Identification of two distinct regions of deletion at 6q in gastric carcinoma

The Potential Role of the T2 Ribonucleases in TME-Based Cancer Therapy

In recent years, there has been a growing interest in developing innovative anticancer therapies targeting the tumor microenvironment (TME). The TME is a complex and dynamic milieu surrounding the tumor mass, consisting of various cellular and molecular components, including those from the host organism, endowed with the ability to significantly influence cancer development and progression. Processes such as angiogenesis, immune evasion, and metastasis are crucial targets in the search for novel anticancer drugs. Thus, identifying molecules with "multi-tasking" properties that can counteract cancer cell growth at multiple levels represents a relevant but still unmet clinical need. Extensive research over the past two decades has revealed a consistent anticancer activity for several members of the T2 ribonuclease family, found in evolutionarily distant species. Initially, it was believed that T2 ribonucleases mainly acted as anticancer agents in a cell-autonomous manner. However, further investigation uncovered a complex and independent mechanism of action that operates at a non-cell-autonomous level, affecting crucial processes in TME-induced tumor growth, such as angiogenesis, evasion of immune surveillance, and immune cell polarization. Here, we review and discuss the remarkable properties of ribonucleases from the T2 family in the context of "multilevel" oncosuppression acting on the TME.

Decreased expression of the long non-coding RNA MLLT4 antisense RNA 1 is a potential biomarker and an indicator of a poor prognosis for gastric cancer

In recent years, the identification of long non-coding RNAs (lncRNAs) led to the analysis of their characteristics in cancer biology. However, the expression of lncRNAs in cancer and their clinical significance remain unclear. In the present study, an investigation of lncRNAs that may be involved in the regulation of metastasis using microarray and polymerase chain reaction analyses resulted in the identification of MLLT4 antisense RNA 1 (MLLT4-AS1) as a significantly downregulated lncRNA in gastric cancer tissue compared with normal adjacent tissue (P=0.006). Furthermore, the downregulation of MLL4-AS1 was significantly associated with advanced Tumor-Node-Metastasis stage (P=0.007) and lymph node metastasis (P=0.008). Cox regression analysis showed that MLLT4-AS1 expression was an independent predictor for overall survival (hazard ratio, 13.136; 95% confidence interval, 5.065–34.068; P<0.001). These data suggest that the decreased expression of MLLT4-AS1 is a potential biomarker and a predictor of a poor prognosis for gastric cancer.

SOD2 targeted gene editing by CRISPR/Cas9 yields Human cells devoid of MnSOD

To date no models exist to study MnSOD deficiency in human cells. To address this deficiency, we created a SOD2-null human cell line that is completely devoid of detectable MnSOD protein expression and enzyme activity. We utilized the CRISPR/Cas9 system to generate biallelic SOD2 disruption in HEK293T cells. These SOD2-null cells exhibit impaired clonogenic activity, which was rescued by either treatment with GC4419, a pharmacological small-molecule mimic of SOD, or growth in hypoxia. The phenotype of these cells is primarily characterized by impaired mitochondrial bioenergetics. The SOD2-null cells displayed perturbations in their mitochondrial ultrastructure and preferred glycolysis as opposed to oxidative phosphorylation to generate ATP. The activities of mitochondrial complex I and II were both significantly impaired by the absence of MnSOD activity, presumably from disruption of the Fe/S centers in NADH dehydrogenase and succinate dehydrogenase subunit B by the aberrant redox state in the mitochondrial matrix of SOD2-null cells. By creating this model we provide a novel tool with which to study the consequences of lack of MnSOD activity in human cells.

Decreased expression of prenyl diphosphate synthase subunit 2 correlates with reduced survival of patients with gastric cancer

BACKGROUND

Identification of novel molecular biomarkers will improve the management of patients with gastric cancer (GC). Prenyl diphosphate synthase subunit 2 (PDSS2) is required for coenzyme Q10 biosynthesis and acts as a tumor suppressor; however, the role and regulatory mechanisms of PDSS2 in GC are not understood. The aim of this study was to determine expression status and regulatory mechanisms of PDSS2 in GC.

METHODS

Associations between expression and methylation of PDSS2 were evaluated using GC cell lines. The clinical significance of PDSS2 expression was evaluated using 238 pairs of surgically resected gastric tissues with subgroup analysis based on GC subtypes.

RESULTS

The expression of PDSS2 mRNA was decreased in 73% of GC cell lines compared with the control non-cancerous cell. The PDSS2 promoter was hypermethylated in cells with decreased PDSS2 expression, and treating these cells with a methylation inhibitor reactivated PDSS2 expression. GC tissues expressed significantly lower mean levels of PDSS2 mRNA compared with adjacent normal tissues (P <0.001). The expression pattern of PDSS2 protein was consistent with that of its mRNA. The decrease of PDSS2 mRNA expression in GC tissues (less than half the level of expression detected in the corresponding normal adjacent tissues) correlated significantly with elevated levels of carbohydrate antigen 19-9 (P = 0.015), lymph node metastasis (P = 0.022), and shorter recurrence-free survival after curative resection (P = 0.022). Further, multivariate analysis identified PDSS2 mRNA expression as an independent prognostic factor (hazard ratio 1.95, 95% confidence interval 1.22-3.09, P = 0.005), and its expression pattern and prognostic significance were similar among three GC subtypes.

CONCLUSIONS

PDSS2 encodes a putative tumor suppressor, and we show here that its expression was regulated by hypermethylation of its promoter in GC cells. Inhibition of PDSS2 mRNA expression may serve as a novel biomarker of all types of GC.

Decreased expression of prenyl diphosphate synthase subunit 2 correlates with reduced survival of patients with gastric cancer

BACKGROUND

Identification of novel molecular biomarkers will improve the management of patients with gastric cancer (GC). Prenyl diphosphate synthase subunit 2 (PDSS2) is required for coenzyme Q10 biosynthesis and acts as a tumor suppressor; however, the role and regulatory mechanisms of PDSS2 in GC are not understood. The aim of this study was to determine expression status and regulatory mechanisms of PDSS2 in GC.

METHODS

Associations between expression and methylation of PDSS2 were evaluated using GC cell lines. The clinical significance of PDSS2 expression was evaluated using 238 pairs of surgically resected gastric tissues with subgroup analysis based on GC subtypes.

RESULTS

The expression of PDSS2 mRNA was decreased in 73% of GC cell lines compared with the control non-cancerous cell. The PDSS2 promoter was hypermethylated in cells with decreased PDSS2 expression, and treating these cells with a methylation inhibitor reactivated PDSS2 expression. GC tissues expressed significantly lower mean levels of PDSS2 mRNA compared with adjacent normal tissues (P <0.001). The expression pattern of PDSS2 protein was consistent with that of its mRNA. The decrease of PDSS2 mRNA expression in GC tissues (less than half the level of expression detected in the corresponding normal adjacent tissues) correlated significantly with elevated levels of carbohydrate antigen 19-9 (P = 0.015), lymph node metastasis (P = 0.022), and shorter recurrence-free survival after curative resection (P = 0.022). Further, multivariate analysis identified PDSS2 mRNA expression as an independent prognostic factor (hazard ratio 1.95, 95% confidence interval 1.22-3.09, P = 0.005), and its expression pattern and prognostic significance were similar among three GC subtypes.

CONCLUSIONS

PDSS2 encodes a putative tumor suppressor, and we show here that its expression was regulated by hypermethylation of its promoter in GC cells. Inhibition of PDSS2 mRNA expression may serve as a novel biomarker of all types of GC.

Downregulation of tumor suppressor QKI in gastric cancer and its implication in cancer prognosis

Gastric cancer (GC) is the fourth most common cancer and second leading cause of cancer-related death worldwide. RNA-binding protein Quaking (QKI) is a newly identified tumor suppressor in multiple cancers, while its role in GC is largely unknown. Our study here aimed to clarify the relationship between QKI expression with the clinicopathologic characteristics and the prognosis of GC. In the 222 GC patients' specimens, QKI expression was found to be significantly decreased in most of the GC tissues, which was largely due to promoter hypermethylation. QKI overexpression reduced the proliferation ability of GC cell line in vitro study. In addition, the reduced QKI expression correlated well with poor differentiation status, depth of invasion, gastric lymph node metastasis, distant metastasis, advanced TNM stage, and poor survival. Multivariate analysis showed QKI expression was an independent prognostic factor for patient survival.

NMD inhibition fails to identify tumour suppressor genes in microsatellite stable gastric cancer cell lines

Background

Gastric cancers frequently show chromosomal alterations which can cause activation of oncogenes, and/or inactivation of tumour suppressor genes. In gastric cancer several chromosomal regions are described to be frequently lost, but for most of the regions, no tumour suppressor genes have been identified yet. The present study aimed to identify tumour suppressor genes inactivated by nonsense mutation and deletion in gastric cancer by means of GINI (gene identification by nonsense mediated decay inhibition) and whole genome copy number analysis.

Methods

Two non-commercial gastric cancer cell lines, GP202 and IPA220, were transfected with siRNA directed against UPF1, to specifically inhibit the nonsense mediated decay (NMD) pathway, and with siRNA directed against non-specific siRNA duplexes (CVII) as a control. Microarray expression experiments were performed in triplicate on 4 × 44 K Agilent arrays by hybridizing RNA from UPF1-transfected cells against non-specific CVII-transfected cells. In addition, array CGH of the two cell lines was performed on 4 × 44K agilent arrays to obtain the DNA copy number profiles. Mutation analysis of GINI candidates was performed by sequencing.

Results

UPF1 expression was reduced for >70% and >80% in the GP202 and IPA220 gastric cancer cell lines, respectively. Integration of array CGH and microarray expression data provided a list of 134 and 50 candidate genes inactivated by nonsense mutation and deletion for GP202 and IPA220, respectively. We selected 12 candidate genes for mutation analysis. Of these, sequence analysis was performed on 11 genes. One gene, PLA2G4A, showed a silent mutation, and in two genes, CTSA and PTPRJ, missense mutations were detected. No nonsense mutations were detected in any of the 11 genes tested.

Conclusion

Although UPF1 was substantially repressed, thus resulting in the inhibition of the NMD system, we did not find genes inactivated by nonsense mutations. Our results show that the GINI strategy leads to a high number of false positives.

Anticancer activity of PDSS2, prenyl diphosphate synthase, subunit 2, in gastric cancer tissue and the SGC7901 cell line

The aim of this study was to assess whether PDSS2 (prenyl diphosphate synthase, subunit 2), a candidate tumor suppressor protein, has a potential anticancer role in human gastric cancer tissue and the SGC7901 gastric cell line. A PDSS2 eukaryotic expression vector was constructed and introduced into SGC7901 cells. The relationship between PDSS2 expression and cell proliferation, cell cycle distribution, and apoptosis in tumor cells was analyzed by RT-PCR, western blotting, the MTT colorimetric assay, flow cytometry, and immunohistochemistry. Increased exogenous PDSS2 expression in vitro is associated with decreased cellular proliferation of the gastric cancer cell line SGC7901. PDSS2 also induced apoptosis in SGC7901 cells by causing cell cycle arrest in the G0/G1 phase. Moreover, a significantly low expression level of PDSS2 protein was found in gastric cancer. Decreased or absent expression of PDSS2 was showed in the gastric tumor biopsy samples analyzed, correlating with cancer differentiation. PDSS2 has potent anticancer activity in gastric cancer tissues and the SGC7901 cell line and is possibly involved in apoptosis in SGC7901 cells.

DNA copy number profiles of gastric cancer precursor lesions

Background

Chromosomal instability (CIN) is the most prevalent type of genomic instability in gastric tumours, but its role in malignant transformation of the gastric mucosa is still obscure. In the present study, we set out to study whether two morphologically distinct categories of gastric cancer precursor lesions, i.e. intestinal-type and pyloric gland adenomas, would carry different patterns of DNA copy number changes, possibly reflecting distinct genetic pathways of gastric carcinogenesis in these two adenoma types.

Results

Using a 5K BAC array CGH platform, we showed that the most common aberrations shared by the 11 intestinal-type and 10 pyloric gland adenomas were gains of chromosomes 9 (29%), 11q (29%) and 20 (33%), and losses of chromosomes 13q (48%), 6(48%), 5(43%) and 10 (33%). The most frequent aberrations in intestinal-type gastric adenoma were gains on 11q, 9q and 8, and losses on chromosomes 5q, 6, 10 and 13, whereas in pyloric gland gastric adenomas these were gains on chromosome 20 and losses on 5q and 6. However, no significant differences were observed between the two adenoma types.

Conclusion

The results suggest that gains on chromosomes 8, 9q, 11q and 20, and losses on chromosomes 5q, 6, 10 and 13, likely represent early events in gastric carcinogenesis. The phenotypical entities, intestinal-type and pyloric gland adenomas, however, do not differ significantly (P = 0.8) at the level of DNA copy number changes.

WIF1, an inhibitor of the Wnt pathway, is rearranged in salivary gland tumors

Chromosome rearrangements involving 12q13-15 are frequent among several tumors, including pleomorphic adenomas. The common molecular target for these aberrations is the HMGA2 gene, but various fusion partners of HMGA2 have been reported in tumors. Here we report the identification of the WNT inhibitory factor 1 (WIF1) gene as a novel HMGA2 fusion partner in a salivary gland pleomorphic adenoma. In normal salivary gland tissue WIF1 is expressed at a high level and HMGA2 is not expressed. However, in the pleomorphic adenoma expressing the HMGA2/WIF1 fusion transcript, we observed re-expression of HMGA2 wild-type transcripts and very low levels of WIF1 expression. These data suggest a possible synergistic effect between upregulation of HMGA2 and downregulation of WIF1. We screened 13 additional benign and malignant salivary gland tumors and detected WIF1 rearrangement in one out of two carcinomas ex-pleomorphic adenoma analyzed. In this malignant tumor, the rearrangement of one WIF1 allele coexists with loss of the other allele, a classic signature of a tumor suppressor gene. WIF1 is an antagonist of the Wnt signaling pathway, which plays a critical role in human cancer. In transgenic mouse models, Wnt activation leads to a high frequency of benign and malignant salivary gland tumors. To our knowledge, this is the first report suggesting that WIF1 is a recurrent target in human salivary gland oncogenesis and that downregulation of WIF1 plays a role in the development and/or progression of pleomorphic adenomas.

Characterization of RNASET2, the first human member of the Rh/T2/S family of glycoproteins

Ribonucleases are ubiquitous enzymes involved in RNA metabolism and are classified in several families on the basis of their structural, catalytic, and biological properties. Here, we describe characterization of the only human member of the Rh/T2/S family of acid hydrolases so far described, named RNASET2. This protein was previously reported to have an interesting biological function in the control of tumourigenesis and metastatization. We show that RNASET2 is present in multiple forms in human cell lines and mouse tissues, one of which represents the full length, glycosylated and secreted form, while the others are proteolytic products. RNASET2 is endowed with catalytic activity as demonstrated with purified recombinant protein expressed in the Baculovirus Expression Vector System and in a human cell line ectopically expressing various types of constructs. Furthermore, we document for this protein a lysosomal localization as described for other members of the Rh/T2/S family of ribonucleases. The results presented herein represent a further advancement toward the molecular understanding of the tumour suppressive properties of the human RNASET2 protein.

A recombinant human RNASET2 glycoprotein with antitumorigenic and antiangiogenic characteristics

BACKGROUND

Human RNASET2 is a T2-RNase glycoprotein encoded by the RNASET2 gene, which is located on chromosome 6 (6q27). Deletion in 6q27 is associated with several human malignancies.

METHODS

A synthetic RNASET2 gene that was optimized for expression in the yeast Pichia pastoris was designed according to the cDNA sequence and was cloned under the control of the methanol-induced promoter fused to the alpha-mating secretion peptide. The recombinant protein was purified from the culture supernatant of transformed P. pastoris through an affinity Sepharose-concanavalin A column. Actin-binding activity was examined by membrane blotting using monoclonal mouse antiactin immunoglobulin M and by cross-linking in solution to G-actin using 1-[3-(dimethylamino)propyl]-3-ethyl-carboimide methiodide. The antiangiogenic activity of RNASET2 (from 0.5 microM to 10 microM) was assessed by a human umbilical vein endothelial (HUVE) cell assay in the presence of 1 microg/mL angiogenin, basic fibroblast growth factor (bFGF), or recombinant human vascular endothelial growth factor (VEGF). Cell colony formation was examined in human colon HT29 cancer cells to assess the antitumorigenic activity of RNASET2 or the enzymatic-inactivated RNASET2 (EI-RNASET2) (1 microM each). In an athymic mouse xenograft model, LS174T human cancer cells were injected subcutaneously. When tumors were palpable, the mice were treated for 3 weeks with RNASET2 (1 mg/kg), paclitaxel (10 mg/kg or 15 mg/kg), or a combination of the 2 drugs.

RESULTS

The recombinant RNASET2 was identified as a 27-kilodalton glycoprotein that possessed the ability to bind actin in vitro. RNASET2 significantly inhibited clonogenicity in HT29 cells. EI-RNASET2 produced a similar effect, suggesting that its antitumorigenic activity is unrelated to its RNase activity. In HUVE cells, RNASET2 inhibited angiogenin-, bFGF-, and VEGF-induced tube formation in a dose-dependent manner. In athymic mice, RNASET2 inhibited the development of an LS174T-derived xenograft by 40%. A synergistic effect was obtained with combined RNASET2 and paclitaxel treatments.

CONCLUSIONS

The current results suggested that RNASET2 represents a new class of antitumorigenic and antiangiogenic drugs, and the findings of this study emphasize the advantage of using agents like RNASET2 in combined therapy.

Downregulation of KiSS-1 expression is responsible for tumor invasion and worse prognosis in gastric carcinoma

KiSS-1 is a promising candidate tumor-suppressor gene and may play a key role in the metastatic cascade. The expression profile and the role of KiSS-1 in cancer progression are largely unknown in most of the cancers, including gastric cancer. In this study, KiSS-1 expression was evaluated by RNase protection assay and localization was done by in situ hybridization in 40 gastric cancers and their adjacent normal gastric mucosa. For comparison with clinicopathologic characteristics and patient prognosis, all patients were divided into 2 groups having high and low KiSS-1 expression by using the median as the cutoff value of KiSS-1 expression as determined by the RNase protection assay. Gastric cancers with low KiSS-1 had frequent venous invasion, distant metastasis and tumor recurrence. Accordingly, patients with low KiSS-1-expressing tumors had a significantly worse overall and disease-free survival. In multivariate analysis, KiSS-1 became the strongest independent prognostic factor among the conventional prognosticators for gastric cancer patients. Collectively, these findings suggest that KiSS-1 may play a crucial role in gastric cancer invasion and could be a useful target for therapeutic intervention.

Allelic loss of chromosome 6q in gastric carcinoma

Loss of the long arm of chromosome 6 (6q) has frequently been reported in gastric carcinoma, and most gastric cancer patients have evidence of intestinal metaplasia in the stomach. However, the relationship between loss of chromosome 6q and intestinal metaplasia has not been studied. In the first part of the study, we define the critical deletion region of chromosome 6q using loss of heterozygosity technique (LOH). Seventeen microsatellite markers were used to detect loss of heterozygosity (LOH) in 37 microdissected gastric tumors. We also examined intestinal metaplasia (IM) foci of the stomach in the same cancer patient (17 cases). Losses on chromosome 6q were detected in high frequency (51%) by LOH. Two distinct regions of common allelic loss were identified: one centered on the marker D6S300 (at 6q16.1) and the second on D6S446 (at 6q27), with LOH frequency of 36% and 31.3%, respectively. The deletions fall into 2 discrete regions, suggesting the existence of at least 2 tumor suppressor genes in 6q. The losses at 6q27 were confirmed by fluorescence in situ hybridization study (FISH). In the cases with LOH in the tumor, no LOH were detected in the autologous IM areas, but losses were detected by FISH. In some cases, these genetic changes may be acquired in the transition from normal gastric mucosa to intestinal metaplasia.

Immunohistochemical expression of Fhit protein in Helicobacter pylori related chronic gastritis, gastric precancerous lesions and gastric carcinoma: correlation with conventional clinicopathologic parameters

OBJECTIVE

Our purpose was to investigate the immunohistochemical expression of Fhit protein in chronic Helicobacter pylori related gastritides, gastric epithelial dysplasia and gastric carcinoma.

DESIGN

Because a subset of chronic H. pylori related gastritides, precancerous lesions and gastric tumours were found to be either entirely negative or to minimally express Fhit protein, it is suggested that alteration of the carcinogen susceptible fragile region within the FHIT gene is an early event in a subset of gastric adenocarcinomas.

METHODS

We carried out immunohistochemical tests on archived material of formalin fixed, paraffin embedded tissues, using the anti-FHIT antibody and the streptavidin-biotin-peroxidase method, in a total of 135 gastric lesions (76 biopsies and 59 surgically resected gastric adenocarcinomas).

RESULTS

In this study, 79% of H. pylori related gastritides showed that the Fhit protein was either completely absent or there was a marked reduction of immunostaining. Similar results were obtained for 76.4% of cases of chronic gastritides with low and high-grade dysplasia, and 56% of gastric adenocarcinomas. A negative result for Fhit protein immunostaining was strongly associated with H. pylori infection (P = 0.0001) and with epithelial dysplasia (P = 0.01) but not with intestinal metaplasia or degree of activity. Additionally, negative or reduced immunostaining for Fhit was associated with the degree of dysplasia and progress of a subset of these lesions to infiltrating adenocarcinoma (P = 0.02). In gastric adenocarcinomas negative or weak immunostaining of the Fhit protein correlated with the histological grade (P = 0.01) and clinical stage of the disease (P = 0.01).

CONCLUSIONS

Our results suggest that, because Fhit protein immunostaining is completely absent in (1) the majority of H. pylori related chronic gastritides, (2) a subset of gastric dysplastic lesions, and (3) a proportion of primary gastric adenocarcinomas, irrespective of histological type, it can play an important role in the early development and progression of some gastric cancers.

Cloning and characterization of the common fragile site FRA6F harboring a replicative senescence gene and frequently deleted in human tumors

The common fragile site FRA6F, located at 6q21, is an extended region of about 1200 kb, with two hot spots of breakage each spanning about 200 kb. Transcription mapping of the FRA6F region identified 19 known genes, 10 within the FRA6F interval and nine in a proximal or distal position. The nucleotide sequence of FRA6F is rich in repetitive elements (LINE1 and LINE2, Alu, MIR, MER and endogenous retroviral sequences) as well as in matrix attachment regions (MARs), and shows several DNA segments with increased helix flexibility. We found that tight clusters of stem-loop structures were localized exclusively in the two regions with greater frequency of breakage. Chromosomal instability at FRA6F probably depends on a complex interaction of different factors, involving regions of greater DNA flexibility and MARs. We propose an additional mechanism of fragility at FRA6F, based on stem-loop structures which may cause delay or arrest in DNA replication. A senescence gene likely maps within FRA6F, as suggested by detection of deletion and translocation breakpoints involving this fragile site in immortal human-mouse cell hybrids and in SV40-immortalized human fibroblasts containing a human chromosome 6 deleted at q21. Deletion breakpoints within FRA6F are common in several types of human leukemias and solid tumors, suggesting the presence of a tumor suppressor gene in the region. Moreover, a gene associated to hereditary schizophrenia maps within FRA6F. Therefore, FRA6F may represent a landmark for the identification and cloning of genes involved in senescence, leukemia, cancer and schizophrenia.

A zinc-finger protein, PLAGL2, induces the expression of a proapoptotic protein Nip3, leading to cellular apoptosis

Pleomorphic adenomas gene-like 2 (PLAGL2) protein containing seven C(2)H(2) zinc finger motifs exhibits DNA binding and transcriptional activation activity and is expressed in response to hypoxia or iron deficiency. To identify the target genes of PLAGL2, we transfected mouse PLAGL2 cDNA into Balb/c3T3 fibroblasts and neuroblastoma Neuro2a cells. Both cells were induced to undergo apoptosis by the expression of PLAGL2 as judged by assays of TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling), DNA fragmentation, propidium iodide staining, and the binding of annexin V to the cell surface. The treatment of the cells with an iron chelator, desferrioxamine, resulted in the induction of apoptosis with a concomitant accumulation of PLAGL2 in the nucleus. The expression of PLAGL2 in Balb/c3T3 cells led to the mRNA expression of a proapoptotic factor, Nip3, which can dimerize with Bcl-2. Nip3 mRNA was also induced in desferrioxamine-treated cells. Furthermore, the Nip3 promoter containing a hypoxia-responsive element was activated by PLAGL2, independent of hypoxia-inducible factor-1 (HIF-1). The transfection of antisense oligonucleotide to mouse Nip3 mRNA into PLAGL2-expressing cells led to a decrease in apoptotic cells compared with sense oligonucleotide-transfected cells. Despite the activation of DNA-HIF-1 binding activity under hypoxic conditions, neither an accumulation of HIF-1 alpha nor the activation of HIF-1 was observed following the expression of PLAGL2. These results indicate that PLAGL2 is located downstream of HIF-1 and suggest that PLAGL2 functions as a tumor suppressor in association with HIF-1.

Allelic gains and losses in distinct regions of chromosome 6 in gastric carcinoma

In gastric cancer, alterations in the long arm of chromosome 6 are a frequent event. Two regions of heterozygous loss have been described: 6q16.3-6q23 and 6q26-6q27. We have evaluated by microsatellite and FISH analyses the 6q status of three cell lines that we established from primary gastric carcinomas xenografted in nude mice, in order to elucidate the underlying mechanisms of 6q alterations. Alterations of the long arm of chromosome 6 were found in all three xenografts and corresponding cell lines. Allelic imbalance (AI) was found in the three cases, by microsatellite analysis. Fluorescence in situ hybridization analyses clearly demonstrated a duplication of the larger part of the 6q arm in all three cell lines. Two of the cell lines and the corresponding xenografts showed, in addition, complete loss of one of the parental alleles at the terminal part of 6q. Thus, the AI observed along the long arm of chromosome 6 is represented by gain of alleles in one distinct chromosomal segment and loss of alleles in another distinct segment.

Involvement of PLAGL2 in activation of iron deficient- and hypoxia-induced gene expression in mouse cell lines

We searched iron-deficient inducible cDNA, using subtraction cloning and mRNA from desferrioxamine-treated mouse macrophage Raw264.7 cells. We identified a pleomorphic adenoma gene like 2 (PLAGL2), one of PLAG superfamily proteins exhibiting antiproliferative properties on tumor cells. Mouse PLAGL2 consists of 496 amino acids with seven C2H2 zinc-fingers. PLAGL2 mRNA was induced in RAW264.7 cells, mouse erythroleukemia cells and Balb/c 3T3 cells when they were treated with desferrioxamine. Hypoxia also increased PLAGL2 mRNA. Expression of PLAGL2 in COS-7 cells led to nuclear localization. PLAGL2 had potential binding ability to GC-rich oligonucleotide and activated transcription of a gene with the binding sequence in transient reporter assay, a finding consistent with a case seen in a PLAGL2 homolog, ZAC-1. Transient co-transfection of PLAGL2 or ZAC1 cDNA and a reporter containing a lactate dehydrogenase A (LDHA) promoter carrying the hypoxia inducible factor-1 responsive element led to an increase in the basal transcription in Balb/c 3T3 and HepG2 cells. Activation in transcription from the LDHA promoter increased by desferrioxamine treatment or hypoxia was further enhanced when PLAGL2 was expressed. We propose that PLAGL2 is involved in the cell cycle arrest and apoptosis of tumor cells by regulating iron depletion- or hypoxia-inducible gene expression.

Chromosomal aberrations in neuroblastoma cell lines identified by cross species color banding and chromosome painting

We have studied cytogenetic rearrangements in karyotypes of five neuroblastoma cell lines [SK-N-AS, SK-N-SH, SH-SY5Y, SK-N-MC, SMS-KCNR] by G-banding, cross species color banding (RxFISH), and fluorescence in situ hybridization (FISH) with chromosome painting probes. Each neuroblastoma cell line had unique modal karyotypic characteristics and showed a variable number of numerical and structural clonal cytogenetic aberrations. The number of rearranged chromosomes in SK-N-AS, SK-N-SH, SH-SY5Y, SK-N-MC, and SMS-KCNR was 11, 3, 7, 14 (tetraploid, 20-21), and 6, respectively. The origins of abnormal chromosomes were effectively analyzed by RxFISH and FISH with multiple chromosome painting probes. The chromosomal origin of the homogeneously staining region in SH-SY5Y was identified as coamplification of chromosome bands 2p13 and 2p24 by chromosome microdissection and FISH. The non-random rearrangements of chromosomes were determined on 1p34 approximately p36, 6q16 approximately q21, 8q24, 9q34, 11q13 approximately q23, 16q23 approximately q24, 17q21, and 22q31. These results may provide useful information for further molecular characterization of neuroblastoma.

Cloning the human and mouse MMS19 genes and functional complementation of a yeast mms19 deletion mutant

The MMS19 gene of the yeast Saccharomyces cerevisiae encodes a polypeptide of unknown function which is required for both nucleotide excision repair (NER) and RNA polymerase II (RNAP II) transcription. Here we report the molecular cloning of human and mouse orthologs of the yeast MMS19 gene. Both human and Drosophila MMS19 cDNAs correct thermosensitive growth and sensitivity to killing by UV radiation in a yeast mutant deleted for the MMS19 gene, indicating functional conservation between the yeast and mammalian gene products. Alignment of the translated sequences of MMS19 from multiple eukaryotes, including mouse and human, revealed the presence of several conserved regions, including a HEAT repeat domain near the C-terminus. The presence of HEAT repeats, coupled with functional complementation of yeast mutant phenotypes by the orthologous protein from higher eukaryotes, suggests a role of Mms19 protein in the assembly of a multiprotein complex(es) required for NER and RNAP II transcription. Both the mouse and human genes are ubiquitously expressed as multiple transcripts, some of which appear to derive from alternative splicing. The ratio of different transcripts varies in several different tissue types.

Cloning and characterization of a senescence inducing and class II tumor suppressor gene in ovarian carcinoma at chromosome region 6q27

Cytogenetic, molecular and functional analysis has shown that chromosome region 6q27 harbors a senescence inducing gene and a tumor suppressor gene involved in several solid and hematologic malignancies. We have cloned at 6q27 and characterized the RNASE6PL gene which belongs to a family of cytoplasmic RNases highly conserved from plants, to man. Analysis of 55 primary ovarian tumors and several ovarian tumor cell lines indicated that the RNASE6PL gene is not mutated in tumor tissues, but its expression is significantly reduced in 30% of primary ovarian tumors and in 75% of ovarian tumor cell lines. The promoter region of the gene was unaffected in tumors cell lines. Transfection of RNASE6PL cDNA into HEY4 and SG10G ovarian tumor cell lines suppressed tumorigenicity in nude mice. When tumors were induced by RNASE6PL-transfected cells, they completely lacked expression of RNASE6PL cDNA. Tumorigenicity was suppressed also in RNASE6PL-transfected pRPcT1/H6cl2T cells, derived from a human/mouse monochromosomic hybrid carrying a human chromosome 6 deleted at 6q27. Moreover, 63.6% of HEY4 clones and 42.8% of the clones of XP12ROSV, a Xeroderma pigmentosum SV40-immortalized cell line, transfected with RNASE6PL cDNA, developed a marked senescence process during in vitro growth. We therefore propose that RNASE6PL may be a candidate for the 6q27 senescence inducing and class II tumor suppressor gene in ovarian cancer.

Chromosomal alterations in paired gastric adenomas and carcinomas

Gastric adenoma is a precancerous lesion of the stomach and its malignant transformation is thought to result from accumulative series of gene alterations. The aim of this study was to determine the pattern of chromosomal changes during gastric carcinogenesis. Pairs of adenoma and carcinoma tissues from 15 gastrectomy cases containing both adenomas and carcinomas in the same (adjacent pairs, 6 cases) and different (non-adjacent pairs, 9 cases) lesions, were analyzed for chromosomal alterations of 39 non-acrocentric chromosomal arms by comparative genomic hybridization (CGH). CGH analysis identified frequent chromosomal alterations in most of the gastric adenomas (14/15, 93%) and all of the carcinomas. The mean number of chromosomal alterations was higher in carcinoma (5.5 for adenoma and 11.7 for carcinoma; P = 0.006, by nonparametric Wilcoxon's test). Losses on the short arm of chromosome 17 were most common in both adenomas (43%) and carcinomas (67%). The pattern of chromosomal alterations in paired gastric adenomas and carcinomas showed greater similarity compared to the non-case pairs and this similarity was increased in the adjacent pairs. Deletion mapping analysis on chromosome 17p also demonstrated that the conserved deletion area was more frequent in the adjacent pairs. Among these 6 adjacent pairs, all had common deletion areas. In contrast, among the 9 non-adjacent pairs, 2 (22%) had common area of deletion, 5 (56%) showed deletion only in the carcinoma, and the remaining 2 (22%) had no deletion on 17p, suggesting diverse genetic changes might be involved in the multiple tumor formation. Our results that common clonal genetic changes between adjacent pairs of gastric adenomas and carcinomas and accumulated genetic changes in the carcinomas provide evidences for the stepwise mode of gastric carcinogenesis through the accumulation of a series of genetic alterations.

Establishment and characterization of chromosomal aberrations in human cholangiocarcinoma cell lines by cross-species color banding

Cholangiocarcinoma (CC), a malignant neoplasm of the biliary epithelium, is usually fatal because of difficulty in early diagnosis and lack of availability of effective therapy. Furthermore, little is known about the genetics and biology of CC. Only a few reports concerning cytogenetic studies of CC have been published, and few cell lines have been established. We recently established four CC cell lines, designated as SCK, JCK, Cho-CK, and Choi-CK, and report the first application of cross-species color banding (RxFISH) and multiple chromosome painting for the characterization of the chromosomal rearrangements of these CC cell lines. Each cell line had unique modal karyotypic characteristics and showed a variable number of numerical and structural clonal cytogenetic aberrations. Chromosomes 3, 6, 7, 8, 12, 14, 17, and 18 were commonly involved in structural abnormalities. Homogeneously staining regions were determined in SCK and JCK, and double minute chromosomes were found in Cho-CK. The chromosomal aberrations of the four CC cell lines were effectively analyzed by RxFISH and FISH with multiple chromosome painting probes. The nonrandom rearrangements suggest candidate regions for isolation of genes related to CC.

Mapping of target regions of allelic loss in primary breast cancers to 1-cM intervals on genomic contigs at 6q21 and 6q25.3

Allelic losses on the long arm of human chromosome 6 are frequently observed in cancers of the ovary, prostate, and breast. To identify the locations of putative tumor suppressor genes on 6q, we examined 192 primary breast cancers for patterns of allelic loss at 16 polymorphic microsatellite loci distributed along this chromosome arm. Allelic losses at one or more loci were observed in 105 (55%) of the tumors examined. Detailed deletion mapping with appropriate yeast artificial chromosome (YAC) contigs identified two distinct commonly deleted regions; one was confined to a 1-cM interval at 6q21 flanked by D6S1040 and D6S262 and the other to a 1-cM interval at 6q25.3 flanked by D6S305 and D6S411. Allelic losses at 6q21 were more frequent in invasive solid tubular and scirrhous carcinomas than in tumors of less aggressive histologic types (P = 0.0006). Allelic loss at 6q25.3 was associated with loss of progesterone receptor (P = 0.0256). Our results suggest the presence of two tumor suppressor genes for breast cancer on 6q that are likely to be associated with tumor progression and / or loss of hormonal dependency.

Analysis of a 69-kb contiguous genomic sequence at a putative tumor suppressor gene locus on human chromosome 6q27

Multiple neoplasias including B-cell non-Hodgkin's lymphoma, breast carcinoma, and ovarian carcinoma, have been associated with frequent deletions of the distal region on the long arm of human chromosome 6, suggesting the presence of one or more tumor suppressor gene(s) at this locus. Loss of heterozygosity analysis of breast and ovarian tumors has further restricted the minimal region of loss within 6q27. To further characterize this genomic region for gene content including putative tumor suppressor genes as well as other elements that may contribute to tumorigenesis, a 68940-bp contiguous sequence, encompassing markers D6S193 and D6S297, was generated by random shotgun sequencing of a cosmid, P1, and PAC contig. In addition, exon trapping was performed utilizing a subset of these clones. Sixteen trapped exons, ranging in size from 44 to 399 bp, span this approximately 69-kb region. Many other putative exons have been identified computationally. Further analysis has identified 13 potential promoters and 13 putative polyadenylation sites in the region. Northern analysis identified a transcript mapping within this interval that is expressed in ovarian, breast, and lymphoid-derived tumor cell lines. Consideration of these data, together with the demonstration of several regions of high CpG content, suggests the possibility of several genes at this locus.

A novel region of deletion on chromosome 6q23.3 spanning less than 500 Kb in high grade invasive epithelial ovarian cancer

Detailed deletion mapping of chromosome 6q sequences in invasive ovarian tumors have implicated several broad regions involving 6q14-16, 6q21-23, 6q25-26, and the telomeric portion in band 6q27 as regions of frequent loss in this malignancy. In order to define regions of loss involved in the development of ovarian cancer, we used 23 polymorphic markers on 6q to examine allelic loss in 25 high-grade, late stage ovarian tumors. Four non-overlapping deletion regions were observed: (1) at 6q21-22.3 (D6S301-D6S292); (2) within a 1 cM region at 23.2-23.3 between markers D6S978-D6S1637 (at D6S311); (3) at 6q26 (between markers D6S411-D6S1277) and (4) at 6q27 with the markers D6S297 and D6S193. The highest region of loss was observed with marker D6S311 (lost in 17 of 19 informative cases, 89%) in 6q23.3, followed by D6S977 and D6S1637 (71 and 55%, respectively). The average fractional allele loss in the high-grade tumors was around 35%. Previous reports have shown 6q27 as the region of most frequent loss in invasive ovarian cancer. However, our results indicate a novel region in 6q23.3 (spanning less than 500 Kb distance between the markers) with the highest loss, implicating this region of chromosome 6q to harbor a putative tumor suppressor gene involved in the development of invasive epithelial ovarian cancer.

In vitro transformation of cell lines from human salivary gland tumors

Explanted cells from salivary gland tumors are particularly difficult to propagate in vitro and not efficiently immortalized by agents such as simian virus 40. Human papillomavirus 16 (HPV16) has been widely used to transform cells of epithelial origin, but its use for salivary gland cell transformation has not been described. In this study, we employed viral constructs containing the E6/E7 genes of HPV16 to infect and stably transform 9 salivary gland tumor cell cultures. Four of the tumor cell cultures were derived from benign tumors and 5 from malignant tumors. All of the original cell cultures were diploid; however, 6 contained subpopulations of cells with structural abnormalities. All 9 cell cultures were successfully transformed, and 8 were immortalized. The resulting cell lines have decreased serum requirements, exhibit a high proliferation rate, are E6/E7-positive and form colonies in soft agar. Immuno-histochemical and molecular studies confirmed that the transformed cells were indeed epithelial/myoepithelial in origin. All of the transformed cell lines had a diploid or near-diploid karyotype, and 2 contained the original translocated chromosomes in all cells. Our report represents a new application of the E6/E7 system in immortalizing salivary gland cell cultures, resulting in retention of the cellular features found in the native tissue without a general destabilization of the karyotype. These types of tissue culture resources should prove useful for positional cloning and functional studies of genes involved in salivary gland oncogenesis.

Different genome organization in two new cell lines established from human gastric carcinoma

Two gastric cancer cell lines, AKG and GK2, were established from a pleural and an ascitic effusion, respectively. GK2 cells have a pseudodiploid karyotype with an add(6)(q27) chromosome in all metaphases examined. The karyotype of AKG cells is highly rearranged: FISH analysis with painting probes has shown that DNA sequences derived from single chromosomes are scattered on several (as many as eight) markers. In this cell line, the C-MYC and the K-RAS oncogenes are amplified. The organization and the copy number of the C-MYC-amplified units are different from the K-RAS units, suggesting that the two oncogenes were amplified independently. The presence of a few marker chromosomes carrying both C-MYC and K-RAS could be due to translocation events that followed the amplification.

Genomic imprinting and cancer

Genomic imprinting is the phenomenon by which individual alleles of certain genes are expressed differentially according to their parent of origin. The alleles appear to be differentially marked during gametogenesis or during the early part of development. This mark is heritable but reversible from generation to generation, implying a stable epigenetic modification. Approximately 25 imprinted genes have been identified to date, and dysregulation of a number of these has been implicated in tumour development. The normal physiological role of many imprinted genes is in the control of cell proliferation and fetal growth, indicating potential mechanisms of action in tumour formation. Both dominant and recessive modes of action have been postulated for the role of imprinted genes in neoplasia, as a result of effective gene dosage alterations by epigenetic modification of the normal pattern of allele specific transcription. The aim of this review is to assess the importance of imprinted genes in generating tumours and to discuss the implications for novel mechanisms of transforming mutation.

hZAC encodes a zinc finger protein with antiproliferative properties and maps to a chromosomal region frequently lost in cancer

We previously reported the identification of mZac, a novel mouse zinc finger protein that shared with p53 the ability to regulate concomitantly apoptosis and cell cycle progression. We describe here the isolation, chromosomal localization, and functional in vitro characterization of its human homolog. hZAC is a widely expressed zinc finger protein that reveals transactivation and DNA-binding activity. hZAC inhibits tumor cell growth through induction of apoptotic cell death and G1 arrest. Thus hZAC, like its mouse counterpart, displays antiproliferative properties through pathways known to be central to the activity of p53. We mapped hZAC on chromosome 6q24-q25, a region frequently deleted in many solid tumors. Indeed, allelic loss at 6q24-q25 has been shown in breast and ovary cancers, melanomas, astrocytomas, and renal cell carcinomas. Furthermore, Abdollahi et al. [Abdollahi, A., Godwin, A. K., Miller, P. D., Getts, L. A., Schultz, D. C., Tagushi, T., Testa, J. R. & Hamilton, T. C. (1997) Cancer Res. 57, 2029-2034] recently isolated ZAC through its loss of expression in a surface epithelial ovary tumor model and accordingly named it Lot for "lost on transformation." In view of these observations, the functional properties we report here provide further arguments to consider hZAC as a tumor suppressor gene candidate.

Cloning and mapping of human chromosome 6q26-q27 deleted in B-cell non-Hodgkin lymphoma and multiple tumor types

Frequent deletions of the distal region on the long arm of chromosome 6 have been reported in multiple human tumors including B-cell non-Hodgkin lymphoma (B-NHL), suggesting the presence of one or more tumor suppressor genes (TSGs) at this locus. Previously, we identified a region of minimal molecular deletion at 6q25-q27 (RMD-1) in B-NHL cases. To facilitate positional cloning efforts to identify the RMD-1 TSG(s), a yeast artificial chromosome (YAC) contig consisting of 110 clones was constructed across 6q26-q27 by sequence-tagged site/probe content mapping. The contig integrates 79 ordered markers including restriction fragment length polymorphisms, minisatellites, microsatellites, YAC-insert termini, expressed sequence tags, and known genes. It spans 34 cM and has a minimal tiling path of approximately 12 clones, covering an estimated 9-14 Mb with nearly every marker on the map showing at least double linkage to its adjacent markers. Dual-color fluorescence in situ hybridization of selected marker pairs on normal pachytene chromosome 6 further confirmed the YAC-based mappings. Utilizing a loss of constitutional heterozygosity assay in the B-NHL tumor panel, 24 additional 6q26-q27 polymorphic markers (21 mapping to the contig) further defined RMD-1 between markers D6S186 proximally and D6S227 distally. The minimal tiling path of the B-NHL RMD-1 consists of approximately 8 YAC clones, providing a size estimate of 5-9 Mb. This interval contains, in their entirety, several smaller candidate TSG critical regions previously delimited in other tumor systems. The AF-6 gene, mapping within RMD-1, revealed no mutations in a small subset of B-NHL. The deletion and physical maps presented herein provide a framework for the identification of the gene(s) involved in B-NHL as well as other malignancies and diseases mapped to this region and provide the initial reagents for large-scale genomic sequencing.

Allelotype analysis of adenocarcinoma of the gastric cardia

To identify chromosomal loci involved in the development of proximal gastric adenocarcinoma, this study delineated the pattern of allelic imbalance in a series of 38 adenocarcinomas arising in the gastric cardia. A total of 137 microsatellite markers covering all autosomal arms, excluding acrocentric arms, were analysed. A mean of 35 out of a total of 39 chromosomal arms studied were informative for each patient. The tumour group demonstrated a high level of allelic imbalance, with an observed median fractional allelic imbalance of 0.47 for the 29 intestinal-type adenocarcinomas and 0.54 for the nine diffuse-type adenocarcinomas. Allelic imbalance was detected in >50% of informative cases in both histological subtypes on a number of chromosomal arms. In the intestinal subtype, these included, 3p (61%), 4q (71%), 5q (59%), 8p (60%), 9p (65%), 9q (83%), 12q (52%), 13q (52%), 17p (78%) and 18q (70%). A higher incidence of allelic imbalance was detected on chromosome 16q in tumours of the diffuse type relative to those of the intestinal type. A more detailed mapping on chromosomes 4q and 6q identified a number of cases with subchromosomal breakpoints. In conclusion, this analysis has indicated regions of the genome potentially involved in the development of proximal gastric carcinomas.