Biomedical subjects

Yalin Guo

Publications and source records attributed to Yalin Guo.

9 recordsLinked to original sources

PubMed2006

Reversal of p15/INK4b hypermethylation in AML1/ETO-positive and -negative myeloid leukemia cell lines.

In vitro and in vivo, myeloid leukemic and preleukemic cells exhibit variable sensitivity to the antiproliferative and proapoptotic effects induced already at low concentrations of DNA methyltransferase (DNMT) inhibitors. The molecular mechanisms underlying this variable sensitivity of leukemic blasts to azanucleosides such as 5-azacytidine and 5-aza-2'-deoxycytidine (DAC) may involve modifier effects of specific fusion proteins such as AML1/ETO. The cyclin-dependent kinase inhibitor p15/INK4b is one potential target of DNA demethylating activity in AML and MDS where it is frequently silenced by hypermethylation. To study sensitivity to DAC in myeloid leukemia cells, we chose the myeloid cell lines Kasumi-1 (expressing AML1/ETO), KG-1 and KG-1a (both AML1/ETO-negative) all of which a highly methylated p15/INK4b gene. Treatment with DAC resulted in dose-dependent regional demethylation of p15/INK4b in Kasumi-1 and KG-1, but only to a modest degree in KG-1a cells. Demethylation was associated with induction of p15/INK4b protein expression. Growth-inhibitory and proapoptotic activity of DAC was significantly higher in Kasumi-1 than in KG-1a cells, and sensitization of cells to a cooperating effect of All-trans retinoic acid and of the histone deacetylase (HDAC) inhibitor Trichostatin A was observed. DAC-induced growth inhibition and apoptosis were enhanced when AML1/ETO was conditionally expressed in AML1/ETO-negative U-937 cells. In conclusion, hypomethylation and reactivation of p15/INK4b in myeloid cell lines are among the molecular events associated with DAC-induced growth arrest and apoptosis. Further studies of AML1/ETO as a modifier of the epigenotype and sensitivity of myeloid cells to inhibitors of DNMTs and HDACs appear warranted.

Azacitidine↗

PubMed2006

T-lymphoid, megakaryocyte, and granulocyte development are sensitive to decreases in CBFbeta dosage.

The family of core-binding factors includes the DNA-binding subunits Runx1-3 and their common non-DNA-binding partner CBFbeta. We examined the collective role of core-binding factors in hematopoiesis with a hypomorphic Cbfb allelic series. Reducing CBFbeta levels by 3- or 6-fold caused abnormalities in bone development, megakaryocytes, granulocytes, and T cells. T-cell development was very sensitive to an incremental reduction of CBFbeta levels: mature thymocytes were decreased in number upon a 3-fold reduction in CBFbeta levels, and were virtually absent when CBFbeta levels were 6-fold lower. Partially penetrant consecutive differentiation blocks were found among early T-lineage progenitors within the CD4- CD8- double-negative 1 and downstream double-negative 2 thymocyte subsets. Our data define a critical CBFbeta threshold for normal T-cell development, and situate an essential role for core-binding factors during the earliest stages of T-cell development.

Alleles↗

PubMed2006

The allantois and chorion, when isolated before circulation or chorio-allantoic fusion, have hematopoietic potential.

The chorio-allantoic placenta forms through the fusion of the allantois (progenitor tissue of the umbilical cord), with the chorionic plate. The murine placenta contains high levels of hematopoietic stem cells, and is therefore a stem cell niche. However, it is not known whether the placenta is a site of hematopoietic cell emergence, or whether hematopoietic cells originate from other sites in the conceptus and then colonize the placenta. Here, we show that the allantois and chorion, isolated prior to the establishment of circulation, have the potential to give rise to myeloid and definitive erythroid cells following explant culture. We further show that the hematopoietic potential of the allantois and chorion does not require their union, indicating that it is an intrinsic property of these tissues. These results suggest that the placenta is not only a niche for, but also a source of, hematopoietic cells.

Allantois↗

PubMed2005

The silence of the genes: epigenetic disturbances in haematopoietic malignancies.

Cancer-associated disturbances of regulated DNA methylation include both global hypomethylation and gene-specific (often even cancer-specific) hypermethylation. Both coexist and have become the subject of intense investigation. In haematological neoplasias, distinct sets of genes, including the p15/INK4b cell cycle inhibitor (mostly in myeloid malignancies) as well as p16/INK4a (only very infrequently in myeloid neoplasia), have been well characterised as to incidence of hypermethylation, concurrent gene inactivation and their re-expression following treatment with DNA methylation inhibitors. Several genes frequently methylated in haematological neoplasias have been studied with respect to their prognostic value. With the advance of low-dose schedules of demethylating agents (explored particularly in the elderly patient population) the rationale for reverting the 'hyper-methylator phenotype' has also prompted in vivo studies of gene reactivation following this type of treatment. However, ubiquitous surrogate markers for the efficacy of this type of treatment need to be developed. These may include reactivated haemoglobin F (HbF), as demethylating agents can result in clinically meaningful induction of HbF in patients with haemoglobinopathies. Because 'cancer testis antigens', which provide powerful signals for T cell cytotoxic activity on solid tumour cells, are usually silenced in leukaemia but can be reactivated in vitro and in vivo, they provide a rationale for an immuno-modulatory effect of demethylating therapy.

DNA Methylation↗

PubMed2004

Telomeres and telomerase in normal and leukemic hematopoietic cells.

Telomere length and telomerase have an important role in normal and malignant hematopoiesis. Telomere erosion can lead to chromosome end fusion and thereby contribute to genomic instability during tumorigenesis. Thus, like complex chromosomal aberrations, telomere length may be a prognostic factor in hematopoietic malignancies. A paper by Sieglova et al. in this issue of Leukemia Research reports on the prognostic impact of telomere shortening in bone marrow (BM) and peripheral blood (PB) specimens of myelodysplastic syndrome (MDS) and MDS converted-AML patients (pts). Their results underline the importance to study telomere biology together with cytogenetics, genomic and proteomic profiling as prognostic factors, in order to improve risk-adapted therapy of MDS and AML pts.

Hematopoietic Stem Cells↗

PubMed2004

Nonclonal neutrophil responses after successful treatment of myelodysplasia with low-dose 5-aza-2'-deoxycytidine (decitabine).

The demethylating agents 5-aza-2'-deoxycytidine (decitabine, DAC) and 5-azacytidine at low doses induce hematologic and cytogenetic remissions in a subset of patients with MDS. It is unclear whether the correction of neutropenia involves differentiation of abnormal granulocyte precursors, or emergence of normal granulopoiesis. A previous study in three MDS patients, analyzing a differentiating activity of GM-CSF, had shown heterogenous granulocyte responses. The objective of our study was to determine the ratio of clonal and nonclonal peripheral blood granulocytes in MDS patients treated with DAC using FISH analysis. In two patients with initial severe neutropenia, an informative cytogenetic marker, complete normalization of peripheral blood neutrophils and a bone marrow cytogenetic response following DAC, >90% of the cells contributing to neutrophil normalization lacked this clonal marker. In one of them, an early and transient increase in clonal neutrophils was compatible also with a modest differentiating effect upon the dysplastic granulocyte precursors, whereas in a third patient, resistant to re-treatment with DAC, no expansion of either granulocyte population occurred. In the responders, leukocyte nadirs following DAC appeared less pronounced after conversion to normal cytogenetics. In conclusion, restoration of nonclonal hematopoiesis may be the predominant effect of DAC both in early and late stages of treatment, at least in patients achieving a hematologic and cytogenetic response.

Aged↗

PubMed2003

Side-population cells from different precursor compartments.

The rapid efflux of the fluorescent DNA-binding dye Hoechst 33342 identifies a rare, so-called side population (SP), which rapidly expels the dye, can reconstitute the bone marrow (BM) of lethally irradiated mice, and has proven negative for most lineage markers including CD34. Because SP cells from human cell sources, such as mobilized peripheral blood [apheresis products (AP)], cord blood (CB), or BM have not been extensively characterized to date, we sought to analyze SP cells from various cell sources. We detected murine SP cells with a median frequency of 0.04% (n = 23) and a 52-fold colony-forming units (CFU) increase compared to unsorted cells (p = 0.028). The median frequency of human SP cells was 0.02% (n = 90), with highest numbers in donor AP, and lower in CB and BM. Human SP cells were mostly CD34(-) and lineage marker-negative. These showed no enrichment in CFU before expansion; however, they displayed a CFU increase after 5-7 days of cytokine-supported suspension culture (10.7-fold at day 5, 7.2-fold at day 7; n = 17) that was significant compared to both input (day 0) SP and to non-SP cells before and after expansion (p < 0.05). SP cells demonstrated a significant long-term culture-initiating cell (LTC-IC) increase of 167-fold (n = 17) as compared to non-SP cells (p = 0.002), with the highest numbers from AP specimens. We conclude that human primitive hematopoietic cells can be isolated via Hoechst staining and that SP cells of various human sources show substantial differences and represent a rare CD34(-) population with stem cell potential.

Animals↗

PubMed2003

CD34- hematopoietic stem cells: current concepts and controversies.

Recent data have suggested that human CD34(-) hematopoietic stem cells (HSCs) exist, challenging the concept that HSCs necessarily and exclusively express the CD34 antigen. In mice, quiescent HSCs have been shown to be mostly CD34(-), but as a consequence of 5-fluorouracil treatment or cytokine stimulation, differentiate into CD34(+) cells. Of particular interest is a novel, specific marker to identify HSCs, namely the Hoechst dye efflux property, with which a distinct side population (SP) is identified. These SP cells are mostly CD34(-), highly enriched for long-term repopulating cells, and durably engraft in sublethally irradiated non-obese diabetic/severe combined immunodeficient mice. Using a semiquantitative reverse transcription-polymerase chain reaction, one of the ATP-binding cassette (ABC) transporters, the breast cancer resistance protein (Bcrp) or ABC transporter G2 (ABCG2), was found to be highly expressed in SP cells as well as other primitive HSCs and to sharply drop with hematopoietic differentiation. Enforced expression of the ABCG2 cDNA resulted in a robust SP phenotype and a reduction in hematopoietic maturation. These data suggest that the Bcrp/ABCG2 gene contributes importantly to the generation of the SP phenotype, which allows for the selection of immature, pluripotent HSCs. The isolation of Bcrp/ABCG2(+) cells appears to be an attractive tool to analyze and characterize HSCs, and may eventually allow for the purification of these cells for clinical purposes. In this review, current concepts on murine and human CD34(-) HSCs and their relationship with CD34(+) HSCs are discussed.

Animals↗

PubMed2002

Telomere maintenance in human B lymphocytes.

Telomere shortening has been causally linked to replicative senescence in human cells. To characterize telomere-length heterogeneity in peripheral blood cells of normal individuals, we analysed the mean length of telomeric repeat sequences in subpopulations of peripheral blood leucocytes, using fluorescence in situ hybridization and flow cytometry (flow-FISH). Although the telomere length of most haematopoietic subsets was within the same range, the mean telomere length was found to be 15% higher in B compared with T lymphocytes in adult peripheral blood. Whereas telomere loss with ageing corresponded to 33 base pairs (bp) per year in T cells, telomere shortening was slower in B cells, corresponding to 15 bp per year. Separation of adult B-lymphocyte subpopulations based on CD27 expression revealed that telomere length was almost 2 kb longer in CD19+CD27+ (memory) compared with CD19+CD27- (naive) cells. Furthermore, peripheral blood B cells were activated in vitro. Whereas B-cell activation with Staphylococcus aureus Cowan strain (SAC) did not increase telomere length, a striking telomere elongation was observed when cells were stimulated with SAC and interleukin 2 to induce plasma cell differentiation. Our observations support the concept that telomere dynamics in B cells are distinct from other haematopoietic cell lineages and that telomere elongation may play an essential role in the generation of long-term B memory cells.

Adolescent↗