Expression of the DCC gene in myelodysplastic syndromes and overt leukemia

Netrin-1 and its receptors in tumorigenesis

Netrin-1 and its receptors DCC (deleted in colorectal cancer) and the UNC5 orthologues (human UNC5A-D and rodent UNC5H1-4) define a new mechanism for both the positive (induction) and negative (suppression) regulation of apoptosis. Accumulating evidence implies that for human cancers, this positive signalling pathway is frequently inactivated. Surprisingly, binding of netrin-1 to its receptors inhibits tumour suppressor p53-dependent apoptosis, and p53 is directly involved in transcriptional regulation of netrin-1 and its receptors. So, the netrin-1 receptor pathways probably play an important part in tumorigenesis.

Configuration of the TP53 gene as an independent prognostic parameter of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) consists of a heterogeneous group of acquired hematopoietic stem cell disorders, characterized by bone marrow failure and leukemic transformation. Since hematological manifestations and clinical outcomes vary widely among MDS patients, a considerable number of studies have tried to identify the prognostic parameters for the stratification of patients into different risk groups. Based on reported risk-based studies, the International Prognostic Scoring System (IPSS) was proposed as a reliable risk assessment method for primary MDS patients, and several validating studies have clarified its usefulness. Critical prognostic parameters of the IPSS consist of chromosome findings, the percentage of marrow blasts, and the number of peripheral blood cytopenias. Although other laboratory findings, including several molecular alterations, have been identified as convincing prognostic factors in MDS, these molecular configurations were not selected as prognostic parameters in the IPSS, because analysis for these alterations were not routinely available for the management of patients with MDS. Because recent advances in molecular genetics may make it available as a routine work-up of MDS in the future, we discuss potential improvement of the IPSS by the addition of molecular analysis to the system, with particular reference to the configuration of the TP53 gene.

Recessive oncogenes: current status

Cell growth is under the control of a variety of positive and negative signals. An imbalance of such signals results in deregulation of cell behavior. Recessive oncogenes or tumor suppressor genes, opposite to dominant oncogenes, encode important cellular proteins which could function as negative regulators of the cell cycle, i.e., cell cycle brakes. Inactivation of recessive oncogenes, by allelic deletion, loss of expression, mutation, or functional inactivation by interacting with oncogene products of DNA tumor viruses or with amplified cellular binding proteins, will lead to uncontrolled cell growth or tumor formation. Besides the classic suppressor genes such as the p53 and RB, a growing number of novel tumor suppressor genes have been identified in recent years. While some tumor suppressor genes have been found to be important for the development of a large number of human malignancies (e.g., the p53 gene), others are more tumor type-specific (e.g., the NF-1 gene). Many human cancer types showed abnormalities of multiple tumor suppressor genes, offering strong support to the concept that tumorigenesis and progression result from an accumulation of multiple genetic alterations. In this review, we will begin with an overview (gene, transcript, protein and mechanisms of action) of the tumor suppressor genes (the RB, p53, DCC, APC, MCC, WT1, VHL, MST1, and BRCA1 genes) identified to date and then discuss the specific involvement of tumor suppressor genes in human malignancies including prostate cancer. Various chromosomal regions which potentially may contain tumor suppressor genes also will be reviewed.

Molecular features of primary MDS with cytogenetic changes

Cytogenetic changes in primary myelodysplastic syndromes (MDS) have been extremely useful to identify clonality and to define specific clinico-pathological entities. More recently, with the development of DNA technology, a bulk of new information has been added to classical cytogenetics. Genes corresponding to chromosomal breakpoints implicated in reciprocal translocations have been cloned. Search for the minimal lost region has been the aim of the so-called deletion mapping approach to pick up the hypothetical suppressor gene(s) critical for typical deletions of MDS. Correlation has been found between gene mutations, deletions, expression, and clinical-hematological or cytogenetic features of MDS. Integration of fluorescence in situ hybridization at DNA level and of immunophenotyping at cellular level is an elegant tool to investigate clonal affiliation in MDS with distinct genetic changes.

Frequent reduction or loss of DCC gene expression in human osteosarcoma

The 'deleted in colon carcinoma' (DCC) gene has been considered a candidate tumour-suppressor gene that encodes for a transmembrane protein with strong structural similarity to members of the superfamily of neural cell adhesion molecules. It has been mapped to the chromosomal region 18q21.1 and it is implicated in cellular differentiation and developmental processes. In human osteosarcoma allelic loss frequently occurs on the long arm of chromosome 18, suggesting a possible involvement of the DCC gene in the pathogenesis of this tumour entity. In the present study the mRNA and protein expression and rearrangements at the DNA level of the DCC gene were addressed in 25 osteosarcomas and several tumour cell lines, including osteosarcoma- and colon carcinoma-derived cell lines. Using an reverse transcriptase polymerase chain reach in (RT-PCR)-based approach DCC expression was found to be lost or substantially reduced in 14 of 19 high-grade osteosarcomas, in three of six lower grade osteosarcomas and most of the tumour cell lines, in contrast to normally differentiated osteoblasts. Immunohistochemical studies on DCC protein expression of 14 selected tumours correlated well with the RT-PCR-based results. In view of the putative tumour-suppressor characteristics of the DCC gene its loss or reduction of expression could be a specific event in the development or progression of many high-grade osteosarcomas.

DCC: is there a connection between tumorigenesis and cell guidance molecules?

Based on the findings reviewed above, DCC remains a strong candidate for the tumor suppressor gene in the 18q21 region that is presumed to be frequently inactivated in colorectal and a number of other cancer types. Although little is known of the specific mechanisms that account for the loss of its expression in most cancers, the recent studies demonstrating an association between loss of DCC expression in colorectal cancers and poor prognosis imply that DCC inactivation may have very significant effects on the cancer cell phenotype. DCC function in normal and cancer cells is still relatively poorly understood. However, recent studies have begun to provide some insights. Based on the results of a number of recent studies, DCC appears likely to have a role in significant role in differentiation, cell fate determination, and migration in the nervous system and perhaps other tissues as well. Though many additional studies are needed to characterize DCC function more definitively, it seems reasonable to predict that such studies are likely to provide new insights into growth control pathways in normal and cancer tissues.

DCC protein expression in hematopoietic cell populations and its relation to leukemogenesis

Using flow cytometry and immunoprecipitation (IP), we have investigated the deleted in colon cancer (DCC) protein expression on the bone marrow (BM) and peripheral blood (PB) cells of 16 normal subjects, 17 myelodysplastic syndrome (MDS) patients, and 10 acute myelogenous leukemia (AML) patients. With regard to the BM mononuclear cells (BM-MNCs) of normal subjects, the DCC protein expression ranged from 6.6 to 57.0%. Two-color flow cytometry revealed that among the IBM-MNCs the DCC protein was clearly expressed on the CD14+, CD13+, and factor 8+ cells, whereas it was low on the CD19+ and CD7+ cells and did not express on the CD34+, CD8+, and the glycophorin A+ cells. Further, the DCC protein expression was not seen on the PB CD11b+ and CD13+ cells. The IP results revealed that the 180-kD DCC protein was detected on the MNCs of both the BM and PB cells by the antibodies AF5, specific for the DCC extracellular domain, and G97-449, specific for the cytoplasmic domain. In contrast, flow cytometry did not detect the DCC protein on any BM-MNC MDS lineages (0.1-1.5%) or on AML leukemic cells (0.1-0.9%). The IP results indicated that the AF5 antibody did not detect the DCC protein on BM-MNCs of three of five MDS patients and four of five AML patients; however, the G97-449 antibody detected the 180-kD DCC protein in two MDS patients in whom AF5 had detected greatly reduced DCC band. These findings suggest that the DCC protein presence appears to be associated with normal hematopoiesis, and that its absence on the surfaces of the BM-MNCs and AML cells may contribute to the MDS and AML pathogenesis.

Inactivation of the DCC tumor suppressor gene in a B-cell lymphoma cell line with the alteration of chromosome 18

A B-cell lymphoma cell line, designated KML-1, was established from pleural effusion of a patient with non-Hodgkin's lymphoma of large-cell type. The lymphoma arose in the pelvis and ran an aggressive clinical course. Chromosome analysis of the cell line exhibited a complex karyotype including the loss of chromosome 18. To evaluate the molecular events in the cell line that may be associated with the development of the lymphoma, we investigated the expression and/or alterations of several classes of human genes, including oncogenes, tumor suppressor genes, and cytokine genes. The expression of the DCC (deleted in colorectal cancer) gene, located on the chromosome 18q21, was extremely reduced in KML-1 cell line, as compared with that in a normal spleen tissue and other 4 lymphoma cell lines by the reverse transcription-polymerase-chain-reaction (RT-PCR) method. This finding suggests that inactivation of the DCC gene might play a role in the pathogenesis of the case of lymphoma.

DCC: linking tumour suppressor genes and altered cell surface interactions in cancer?

The Deleted in Colorectal Cancer (DCC) gene is a candidate tumour suppressor gene encoding a neural cell adhesion molecule-like transmembrane protein. Over the last year, data supporting DCC inactivation in multiple tumour types have continued to accumulate. Functional studies suggest that DCC may participate in signalling pathways that regulate cell proliferation and/or differentiation, two cellular processes that often go awry during tumorigenesis.

DCC (deleted in colorectal cancer) inactivation in hematological malignancies

DCC (Deleted in Colorectal Cancer) is a putative tumor suppressor gene located on chromosome band 18q21. Allelic deletions of one DCC locus have been found in more than 70% of colorectal carcinomas. Loss of DCC expression has been detected in 80% of all colorectal cancers and in many other types of tumor. DCC is expressed in normal bone marrow and peripheral lymphocytes, nevertheless DCC expression was absent or greatly reduced in 30% of acute leukemias and in 25% of Chronic Myelogenous Leukemias (CML). DCC encodes a transmembrane glycoprotein closely related to the adhesion molecules of the Neural Cell Adhesion Molecule (N-CAM) family. Glycoproteins of this family function like cell surface receptors and are involved in the regulation of many functions including cell recognition and cell differentiation. Highly specialized adhesion molecules participate in the regulation of hemopoiesis by mediating the interactions of hemopoietic cells with the components of the bone marrow microenvironment. Therefore, loss of DCC, as well as loss or alteration of other adhesion receptors, could contribute to leukemogenesis by impairing the interactions of the hemopoietic cells with the bone marrow microenvironment.

DCC: linking tumor suppressor genes and altered cell surface interactions in cancer?

The gene deleted in colorectal cancer (DCC) is a candidate tumor suppressor gene encoding a neural cell adhesion molecule like transmembrane protein. Over the past year, data supporting DCC inactivation in multiple tumor types have continued to accumulate. Functional studies suggest that DCC may participate in signaling pathways that regulate cell proliferation and/or differentiation, two cellular processes that often go awry during tumorigenesis.

Epidemiological and etiological aspects of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are increasingly recognized as a cause of bone marrow failure, and are at least as frequent as acute myeloid leukemias. While the overall incidence is about 2-4/100,000/year, incidence figures rise steeply with age. Incidence rates of 20-30/100,000/year in persons over 70 demonstrate that MDS are among the most common hematological neoplasias in this age group. However, due to difficulties of diagnosis and classification, patient registration in population-based registers is far from complete. As a prerequisite for truly representative statistics, future revisions of disease classification systems must incorporate MDS as a separate group of disorders. The difficulties in conducting epidemiological studies also impede the identification of risk factors for the development of MDS. Current knowledge of occupational risk factors is also reviewed here. More rapid progress in our understanding of MDS may come from recent advances in methodology that have begun to shed some light on the cytogenetic and molecular aspects of leukemogenesis in general, and MDS in particular. Non-random chromosomal changes can be found in about 50% of cases at diagnosis, but they are probably late events in the evolution of MDS, reflecting the progressive genomic instability of the premalignant clone. Proto-oncogene mutations have also been suggested to be relevant to the pathogenesis of MDS, but longitudinal studies of point mutations of the N-ras proto-oncogene revealed that such events, although often associated with rapid deterioration and transformation to AML, also appear to be late events during the course of disease. Therefore, it remains a major challenge to identify those lesions that initiate the multistep development of preleukemia. As the incidence of MDS correlates strongly with age, it is reasonable to presume that age-dependent changes of the hematopoietic system may play a role in the initiation of MDS. Aging is probably associated with a compromised marrow reserve through reduction in the size of the stem cell pool. Through increased proliferative activity, the remaining stem cells may be particularly vulnerable to mutagenic insults. Immunological attack on stem cells, mitochondrial DNA mutations, and the regulatory influence of the hematopoietic microenvironment must also be considered as possibly contributing to the early stages of MDS.

Expression of the DCC gene in human hematological malignancies

Inactivation of the deleted in colorectal carcinoma (DCC) tumor suppressor gene has been reported not only in colorectal carcinoma but also in other human malignancies. In order to evaluate the role of the DCC gene in leukemogenesis, we examined DCC expression using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Expression of the DCC gene was reduced or absent in 10 of 39 (26%) patients with acute myelogenous leukemia (AML), three of 14 (29%) patients with acute lymphocytic leukemia (ALL), seven of 33 (21%) patients with chronic myelogenous leukemia (CML), three of 39 (8%) patients with myelodysplastic syndromes (MDS), and five of nine (56%) patients with overt leukemia progressed from MDS. These findings suggest that inactivation of the DCC gene contributes to some instances of leukemogenesis.