Tumor suppressor genes studied by cell hybridization and chromosome transfer

Human endogenous retroviruses in cancer: Expression, regulation and function

Human endogenous retroviruses (HERVs) are the remnants of ancient retroviruses that infected human germline cells and became integrated into the human genome millions of years ago. Although most of these sequences are incomplete and silent, several potential pathological roles of HERVs have been observed in numerous diseases, such as multiple sclerosis and rheumatoid arthritis, and especially cancer, including breast cancer and pancreatic carcinoma. The present review investigates the expression signatures and complex regulatory mechanisms of HERVs in cancer. The long terminal repeats-driven transcriptional initiation of HERVs are regulated by transcription factors (such as Sp3) and epigenetic modifications (such as DNA methylation), and are influenced by environmental factors (such as ultraviolet radiation). In addition, this review focuses on the dual opposing effects of HERVs in cancer. HERVs can suppress cancer via immune activation; however, they can also promote cancer. HERV env gene serves a prime role in promoting carcinogenesis in certain malignant tumors, including breast cancer, pancreatic cancer, germ cell tumors, leukemia and Kaposi's sarcoma. Also, HERV ENV proteins can promote cancer via immune suppression. Targeting ENV proteins is a potential future antitumor treatment modality.

The role of syncytins in human reproduction and reproductive organ cancers

Human life begins with sperm and oocyte fusion. After fertilization, various fusion events occur during human embryogenesis and morphogenesis. For example, the fusion of trophoblastic cells constitutes a key process for normal placental development. Fusion in the placenta is facilitated by syncytin 1 and syncytin 2. These syncytins arose from retroviral sequences that entered the primate genome 25 million and more than 40 million years ago respectively. About 8% of the human genome consists of similar human endogenous retroviral (HERVs) sequences. Many are inactive because of mutations or deletions. However, the role of the few that remain transcriptionally active has not been fully elucidated. Syncytin proteins maintain cell-cell fusogenic activity based on ENV: gene-mediated viral cell entry. In this review, we summarize how syncytins and their receptors are involved in fusion events during human reproduction. The significance of syncytins in tumorigenesis is also discussed.

Expression of the miR-302/367 cluster in glioblastoma cells suppresses tumorigenic gene expression patterns and abolishes transformation related phenotypes

Cellular transformation is initiated by the activation of oncogenes and a closely associated developmental reprogramming of the epigenetic landscape. Transcription factors, regulators of chromatin states and microRNAs influence cell fates in development and stabilize the phenotypes of normal, differentiated cells and of cancer cells. The miR‐302/367 cluster, predominantly expressed in human embryonic stem cells (hESs), can promote the cellular reprogramming of human and mouse cells and contribute to the generation of iPSC. We have used the epigenetic reprogramming potential of the miR‐302/367 cluster to “de‐program” tumor cells, that is, hift their gene expression pattern towards an alternative program associated with more benign cellular phenotypes. Induction of the miR‐302/367 cluster in extensively mutated U87MG glioblastoma cells drastically suppressed the expression of transformation related proteins, for example, the reprogramming factors OCT3/4, SOX2, KLF4 and c‐MYC, and the transcription factors POU3F2, SALL2 and OLIG2, required for the maintenance of glioblastoma stem‐like tumor propagating cells. It also diminished PI3K/AKT and STAT3 signaling, impeded colony formation in soft agar and cell migration and suppressed pro‐inflammatory cytokine secretion. At the same time, the miR‐302/367 cluster restored the expression of neuronal markers of differentiation. Most notably, miR‐302/367 cluster expressing cells lose their ability to form tumors and to establish liver metastasis in nude mice. The induction of the miR‐302/367 cluster in U87MG glioblastoma cells suppresses the expression of multiple transformation related genes, abolishes the tumor and metastasis formation potential of these cells and can potentially become a new approach for cancer therapy.

What's new?

The transformation of normal cells into malignant cells shares many similarities with the reprogramming of somatic cells into pluripotent cells, raising the possibility that reprogramming factors may be used to counteract cellular transformation. This study demonstrates that reversion of transformation and normalization of cellular properties can be achieved in highly‐aberrant glioblastoma cells through the expression of the miR‐302/367 cluster. miR‐302/367 drastically changes the gene expression pattern and abolishes transformation‐related phenotypes in a coordinated fashion. miR‐302/367 prevents tumor and metastasis formation and restores features of neuronal differentiation. Such “deprogramming” of tumor cells could potentially become a new concept for cancer therapy.

Replication of somatic micronuclei in bovine enucleated oocytes

Background

Microcell-mediated chromosome transfer (MMCT) was developed to introduce a low number of chromosomes into a host cell. We have designed a novel technique combining part of MMCT with somatic cell nuclear transfer, which consists of injecting a somatic micronucleus into an enucleated oocyte, and inducing its cellular machinery to replicate such micronucleus. It would allow the isolation and manipulation of a single or a low number of somatic chromosomes.

Methods

Micronuclei from adult bovine fibroblasts were produced by incubation in 0.05 μg/ml demecolcine for 46 h followed by 2 mg/ml mitomycin for 2 h. Cells were finally treated with 10 μg/ml cytochalasin B for 1 h. In vitro matured bovine oocytes were mechanically enucleated and intracytoplasmatically injected with one somatic micronucleus, which had been previously exposed [Micronucleus- injected (+)] or not [Micronucleus- injected (−)] to a transgene (50 ng/μl pCX-EGFP) during 5 min. Enucleated oocytes [Enucleated (+)] and parthenogenetic [Parthenogenetic (+)] controls were injected into the cytoplasm with less than 10 pl of PVP containing 50 ng/μl pCX-EGFP. A non-injected parthenogenetic control [Parthenogenetic (−)] was also included. Two hours after injection, oocytes and reconstituted embryos were activated by incubation in 5 μM ionomycin for 4 min + 1.9 mM 6-DMAP for 3 h. Cleavage stage and egfp expression were evaluated. DNA replication was confirmed by DAPI staining. On day 2, Micronucleus- injected (−), Parthenogenetic (−) and in vitro fertilized (IVF) embryos were karyotyped. Differences among treatments were determined by Fisher′s exact test (p≤0.05).

Results

All the experimental groups underwent the first cell divisions. Interestingly, a low number of Micronucleus-injected embryos showed egfp expression. DAPI staining confirmed replication of micronuclei in most of the evaluated embryos. Karyotype analysis revealed that all Micronucleus-injected embryos had fewer than 15 chromosomes per blastomere (from 1 to 13), while none of the IVF and Parthenogenetic controls showed less than 30 chromosomes per spread.

Conclusions

We have developed a new method to replicate somatic micronuclei, by using the replication machinery of the oocyte. This could be a useful tool for making chromosome transfer, which could be previously targeted for transgenesis.

Effects of different levels of organic and inorganic chromium on growth performance and immunocompetence of broilers under heat stress

This experiment was carried out to investigate the effects of different levels of organic and inorganic chromium on the performance, immune function and some serum mineral concentrations of broilers under heat stress condition (23.9-37°C cycling). A total of 150 one-day-old broiler chicks according to a completely randomized design were assigned into five treatment groups. Each treatment consisted of three replicates and each replicate contained ten chicks. Chicks were fed on corn-soybean meal basal diets with added different concentrations of chromium (0, 600 and 1,200 μg kg(-1) chromium chloride or 600 and 1,200 μg/kg chromium L-methionine) from 1 to 49 days of age. Humoral immunity was assessed by intravenous injection of 7% sheep red blood cell (SRBC) followed by evaluation of serum for antibody titers in primary and secondary responses. Cell-mediated immunity was assessed by the cutaneous basophil hypersensitivity (CBH) test to phytohemagglutinin (PHA)-P at day 32 and PHA-M at day 48. Heterophil/lymphocyte (H/L) ratio was also measured as a reliable indicator of stress. The body mass, feed intake and conversion ratio were not influenced by dietary chromium (P > 0.05). Dietary supplementation of both organic and inorganic chromium significantly increased primary and secondary antibody responses (P < 0.01), and also improved H/L ratio (P < 0.05), CBH response (P < 0.01) as well as relative weights of thymus (P < 0.05) and spleen (P < 0.01). Both dietary organic and inorganic chromium caused an increase in serum concentrations of Cr and Zn (P < 0.01), but decreased the serum concentration of Cu (P < 0.01). These results suggest that supplemental chromium especially in organic form offers a good management practice to reduce heat stress-related depression in immunocompetence of broiler chicks.

Biological behaviors and proteomics analysis of hybrid cell line EAhy926 and its parent cell line A549

Background

It is well established that cancer cells can fuse with endothelial cells to form hybrid cells spontaneously, which facilitates cancer cells traversing the endothelial barrier to form metastases. However, up to now, little is known about the biologic characteristics of hybrid cells. Therefore, we investigate the malignant biologic behaviors and proteins expression of the hybrid cell line EAhy926 with its parent cell line A549.

Methods

Cell counting and flow cytometry assay were carried out to assess cell proliferation. The number of cells attached to the extracellular matrix (Matrigel) was measured by MTT assay for the adhesion ability of cells. Transwell chambers were established for detecting the ability of cell migration and invasion. Tumor xenograft test was carried out to observe tumorigenesis of the cell lines. In addition, two-dimensional electrophoresis (2-DE) and mass spectrometry were utilized to identify differentially expressed proteins between in Eahy926 cells and in A549 cells.

Results

The doubling time of EAhy926 cell and A549 cell proliferation was 25.32 h and 27.29 h, respectively (P > 0.1). Comparing the phase distribution of cell cycle of EAhy926 cells with that of A549 cells, the percentage of cells in G0/G1 phase, in S phase and in G2/M phase was (63.7% ± 2.65%) VS (60.0% ± 3.17%), (15.4% ± 1.52%) VS (13.8% ± 1.32%), and (20.9% ± 3.40%) VS (26.3% ± 3.17%), respectively (P > 0.05). For the ability of cell adhesion of EAhy926 cells and A549 cells, the value of OD in Eahy926 cells was significantly higher than that in A549 cells (0.3236 ± 0.0514 VS 0.2434 ± 0.0390, P < 0.004). We also found that the migration ability of Eahy926 cells was stronger than that of A549 cells (28.00 ± 2.65 VS 18.00 ± 1.00, P < 0.01), and that the invasion ability of Eahy926 cells was significantly weak than that of A549 cells (15.33 ± 0.58 VS 26.67 ± 2.52, P < 0.01). In the xenograft tumor model, expansive masses of classic tumor were found in the A549 cells group, while subcutaneous inflammatory focuses were found in the EAhy926 cells group. Besides, twenty-eight proteins were identified differentially expressed between in EAhy926 cells and in A549 cells by proteomics technologies.

Conclusion

As for the biological behaviors, the ability of cell proliferation in Eahy926 cells was similar to that in A549 cells, but the ability in adhesion and migration of Eahy926 cells was higher. In addition, Eahy926 cells had weaker ability in invasion and could not form tumor mass. Furthermore, there were many differently expressed proteins between hybrid cell line Eahy926 cells and A549 cells, which might partly account for some of the differences between their biological behaviors at the molecular level. These results may help to understand the processes of tumor angiogenesis, invasion and metastasis, and to search for screening method for more targets for tumor therapy in future.

Cell fusions in mammals

Cell fusions are important to fertilization, placentation, development of skeletal muscle and bone, calcium homeostasis and the immune defense system. Additionally, cell fusions participate in tissue repair and may be important to cancer development and progression. A large number of factors appear to regulate cell fusions, including receptors and ligands, membrane domain organizing proteins, proteases, signaling molecules and fusogenic proteins forming alpha-helical bundles that bring membranes close together. The syncytin family of proteins represent true fusogens and the founding member, syncytin-1, has been documented to be involved in fusions between placental trophoblasts, between cancer cells and between cancer cells and host cells. We review the literature with emphasis on the syncytin family and propose that syncytins may represent universal fusogens in primates and rodents, which work together with a number of other proteins to regulate the cell fusion machinery.

Are postnatal hemangioblasts generated by dedifferentiation from committed hematopoietic stem cells?

Cell dedifferentiation occurs in different cell systems. In spite of a relative paucity of data it seems reasonable to assume that cell dedifferentiation exists in reversible equilibrium with differentiation, to which cells resort in response to intercellular signals. The current literature is indeed compatible with the concept that dedifferentiation is guided by structural rearrangements of nuclear chromatin, directed by epigenetic cell memory information available as silenced genes stored on heterochromatin, and that gene transcription exists in reversible "fluctuating continua" during parental cell cycles. Here, we review the molecular mechanisms of cell dedifferentiation and suggest for hematopoietic development that postnatal hemangioblasts are generated by dedifferentiation of committed hematopoietic stem cells.

Prognostic role of syncytin expression in breast cancer

Breast cancer cells were recently found to produce syncytin, an endogenous retroviral protein implicated in cell fusion, immune regulation, and nitric oxide synthase expression. To determine whether syncytin has a prognostic role in breast cancer, we investigated a series of 165 premenopausal lymph node-negative women for syncytin expression using an immunocytochemical scoring system. Results were analyzed with the Kaplan-Meier method and with the Cox proportional hazard model. Syncytin expression was observed in 38% of the patients, and the degree of syncytin expression constituted a positive prognostic indicator for recurrence-free survival. In addition, we examined a second series of 54 consecutively operated breast cancer patients of all categories and the results supported the conclusions made from the first study. Thus, syncytin expression constitutes a positive prognostic factor in breast cancer--a phenomenon that may be related to the involvement of syncytin in mediating fusions between breast cancer cells and endothelial cells.

Down regulation of 3p genes,LTF, SLC38A3 andDRR1, upon growth of human chromosome 3–mouse fibrosarcoma hybrids in severe combined immunodeficiency mice

We have applied a functional test for tumour antagonizing genes based on human chromosome 3 (chr3)-mouse fibrosarcoma A9 MCHs that were studied in vitro and after growth as tumours in severe combined immunodeficiency (SCID) mice. Previously, we reported that 9 out of the 36 SCID-tumours maintained the transferred chr3 ("chr3+" tumours), but lost the expression of the known human TSG fragile histidine triad gene (FHIT) in contrast to 14 other 3p-genes examined. Here we report the results of the duplex RT-PCR analysis of 9 "chr3+" tumours and 3 parental MCHs. We have examined the expression of 34 human 3p-genes from known cancer-related regions of instability, including 13 genes from CER1 defined by us previously at 3p21.33-p21.31 and 10 genes from the LUCA region at 3p21.31. We have found that in addition to FHIT, expression of the LTF gene from CER1 at 3p21.33-p21.31 was lost in all 9 tumours analyzed. The transcript of the solute carrier family 38 member 3 gene (SLC38A3) gene from LUCA region at 3p21.31 was not found in 8 and was greatly reduced in 1 out of these 9 tumours. Expression of the down-regulated in renal cell carcinoma gene (DRR1) gene at 3p14.2 was lost in 7 and down regulated in 2 "chr3+" tumours. In the SCID-tumour derived cell lines treatment with 5-aza-2'-deoxycytidine restored the mRNA expression of LTF, indicating the integrity of DNA sequences. Notably that transcription of the LTF and 2 flanking genes, LRRC2 and TMEM7, as well as transcription of the SLC38A3 gene, were also impaired in all 5 RCC cell lines analyzed. Our data indicate these genes as putative tumour suppressor genes.

The manipulation of chromosomes by mankind: the uses of microcell-mediated chromosome transfer

Microcell-mediated chromosome transfer (MMCT) was a technique originally developed in the 1970s to transfer exogenous chromosome material into host cells. Although, the methodology has not changed considerably since this time it is being used to great success in progressing several different fields in modern day biology. MMCT is being employed by groups all over the world to hunt for tumour suppressor genes associated with specific cancers, DNA repair genes, senescence-inducing genes and telomerase suppression genes. Some of these genomic discoveries are being investigated as potential treatments for cancer. Other fields have taken advantage of MMCT, and these include assessing genomic stability, genomic imprinting, chromatin modification and structure and spatial genome organisation. MMCT has also been a very useful method in construction and manipulation of artificial chromosomes for potential gene therapies. Indeed, MMCT is used to transfer mainly fragmented mini-chromosome between cell types and into embryonic stem cells for the construction of transgenic animals. This review briefly discusses these various uses and some of the consequences and advancements made by different fields utilising MMCT technology.

Search for unknown tumor-antagonizing genes

Following the ingenious prediction of Alfred Knudson in 1971, the first tumor suppressor gene, RB1, has been isolated. Its product, the RB1 protein, was found to play a major role in the control of the cell cycle. The loss of heterozygosity (LOH) technique, introduced by Cavenee and colleagues, was an important milestone toward the confirmation of Knudson's hypothesis and the identification of the gene. Subsequently, the LOH technique has provided important clues that have led to the discovery of other tumor suppressor genes. Most of them play important roles in the regulation of the cell cycle and/or of apoptosis. Circumstantial evidence suggests that still other and perhaps many unknown genes may participate in the protection of the organism against malignant growth. The numerous genome losses in tumors, detected by LOH, comparative genomic hybridization, and by cytogenetic techniques, support this possibility. The early work of one of us (G.K.), together with Henry Harris and Francis Wiener, had shown that the malignant phenotype can be suppressed by hybridizing malignant with low- or non-tumorigenic cells. However, analysis of this phenomenon failed to assign the inhibition of tumorigenicity to any particular gene. We have pursued the search for new tumor-antagonizing genes with two unconventional approaches, focusing on human chromosomal subband 3p21.3, a region frequently targeted by cytogenetically detectable deletions. We have detected four clusters of candidate tumor suppressor genes at 3p21.3 by a combination of deletion mapping and the "elimination test." These findings raise the question whether the number and variety of genes that may contribute to the defense against uncontrolled proliferation may have been underestimated.

Chromosome 17p13.2 transfer reverts transformation phenotypes and fas-mediated apoptosis in breast epithelial cells

Transformation of the human breast epithelial cells (HBEC) MCF-10F with the carcinogen benz(a)pyrene (BP) into BP1-E cells resulted in the loss of the chromosome 17 p13.2 locus (D17S796 marker) and formation of colonies in agar-methocel (colony efficiency (CE)), loss of ductulogenic capacity in collagen matrix, and resistance to anti-Fas monoclonal antibody (Mab)-induced apoptosis. For testing the role of that specific region of chromosome 17 in the expression of transformation phenotypes, we transferred chromosome 17 from mouse fibroblast donors to BP1-E cells. Chromosome 11 was used as negative control. After G418 selection, nine clones each were randomly selected from BP1-E-11neo and BP1-E-17neo hybrids, respectively, and tested for the presence of the donor chromosomes by fluorescent in situ hybridization and polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) analyses. Sensitivity to Fas Mab-induced apoptosis and evaluation of transformation phenotype expression were tested in MCF-10F, BP1-E, and nine BP1-E-11neo and BP1-E-17neo clones each. Six BP1-E-17neo clones exhibited a reversion of transformation phenotypes and a dose dependent sensitivity to Fas Mab-induced apoptosis, behaving similarly to MCF-10F cells. All BP1-E-11neo, and three BP1-E-17neo cell clones, like BP1-E cells, retained a high CE, loss of ductulogenic capacity, and were resistant to all Fas Mab doses tested. Genomic analysis revealed that those six BP1-E-17neo clones that were Fas-sensitive and reverted their transformed phenotypes had retained the 17p13.2 (D17S796 marker) region, whereas it was absent in all resistant clones, indicating that the expression of transformation phenotypes and the sensitivity of the cells to Fas-mediated apoptosis were under the control of genes located in this region.

Coincidence of synteny breakpoints with malignancy-related deletions on human chromosome 3

We have found previously that during tumor growth intact human chromosome 3 transferred into tumor cells regularly looses certain 3p regions, among them the approximately 1.4-Mb common eliminated region 1 (CER1) at 3p21.3. Fluorescence in situ hybridization analysis of 12 mouse orthologous loci revealed that CER1 splits into two segments in mouse and therefore contains a murine/human conservation breakpoint region (CBR). Several breaks occurred in tumors within the region surrounding the CBR, and this sequence has features that characterize unstable chromosomal regions: deletions in yeast artificial chromosome clones, late replication, gene and segment duplications, and pseudogene insertions. Sequence analysis of the entire 3p12-22 revealed that other cancer-associated deletions (regions eliminated from monochromosomal hybrids carrying an intact chromosome 3 during tumor growth and homozygous deletions found in human tumors) colocalized nonrandomly with murine/human CBRs and were characterized by an increased number of local gene duplications and murine/human conservation mismatches (single genes that do not match into the conserved chromosomal segment). The CBR within CER1 contains a simple tandem TATAGA repeat capable of forming a 40-bp-long secondary hairpin-like structure. This repeat is nonrandomly localized within the other tumor-associated deletions and in the vicinity of 3p12-22 CBRs.

Candidate tumor suppressor, HCCS-1, is downregulated in human cancers and induces apoptosis in cervical cancer

To identify the genes involved in cervical carcinogenesis, we applied the mRNA differential display method and identified a candidate tumor suppressor gene, HCCS-1, which was present in normal cervical tissue but absent in cervical cancer, metastatic lymph node and CUMC-6 cervical cancer cell line. HCCS-1 transcripts were expressed in many normal tissues including leukocyte, lung, spleen, liver, heart and uterine cervix. Its expression was absent in 8 human cancer cell lines. HCCS-1-transfected HeLa cells exhibited growth inhibition by about 50%. This inhibitory effect of HCCS-1 on cervical cancer cells was associated with apoptotic process including DNA fragmentation. HCCS-1-transfected HeLa cells were shown to release cytochrome c from mitochondria, which activates caspase-9 and -3 and finally results in cleavage of poly(ADP-ribose) polymerase. Apoptosis formation was detected by propidium-iodide/annexin V. HCCS-1-transfected HeLa cells were more sensitive to adriamycin or UVC ray triggered apoptosis. These results suggest that HCCS-1 is downregulated in multiple human tumor types and may serve as a candidate tumor suppressor gene through apoptotic pathway against human cervical cancer.

Functional identification of LZTS1 as a candidate prostate tumor suppressor gene on human chromosome 8p22

Deletions in the 8p21-22 region of the human genome are among the most common genetic alterations in prostate carcinomas. Several studies in different tumor tissues, including prostate, indicate that there are probably multiple tumor suppressor genes (TSGs) present in this region. To identify candidate TSGs on 8p22 a YAC contig spanning this region was assembled and YAC clones retrofitted with a selectable marker (neo) were transferred into rat prostate AT6.2 cells. Two overlapping YAC clones showed greatly reduced colony-forming efficiency, indicating they may carry a TSG. Two BAC clones encompassing the overlapping region also appeared to exert suppressive effects on the growth of AT6.2 cells. Database searches for genes mapped to the critical region identified a gene known as FEZ1 (LZTS1) as a potential candidate suppressor gene. Subsequent experiments showed that over-expression of LZTS1 cDNA inhibited stable colony-forming efficiencies of AT6.2, HEK-293 and LNCaP cells. In contrast, LZTS1-transfected Rat-1 and RM1 cells were growth-stimulated. Database searches also identified additional isoforms of the LZTS1 mRNA, as well as LZTS1 protein domains reminiscent of those found in transcription factors. Together these data suggest that the LZTS1 gene is involved in the regulation of cell growth and its loss of function may contribute to the development of prostatic carcinomas, as well as other cancers.

Oligonucleotide microarray expression analysis of genes whose expression is correlated with tumorigenic and non-tumorigenic phenotype of HeLa x human fibroblast hybrid cells

In order to understand the differences and similarities between tumorigenic and non-tumorigenic HeLaxhuman fibroblast hybrids, gene expression profiles were examined with synthetic oligonucleotide arrays containing nearly 7000 gene probe sets. We used two pairs of genetically related hybrids, each pair representing individual clones of non-tumorigenic and tumorigenic segregant hybrids, respectively. Analysis of six possible comparisons, utilizing two algorithms, identified 204 genes with differential expression. The greater number of differentially expressed genes was observed when non-tumorigenic hybrids were compared with tumorigenic segregants. Fifteen and 14 genes, respectively, were consistently found to be differentially expressed in non-tumorigenic and tumorigenic cells. Among those 29 differentially expressed genes, three (intestinal alkaline phosphatase, caveolin-1, and solute carrier family2, member3) have been reported previously to be associated with the tumorigenic phenotype, using the same hybrid pairs. In addition, among the genes previously detected by differential display, 78% of them exhibited more than 5-fold change, demonstrating a high consistency between the two methods of differential gene expression. These findings suggest that synthetic oligonucleotide arrays are a powerful and highly reproducible tool to identify those genes whose expression is associated with certain phenotypes.

Similar regions of human chromosome 3 are eliminated from or retained in human/human and human/mouse microcell hybrids during tumor growth in severe combined immunodeficient (SCID) mice

By passaging microcell hybrids (MCHs) containing human chromosome 3 (chr3) on A9 mouse fibrosarcoma background through severe combined immunodeficient (SCID) mice (elimination test), we have previously defined a 1-Mb-long common eliminated region 1 (CER1) at 3p21.3, a second eliminated region (ER2) at 3p21.1-p14 and a common retained region (CRR) at 3q26-qter. In the present work, chr3 was transferred by microcell fusion into the human nonpapillary renal cell carcinoma line KH39 that contained uniparentally disomic chr3. Four MCHs were generated. Compared with KH39, they developed fewer and smaller tumors, which grew after longer latency periods in SCID mice. The tumors were analyzed in comparison with corresponding MCHs by chr3 arm-specific painting, 19 fluorescent in situ hybridization (FISH) probes, and 27 polymorphic markers. Three MCHs that maintained the intact exogenous chr3 in vitro lost one 3p copy in all 11 tumors. Seven of 11 tumors lost the exogenous 3p, whereas four tumors contained mixed cell populations that lacked either the exogenous or one endogenous KH39 derived 3p. In one MCH the exogenous chr3 showed deletions within CER1 and ER2 already in vitro. It remained essentially unchanged in 8/9 derived tumors. The third, exogenous copy of the 3q26-q27 region (part of CRR) was retained in 16/20 tumors. It can be concluded that the human/human MCH-based elimination test identifies similar eliminated and retained regions on chr3 as the human/murine MCH-based test.

Functional evidence for an ovarian cancer tumor suppressor gene on chromosome 22 by microcell-mediated chromosome transfer

The identity of many tumor suppressor genes important in epithelial ovarian cancer tumorigenesis remains unknown. In an effort to localize a novel tumor suppressor on chromosome 22, a psv2neo tagged human chromosome 22 was transferred into the malignant epithelial ovarian cancer cell line, SKOv-3, by microcell-mediated chromosome transfer. Complete suppression of the transformed phenotype was observed in 16 of 18 individual microcell hybrid clones as evidenced by the complete abrogation of cell growth under anchorage-independent conditions. In vitro doubling times were also dramatically reduced, as was the ability to form subcutaneous tumors in CD1 nu/nu mice. Only one polymorphic marker, D22S429, segregated with decreased transformation and tumorigenic potential, suggesting that an unrecognized tumor suppressor may localize to chromosome 22q11-q12. These data provide functional support for the presence of a novel tumor suppressor locus (or loci) on chromosome 22 that is important in ovarian cancer tumorigenesis.

The molecular biology of cancer

The process by which normal cells become progressively transformed to malignancy is now known to require the sequential acquisition of mutations which arise as a consequence of damage to the genome. This damage can be the result of endogenous processes such as errors in replication of DNA, the intrinsic chemical instability of certain DNA bases or from attack by free radicals generated during metabolism. DNA damage can also result from interactions with exogenous agents such as ionizing radiation, UV radiation and chemical carcinogens. Cells have evolved means to repair such damage, but for various reasons errors occur and permanent changes in the genome, mutations, are introduced. Some inactivating mutations occur in genes responsible for maintaining genomic integrity facilitating the acquisition of additional mutations. This review seeks first to identify sources of mutational damage so as to identify the basic causes of human cancer. Through an understanding of cause, prevention may be possible. The evolution of the normal cell to a malignant one involves processes by which genes involved in normal homeostatic mechanisms that control proliferation and cell death suffer mutational damage which results in the activation of genes stimulating proliferation or protection against cell death, the oncogenes, and the inactivation of genes which would normally inhibit proliferation, the tumor suppressor genes. Finally, having overcome normal controls on cell birth and cell death, an aspiring cancer cell faces two new challenges: it must overcome replicative senescence and become immortal and it must obtain adequate supplies of nutrients and oxygen to maintain this high rate of proliferation. This review examines the process of the sequential acquisition of mutations from the prospective of Darwinian evolution. Here, the fittest cell is one that survives to form a new population of genetically distinct cells, the tumor. This review does not attempt to be comprehensive but identifies key genes directly involved in carcinogenesis and demonstrates how mutations in these genes allow cells to circumvent cellular controls. This detailed understanding of the process of carcinogenesis at the molecular level has only been possible because of the advent of modern molecular biology. This new discipline, by precisely identifying the molecular basis of the differences between normal and malignant cells, has created novel opportunities and provided the means to specifically target these modified genes. Whenever possible this review highlights these opportunities and the attempts being made to generate novel, molecular based therapies against cancer. Successful use of these new therapies will rely upon a detailed knowledge of the genetic defects in individual tumors. The review concludes with a discussion of how the use of high throughput molecular arrays will allow the molecular pathologist/therapist to identify these defects and direct specific therapies to specific mutations.

Altered response of a human squamous cell carcinoma cell line to 1, 25-dihydroxyvitamin D(3) after transfer of a normal chromosome 11

Previous work in our laboratory using functional assays for tumorigenicity identified a tumor suppressor element on human chromosome 11q for the cutaneous squamous cell carcinoma cell line A388.6TG.c2. In this report, we screened a variety of agents for differential effects on A388.6TG.c2 compared to a growth-suppressed chromosome 11 microcell hybrid of A388.6TG.c2. One of the agents, 1, 25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3); calcitriol), exerted a growth-altering effect on A388.6TG.c2, which formed rounded cell clusters across the surface of the raft by Day 6 of treatment. In contrast, full-length chromosome 11 hybrids of A388.6TG.c2, as well as two other squamous cell carcinoma cell lines (FaDu and A431), when treated with 1,25(OH)(2)D(3), failed to demonstrate this cell-clumping phenotype. To pursue the hypothesis that the growth suppressor element is involved in altering the response to 1, 25(OH)(2)D(3), we tested microcell hybrids carrying t(X;11) chromosomes lacking large portions of 11q. Although these hybrids, like the parent A388.6TG.c2 cells, demonstrated extensive growth in organotypic cultures, they failed to form cell clusters with 1, 25(OH)(2)D(3) treatment. These results suggest that the chromosome 11 element that alters the response to 1,25(OH)(2)D(3) is distinct from the growth-suppressing element. An examination of differentiation marker expression revealed identical patterns of basal and suprabasal markers for A388.6TG.c2 and for a chromosome 11 hybrid with or without treatment with 1,25(OH)(2)D(3). Finally, characterization of candidate tumor suppressor gene PPP2R1B, which encodes for a subunit of protein phosphatase 2A (PP2A), showed seemingly insignificant alterations by cDNA sequence analysis. Collectively, the data suggest that human chromosome 11 contains two different tumor suppressor elements that may account for the two areas of loss of heterozygosity observed on the long arm of this chromosome.

A functional investigation of tumor suppressor gene activities in a nasopharyngeal carcinoma cell line HONE1 using a monochromosome transfer approach

Monochromosome transfers of selected chromosomes into a nasopharyngeal carcinoma (NPC) cell line were performed to determine if tumor suppressing activity for NPC mapped to chromosomes 9, 11, and 17. Current information from cytogenetic and molecular allelotyping studies indicate that these chromosomes may harbor potential tumor suppressor genes vital to NPC. The present results show the importance of CDKN2A on chromosome 9 in NPC development. There was no functional suppression of tumor development in nude mice with microcell hybrids harboring the newly transferred chromosome 9 containing an interstitial deletion at 9p21, whereas transfection of CDKN2A into the NPC HONE1 cells resulted in obvious growth suppression. Whereas intact chromosome 17 transfers into HONE1 cells showed no functional suppression of tumor formation, chromosome 11 was able to do so. Molecular analysis of chromosome 11 tumor segregants indicated that at least two tumor suppressive regions mapping to 11q13 and 11q22-23 may be critical for the development of NPC.

Targets of extinction: identification of genes whose expression is repressed as a consequence of somatic fusion between cells representing basal and luminal mammary epithelial phenotypes

The use of somatic cell hybrids has led to an increased understanding of the ‘negative’ regulation of cellular phenotype. Using somatic cell hybrids constructed between human breast cells that represent differing stages of malignancy but also display differing phenotypes from the same tissue, we present experimental results suggesting that luminal epithelial characteristics are controlled by repressive mechanisms. Fusion of HBL 100 cells, non-tumorigenic and characteristic of the basal cell lineage, with MCF-7 or MDA-MB-468 malignant breast cancer cells, characteristic of the luminal lineage, resulted in hybrid cells that displayed the phenotype of the HBL 100 cells. Using representational difference analysis, a panel of genes whose expression was repressed in the hybrid between HBL 100 and MDA-MB-468 was identified. This analysis revealed markers of luminal epithelial cells to be repressed, including Ep-CAM, cytokeratin 19 and E-cadherin. These markers were found to be coordinately re-expressed in variant hybrid cells indicating that the observed repression is reversible. Integrin (alpha)(v)(beta)(3) expression was found to be in mutual exclusivity to the luminal epithelial markers, thereby revealing a bidirectional ‘switch’ in the pattern of gene expression in this system. Finally, the expression of Ep-CAM was found to be lost in heterokaryons produced by fusion of HBL 100 and MCF-7 or MDA-MB-468 cells suggesting that the extinction of this gene in hybrid cells is the consequence of a trans-acting factor(s) synthesized by the HBL 100 cells. These data suggest that a number of markers of luminal cell differentiation in the mammary gland can be controlled through negative mechanisms and that such control of phenotype is highly coordinated.

Protein expression and functional analysis of the FHIT gene in human tumor cells

BACKGROUND

The fragile histidine triad (FHIT) gene at chromosome 3p14.2 has been proposed to be a candidate tumor suppressor gene in human cancers. To test whether FHIT exhibits the functional properties of a tumor suppressor gene, we studied the expression of its protein (pFHIT) in human carcinoma cells and examined the ability of FHIT to inhibit the neoplastic phenotype of cancer cells.

METHODS

Subcellular localization and patterns of protein expression in tumor cells were determined by immunohistochemical analysis and immunoblotting with the use of polyclonal anti-pFHIT antisera. In tumor cells with undetectable pFHIT, we examined the effect of recombinant pFHIT expression on morphology, growth rate, colony formation, and in vivo tumor formation.

RESULTS

We demonstrated that pFHIT is a cytoplasmic 17-kd polypeptide whose expression could not be detected in 30 of 52 human carcinoma cell lines tested. We observed, however, that the stable overexpression of pFHIT did not alter cell morphology, inhibit colony formation, or inhibit cell proliferation in vitro. Furthermore, overexpression of pFHIT did not lead to altered cell cycle kinetics in dividing cells. The in vivo tumorigenicity of a tumor cell line that expressed high levels of recombinant pFHIT was equivalent to that of control transfectants and of parental cells.

CONCLUSIONS

These results suggest that the replacement of pFHIT in human carcinoma cells does not suppress tumor cell growth and that this protein may be involved in tumorigenesis in ways that are distinct from the "classic" tumor suppressor paradigm.

Effect of chromium nicotinic acid supplementation on selected cardiovascular disease risk factors

The effects of daily supplemental chromium (200 micrograms) complexed with 1.8 mg nicotinic acid on plasma glucose and lipids, including total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides, were assessed in 14 healthy adults and 5 adults with noninsulin-dependent diabetes mellitus (NIDDM) using a double-blind crossover study with 8-wk experimental periods. Eight of the 14 healthy subjects and all 5 subjects with NIDDM also underwent an oral glucose tolerance test with assessment of 90 min postprandial plasma glucose and insulin concentrations. No statistically significant effects of chromium nicotinic acid supplementation were found on plasma insulin, glucose, or lipid concentrations, although chromium nicotinic acid supplementation slightly lowered fasting plasma total and LDL cholesterol, triglycerides, and glucose concentrations, and 90-min postprandial glucose concentrations in individuals with NIDDM.

Low frequency of loss of heterozygosity at the nevoid basal cell carcinoma locus and other selected loci in appendageal tumors

Previous studies of loss heterozygosity (LOH) have revealed distinct patterns of allelic loss in some skin tumors. In basal cell carcinomas (BCCs) loss of heterozygosity is virtually restricted to chromosome 9, whereas in squamous cell carcinomas (SCCs) and actinic keratoses loss is more widespread involving chromosomes 3, 9, 13, and 17. Because there are histological similarities between BCCs and some appendageal tumors, and because lines of evidence suggest that BCCs are appendageal in origin, we carried out a limited allelotype in 41 appendageal tumors. The overall frequency of allelic loss was low (4 out of 247 informative loci; 1.6%). LOH was seen in a proliferating trichilemmal cyst (17p), a sebaceous epithelioma (17q), an eccrine porocarcinoma (17q), a trichoepithelioma (9q), and in two basal cell carcinomas showing eccrine or granular cell differentiation that were originally misdiagnosed (9Q). The pattern of loss in this mixed group of appendageal tumors shows differences from both BCCs and SCCs, and further emphasizes the unique genetic profile and behavior of BCCs. The finding of 9q loss in BCCs with eccrine or granular cell differentiation shows that 9q loss occurs in differential histological subtypes of BCCs.

Antisense oncogene and tumor suppressor gene therapy of cancer

Rapid advances in cancer gene therapy are driven by an explosive development of gene transfer technology and a strong demand for seeking alternatives to unsatisfactory conventional cancer therapies. Discovery of the genetic basis of cancer has indicated that cancer is a disease of genes. Among a variety of approaches to gene therapy of cancer, antisense oncogene and tumor suppressor gene therapy of cancer are the two strategies that aim at correcting genetic disorders of cancer through suppression of the abnormal expression of the proliferative genes. The potential effectiveness of these approaches is promised by their precise targeting at the mechanisms of the disease. Examples of several preclinical studies of these types of approaches that led to the approval of clinical trials are reviewed. Limitation and future development of these approaches are also discussed.

Genetic alterations in non-melanoma skin cancer

Non-melanoma skin cancer is common and offers unrivaled opportunities to relate genetic changes to clinical and biologic behavior. Recent technical advances in molecular biology render genetic analysis of even the smallest skin cancers possible. In this review I will discuss the role of p53 gene in skin carcinogenesis, the relation between p53 immunostaining and p53 mutation, and recent evidence for the involvement of putative tumor suppressor genes both on chromosome 9 and other chromosomes in non-melanoma skin cancer.

An anti-oncogenic action of the polyomavirus large-T (LT) antigen in HeLa and SiHa tumor cells

HeLa (HPV-18) and SiHa (HPV-16) cell lines were transfected with the plasmid LTneo. Two new phenotypes cells, called, HLT and SLT, respectively, were propagated in culture after the transfection by calcium phosphate precipitation procedure, followed by G-418 selection. We noticed that in vitro characteristics of both cell lines HeLa and SiHa are affected by transfection of the LT gene into their genome: HLT and SLT growth rate decreased in culture compared to their parental cell lines HeLa and SiHa; HLT and SLT observed under the microscope appeared markedly different but similar to normal cervical epithelium; HLT and SLT are not able to grow in semi-solid medium; they are anchorage-dependent. Investigation of in vivo properties of HLT and SLT was done by injection in 1-month-old nude mice; they are not able to produce tumors. In conclusion, the genetic transfection of HeLa and SiHa with the immortalizing gene decreases the cancerous properties of both cell lines in vitro as well as in vivo. In this context, LT functions as an anti-oncogene, a growth-regulatory protein. This would seem to conflict with its function as an oncogene in the multiple step carcinogenic process.