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

Oncogenic and tumor suppressor genes expression in myeloproliferative neoplasms: The hidden side of a complex pathology

Background

The present study aimed to explore the changes in the expressions of six tumor‐related genes in myeloproliferative neoplasms (MPNs). The study population included 130 patients with MPNs (52 with chronic myeloid leukemia (CML), 49 with essential thrombocythemia (ET), 20 with polycythemia vera (PV), and 9 with primary myelofibrosis (PMF)) and 51 healthy individuals.

Methods

The expression profiling of six genes (ADAMTS18, CMTM5, CDKN2B, DCC, FHIT, and WNT5B) in the peripheral blood granulocyte cells was explored by real‐time quantitative reverse transcription polymerase chain reaction.

Results

The patients with MPNs showed significant downregulation of CMTM5 (EFC = 0.66) and DCC (EFC = 0.65) genes in contrast to a non‐significant upregulation of ADAMTS18, CDKN2B, FHIT, and WNT5B genes. Downregulation of DCC was consistent in all subtypes of MPN (EFC range: 0.591–0.860). However, CMTM5 had a 1.22‐fold upregulation in PMF in contrast to downregulation in other MPN subtypes (EFC range: 0.599–0.775). The results revealed a significant downregulation in CMTM5 and DCC at below 60‐years of age. Furthermore, female patients showed a clear‐cut downregulation in both CMTM5 and DCC (EFC DCC: 0.436 and CMTM5: 0.570), while male patients presented a less prominent downregulation with a borderline p‐value only in DCC (EFC: 0.69; p = 0.05).

Conclusions

Chronic myeloid leukemia cases showed a significant upregulation of WNT5B, as a known oncogenesis gene. Two tumor suppressor genes, namely DCC and CMTM5, were downregulated in the patients with MPNs, especially in females and patients below 60 years of age.

Locally disordered methylation forms the basis of intratumor methylome variation in chronic lymphocytic leukemia

Intratumoral heterogeneity plays a critical role in tumor evolution. To define the contribution of DNA methylation to heterogeneity within tumors, we performed genome-scale bisulfite sequencing of 104 primary chronic lymphocytic leukemias (CLLs). Compared with 26 normal B cell samples, CLLs consistently displayed higher intrasample variability of DNA methylation patterns across the genome, which appears to arise from stochastically disordered methylation in malignant cells. Transcriptome analysis of bulk and single CLL cells revealed that methylation disorder was linked to low-level expression. Disordered methylation was further associated with adverse clinical outcome. We therefore propose that disordered methylation plays a similar role to that of genetic instability, enhancing the ability of cancer cells to search for superior evolutionary trajectories.

Novel oncogene amplifications in tumors from a family with Li-Fraumeni syndrome

Li-Fraumeni syndrome (LFS) represents an inherited tumor syndrome that is typically caused by germline mutations of the tumor suppressor gene TP53. TP53 dysfunction secondarily disturbs the genetic integrity of the cell. Here, we report a family with LFS harboring a germline TP53 mutation (R248W) located in the functional domain of the protein that binds to the minor groove of the DNA. In this family, tumors of the central nervous system were diagnosed as primary malignancies in all carriers of the mutation. The index patient developed an anaplastic medulloblastoma with unusual genomic profile exhibiting six distinct high-level genomic amplifications, two of them targeting the MYCN and GLI2 genes, respectively. In an extrarenal rhabdoid tumor from the same patient, we found a novel high-level amplification of the MYC oncogene. The father of this patient was diagnosed with myxopapillary ependymoma (WHO degrees I), whereas a brother died from an early relapse of a choroid plexus carcinoma. The analysis of this LFS familiy thus revealed novel oncogene amplifications as different second hits that are likely to also play a role in the pathogenesis of their sporadic counterparts.

TGFbetaR2 aberrant methylation is a potential prognostic marker and therapeutic target in multiple myeloma

Multiple myeloma (MM) is an incurable hematological malignancy. Different studies demonstrated the occurrence of genetic and epigenetic alterations in MM. The aberrant methylation is one of the most frequent epigenetic alterations in human genome. This study evaluated the aberrant methylation status of 20 genes in 51 MM samples by quantitative methylation-specific PCR (QMSP) and compared the methylation profile with clinicopathological characteristics of the patients. The QMSP analyses showed that PTGS2 (100.0%), SFN (100.0%), CDKN2B (90.2%), CDH1 (88.2%), ESR1 (72.5%), HIC1 (70.5%), CCND2 (62.7%), DCC (45.1%) and TGFbetaR2 (39.2%) are frequently hypermethylated in MM while aberrant methylation of RARbeta (16.6%), MGMT (12.5%), AIM1 (12.5%), CDKN2A (8.3%), SOCS1 (8.3%), CCNA1 (8.3%) and THBS1 (4.1%) are rare events. There was no methylation of GSTP1, MINT31, p14ARF and RB1 in the samples tested. Hypermethylation of ESR1 was correlated positively with isotype IgA, while aberrant methylation of THBS1 correlated negatively with isotype IgG. Furthermore, hypermethylation of DCC and TGFbetaR2 were correlated with poor survival. The multivariate analysis showed ISS and TGFbetaR2 hypermethylation strongly correlated with poor outcome. This study represents the first quantitative evaluation of promoter methylation in MM and our data provide evidence that TGFbetaR2 hypermethylation, besides ISS, may be useful as prognostic indicator in this disease.

Multistep pathogenesis of leukemia via the MLL-AF4 chimeric gene/Flt3 gene tyrosine kinase domain (TKD) mutation-related enhancement of S100A6 expression

OBJECTIVE

Concerning MLL-AF4 leukemogenesis, previous mouse models suggest that the tumorigenesis capacity of MLL-AF4 alone is insufficient for causing leukemia. Based on the finding that an Fms-like tyrosine kinase 3 (Flt3) gene mutation in the tyrosine kinase domain (TKD) was observed in approximately 15% of mixed lineage leukemia (MLL), we investigated synergistic leukemogenesis effects of the two genes in vitro.

MATERIALS AND METHODS

In a mouse interleukin-3 (IL-3)-dependent cell line, 32Dc, expression of MLL-AF4 and mutant Flt3 was induced using a lentiviral vector. We analyzed apoptosis induction in the absence of IL-3 and the granulocyte colony-stimulating factor-related induction of differentiation, gene expression profiling, and the mechanism involved in the synergistic effects of MLL-AF4 and Flt3-TKD.

RESULTS

Neither Flt3-expressing 32Dc (32Dc(Flt3-TKD)) nor MLL-AF4-expressing 32Dc (32Dc(MLL-AF4)) acquired IL-3-independent proliferative capacity in semisolid/liquid media. However, Flt3-TKD+MLL-AF4-expressing 32Dc (32Dc(Flt3-TKD+MLL-AF4)) acquired a non-IL-3-dependent proliferative capacity by inhibiting apoptosis in the two media. The 32Dc(Flt3-TKD) and 32Dc(MLL-AF4) cells differentiated into granulocytes in the presence of granulocyte colony-stimulating factor. However, in the 32Dc(Flt3-TKD+MLL-AF4) cells, there was no differentiation. Subsequently, we performed gene expression profiling. The enhancement of Hox genes expression was not identified. However, expression of S100A6 was synergistically enhanced in the presence of both MLL-AF4 and Flt3-TKD genes. Moreover, anti-S100A6 small interfering RNA downregulated leukemic proliferation.

CONCLUSION

We conclude that their synergistic enhancement of S100A6 expression plays an important role in MLL-AF4-associated leukemogenesis.

Myeloproliferative disease in transgenic mice expressing P230 Bcr/Abl: longer disease latency, thrombocytosis, and mild leukocytosis

P230 Bcr/Abl has been associated with indolent myeloproliferative disease (MPD). We generated transgenic mice expressing P230Bcr/Abl driven by the promoter of the long terminal repeat of the murine stem cell virus of the MSCV neo P230 BCR/ABL vector. Two founder mice exhibited mild granulocytosis and marked thrombocytosis and developed MPD. The disease of one founder mouse, no. 13, progressed to extramedullary myeloblastic crisis in the liver at 12 months old. The other founder mouse, no. 22, was found to have chronic-phase MPD with large populations of megakaryocytes and granulocytes in an enlarged spleen. The transgenic progeny of no. 22 clearly exhibited MPD at 15 months old. These results showed that P230Bcr/Abl had leukemogenic properties and induced MPD. The phenotype of the MPD caused by P230Bcr/Abl was characterized by mild granulocytosis, a high platelet count, infiltration of megakaryocytes in some organs, and a longer disease latency compared with the MPD caused by P210Bcr/Abl.

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.

Abnormality of c-kit oncoprotein in certain patients with chronic myelogenous leukemia--potential clinical significance

Chronic myelogenous leukemia (CML) is characterized by the Philadelphia (Ph) chromosome and bcr/abl gene rearrangement which occurs in pluripotent hematopoietic progenitor cells expressing the c-kit receptor tyrosine kinase (KIT). To elucidate the biological properties of KIT in CML leukemogenesis, we performed analysis of alterations of the c-kit gene and functional analysis of altered KIT proteins. Gene alterations in the c-kit juxtamembrane domain of 80 CML cases were analyzed by reverse transcriptase and polymerase chain reaction-single strand conformation polymorphism (RT-PCR-SSCP). One case had an abnormality at codon 564 (AAT --> AAG, Asn --> Lys), and six cases had the same base abnormality at codon 541 (ATG --> CTG, Met --> Leu) in the juxtamembrane domain. Because the change from Met to Leu at codon 541 was a conservative one which was also observed in the normal population and normal tissues of CML patients, it probably represents a polymorphic variation. Although samples of hair roots and leukemic cells from the chronic phase of one CML patient showed no abnormality, an abnormality at codon 541 (ATG --> CTG, Met --> Leu) was found only at blastic crisis (BC) of this case. In the case with the abnormality at codon 564, the mutation was detected only in a sample of leukemic cells collected at BC. To examine the biological consequence and biological significance of these abnormalities, murine KIT(L540) and KIT(K563) expression vectors were introduced into interleukin-3 (IL-3)-dependent murine Ba/F3 cells to study their state of tyrosine phosphorylation and their growth rate. Ba/F3 cells expressing KIT(WT), KIT(L540) and KIT(K563) showed dose-dependent tyrosine phosphorylation after treatment with increasing concentrations of recombinant mouse stem cell factor (rmSCF). The cells expressing KIT(L540) and KIT(K563) were found to have greater tyrosine phosphorylation than cells expressing KIT(WT) at 0.1 and 1.0 ng/ml of rmSCF. The Ba/F3 cells expressing KIT(K563) proliferated in response to 0.1 and 1.0 ng/ml of rmSCF as well as IL-3. The Ba/F3 cells expressing KIT(L540)showed a relatively higher proliferative response to 0.1 ng/ml of rmSCF than the response of cells expressing KIT(WT). These mutations and in vitro functional analyses raise the possibility that the KIT abnormalities influence the white blood cell counts (P < 0.05) and survival (P < 0.04) of CML patients.

Philadelphia chromosome-positive acute myeloid leukemia with tetraploidy

The patient was a 62-year-old man. His hematological data in April 2000 had shown no abnormalities, but he was referred to our hospital because of a fever and leukocytosis in June 2000. The peripheral blood showed 29.8 x 10(9)/L white blood cells, with 68.0% blasts. A bone marrow aspirate showed hypercellularity with a proliferation of large leukemic blasts. The leukemic cells were positive for CD13 (91%), CD33 (54.8%), CD34 (94.5%), and HLA-DR (97.9%). Some leukemic cells (15.6%) also expressed CD14. Cytogenetic analysis revealed 92,XXYY,t(9;22)(q34;q11)x2 in all 20 metaphase cells. Reverse transcriptase polymerase chain reaction analysis detected the minor BCR/ABL messenger RNA (mRNA) but failed to detect the major BCR/ABL mRNA. The patient achieved complete remission after induction chemotherapy, with no evidence of Philadelphia chromosome (Ph) or minor BCR/ABL mRNA. Ph-positive acute myeloid leukemia (Ph-AML) has rarely been reported. Herein, we report a case of Ph-AML with tetraploidy and review the previously reported Ph-AML cases.

[Abnormalities of the p53, N-ras, DCC and FLT-3 genes in myelodysplastic syndromes]

The molecular mechanism of carcinogenesis is a multistep process that is characterized by both activation of oncogenes and inactivation of tumor suppressor genes. In the present study, mutations of N-ras, p53 and FMS-like tyrosine kinase 3 (FLT-3) genes and loss of expression of the deleted in colorectal carcinoma (DCC) gene were analyzed in 59 patients with myelodysplastic syndromes (MDS). Mutations of N-ras, p53, and FLT-3 genes were detected in 7, 7, 1 of the 59 patients with MDS, respectively. Loss of DCC expression was detected in 16 patients. Type of MDS patients with N-ras mutation were all refractory anemia with excess of blasts in transformation (RAEB-T). Abnormalities of p53 and DCC genes were significantly associated with survival time (p< 0.02, p< 0.004, respectively).

Establishment of a near-triploid human B-cell lymphoma cell line with t(14;18) and a p53 gene point mutation

We report a rare large B-cell non-Hodgkin's lymphoma having a characteristic near-triploid cell population with add(17)(p22) and t(14;18)(q32;q21) translocation. We also established and characterized a new cell line (TK cell) derived from the present lymphoma. A codon 180 mutation (GAG --> GAT) in the p53 gene was detected. t(14;18)(q32;q21) was revealed juxtaposition of the bcl-2 and JH genes. Immunoprecipitation analyses of p53 and bcl-2 revealed that abnormality of the p53 protein and aberrant bcl-2 expression, which may protect cells from apoptosis, may be critical to the development of leukaemogenesis exhibiting near-triploid chromosomes.

Establishment of a cell line with variant BCR/ABL breakpoint expressing P180BCR/ABL from late-appearing Philadelphia-positive acute biphenotypic leukemia

In acute leukemia (AL) with a late-appearing Philadelphia (la-Ph) translocation, it is unclear whether these translocations arise from the same molecular event as classical Ph translocations. In order to elucidate the molecular events of la-Ph and subsequent translocations of la-Ph leukemia, we performed molecular analysis on the complex rearrangements, in a cell line, MY, which was established from bone marrow mononuclear cells of a patient with a la-Ph acute biphenotypic leukemia. This la-Ph, expressing an acute lymphoblastic leukemia (ALL)-type BCR/ABL transcript, produces a novel P180BCR/ABL fusion protein reflecting deletion of 174 bases (58 amino acids) encoded by the a2 exon of the ABL gene. An immune complex kinase assay showed that this protein had autophosphorylation activity. Fluorescence in situ hybridization (FISH) in conjunction with G-banding analysis revealed that the initial der(9)t(9;22)(q34;q11) progressed to a der(9)(9pter-->9q34::22q11-->22q13::5q11.2 -->5q15:: 10q23-->10qter) by, first, a three-way translocation among the der(9)t(9;22)(q34;q11), chromosome 5, and the normal chromosome 22, and then a subsequent translocation with chromosome 10. Moreover, both the end-stage leukemic cells of the patient and the MY cell line had another translocation, t(X;12)(p11.2;p13). The 12p breakpoint was located near the ETV6 gene by analysis of pulsed-field gel electrophoresis, but transcription of ETV6 was unaffected. Tumorigenicity analysis indicated that an additional translocation, t(2;3)(p16;q29), may have caused a more malignant clone, because only MY cells with the t(2;3)(p16;q29) were capable of growing subcutaneously in nude mice within 40 days. The molecular events of leukemogenesis and leukemic progression in the present la-Ph AL occurred by accumulation of unique translocations. This cell line, MY, expressing a novel variant P180BCR/ABL protein with a deletion of the a2 exon of the ABL gene, may be useful for elucidating the pathophysiology of this fusion protein and for studying ETV6-related leukemogenesis and t(2;3), as well as the molecular mechanisms of the complex translocations.

Reduced expression of deleted colorectal carcinoma (DCC) protein in established colon cancers

Using a bacterial fusion protein, a deleted colorectal carcinoma (DCC)-specific monoclonal antibody (MAb) 127-22 was established. Although MAb 127-22 reacted with almost all normal tissues, it did not react or only weakly reacted with many cancer cell lines, including colonic cancer lines, in flow cytometry. In Western immunoblots, the MAb reacted with a single 190-kDa molecule in a myeloma line Ara-10 extract. This component was scarcely detected in colonic cancer cell lines. Immunoblots of samples from 25 pairs of colonic cancers and adjacent normal tissues and from five adenoma tissues revealed that all normal colonic and adenoma tissues significantly expressed the DCC protein, whereas colonic cancer tissues showed poor expression. These results indicate not only deletion of and lowered mRNA expression of the DCC gene, but also marked reduction of DCC protein occurred in colonic cancer tissues. In addition, colonic cancer patients with liver metastasis expressed significantly lower levels of DCC than those without, suggesting the prognostic value of DCC expression.