type cell-transplanted mice (P= 0.0043, P= 0.0060). Furthermore, immunofluorescence and immunoprecipitation assays showed that GPRC5A regulated ABCB1 expression by direct binding.Conclusion GPRC5A reduces lung adenocarcinoma proliferation via inhibiting ABCB1 expression. The pathway by which GPRC5A regulates ABCB1 expression needs to be investigated.

Differential mRNA Expressions in HCMV infected HUVECs.

Objective: The aim was to identify the gene expressions of human cytomegalovirus (HCMV)-infected human umbilical vein endothelial cells (HUVECs) and to study its possible pathogenic mechanism on atherosclerosis using microarray technology. Methods: The gene expression differences in HCMV AD169 strain-infected HUVECs were studied by the microarray technology to explore the potential molecular mechanism of HCMV infection. The qPCRs were performed to verify the transcriptome results. Results: A total of 2,583 differentially expressed genes, including 407 down-regulated genes and 2,176 up-regulated genes, were detected by the systematic bioinformatics analysis. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the significantly differentially expressed genes were mainly involved in regulating protein kinase activity, inflammatory response, ubiquitination, protein phosphorylation, cell metabolism, and exosomes, among which 12 genes had significant changes and were screened by protein-protein interaction (PPI) analysis and verified by qPCR. The experimental qPCR results were consistent with the microarray results. Conclusion: The GO and KEGG analyses revealed that the regulation of protein kinase activity, inflammatory response, ubiquitination, protein phosphorylation, and cell metabolism played important roles in the process of endothelial cell infection. Furthermore, 12 genes were involved in the process of HCMV infection of endothelial cells and contributed to the current understanding of the infection and pathogenic mechanisms of atherosclerosis.

A novel methodology of the myeloid-derived suppressor cells (MDSCs) generation with splenic stroma feeder cells.

Myeloid-derived suppressor cells (MDSCs) are a significant obstacle for immunotherapy of cancer. It is of great clinical relevance to study the mechanism of MDSCs accumulation in mouse spleens and establish a stable method to obtain high-purity MDSCs in vitro for further research. Here, we established a new method for amplifying a large number of highly pure MDSCs in vitro. To mimic the microenvironment of MDSCs development in vivo, mouse splenic stroma feeder cells and serum-free medium containing granulocyte-macrophage colony stimulating factor (GM-CSF) were used to induce myeloid precursors in mouse bone marrow cells, which differentiate into MDSCs. Development and immunological functions of the cells were monitored both in vivo and in vitro. A total of 4 × 108 MDSCs could be obtained from the bone marrow from one mouse, the ratio of CD11b+Gr-1+ MDSCs could reach 93.8% ± 3.3% after nine days of culture in vitro. Cultured MDSCs maintained a similar immunophenotype with MDSCs found in tumor-bearing mice. Colony forming assay in vitro and in vivo demonstrated that these were myeloid precursor cells. These cells generated high levels of reactive oxygen species and arginase 1 to prevent proliferation of CD8+ T cells in vitro. These also increased regulatory T (Treg) cells in blood while promoting the growth of lymphoma in vivo. In addition, cultured MDSCs effectively inhibited acute graft-versus-host disease (aGVHD). Our findings suggest that mouse splenic stroma plays an important role in the generation of MDSCs and represent a preliminary mechanism for the accumulation of MDSCs in spleens, and thereby lay the foundation for basic research and the clinical application of MDSCs.

Acetoacetate extract of pleione bulbocodioides (franch. ) rolfe induces apoptosis of human leukemia thp-1cells through a mitochondria-regulated intrinsic apoptotic pathway / Extrato de acetoacetato de Pleione bulbocodioides (Franch. ) Rolfe induz a apoptose de células THP-1 de leucemia humana através de uma via apoptótica intrínseca regulada por mitocôndrias

The tubers of three orchidaceous plants, includingPleione bulbocodioides (Franch.) Rolfe, have been used as 'Shan-Ci-Gu' in traditional Chinese medicine for the treatment of bacterial infections and cancers for thousands of years. In this study, the effects of an acetoacetate (EtOAc) extract of P. bulbocodioides on the cell viability and apoptosis of THP-1 (human acute monocytic leukemia cell line) cells and its interaction with possible apoptotic pathways were investigated. THP-1 cells were treated with the EtOAc extract of P. bulbocodioides at different concentrations. The results showed that THP-1 cell viability was significantly inhibited by the EtOAc extract ofP. bulbocodioides with an IC50 of 51.37±2.68 µ g/ mL at 24 h. The examination of cytotoxic effects on healthy cells showed that the EtOAc extract of P. bulbocodioidesdid not show any effect on healthy Vero cells. Selectivity indexes were greater than 15.57, suggesting that the EtOAc extract of P. bulbocodioides had selective toxicity against THP-1 cells. The results of annexin V-FITC/PI and DAPI staining showed that the EtOAc extract of P. bulbocodioides induced cell apoptosis in a dose-dependent manner. The apoptotic rate was increased in the treatment groups compared with that in the control group (P<0.05). The distribution of cells in the G2 phase of the cell cycle increased along with typical cell apoptosis-induced morphological changes. The levels of the pro-apoptotic proteins Bax, cleaved PARP and cleaved caspase-3 increased with increasing concentration of acetoacetate extract of P. bulbocodioides, while the anti-apoptosis protein Bcl-2 was downregulated. Cyt c and AIF, which are characteristic proteins of the mitochondria-regulated intrinsic apoptosis pathway, also increased in the cytosol with increasing concentrations of the EtOAc extract of P. bulbocodioides. These results showed that the EtOAc extract of P. bulbocodioidessignificantly inhibits cell viability and induces cell apoptosis in the human leukemia cell line THP-1 through a mitochondria-regulated intrinsic apoptotic pathway

Os tubérculos de três plantas orquidáceas, incluindo Pleione bulbocodioides (Franch.) Rolfe, têm sido usados como "Shan-Ci-Gu" na medicina tradicional chinesa para o tratamento de infecções bacterianas e cânceres por milhares de anos. Neste estudo, os efeitos de um extrato de acetoacetato (EtOAc) de P. bulbocodioides na viabilidade celular e apoptose de células THP-1 (linhagem celular de leucemia monocítica aguda humana) e sua interação com possíveis vias apoptóticas foram investigados. As células THP-1 foram tratadas com o extrato EtOAc de P. bulbocodioides em diferentes concentrações. Os resultados mostraram que a viabilidade das células THP-1 foi significativamente inibida pelo extrato EtOAc de P. bulbocodioides com IC50 de 51,37 ± 2,68 µ g/mL às 24 h. O exame dos efeitos citotóxicos em células saudáveis mostrou que oextrato de EtOAc de P. bulbocodioides não mostrou nenhum efeito sobre células Vero saudáveis. Os índices de seletividade foram maiores que 15,57, sugerindo que o extrato de EtOAc de P. bulbocodioides teve toxicidade seletiva contra as células THP-1. Os resultados da coloração da anexina V-FITC/PI e DAPI mostraram que o extrato de EtOAc de P. bulbocodioides induziu a apoptose celular de maneira dose-dependente. A taxa de apoptose foi aumentada nos grupos de tratamento em comparação com o grupo controle (P <0,05). A distribuição de células na fase G2 do ciclo celular aumentou juntamente com alterações morfológicas típicas induzidas pela apoptose celular. Os níveis das proteínas pró-apoptóticas Bax, PARP clivada e caspase-3 clivada aumentaram com o aumento da concentração do extrato acetoacetato de P. bulbocodioides, enquanto a proteína anti-apoptose Bcl-2 foi regulada negativamente. Cyt c e AIF, que são proteínas características da via de apoptose intrínseca regulada por mitocôndrias, também aumentaram no citosol com concentrações crescentes do extrato de EtOAc de P. bulbocodioides. Estes resultados mostraram que o extrato de EtOAc de P. bulbocodioides inibe significativamente a viabilidade celular e induz a apoptose na linha celular de leucemia humana THP-1 através de uma via apoptótica intrínseca regulada por mitocôndrias.

Cooperative Activity of GABP with PU.1 or C/EBPε Regulates Lamin B Receptor Gene Expression, Implicating Their Roles in Granulocyte Nuclear Maturation.

Nuclear segmentation is a hallmark feature of mammalian neutrophil differentiation, but the mechanisms that control this process are poorly understood. Gene expression in maturing neutrophils requires combinatorial actions of lineage-restricted and more widely expressed transcriptional regulators. Examples include interactions of the widely expressed ETS transcription factor, GA-binding protein (GABP), with the relatively lineage-restricted E-twenty-six (ETS) factor, PU.1, and with CCAAT enhancer binding proteins, C/EBPα and C/EBPε. Whether such cooperative interactions between these transcription factors also regulate the expression of genes encoding proteins that control nuclear segmentation is unclear. We investigated the roles of ETS and C/EBP family transcription factors in regulating the gene encoding the lamin B receptor (LBR), an inner nuclear membrane protein whose expression is required for neutrophil nuclear segmentation. Although C/EBPε was previously shown to bind the Lbr promoter, surprisingly, we found that neutrophils derived from Cebpe null mice exhibited normal Lbr gene and protein expression. Instead, GABP provided transcriptional activation through the Lbr promoter in the absence of C/EBPε, and activities supported by GABP were greatly enhanced by either C/EBPε or PU.1. Both GABP and PU.1 bound Ets sites in the Lbr promoter in vitro, and in vivo within both early myeloid progenitors and differentiating neutrophils. These findings demonstrate that GABP, PU.1, and C/EBPε cooperate to control transcription of the gene encoding LBR, a nuclear envelope protein that is required for the characteristic lobulated morphology of mature neutrophils.

Marsdenia tenacssima extract and its functional components inhibits proliferation and induces apoptosis of human Burkitt leukemia/lymphoma cells in vitro and in vivo.

Burkitt lymphoma is a fast growing non-Hodgkin lymphoma that occurs primarily in young males. The causes of Burkitt lymphoma include chromosome rearrangement and virus infection, but accurate and complete reasons remain to be discovered. The available treatment for Burkitt lymphoma is chemotherapy and radiation therapy. It is a highly aggressive B-cell neoplasm with not all patients cured, in spite of current therapies. This study evaluated the effects of traditional Chinese medicine Marsdenia tenacssima (MTE) and its component compound Tenacigenoside A (TGTA) and 11α-O-benzoyl-12ß-O-acetyltenacigenin B (TGTB) on human Burkitt lymphoma growth. It was observed that MTE, TGTA or TGTB inhibited cell growth and induced apoptosis of Burkitt lymphoma cells in culture. In lymphoma bearing NOD/SCID nude mice, both TGTA and TGTB inhibited tumor growth and improved animal survival. TGTA and TGTB significantly increased tumor cell apoptosis on lymphoma bearing mice, primarily through down-regulation of BCL2 and BCL-XL and up-regulation of BID.

Progression of Large Lymphoma Is Significantly Impeded with a Combination of Gemcitabine Chemotherapy and Dendritic Cells Intra-Tumor Vaccination.

Relapsed, refractory lymphoma remains to be a challenge and lacks efficient treatment. Some tumor cells escape from treatment, become resistant to chemotherapeutic agents, and rapidly regenerate into large tumors. Lymphoma cells induce accumulation of Gr-1(+-)CD11b(+) myeloid derived suppressor cells (MDSCs) in lymphatic organs and their vicinity. MDSCs enable tumor cells to escape from immune cells mediated surveillance and attack. Gemcitabine is a chemotherapeutic agent that eliminates both tumor cells and MDSCs, improving the immune environment favorable for subsequent treatment. We evaluated the effects of low dose gemcitabine combined with intra-tumorally delivered dendritic cells (DCs) for the treatment of A20 large-size lymphoma. We showed that MDSCs increased markedly in lymphoma-bearing mice, and that gemcitabine significantly increased the apoptosis of MDSCs. Treatment of lymphoma with either gemcitabine or intra-tumoral DCs alone could not inhibit tumor growth or rescue lymphoma-bearing mice. Treatment of lymphoma with small dose gemcitabine followed by intra-tumorally injected DCs significantly improved the efficacy of either individual treatment by reducing MDSCs, inducing onsite DCs maturation, eliminating tumor cells, inhibiting tumor growth and relapse, and extending the survival of the lymphoma-bearing mice, partly through the induction of the IFNγ secreting cells and the activation of cytotoxic lymphocytes. We showed that NK cells and CD8(+ )T cells were the major effectors to mediate the inhibition of tumor growth. Thus, the observation that gemcitabine synergizes DCs mediated immunotherapy to improve the efficacy of large size lymphoma treatment provides an experimental basis for the combination of chemotherapy and immunotherapy for the efficient treatment of relapsed or refractory lymphoma.

Impact on survival of the number of lymph nodes resected in patients with lymph node-negative gastric cancer.

BACKGROUND: Patients with lymph node-negative gastric cancer show a better overall survival rate than those who have a pathological lymph node-positive gastric cancer. But a large number of patients still develop recurrence. We aimed to explore the significant prognostic factors of lymph node-negative gastric cancer and determine how many lymph nodes should be removed. METHODS: A total of 3103 patients who underwent radical operation are identified from the Surveillance, Epidemiology, and End Results database. Standard survival methods and restricted multivariable Cox regression models were applied. RESULTS: The overall survival rate was significantly higher with an increasing number of negative lymph node resected. Among the 843 patients who had the exact T stage, the overall survival rate was significantly better in T3-4 group with more than 15 lymph nodes resected (P < 0.001) but not in T1-2 stage patients (P = 0.44). A further 25 more lymph nodes resection did not show additional survival benefits. Multivariate analysis of patients demonstrated that age, depth of tumor invasion, and the number of lymph nodes resected were the significant and independent prognostic factors. CONCLUSIONS: A lymphadenectomy with more than 15 lymph nodes removal should be performed for T3-4 lymph node-negative gastric cancer. But the survival benefit of a lymphadenectomy with more than 25 lymph nodes removal is disputed. And the further treatment should refer to the prognostic indicators.

GABP transcription factor (nuclear respiratory factor 2) is required for mitochondrial biogenesis.

Mitochondria are membrane-bound cytoplasmic organelles that serve as the major source of ATP production in eukaryotic cells. GABP (also known as nuclear respiratory factor 2) is a nuclear E26 transformation-specific transcription factor (ETS) that binds and activates mitochondrial genes that are required for electron transport and oxidative phosphorylation. We conditionally deleted Gabpa, the DNA-binding component of this transcription factor complex, from mouse embryonic fibroblasts (MEFs) to examine the role of Gabp in mitochondrial biogenesis, function, and gene expression. Gabpα loss modestly reduced mitochondrial mass, ATP production, oxygen consumption, and mitochondrial protein synthesis but did not alter mitochondrial morphology, membrane potential, apoptosis, or the expression of several genes that were previously reported to be GABP targets. However, the expression of Tfb1m, a methyltransferase that modifies ribosomal rRNA and is required for mitochondrial protein translation, was markedly reduced in Gabpα-null MEFs. We conclude that Gabp regulates Tfb1m expression and plays an essential, nonredundant role in mitochondrial biogenesis.

GABP transcription factor is required for development of chronic myelogenous leukemia via its control of PRKD2.

Hematopoietic stem cells (HSCs) are the source of all blood lineages, and HSCs must balance quiescence, self-renewal, and differentiation to meet lifelong needs for blood cell development. Transformation of HSCs by the breakpoint cluster region-ABL tyrosine kinase (BCR-ABL) oncogene causes chronic myelogenous leukemia (CML). The E-twenty six (ets) transcription factor GA binding protein (GABP) is a tetrameric transcription factor complex that contains GABPα and GABPß proteins. Deletion in bone marrow of Gabpa, the gene that encodes the DNA-binding component, caused cell cycle arrest in HSCs and profound loss of hematopoietic progenitor cells. Loss of Gabpα prevented development of CML, although mice continued to generate BCR-ABL-expressing Gabpα-null cells for months that were serially transplantable and contributed to all lineages in secondary recipients. A bioinformatic screen identified the serine-threonine kinase protein kinase D2 (PRKD2) as a potential effector of GABP in HSCs. Prkd2 expression was markedly reduced in Gabpα-null HSCs and progenitor cells. Reduced expression of PRKD2 or pharmacologic inhibition decreased cell cycling, and PRKD2 rescued growth of Gabpα-null BCR-ABL-expressing cells. Thus, GABP is required for HSC cell cycle entry and CML development through its control of PRKD2. This offers a potential therapeutic target in leukemia.

[Determination of translocatable matter of rice by near infrared reflectance spectroscopy].

The potential of predicting translocatable matter of rice with near infrared reflectance spectroscopy (NIRS) was studied. Using 7 varieties of rice planted in Danzhou of Hainan province as materials, the method of neutral detergent fiber added amylase with NIRS was examined to establish calibration model of predicting translocatable matter of stem and panicle of rice. The results indicated that partial least square(PLS1) is the best regression statistic method for calibration model; The differences of results of the spectral data pretreatment methods for calibration model were insignificant; Because of the high prediction accuracy, the final calibration model was chosen using "no spectral data pretreatment" + "PLS1"; Determination coefficient of external validation and root mean square errors of prediction of the calibration model of stem and panicle was 0.991 2, 0.008 1, 0.961 1 and 0.022 6, respectively.

PU.1 is essential for CD11c expression in CD8(+)/CD8(-) lymphoid and monocyte-derived dendritic cells during GM-CSF or FLT3L-induced differentiation.

Dendritic cells (DCs) regulate innate and acquired immunity through their roles as antigen-presenting cells. Specific subsets of mature DCs, including monocyte-derived and lymphoid-derived DCs, can be distinguished based on distinct immunophenotypes and functional properties. The leukocyte integrin, CD11c, is considered a specific marker for DCs and it is expressed by all DC subsets. We created a strain of mice in which DCs and their progenitors could be lineage traced based on activity of the CD11c proximal promoter. Surprisingly, we observed levels of CD11c promoter activity that were similar in DCs and in other mature leukocytes, including monocytes, granulocytes, and lymphocytes. We sought to identify DNA elements and transcription factors that regulate DC-associated expression of CD11c. The ets transcription factor, PU.1, is a key regulator of DC development, and expression of PU.1 varies in different DC subsets. GM-CSF increased monocyte-derived DCs in mice and from mouse bone marrow cultured in vitro, but it did not increase CD8(+) lymphoid-derived DCs or B220(+) plasmacytoid DCs. FLT3L increased both monocyte-derived DCs and lymphoid-derived DCs from mouse bone marrow cultured in vitro. GM-CSF increased the 5.3 Kb CD11c proximal promoter activity in monocyte-derived DCs and CD8(+) lymphoid-derived DCs, but not in B220(+) plasmacytoid DCs. In contrast, FLT3L increased the CD11c proximal promoter activity in both monocyte-derived DCs and B220(+) plasmacytoid DCs. We used shRNA gene knockdown and chromatin immunoprecipitation to demonstrate that PU.1 is required for the effects of GM-CSF or FLT3L on monocyte-derived DCs. We conclude that both GM-CSF and FLT3L act through PU.1 to activate the 5.3 Kb CD11c proximal promoter in DCs and to induce differentiation of monocyte-derived DCs. We also confirm that the CD11c proximal promoter is not sufficient to direct lineage specificity of CD11c expression, and that additional DNA elements are required for lineage-specific CD11c expression.

Phospho-SXXE/D motif mediated TNF receptor 1-TRADD death domain complex formation for T cell activation and migration.

In TNF-treated cells, TNFR1, TNFR-associated death domain protein (TRADD), Fas-associated death domain protein, and receptor-interacting protein kinase proteins form the signaling complex via modular interaction within their C-terminal death domains. In this paper, we report that the death domain SXXE/D motifs (i.e., S381DHE motif of TNFR1-death domain as well as S215LKD and S296LAE motifs of TRADD-death domain) are phosphorylated, and this is required for stable TNFR1-TRADD complex formation and subsequent activation of NF-κB. Phospho-S215LKD and phospho-S296LAE motifs are also critical to TRADD for recruiting Fas-associated death domain protein and receptor-interacting protein kinase. IκB kinase ß plays a critical role in TNFR1 phosphorylation of S381, which leads to subsequent T cell migration and accumulation. Consistently, we observed in inflammatory bowel disease specimens that TNFR1 was constitutively phosphorylated on S381 in those inflammatory T cells, which had accumulated in high numbers in the inflamed mucosa. Therefore, SXXE/D motifs found in the cytoplasmic domains of many TNFR family members and their adaptor proteins may serve to function as a specific interaction module for the α-helical death domain signal transduction.

GABP transcription factor is required for myeloid differentiation, in part, through its control of Gfi-1 expression.

GABP is an ets transcription factor that regulates genes that are required for myeloid differentiation. The tetrameric GABP complex includes GABPα, which binds DNA via its ets domain, and GABPß, which contains the transcription activation domain. To examine the role of GABP in myeloid differentiation, we generated mice in which Gabpa can be conditionally deleted in hematopoietic tissues. Gabpa knockout mice rapidly lost myeloid cells, and residual myeloid cells were dysplastic and immunophenotypically abnormal. Bone marrow transplantation demonstrated that Gabpα null cells could not contribute to the myeloid compartment because of cell intrinsic defects. Disruption of Gabpa was associated with a marked reduction in myeloid progenitor cells, and Gabpα null myeloid cells express reduced levels of the transcriptional repressor, Gfi-1. Gabp bound and activated the Gfi1 promoter, and transduction of Gabpa knockout bone marrow with Gfi1 partially rescued defects in myeloid colony formation and myeloid differentiation. We conclude that Gabp is required for myeloid differentiation due, in part, to its regulation of the tran-scriptional repressor Gfi-1.

[A review on the environmental behaviors and toxicity assessment of chromium in soil-plant systems].

As a result of the wide use of chromium (Cr) and its compounds as well as the exposure of the Cr-containing wastes, air, soil, water and food could be polluted by Cr in varying degrees. Cr is a toxic element that occurs in highly variable oxidation states. Accordingly, environmental chromium pollution, especially the soil contamination with Cr, has become one of the focuses of environmental science. In this review, the factors influencing the transport, transformation and the ecotoxicity of chromium were summarized, for example, soil properties (pH, Eh, organic matter, clay minerals), species and concentrations of Cr and the plant species. Based on this, the evaluation methods of chromium ecological risk in the soil-plant systems were covered by taking the comprehensive analysis of eco-toxicological data of plants, soil microorganisms and soil animals in the soil-plant systems. Finally, the possible shortages and prospects of chromium research in this field were discussed.

Retinoic acid signaling in myelopoiesis.

PURPOSE OF REVIEW: For decades, retinoic acid has been known to alter the proliferation and differentiation of myeloid cells. Currently, retinoic acid is a front-line agent in the treatment of certain forms of acute myelogenous leukemia. In this review, we focus on recent advances in our understanding of the mechanisms by which retinoids affect growth and proliferation of myeloid cells and contribute to the pathogenesis of leukemia. We have not attempted to summarize the related clinical literature. RECENT FINDINGS: The past 2 years have yielded important understanding of the mechanisms by which retinoids and their nuclear receptors interact with other signal transduction pathways and transcription factors to modify chromatin, alter gene expression, and participate in normal myeloid differentiation and leukemogenesis. Important advances regarding cell biology, molecular biology, biochemistry, and animal studies of retinoids and myeloid differentiation are reviewed. SUMMARY: Greater understanding of the role of retinoids and their receptors in myeloid cell growth and differentiation provides important insight into normal myelopoiesis. These findings have resulted in successful rational approaches to the treatment of acute leukemia and provide the promise of improved treatments in the near future.

The Ets transcription factor GABP is required for cell-cycle progression.

The transition from cellular quiescence (G0) into S phase is regulated by the mitogenic-activation of D-type cyclins and cyclin-dependent kinases (Cdks), the sequestration of the Cdk inhibitors (CDKIs), p21 and p27, and the hyperphosphorylation of Rb with release of E2F transcription factors. However, fibroblasts that lack all D-type cyclins can still undergo serum-induced proliferation and key E2F targets are expressed at stable levels despite cyclical Rb-E2F activity. Here, we show that serum induces expression of the Ets transcription factor, Gabpalpha, and that its ectopic expression induces quiescent cells to re-enter the cell cycle. Genetic disruption of Gabpalpha prevents entry into S phase, and selectively reduces expression of genes that are required for DNA synthesis and degradation of CDKIs, yet does not alter expression of D-type cyclins, Cdks, Rb or E2Fs. Thus, GABP is necessary and sufficient for re-entry into the cell cycle and it regulates a pathway that is distinct from that of D-type cyclins and CDKs.

Stat3 cleavage by caspases: impact on full-length Stat3 expression, fragment formation, and transcriptional activity.

Stat3 and its isoforms belong to a family of cytoplasmic transcription factors that affect the synthesis of various proteins. Caspases are cysteinyl-aspartate proteases that function under apoptotic and non-apoptotic conditions. We now report that, in addition to transcriptional splicing, Stat3 fragmentation can be mediated by caspases. Caspase activation in DU145 cells was achieved by staurosporine (STS) exposure, and Western analysis revealed a reduction in full-length Stat3 (fl-Stat3) expression that was caspase-mediated. This proteolytic relationship was further studied by exposing purified Stat3 protein to a mixture of active caspases under cell-free conditions. This demonstrated that caspases directly cleaved Stat3 and Stat3 cleavage was accompanied by the apparent formation of cleavage fragment(s). Stat3 cleavage fragments, reflecting multiple caspase cleavage sites, also were observed in vitro following STS exposure in DU145 cells and in HEK293T cells transfected to express Stat3 truncation mutants. The impact of cleavage on Stat3 transcriptional activity next was assessed and revealed that cleavage of fl-Stat3 was accompanied by reductions in Stat3-DNA binding, Stat3-driven reporter protein (luciferase) activity, and the expression of selected Stat3-dependent genes. Further, reduced Stat3 expression correlated with increased sensitivity to apoptotic stimuli. In concomitant experiments, reporter activity was assessed in Stat3 truncation mutant-expressing HEK293T cells and revealed that, under non-apoptotic conditions, expression of different Stat3 fragments induced differential effects on Stat3-driven luciferase activity. These findings demonstrate that fl-Stat3 undergoes proteolytic processing by caspases that reduces its expression and leads to the formation of cleavage fragments that may modulate Stat3 transcriptional activity.