Involvement of a human endogenous retroviral sequence (THE-7) in a t(7;14)(q21;q32) chromosomal translocation associated with a B cell chronic lymphocytic leukemia

HERVs and Cancer-A Comprehensive Review of the Relationship of Human Endogenous Retroviruses and Human Cancers

Genomic instability and genetic mutations can lead to exhibition of several cancer hallmarks in affected cells such as sustained proliferative signaling, evasion of growth suppression, activated invasion, deregulation of cellular energetics, and avoidance of immune destruction. Similar biological changes have been observed to be a result of pathogenic viruses and, in some cases, have been linked to virus-induced cancers. Human endogenous retroviruses (HERVs), once external pathogens, now occupy more than 8% of the human genome, representing the merge of genomic and external factors. In this review, we outline all reported effects of HERVs on cancer development and discuss the HERV targets most suitable for cancer treatments as well as ongoing clinical trials for HERV-targeting drugs. We reviewed all currently available reports of the effects of HERVs on human cancers including solid tumors, lymphomas, and leukemias. Our review highlights the central roles of HERV genes, such as gag, env, pol, np9, and rec in immune regulation, checkpoint blockade, cell differentiation, cell fusion, proliferation, metastasis, and cell transformation. In addition, we summarize the involvement of HERV long terminal repeat (LTR) regions in transcriptional regulation, creation of fusion proteins, expression of long non-coding RNAs (lncRNAs), and promotion of genome instability through recombination.

Acute Myeloid Leukemia With a Rare t(7;14)(q21;q32) and Trisomy 4 With Poor Clinical Outcome: A Case Report

Objectives

Recurrent cytogenetic abnormalities and/or molecular aberrations play an important role in the diagnosis and prognostification of acute myeloid leukemia (AML). We describe a case of a 40 year old woman diagnosed with de novo AML with a novel t(7;14)(q21,q32) and trisomy 4 with poor clinical outcome. Methods: Morphologic, flow cytometry and cytogenetic results of the patient's peripheral blood and bone marrow samples were analyzed.

Results

The diagnostic bone marrow was hypercellular for age (>95%) with increased blasts (62%) that by flow cytometry exhibited myeloid differentiation with a few T/NK lineage markers. Cytogenetics showed a t(7;14)(q21,q32) and trisomy 4. The patient had extremely poor response to two rounds of induction chemotherapy with persistent leukemia following therapy.

Conclusion

To the best of our knowledge, the t(7;14) is a novel cytogenetic abnormality that has not been reported previously in acute myeloid leukemia, and is important to report as it appears to be associated with poor prognosis.

Translocation t(2;7)(p11;q21) associated with the CDK6/IGK rearrangement is a rare but recurrent abnormality in B-cell lymphoproliferative malignancies

Structural abnormalities of chromosome 7q have been regularly reported in chronic B-cell lymphoproliferative disorders. They include chromosomal translocations involving 7q21, leading to overexpression of the CDK6 gene. Three different translocations, t(7;14)(q21;q32), t(7;22)(q21;q11), and t(2;7)(p11;q21), leading to the juxtaposition of the CDK6 gene with a immunoglobulin gene enhancer during B-cell differentiation, have been described. In the past 2 years, we identified three patients with lymphoproliferative malignancy associated with a t(2;7)(p11;q21). Fluorescent in situ hybridization using an IGK probe and a library of bacterial artificial chromosome (BAC) clones located in bands 7q21.2 and 7q21.3, containing CDK6, revealed that the telomeric part of the IGK probe was translocated on the der(7) within a 51-kb region upstream of the transcriptional start site of CDK6. A total of 23 patients with indolent B-cell lymphoproliferative disorders and juxtaposition of the IG and CDK6 genes, including 20 with IGK and CDK6 juxtaposition, have been reported thus far. This rearrangement leads to the overexpression of CDK6, which encodes a cyclin-dependent protein kinase involved in cell cycle G1 phase progression and G1/S transition.

Clinicopathologic features of CDK6 translocation-associated B-cell lymphoproliferative disorders

Cyclin-dependent protein kinase 6 (CDK6), in cooperation with cyclin Ds, drives cell cycle progression from G1 to S phase through phosphorylation and subsequent inactivation of retinoblastoma 1 protein. Alteration of this pathway results in both nonhematologic and hematologic malignancies, which include a small subset of B-cell lymphoproliferative disorders (BLPDs). We identified 5 cases of BLPD that carried CDK6 chromosomal translocations and characterized their clinical, pathologic, immunophenotypic, and genetic features. Common clinical characteristics included marked neoplastic lymphocytosis, systemic lymphadenopathy, splenomegaly, and bone marrow involvement. Three patients were diagnosed with low-grade B-cell lymphoma and had an indolent clinical course, and 2 patients (one who transformed to large B-cell lymphoma, and the other who was initially diagnosed with a high-grade B-cell lymphoma) had an aggressive clinical course. Immunophenotypically, the neoplastic B cells expressed CD5, CDK6, and cytoplasmic retinoblastoma 1 protein in all cases, expressed phospho-RB, p27kip1, and cyclin D2 in most cases, and uniformly lacked expression of all other cyclins. In 4 cases, the CDK6 translocation partner was kappa immunoglobulin light-chain gene; and in the fifth case, the CDK6 translocation partner was unknown. These distinct clinicopathologic and cytogenetic features distinguish the CDK6 translocation-associated BLPDs (CDK6-BLPDs) from other mature B-cell lymphomas.

Cell kinetics and cell cycle regulation in lymphomas

The proliferative indices of non-Hodgkin's lymphomas are useful prognostic indicators and provide information independent of other histological and clinical variables. However, proliferative indices alone do not suffice to characterise cell growth. A high cell production rate may be compensated, almost or fully, by a high cell deletion rate. A re-evaluation of parameters of cell kinetics in view of our increasing knowledge of the molecular pathways of cell cycle control may provide more prognostic information for the management of patients with malignant lymphomas.

Expression of a human endogenous retrovirus, HERV-K, in the blood cells of leukemia patients

Human endogenous retroviral sequences (HERVs) are believed to be possible pathogenic agents in carcinogenesis. HERV-K is the most biologically active form, since members of this family have intact open reading frames for the gag, pol or env genes. Antibody response against HERV-K peptides has been reported in leukemia patients, suggesting a possible overexpression of this sequence in leukemic cells. Using real-time quantitative RT-PCR (TaqMan), we found that in six of the eight leukemia samples we collected, transcriptional activity of HERV-K10-like gag gene was 5- to 10-fold higher than in normal peripheral blood mononuclear cells (PBMCs) or mononuclear cells from cord blood. The overexpression was marked enough to be detected by Northern blot. In addition, there was no significant variation of HERV-K expression in normal PBMCs after exposure to different factors (PHA, gamma irradiation, 5-azacytidine) that potentially modulate HERV expression. This suggests that HERV-K relative overexpression in leukemia samples might be specifically associated with tumor development. The origin of these transcriptional variations is therefore worth being investigated further.

Coding region of the sorbin gene in different species

The coding region of 153 amino-acid sorbin, isolated from porcine intestine has been cloned and sequenced in pig, human and rat. The coding region includes 459 bases comprising the 5' region of 24 bases, the middle region named "sorbin-like sequence" (25-432) and the 3' region (433-459). The peptidic C-terminal segment presents the biological activity: absorption of water and electrolytes from the intestine and gall-bladder. The cDNA homology between the three species was 95%. Three forms of mRNA were found, two major forms (6.5 and 8 Kb) and one minor (4.5 Kb).

Cyclin D3 is a target gene of t(6;14)(p21.1;q32.3) of mature B-cell malignancies

Chromosomal translocation t(6;14)(p21.1;q32.3) has been reported as a rare but recurrent event not only in myeloma and plasma cell leukemia but also in diffuse large B-cell non-Hodgkin lymphoma (B-NHL) (diffuse large B-cell lymphoma [DLBCL]) and splenic lymphoma with villous lymphocytes (SLVL); however, the nature of the target gene(s) has not been determined. This study identified t(6;14)(p21.1;q32.3) in 3 cases of transformed extranodal marginal zone B-NHL, in 1 case of SLVL, and in 1 case of a low-grade B-cell lymphoproliferative disorder. In a sixth case, a CD5(+) DLBCL, the translocation was identified by molecular cloning in the absence of cytogenetically detectable change. Two chromosomal translocation breakpoints were cloned by using long-distance inverse polymerase chain reaction methods. Comparison with the genomic sequence for chromosome 6p21.1 showed breakpoints approximately 59 and 73.5 kilobases 5' of the cyclin D3 (CCND3) gene with no other identifiable transcribed sequences in the intervening region. Although Southern blotting with derived genomic 6p21.1 probes failed to detect other rearrangements, fluorescent in situ hybridization assays, using BAC (bacterial artificial chromosome) clones spanning and flanking the CCND3 locus, along with probes for IGH confirmed localization of 6p21.1 breakpoints within the same region, as well as fusion of the CCND3 and IGH loci. Furthermore, in all cases, high-level expression of CCND3 was demonstrated at RNA and/or protein levels by Northern and Western blotting and by immunohistochemistry. These data implicate CCND3 as a dominant oncogene in the pathogenesis and transformation in several histologic subtypes of mature B-cell malignancies with t(6;14)(p21.1;q32.3) and suggest that CCND3 overexpression seen in about 10% of DLBCL cases may have a genetic basis.

Multiple sclerosis retrovirus particles and recombinant envelope trigger an abnormal immune response in vitro, by inducing polyclonal Vbeta16 T-lymphocyte activation

A retroviral element (MSRV) defining a family of genetically inherited endogenous retroviruses (HERV-W) has recently been characterized in cell cultures from patients with multiple sclerosis (MS). To address the possible relationship with MS, direct detection of circulating virion RNA was proposed but revealed technically difficult to perform in standardized conditions, in the face of multiple endogenous HERV-W copies. A parallel approach has evaluated MSRV potential pathogenicity in relation to characteristic features of multiple sclerosis, in particular, T-lymphocyte-mediated immunopathology. We report here that MSRV particles induce T-lymphocyte response with a bias in the Vbeta16 chain usage in surface receptor, whatever the HLA DR of the donor. A recombinant MSRV envelope-but not core-protein reproduced similar nonconventional activation. Molecular analysis of Vbeta CDR3 showed that Vbeta16 expansions are polyclonal. Our results thus provide evidence that MSRV envelope protein can trigger an abnormal immune response with similar characteristics to that of superantigens.

Dysregulation of cyclin dependent kinase 6 expression in splenic marginal zone lymphoma through chromosome 7q translocations

The increased or inappropriate expression of genes with oncogenic properties through specific chromosome translocations is an important event in the pathogenesis of B-cell lymphoproliferative diseases. Recent studies have found deletions or translocations of chromosome 7q to be the most common cytogenetic abnormality observed in SLVL, a leukemic variant of SMZL, with the q21-q22 region being most frequently affected. In three patients with translocations between chromosomes 2 and 7, the cloning of the breakpoints at 7q21 revealed that each was located within a small region of DNA 3.6 kb upstream of the transcription start site of cyclin dependent kinase 6 (CDK6). In each case the translocation event was consistent with aberrant VJ recombination between the immunoglobulin light chain region (Ig kappa) on chromosome 2p12 and DNA sequences at 7q21, resembling the heptamer recombination site. The t(7;21) breakpoint in an additional patient with splenic marginal zone lymphoma (SMZL), resided 66 kb telomeric to the t(2;7) breakpoints juxtaposing CDK6 to an uncharacterized transcript. In two of the SLVL patient samples, the CDK6 protein was found to be markedly over expressed. These results suggest that dysregulation of CDK6 gene expression contributes to the pathogenesis of SLVL and SMZL.

A novel B-CLL specific nuclear protein (p44/46)

Our previous results indicated some diversities in electrophoretic patterns of proteins from different cellular fractions, i.e. nuclear, mitochondrial, microsomal and cytosolic isolated from mononuclear cells from the peripheral blood of B cell chronic lymphocytic leukemia (B-CLL) patients and healthy donors. Major differences were observed in electrophoretic banding of nuclear proteins from normal and transformed cells, especially in molecular mass region of 37 52 kDa. Electrophoretically-specific nuclear protein with molecular mass of 44/46 kDa of cells originating from B-CLL patients was used for raising polyclonal antiserum. As it was determined by Western blot technique (with alkaline phosphatase) obtained antiserum recognized 44/46 kDa antigen of nuclear fraction from B-CLL and acute lymphoblastic leukemia (ALL) cells, but not from normal ones. Our preliminary data were revealed that this antiserum shows no crossreactivity with leukemic nuclear proteins of patients with T cell chronic lymphocytic leukemia (T-CLL) and neither with nuclear polypeptides from either normal or cancerous (adenocarcinoma) stomach and colon mucosa. Immunological analysis was shown that higher expression of this particular antigen seems to correlate with progression of B-CLL.