Frequent loss of heterozygosity in the region of D1S450 at 1p36.2 in myelodysplastic syndromes

Suppression of C6 gliomas via application of rat hyperplasia gene

BACKGROUND

Among all neurological tumors, tumor incidence of the neuroepithelial tissue is the highest, where 50% are gliomas. Treatment for gliomas has traditionally included surgery and adjuvant therapy. With advancements in medicine, gene therapy has entered the clinical setting, in which control of tumor growth, tumor volume and decrease of supply of blood to the tumor have been observed. Rat hyperplasia suppressor gene (rHSG) has been proven to inhibit the injury-mediated proliferation of vascular smooth muscle cells.

METHODS

A recombinant adenovirus, Adv-rHSG-GFP, was constructed and characterized by in vitro and in vivo studies. The function of rHSG on cell proliferation was determined in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) exclusion assay and plate clone formation, while a C6/Sprague Dawley rat glioma model was established to observe the effect of rHSG in vivo.

RESULTS

Overexpression of rHSG displayed a strong effect on suppressing C6 cells proliferation in vitro and growth of glioma in vivo, which suggests the use of rHSG as a possible treatment strategy for glioma. p21Cip1, p27Kip1 and proliferating cell nuclear antigen were found to be involved in the tumor suppression mechanism of rHSG.

CONCLUSIONS

rHSG can markedly inhibit of the growth of rat glioma cells. The suppression mechanism of rHSG may be related to cell cycle regulation, which shows that rHSG is a potential therapeutic target of glioma tumor. This preclinical study supports a further in-depth study on the effect of rHSG on cell proliferation, migration and change in the extracellular matrix component of glioma cells.

Frequent losses of heterozygosity in the mitofusin 2 gene in hepatocellular carcinoma: their relationship to clinicopathological features

BACKGROUND

The aim of the study was to determine the features of loss of heterozygosity in the mitofusin 2 gene and their association with clinicopathological characteristics of hepatocellular carcinoma.

METHODOLOGY

Loss of heterozygosity of four microsatellite loci were detected in tumors and their adjacent normal tissues of 29 surgically resected hepatocellular carcinomas using an ABI3130xl automated sequencer.

RESULTS

The results showed the incidences of loss of heterozygosity on microsatellite loci D1S2667, D1S2740, D1S434, and D1S228 were 21%, 23%, 21%, and 22%, respectively. Loss of heterozygosity in the mitofusin 2 gene was closely correlated with age, degree of differentiation, capsule integrity, and tumor size (P <0.05) but was not correlated with gender, thrombosis, liver cirrhosis, or alpha-fetoprotein levels (P >0.05).

CONCLUSIONS

Frequent loss of heterozygosity in the mitofusin 2 gene exists in hepatocellular carcinoma. Loss of heterozygosity, which represents a tumor suppressor gene pathway, may play a critical role in the occurrence and development of hepatocellular carcinoma.

Refinement of 1p36 alterations not involving PRDM16 in myeloid and lymphoid malignancies

Fluorescence in situ hybridization was performed to characterize 81 cases of myeloid and lymphoid malignancies with cytogenetic 1p36 alterations not affecting the PRDM16 locus. In total, three subgroups were identified: balanced translocations (N = 27) and telomeric rearrangements (N = 15), both mainly observed in myeloid disorders; and unbalanced non-telomeric rearrangements (N = 39), mainly observed in lymphoid proliferations and frequently associated with a highly complex karyotype. The 1p36 rearrangement was isolated in 12 cases, mainly myeloid disorders. The breakpoints on 1p36 were more widely distributed than previously reported, but with identifiable rare breakpoint cluster regions, such as the TP73 locus. We also found novel partner loci on 1p36 for the known multi-partner genes HMGA2 and RUNX1. We precised the common terminal 1p36 deletion, which has been suggested to have an adverse prognosis, in B-cell lymphomas [follicular lymphomas and diffuse large B-cell lymphomas with t(14;18)(q32;q21) as well as follicular lymphomas without t(14;18)]. Intrachromosomal telomeric repetitive sequences were detected in at least half the cases of telomeric rearrangements. It is unclear how the latter rearrangements occurred and whether they represent oncogenic events or result from chromosomal instability during oncogenesis.

Mosaicism due to myeloid lineage–restricted loss of heterozygosity as cause of spontaneous Rh phenotype splitting

Spontaneous Rh phenotype alteration interferes with pretransfusion and prenatal blood group examinations and may potentially indicate hematologic disease. In this study, the molecular background of this biologic phenomenon was investigated. In 9 patients (3 with hematologic disease), routine RhD typing showed a mixture of D-positive and D-negative red cells not attributable to transfusion or hematopoietic stem-cell transplantation. In all patients, congenital and acquired chimerism was excluded by microsatellite analysis. In contrast to D-positive red cells, D-negative subpopulations were also negative for C or E in patients genotyped CcDdee or ccDdEe, respectively, which suggested the presence of erythrocyte precursors with an apparent homozygous cde/cde or hemizygous cde/— genotype. Except for one patient with additional Fyb antigen anomaly, no other blood group systems were affected. RH genotyping of single erythropoietic burst-forming units, combined with microsatellite analysis of blood, different tissues, sorted blood cell subsets, and erythropoietic burst-forming units, indicated myeloid lineage–restricted loss of heterozygosity (LOH) of variable chromosome 1 stretches encompassing the RHD/RHCE gene loci. Fluorescent in situ hybridization studies indicated that LOH was caused by either somatic recombination or deletion. Therefore, most cases of spontaneous Rh phenotype splitting appear to be due to hematopoietic mosaicism based on LOH on chromosome 1.

FISH analysis of hematological neoplasias with 1p36 rearrangements allows the definition of a cluster of 2.5 Mb included in the minimal region deleted in 1p36 deletion syndrome

Rearrangements in the distal region of the short arm of chromosome 1 are recurrent aberrations in a broad spectrum of human neoplasias. However, neither the location of the breakpoints (BP) on 1p36 nor the candidate genes have been fully determined. We have characterized, by fluorescence in situ hybridization (FISH), the BP in 26 patients with hematological neoplasias and 1p36 rearrangements in the G-banding karyotype. FISH allowed a better characterization of all samples analyzed. Nine cases (35%) showed reciprocal translocations, 15 (58%) unbalanced rearrangements, and two (7%) deletions. We describe two new recurrent aberrations. In 18 of the 26 cases analyzed the BP were located in band 1p36, which is 25.5 Mb long. In 14 of these 18 cases (78%) and without distinction between myeloid and lymphoid neoplasias, the BP clustered in a 2.5 Mb region located between 1p36.32 and the telomere. Interestingly, this region is contained in the 10.5 Mb cluster on 1p36.22-1pter defined in cases with 1p36 deletion syndrome. The 2.5 Mb region, located on 1p36.32-1pter, has a higher frequency of occurrence of tandem repeats and segmental duplications larger than 1 kb, when compared with the 25.5 Mb of the complete 1p36 band. This could explain its proneness for involvement in chromosomal rearrangements in hematological neoplasias.

p53 alterations in myeloid leukemia

Although most solid tumors contain inactivating mutations of the p53 tumor suppressor, hematological malignancies do not contain frequent alterations in the p53 gene (<20%). How these tumors arise in the presence of a super tumor suppressor like p53 remains to be elucidated. Given the number of downstream effectors of p53, it is likely that critical targets of p53 are inactivated in leukemia, bypassing the requirement for p53 gene mutations in these tumors. This review describes new biochemical and transcriptional activities of p53 as well as the status of p53 in acute myelogenous leukemia and chronic myelogenous leukemia.

Partial deletion of chromosome 1 in a case of acute myelocytic leukemia

Acute myelocytic leukemia (AML) is a malignant disease characterized by the proliferation of immature myelocytic precursor cells causing the disruption of normal bone marrow function. Many chromosomal aberrations have been described in AML including translocations, inversions, deletions, and additions. Here we describe a novel deletion of chromosome 1, del(1)(p34p36) in a case of AML, French-American-British classification M1, in a previously healthy 33-year-old male. This isolated cytogenetic abnormality occurred in 33% of the myeloblasts examined at diagnosis. Subsequent cytogenetic analyses conducted on marrow following induction and consolidation therapy demonstrated a normal male karyotype in all cells examined. The patient remains in clinical and hematological remission 22 months following diagnosis. The presence of 1p abnormalities in AML and other malignancies is reviewed, as are candidate tumor suppressor genes in the 1p34 approximately p36 region. The implications of chromosome 1p abnormalities on clinical outcome are also discussed.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.