Mice with a Mutation in the Mdm2 Gene That Interferes with MDM2/Ribosomal Protein Binding Develop a Defect in Erythropoiesis.

MDM2, an E3 ubiquitin ligase, is an important negative regulator of tumor suppressor p53. In turn the Mdm2 gene is a transcriptional target of p53, forming a negative feedback loop that is important in cell cycle control. It has recently become apparent that the ubiquitination of p53 by MDM2 can be inhibited when certain ribosomal proteins, including RPL5 and RPL11, bind to MDM2.

Impaired Telomere Maintenance and Decreased Canonical WNT Signaling but Normal Ribosome Biogenesis in Induced Pluripotent Stem Cells from X-Linked Dyskeratosis Congenita Patients.

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome characterized by the presence of short telomeres at presentation. Mutations in ten different genes, whose products are involved in the telomere maintenance pathway, have been shown to cause DC. The X-linked form is the most common form of the disease and is caused by mutations in the gene DKC1, encoding the protein dyskerin.

Slow growth and unstable ribosomal RNA lacking pseudouridine in mouse embryonic fibroblast cells expressing catalytically inactive dyskerin.

Pseudouridine is the most abundant modified nucleotide in ribosomal RNA throughout eukaryotes and archaea but its role is not known. Here we produced mouse embryonic fibroblast cells expressing only catalytically inactive dyskerin, the pseudouridine synthase that converts uridine to pseudouridine in ribosomal RNA. The mutant dyskerin protein, D125A, was extremely unstable but cells were able to divide and grow very slowly.

Accelerated hematopoietic stem cell aging in a mouse model of dyskeratosis congenita responds to antioxidant treatment.

Mutations in DKC1, encoding telomerase associated protein dyskerin, cause X-linked dyskeratosis congenita (DC), a bone marrow (BM) failure, and cancer susceptibility syndrome. Decreased accumulation of telomerase RNA resulting in excessive telomere shortening and premature cellular senescence is thought to be the primary cause of disease in X-linked DC. Affected tissues are those that require constant renewal by stem cell activity.

Anomalous electrophoretic migration of newly synthesized ribosomal RNAs and their precursors from cells with DKC1 mutations.

Mutations in the X-linked gene, DKC1, encoding dyskerin, cause dyskeratosis congenita by leading to decreased telomerase activity and causing short telomeres. Dyskerin is also a pseudouridine synthase that modifies nascent ribosomal and other RNAs and it is not known if this function is affected by the mutations. Here we show that newly synthesized ribosomal RNA, extracted from human and mouse cells with pathogenic mutations, shows anomalous mobility in agarose gels under certain denaturation conditions.

Variable expression of Dkc1 mutations in mice.

In humans mutations in DKC1, cause the rare bone marrow failure syndrome dyskeratosis congenita. We have used gene targeting to produce mouse ES cells with Dkc1 mutations that cause DC when in humans. The mutation A353V, the most common human mutation, causes typical DC to very severe DC in humans.

Dyskerin, telomerase and the DNA damage response.

The bone marrow failure syndrome Dyskeratosis congenita (DC), though rare, has attracted a great deal of attention in the last few years because it is caused by mutations in genes whose products are involved in telomere maintenance. The disease presents with a variety of features that can all be due to failure of tissues that require constant renewal via stem cell activity. It is thought this is caused by defects in telomere maintenance leading eventually to cell cycle arrest or cell death caused by critically short telomeres.

A pathogenic dyskerin mutation impairs proliferation and activates a DNA damage response independent of telomere length in mice.

Telomeres are nucleoprotein structures that cap the ends of chromosomes, protecting them from exonucleases and distinguishing them from double-stranded breaks. Their integrity is maintained by telomerase, an enzyme consisting of a reverse transcriptase, TERT and an RNA template, TERC, and other components, including the pseudouridine synthase, dyskerin, the product of the DKC1 gene. When telomeres become critically short, a p53-dependent pathway causing cell cycle arrest is induced that can lead to senescence, apoptosis, or, rarely to genomic instability and transformation.

Gain-of-function mutation of GATA-2 in acute myeloid transformation of chronic myeloid leukemia.

Acquisition of additional genetic and/or epigenetic abnormalities other than the BCR/ABL fusion gene is believed to cause disease progression in chronic myeloid leukemia (CML) from chronic phase to blast crisis (BC). To gain insights into the underlying mechanisms of progression to BC, we screened DNA samples from CML patients during blast transformation for mutations in a number of transcription factor genes that are critical for myeloid-lymphoid development. In 85 cases of CML blast transformation, we identified two new mutations in the coding region of GATA-2, a negative regulator of hematopoietic stem/progenitor cell differentiation.

The investigation of mutation and single nucleotide polymorphism of receptor tyrosine kinases and downstream scaffold molecules in acute myeloid leukemia.

We investigate the role of mutations of receptor tyrosine kinases as well as their downstream scaffold molecules in leukemogenesis of acute myeloid leukemia (AML) in Chinese patients. Genes of interest included FLT3, PDGFRbeta, KDR, CSF2Rbeta, SOCS1, PIAS3 and SHIP. The coding sequence of these genes was analysed by the reverse transcription-polymerase chain reaction to search novel mutations.

[Study of mutation and single nucleotide polymorphism of PDGFRbeta and SHIP gene in acute myeloid leukemia].

Objective: To investigate the significance of mutation and single nucleotide polymorphism (SNP) of class III receptor tyrosine kinases such as PDGFRbeta and SHIP in acute myeloid leukemia (AML) patients.

Methods: Screening of the mutation and SNP of PDGFRbeta and SHIP by genomic PCR, RT-PCR, directly sequencing and Mass-ARRAY system was carried out in 273 AML patients.

Results: The mutations of PDGFRbeta R685C and SHIP Q1153L were detected for the first time in AML patients.

Trans-repressive effect of NUP98-PMX1 on PMX1-regulated c-FOS gene through recruitment of histone deacetylase 1 by FG repeats.

The formation of fusion genes between NUP98 and members of the HOX family represents a critical factor for the genesis of acute leukemia or acute transformation of chronic myeloid leukemia (CML). To gain insights into the molecular mechanisms underlying the leukemogenesis of NUP98-HOX fusion products, we cloned NUP98-PMX1 from a CML-blast crisis patient with t(1;11) as a secondary chromosomal translocation, and functionally studied the fusion products in detail through various molecular and protein biochemical assays. In addition to many interesting features, we have found that the NUP98-PMX1 fusion protein exerts a repressive effect on PMX1 or serum response factor-mediated c-FOS activation, probably through the recruitment of a common corepressor histone deacetylase 1 by FG domains of the NUP98-PMX1 fusion protein.

[Detection and quantification of BCR-ABL transcripts in patients with chronic myeloid leukemia by real-time quantitative reverse transcriptase polymerase chain reaction].

Objective: To investigate the effect of real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) approach in chronic myeloid leukemia (CML) for detecting the minimal residual disease (MRD) or monitoring the treatment response and predicting the prognosis.

Methods: Fifty-six CML patients, 39 males and 17 females, aged 39 (16 approximately 66), with disease history and frozen RNA specimens were studied, 31 of which were in the incipient chronic phase, 7 in the accelerated phase, and 17 in the rapidly progressing phase. Three or more frozen RNA specimens collected before and after treatment were preserved in 11 of the patients.

Association between single nucleotide polymorphisms in deoxycytidine kinase and treatment response among acute myeloid leukaemia patients.

Development of resistance to 1-beta-arabinofuranosylcytosine (AraC) is a major obstacle in the treatment of patients with acute myeloid leukaemia (AML). Deficiency of functional deoxycytidine kinase (dCK) plays an important role in AraC resistance in vitro. We screened 5378 bp sequences of the dCK gene, including all exons and the 5' flanking region, and identified two single nucleotide polymorphisms (SNPs) in the regulatory region (rSNPs) with high allele frequencies.

All-trans retinoic acid/As2O3 combination yields a high quality remission and survival in newly diagnosed acute promyelocytic leukemia.

Both all-trans retinoic acid (ATRA) and arsenic trioxide (As(2)O(3)) have proven to be very effective in obtaining high clinical complete remission (CR) rates in acute promyelocytic leukemia (APL), but they had not been used jointly in an integrated treatment protocol for remission induction or maintenance among newly diagnosed APL patients. In this study, 61 newly diagnosed APL subjects were randomized into three treatment groups, namely by ATRA, As(2)O(3), and the combination of the two drugs. CR was determined by hematological analysis, tumor burden was examined with real-time quantitative RT-PCR of the PML-RAR alpha (promyelocytic leukemia-retinoic acid receptor alpha) fusion transcripts, and side effects were evaluated by means of clinical examinations.