The approaching era of the tumor suppressor genes

Cell Fusion in Malignancy: A Cause or Consequence? A Provocateur or Cure?

Cell fusion has been observed in malignancy, and cancer cells have been found especially apt to fuse with other cells. Investigation of human and experimental malignancies suggests spontaneous fusion of normal cells can induce manifold genetic changes and manifestations of malignant transformation. Fusion of transformed cells with other cells can promote the progression of cancer to more malignant forms. However, observations in various fields suggest cell fusion also potentially contributes to natural defenses against cancer. Thus, cell fusion potentially corrects genetic and/or phenotypic changes underlying malignant transformation. Cell fusion also might help nonmalignant cells in tumors thwart tumor growth. Perhaps most importantly, cell fusion may generate genetic changes that lead to the expression of neoantigens, provide the mass of neoantigen expression needed to elicit immunity, and promote the function of antigen-presenting cells in a way that favors protective immunity as a defense against malignancy. To the extent that cell fusion promotes cellular, tissue, and/or systemic resistance to malignancy, the propensity of tumor cells to fuse with other cells might constitute a natural defense against malignancy.

Onco-Suppressor Genes in Human Cancer

The analysis of the molecular mechanisms governing multistep carcinogenesis became experimentally approachable since the identification and characterization in tumor cells of altered or activated versions of cellular genes (oncogenes) that normally control cell growth and differentiation. The activating mutations confer new properties to the oncogene products and should therefore be considered as gain of function mutations. In addition, the oncogenes appear to act as dominant genetic traits since they act also in the presence of the homologous wild-type allele. However, the concept of a dominance of the transformed phenotype has been challenged by early experiments with somatic cell hybrids which showed that the fusion of normal and malignant cells may suppress the tumorigenic phenotype. The suppression or reversion of the malignant phenotype by the introduction of a normal chromosome into a tumor cell line has lent support to the idea that a family of cellular genes are coding for factors capable to interact with the cell-growth control machinery. These genes seem to reconstitute the normal control of cell growth even in the presence of an activated oncogene. In addition, a two-mutation model has been proposed to explain the epidemiological and clinical features of childhood cancers. According to the model, the development of these malignancies can be caused by the loss or inactivation of both alleles of cellular genes, as suggested by the somatic cell hybrid experiments where the function of the inactivated genes is restored by the contribution of those derived from the normal parental cells. This family of genes is designated as onco-suppressor genes since their product is necessary for the normal regulated cell growth and is lacking or inactivated in malignant cells. At gene level they should be considered as recessive genetic traits, since the tumor phenotype appears when both alleles of an oncosuppressor gene are inactivated. The mutations affecting their normal functions belong to the type « loss of function ». The molecular analysis of retinoblastoma has led to the cloning and sequencing of the related onco-suppressor gene (RB gene) whose product displays the features of a gene-regulatory protein. In addition, a binding between the RB product and various viral onco-proteins (E1A, large T, E7) has been demonstrated, thus suggesting a mechanism of RB inactivation by which some DNA viruses can transform the host cell. Finally, the increasing availability of DNA markers, defining restriction fragment length polymorphisms, has led to the mapping of the loci of inherited predisposition for familial cancer syndromes such as MEN-1, VHL and NF-2 and to the extension to common cancers of the allele losses analysis that can reveal onco-suppressor gene inactivation. This indirect approach has suggested the occurrence of different onco-suppressor genes for sporadic breast, colonic and lung cancers, bladder carcinoma, germinal tumors of the testis and malignant melanoma. In particular, colonic cancer provides a significant example of a possible multistep scenario for carcinogenesis in humans in which activated oncogenes (e.g. ras) and inactivated putative onco-suppressor genes (on chromosome 17 and 18) coexist in the same cell.

Genomic Alterations in Human Breast Cancer: A Review

We review and discuss data on the genetic alterations documented in human breast carcinomas at the molecular level. These alterations may result in: 1) deletion of genetic material (chromosome 11p, 13q, 3p, 1q, 17p); 2) amplification of genes or entire chromosomal segments (c-myc, c-erb-B2, locus DF3/PUM, loci on 11q13); 3) rearrangements (c-myc); 4) point mutations (c-ras). Presently available informations do not allow the development of cohesive pathogenetic models but indicate that the molecular basis of human breast cancer is heterogeneous.

The SWI/SNF ATPases Are Required for Triple Negative Breast Cancer Cell Proliferation

The Brahma (BRM) and Brahma-related Gene 1 (BRG1) ATPases are highly conserved homologs that catalyze the chromatin remodeling functions of the multi-subunit human SWI/SNF chromatin remodeling enzymes in a mutually exclusive manner. SWI/SNF enzyme subunits are mutated or missing in many cancer types, but are overexpressed without apparent mutation in other cancers. Here, we report that both BRG1 and BRM are overexpressed in most primary breast cancers independent of the tumor's receptor status. Knockdown of either ATPase in a triple negative breast cancer cell line reduced tumor formation in vivo and cell proliferation in vitro. Fewer cells in S phase and an extended cell cycle progression time were observed without any indication of apoptosis, senescence, or alterations in migration or attachment properties. Combined knockdown of BRM and BRG1 showed additive effects in the reduction of cell proliferation and time required for completion of cell cycle, suggesting that these enzymes promote cell cycle progression through independent mechanisms. Knockout of BRG1 or BRM using CRISPR/Cas9 technology resulted in the loss of viability, consistent with a requirement for both enzymes in triple negative breast cancer cells.

Progress against cancer (1971-2011): how far have we come?

'The big C', a common euphemism for cancer, has loomed large on the collective psyche of the mankind for centuries, not least because of the relative dearth of effective treatment against this disease but its ability to relentlessly evade them and come back to haunt us. However, the struggle against cancer took a decisive turn in 1971 when a relentless campaigning by health activists eventually led to signing of the National Cancer Act in the United States, an unprecedented event in the history of diseases. As we commemorate the 40th anniversary of the signing of that historic legislation, an assessment of the progress against cancer would naturally help us understand how we have fared so far in this struggle and guide us in our efforts to re-strategize and re-deploy our limited resources to their best use against this immortal enemy.

The synthetic androgen mibolerone induces transient suppression of the transformed phenotype in an androgen responsive human prostatic carcinoma cell line

The synthetic androgen mibolerone elicits a set of distinct changes in the behaviour of an androgen responsive human prostatic carcinoma cell line (LNCaP). Inhibition of cell proliferation, induction of morphological change and of a prostate specific mRNA, and inhibition of colony formation in soft agar are induced by very low concentrations of mibolerone. The natural androgen dihydrotestosterone is much less effective. The changes in growth characteristics and morphology are reverted by excess antiandrogen, i.e. cyproterone acetate or hydroxyflutamide. Cell lines lacking androgen receptors (PC-3, DU 145 and MRC-5) are completely unresponsive to mibolerone. Taken together, our results indicate androgen receptor mediated suppression of the transformed phenotype in LNCaP cells.

Localization in man of fifteen DNA sequences within the chromosome segment 13q12-q22

Fifteen human chromosome 13 specific DNA fragments, isolated from a lambda phage genomic library, were localized within the segment 13q12-q22. One was mapped to 13q12.1-q12.2, three to 13q12.3-q13.1, one to 13q14,1-q14.2, five to 13q14.1-q21.1, one to 13q21.1-q21.2, two to 13q21.2, and one to 13q22.1, and one to 13q22. The localization was performed by hybridization to Southern blots of a panel of human cell lines with overlapping deletions in 13q, and for three probes also by in situ hybridization to metaphase chromosomes.

Cellular proteins that are targets for transformation by DNA tumour viruses

Small DNA tumour viruses produce proteins that redirect cellular gene expression and growth control. The E1A polypeptides of adenovirus perform the functions of transcriptional activation and cellular transformation. These two functions are carried out by different domains within the E1A protein. The E1A protein associates with several cellular proteins, including the product of the retinoblastoma gene, pRb-1. Mutational analysis correlates transformation with the sites required for binding pRb and two other cellular proteins, p107 and a 300 kDa polypeptide. This correlation suggests that these proteins are targets for E1A-mediated transformation. Transforming proteins from other small DNA tumour viruses interact with pRb, raising the possibility that a common event in viral transformation is the inactivation of proteins that inhibit cellular proliferation. The role of the E1A-associated 60 kDa protein, p60, in transformation is being investigated. In the absence of E1A, p60 binds to the human homologue of the Schizosaccharomyces pombe cdc2 gene product, p34, to form a complex that has kinase activity that oscillates during the cell cycle. Ongoing studies of the effect of adenovirus infection, and specifically E1A expression, on this cellular kinase may provide clues to how E1A overcomes cell cycle controls and transforms cells.

A genetic basis for tumour suppression

The technique of somatic cell hybridization has established the phenomenon of tumour suppression and provided evidence for a genetic basis for suppression. Further refinements aimed at eventually identifying 'tumour suppressor' genes include the use of monochromosome transfer via microcell hybridization. The application of this technique to the study of tumour suppression in tumorigenic HeLa cell x fibroblast hybrids, Wilms' tumour, retinoblastoma and osteosarcoma cells is described. The issue of whether tumour suppression involves a direct effect on expression of activated oncogenes is discussed. Transformation of normal human cells in culture by activated cellular oncogenes is an extremely rare event. This may be due to a relatively greater genomic stability of human cells compared to rodent cells. We describe the use of a spontaneously immortalized human keratinocyte cell line, HaCaT, for studies of the effects of introduction of activated c-Ha-ras oncogene into these cells, with particular reference to tumorigenic conversion.

Loss of genetic information in cancer

The determination and comparison of genotypic combinations at genomic loci in normal and tumour tissues from patients with various types of cancer have defined the chromosomal locations of loci at which recessive mutations play a role in disease. The predisposing nature of some of these mutant alleles is exemplified in studies of retinoblastoma and osteogenic sarcoma. These two clinically associated diseases share a pathogenetically causal predisposition that maps to chromosome position 13q14. A similar mechanism at 11p15.5 is involved in the development of the embryonal variant of rhabdomyo-sarcoma, Wilms' tumour and hepatoblastoma. Finally, genomic alteration of chromosome 10 is apparent in glioblastomas and mixed tumours of glioblastoma/astrocytoma grade III but not in homogenous astrocytoma grades II or III, suggesting the definition of a locus involved in tumour progression and, perhaps, an approach to molecular genetic staging of tumours.

Gene therapy in clinical medicine

Although the field of gene therapy has experienced significant setbacks and limited success, it is one of the most promising and active research fields in medicine. Interest in this therapeutic modality is based on the potential for treatment and cure of some of the most malignant and devastating diseases affecting humans. Over the next decade, the relevance of gene therapy to medical practices will increase and it will become important for physicians to understand the basic principles and strategies that underlie the therapeutic intervention. This report reviews the history, basic strategies, tools, and several current clinical paradigms for application.

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.

Retinoblastoma tumor suppressor and genome stability

Retinoblastoma gene (Rb) is the prototype of tumor suppressors. Germline mutation in the retinoblastoma gene is susceptible to cancer and reintroduction of wild-type Rb is able to suppress neoplastic phenotypes. The fundamental cellular functions of Rb in the control of cell growth and differentiation are important for its tumor suppression. In general, cancer susceptibility caused by inactivation of a tumor suppressor gene results from genome instability. Accordingly, Rb may function in the maintenance of chromosome stability by influencing mitotic progression, faithful chromosome segregation, and structural remodeling of mitotic chromosomes. Rb is also implicated in the regulation of replication machinery and in the control of cell cycle checkpoints in response to DNA damage, further supporting such a role for Rb. Moreover, the mechanistic basis for Rb-mediated transcriptional repression has revealed its connection to global chromatin remodeling. It is likely that Rb suppresses tumor formation by virtue of its multiple biological activities, and a theme throughout its multiple cellular functions is its central role in controlling activities that involve chromatin remodeling. A model in which Rb controls global genome fluidity is thus proposed. Finally, a recent study provides direct evidence indicating that loss of Rb function leads to genome instability. Therefore, tumor suppressors have a common role in the maintenance of genome stability, and such a role may be pivotal for their functions in tumor suppression.

Sustained production of H(2)O(2) activates pro-matrix metalloproteinase-2 through receptor tyrosine kinases/phosphatidylinositol 3-kinase/NF-kappa B pathway

A rate-limiting step of tumor cell metastasis is matrix degradation by active matrix metalloproteinases (MMPs). It is known that reactive oxygen species are involved in tumor metastasis. Sustained production of H(2)O(2) by phenazine methosulfate (PMS) induced activation of pro-MMP-2 through the induction of membrane type 1-MMP (MT1-MMP) expression in HT1080 cells. MMP-2, MMP-9, and tissue inhibitor of metalloproteinase-1 and -2 levels were changed negligibly by PMS. A one time treatment with H(2)O(2) did not induce activation of MMPs. It was also demonstrated that superoxide anions and hydroxyl radicals were not related to PMS action. PMS-induced pro-MMP-2 activation was regulated by the receptor tyrosine kinases, especially the receptors of platelet-derived growth factor and vascular endothelial growth factor, and downstream on the phosphatidylinositol 3-kinase/NF-kappa B pathway but not Ras, cAMP-dependent protein kinase, protein kinase C, and mitogen-activated protein kinases. PMS did not induce pro-MMP-2 activation in T98G and NIH3T3 cells. This may be related to a low level of MT1-MMP, indicating a threshold level of MT1-MMP is important for pro-MMP-2 activation. Furthermore, PMS increased cell motility and invasion but decreased cell-cell interaction. Cell-matrix interaction was not affected by PMS.

15-Deoxy-delta12,14-prostaglandin J2 induces apoptosis of a thyroid papillary cancer cell line (CG3 cells) through increasing intracellular iron and oxidative stress

Treatment of carcinoma cell lines with 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2), a natural ligand of the peroxisome proliferator-activated receptor-gamma, has been reported to induce apoptosis and/or inhibit proliferation. In this study, we investigated the cytotoxic effect and the action mechanisms of 15d-PGJ2 in a thyroid papillary cancer cell line, CG3. The results indicate that 15d-PGJ2 caused cytotoxicity and increased the amount of intracellular reactive oxygen species (ROS) in these cells. Mitochondrial oxidative phosphorylation inhibitors (carbonyl cyanide m-chloro-phenylhydrazone, oligomycin, cyclosporin A and rotenone), NADPH oxidase inhibitor (diphenyleneiodonium), xanthine oxidase inhibitor (allopurinol) and NO synthase inhibitor (N-monomethyl-L-arginine acetate) did not reduce the generation of ROS. However, catalase, N-acetyl-cysteine and the iron chelator desferri-oxamine decreased the intracellular ROS of 15d-PGJ2-treated CG3 cells. Furthermore, 15d-PGJ2 enhanced the accumulation of iron in the CG3 cells. These data suggest that 15d-PGJ2 induces the generation of ROS by enhancing the accumulation of intracellular iron and that the increased oxidative stress may cause apoptosis of CG3 cells.

Spontaneous regression of neoplasms: new possibilities for immunotherapy

In mammalian cells, neoplastic transformation is directly associated with the expression of oncogenes, loss or simple inactivation of the function of tumour suppressor genes and the production of certain growth factors. Genes for suppression of the development of the neoplastic cellular immunophenotype, as well as inhibitory growth factors, have regulatory functions within the normal processes of cell division and differentiation. Telomerase (a ribonucleoprotein polymerase) activation is frequently detected in various neoplasms. Telomerase activation is regarded as essential for cell immortalisation and its inhibition may result in spontaneous regression of neoplasms. This phenomenon of neoplasms occurs when the malignant tissue mass partially or completely disappears without any treatment or as a result of a therapy considered inadequate to influence systemic neoplastic growth. This definition makes it clear that the term 'spontaneous regression' applies to neoplasms in which the overall malignant disease is not necessarily cured and to cases where the regression may not be complete or permanent. A number of possible mechanisms of spontaneous regression are reviewed, with the understanding that no single mechanism can completely account for this phenomenon. The application of the newest immunological, molecular biological and genetic insights for more individualised and adequate antineoplastic immunotherapy (alternative biotherapy) is also discussed.

Cell cycle arrest is sufficient for p53-mediated tumor regression

p53 gene therapy can induce tumor regression, but the low efficacy of in vivo gene transfer has greatly hampered the mechanistic analysis of this antitumoral activity. We therefore used a p53-null human NSCLC cell line in which we reintroduced the wild-type p53 gene under control of a tetracycline-dependent promoter. P53 induction provokes cell cycle arrest in G0/G1 and G2/M phase, an up-regulation of p21, a down-regulation of cyclin B1 and appearance of senescence features without down-regulation of human telomerase reverse transcriptase. No detectable morphological changes of apoptosis nor procaspase-3 activation are observed. In subcutaneous tumors grafted in nude mice, the induction of p53 expression leads to a complete and longlasting tumor regression in 28 days which is associated with cell cycle arrest, but not detectable apoptosis nor inhibition of angiogenesis. These results show that irreversible cell cycle arrest is sufficient to elicit tumor regression after p53 gene transfer in p53-deficient tumor cells.

Global analysis of differential gene expression after transformation with the v-H-ras oncogene in a murine tumor model

Mouse PB-3c mast cells stably transfected with the v-H-ras oncogene induce tumor formation in vivo when implanted into mice. Such tumor cells are characterized by an autocrine IL-3 loop. DNA microarrays allow simultaneous transcript imaging of several thousand genes and the technique was applied in this tumor model to analyse gene expression following malignant transformation. Using three independent tumor lines derived from the same precursor the expression of about 400 out of 11 000 genes was modulated in each tumor. A subset of only 75 genes (0.68%) is shared and up- or downregulated in all three lines. A significant portion of this gene pool possesses functions related to tumorigenesis such as cell adhesion, signaling or transcriptional regulation. Apart from a number of expressed sequence tags (EST's) we find downregulation of four interferon-inducible genes in the tumor lines. Finally, when we extrapolate our data to the complete mouse genome, we estimate that about 500 genes are differentially expressed in tumor cells compared to the precursor cell PB-3c.

The retinoblastoma gene: a prototypic and multifunctional tumor suppressor

Genome instability has been implicated in the generation of multiple somatic mutations that underlie cancer. Germline mutation in the retinoblastoma (RB) gene leads to tumor formation in both human and experimental animal models, and reintroduction of wild-type RB is able to suppress neoplastic phenotypes. Rb governs the passage of cells through the G1 phase-restriction point and this control is lost in most cancer cells. Rb has also been shown to promote terminal differentiation and prevent cell cycle reentry. Recent studies implicate Rb in mitotic progression, faithful chromosome segregation, checkpoint control, and chromatin remodeling, suggesting that Rb may function in the maintenance of genome integrity. It is likely that Rb suppresses tumor formation by virtue of its multiple biological activities. A single protein capable of performing multiple antioncogenic functions may be a common characteristic of other tumor suppressors including p53 and BRCA1/2.

Neoplastic transformation and tumorigenesis associated with sam68 protein deficiency in cultured murine fibroblasts

Sam68 is a multimeric 68-kDa RNA-binding nuclear protein of unknown function that interacts with, and is tyrosine-phosphorylated by, the oncogenic protein Src during mitosis. Random homozygous knock-out (RHKO) is a retroviral-based antisense RNA strategy that can identify chromosomal genes whose functional disablement leads to reversible tumorigenic capabilities. Here we report that RHKO-induced Sam68 deficiency results in neoplastic transformation of murine NIH3T3 fibroblasts. Whereas simple haploinsufficiency of Sam68 produced by insertion mutagenesis in a single chromosomal allele did not detectably affect cell growth, reduction of Sam68 protein to <25% of the wild type level was associated with anchorage-independent growth, defective contact inhibition, and the ability to form metastatic tumors in nude mice. These properties were reversed by cessation of RHKO inactivation. Our findings, which indicate that the Sam68 protein level can prominently affect cell proliferation, implicate Sam68 function in tumorigenesis. Consistent with these results is evidence that cells undergoing mitosis show a dramatic reduction in the level of Sam68 protein.

Antisense RNA-mediated deficiency of the calpain protease, nCL-4, in NIH3T3 cells is associated with neoplastic transformation and tumorigenesis

We previously have described the use of an antisense RNA strategy termed random homozygous knock-out (RHKO) to identify negative regulators of cell proliferation. Here we report the discovery that RHKO-mediated deficiency of the nCL-4 calpain protease results in cellular transformation of and tumorigenesis by murine NIH3T3 fibroblasts. We isolated cell clones able to form colonies on 0.5% soft agar and found that these cells generated tumors when injected subcutaneously into nude mice. The gene inactivated by RHKO was identified as nCL-4 by genomic library screening, transcript analysis, and DNA sequencing. Anchorage-independent growth, as indicated by colony formation on soft agar, was reversed by reversal of antisense-mediated homozygous inactivation, but continued haplo-insufficiency of nCL-4 resulting from insertional mutagenesis of one nCL-4 allele was associated with persistent tumorigenesis. nCL-4 cDNA expressed in naive 3T3 cells in the antisense, but not sense, direction under control of the cytomegalovirus early promoter reproduced the anchorage-independent growth effects of RHKO. Our results implicate deficiency of the nCL-4 calpain protease in neoplastic transformation.

Mutation of p53 gene codon 63 in saliva as a molecular marker for oral squamous cell carcinomas

The inactivation of tumor suppressor gene (TSG) is important during multistage carcinogenesis. The p53 TSG is frequently mutated in oral squamous cell carcinomas. These mutations can serve as very specific markers for the presence of tumor cells in a background of normal cells. In this study, 10 oral squamous cell carcinoma patients and 27 normal dental students were collected from Chung Shan Medical and Dental College Hospital, Taichung, Taiwan. Extractions of DNA from saliva were obtained. Exon 4 and intron 6 within the p53 gene were amplified with polymerase chain reactions (PCRs) followed by DNA sequence analysis. DNA sequence analysis of PCR products revealed that five of eight (62.5%) tumor saliva samples and five of 27 (18. 52%) healthy saliva samples contained p53 exon 4 codon 63 mutations. These results were significantly different by using Chi-square test (P<0.05). The majority of the base substitutions were C deletions. Probable hot spots for the mutation were identified at exon 4 codon 63, which has not been observed before in head and neck cancers. Our study indicated that mutation of p53 codon 63 in saliva might be a molecular marker for oral squamous cell carcinomas. In addition, the amount of DNA recovered from saliva in most cases is sufficiently large and its quality suitable to enable PCR amplification which could be used in the search for mutations. The protocol described is rapid, cheap, and easy to perform, and may be useful for epidemiological studies for oral carcinogenesis.

Oxidative stress and cell cycle checkpoint function

Oxidative stress and the damage that results from it have been implicated in a wide number of disease processes including atherosclerosis, autoimmune disorders, neuronal degeneration, and cancer. Reactive oxygen species (ROS) are ubiquitous and occur naturally in all aerobic species, coming from both exogenous and endogenous sources. ROS are quite reactive and readily damage biological molecules, including DNA. While the damaging effects of ROS on DNA have been intensively studied, the effects of oxidative damage on cell cycle checkpoint function have not. Here will we review several biologically important ROS and their sources, the cell cycle, checkpoints, and current knowledge about the effects of ROS on initiating checkpoint responses.

Molecular interactions of cancer and age

The authors believe that the aging process--the loss of youthful resilience--is caused by the decline of many hormones. By restoring these hormone levels, the decay associated with old age can be eliminated and in some cases, perhaps reversed. The hormones that naturally occur in the body should be replenished through a medically sound regimen. The hormones must work together. The data indicate that aging occurs at two levels: systemically and cellularly. Systemic controls regulate the rates of intracellular enzymatic processes that accelerate to protect against aging.

Interaction between the pRb2/p130 C-terminal domain and the N-terminal portion of cyclin D3

An association between cyclin D3 and the C-terminal domain of pRb2/p130 was demonstrated using the yeast two-hybrid system. Further analysis restricted the epitope responsible for the binding within the 74 N-terminal amino acids of cyclin D3, independent of the LXCXE amino acid motif present in the D-type cyclin N-terminal region. In a coprecipitation assay in T98G cells, a human glioblastoma cell line, the C-terminal domain of pRb2/p130 was able to interact solely with cyclin D3, while the corresponding portion of pRb interacted with either cyclin D3 or cyclin D1. In T98G cells, endogenous cyclin D3-associated kinase activity showed a clear predisposition to phosphorylate preferentially the C-terminal domain of pRb2/p130, rather than that of pRb. This propensity was also confirmed in LAN-5 human neuroblastoma cells, where phosphorylation of the pRb2/p130 C-terminal domain and expression of cyclin D3 also decreased remarkably in the late neural differentiation stages.

Reversible tumorigenesis induced by deficiency of vasodilator-stimulated phosphoprotein

Random homozygous knockout (RHKO) is an antisense RNA strategy capable of identifying genes whose homozygous functional inactivation yields a selectable phenotype in cells growing in culture. Using this approach, we isolated NIH 3T3 fibroblast clones that showed the ability to form colonies on 0.5% agar and tumors in nude mice. The gene inactivated in one of these clones was found to encode VASP (vasodilator-stimulated phosphoprotein), a previously identified protein that binds to components of the cadherin-catenin junctional complex and has been implicated in cell-cell interactions, the formation of actin filaments, and the transmission of signals at the cytoskeleton-membrane interface. Fibroblasts made deficient in VASP by RHKO showed loss of contact inhibition, and consequently, continued cell division past confluence. Restoration of VASP function by reversal of RHKO yielded cells that had lost the neoplastic capabilities acquired during RHKO. Overproduction of VASP mRNA in the sense or antisense orientation from expression constructs introduced by transfection into naive NIH 3T3 fibroblasts also resulted in neoplastic transformation, implying that normal cell growth may require the maintenance of VASP expression within a narrow range. Our results implicate VASP in tumorigenesis and/or cancer progression.

p53 mutations in tumors derived from irradiated human thyroid epithelial cells

A non-tumorigenic human thyroid epithelial cell line (HTori-3) has been transformed into tumorigenic cells by exposure in vitro to alpha particles or gamma-radiation. These transformants were tumorigenic in athymic nude mice and tumors were transplantable into other nude mice. To further characterize processes involved in neoplastic progression, the tumor cell lines derived from these radiation-induced primary tumors were screened for mutations in the p53 tumor suppressor gene. p53 mutation was detected by single-strand conformation polymorphism (SSCP) analysis of exons 5 to 8 inclusive. Mutations detected by SSCP analysis were confirmed by sequencing. Mutations were detected in all four exons analysed, although there was no correlation between dose, LET or mutation position or frequency. Mutations in p53 exons 6 and 7 have been reported in the childhood papillary thyroid carcinomas in Belarus presumably as a result of radioiodine fall-out. Similarly here, p53 mutations are induced experimentally during the development of human thyroid tumors generated by irradiation of a human thyroid epithelial cell line in vitro.

Cloning and Characterization of a Lymphoid-Specific, Inducible Human Protein Tyrosine Phosphatase, Lyp

Protein tyrosine phosphatases act in conjunction with protein kinases to regulate the tyrosine phosphorylation events that control cell activation and differentiation. We have isolated a previously undescribed human phosphatase, Lyp, that encodes an intracellular 105-kD protein containing a single tyrosine phosphatase catalytic domain. The noncatalytic domain contains four proline-rich potential SH3 domain binding sites and an NXXY motif that, if phosphorylated, may be recognized by phosphotyrosine binding (PTB) domains. Comparison of the Lyp amino acid sequence with other known proteins shows 70% identity with the murine phosphatase PEP. The human Lyp gene was localized to chromosome 1p13 by fluorescence in situ hybridization analysis. We also identified an alternative spliced form of Lyp RNA, Lyp2. This isoform encodes a smaller 85-kD protein with an alternative C-terminus. The lyp phosphatases are predominantly expressed in lymphoid tissues and cells, with Lyp1 being highly expressed in thymocytes and both mature B and T cells. Increased Lyp1 expression can be induced by activation of resting peripheral T lymphocytes with phytohemagglutinin or anti-CD3. Lyp1 was found to be constitutively associated with the proto-oncogene c-Cbl in thymocytes and T cells. Overexpression of lyp1 reduces Cbl tyrosine phosphorylation, suggesting that it may be a substrate of the phosphatase. Thus, Lyp may play a role in regulating the function of Cbl and its associated protein kinases.

Significance of angiogenesis in cancer therapy

BACKGROUND

For most solid tumours, surgery remains the most effective primary treatment. Despite apparently curative resection, significant numbers of patients develop secondary disease due to growth of undetected micrometastases. The ability of a tumour to metastasize is related to the degree of angiogenesis it induces. In addition, micrometastases rely on new vessel formation to provide the nutrients necessary for growth. A better understanding of how tumours acquire their blood supply may lead to more effective adjuvant therapies and improve survival following surgery.

METHODS

A systematic review of the literature on angiogenesis between 1971 and 1997 was performed using the Medline database to ascertain current thinking on angiogenesis and its relevance in oncological surgery.

RESULTS

Angiogenesis is a physiological process subject to autocrine and paracrine regulation which has the potential to become abnormal and play a part in a number of pathological states, including cancer. Increased angiogenic stimuli in the perioperative period, associated with concomitant reduction in tumour-derived antiangiogenic factors following resection of a primary tumour, result in a permissive environment which allows micrometastases to grow.

CONCLUSION

Recognition of the role of angiogenesis in metastatic tumour growth represents a significant development in our understanding of tumour biology. The development of antiangiogenic agents offers new promise in the treatment of malignancy. Such agents may prevent or control the development and growth of primary and metastatic tumours.

Expression of E-cadherin adhesion molecule in vocal cord carcinomas

E-cadherin is a 120 kDa transmembrane protein that plays a major role in the maintenance of cell-cell adhesion in epithelial tissues. In the present study its expression was examined immunohistochemically for the first time using paraffin-embedded archival tissues of 38 vocal cord carcinomas. Ten cases of vocal cord polyps were used as positive controls. According to our criteria, results showed that all but one of the polyps, in which staining was lost, had strong or moderate E-cadherin expression, whereas 32% of the cases with tumors showed preserved staining, and 68% of cases showed a reduced staining. E-cadherin expression was significantly correlated with histological stages, with a greater expression in carcinoma in situ and microinvasive carcinoma than in invasive carcinoma (P = 0.010). A significant correlation was also found between E-cadherin expression and the degree of tumor differentiation (P = 0.018). Some of these findings were consistent with previously published data using fresh tissues. Our study provides evidence that E-cadherin may be linked to progression and differentiation of laryngeal cancer and could play a role as a tumor-suppressor gene in this cancer.

The role of p53 tumor suppressor gene in human head and neck tumorigenesis

Molecular genetics has led to new insights into diagnosis and treatment of human cancer. The alterations of tumor suppressor genes like retinoblastoma, p53 and others may have an important role in tumorigenesis. Mutations of p53 have been found in a majority of human malignancies including head and neck cancer. The distribution of p53 is different between types of tumors, suggesting environmental exposure as a cause active factor. The p53 mutation in head and neck tumors is an early event and appears to have a hot spot region at codons 238-248. While mutation and loss of heterozygosity at p53 are important in the genesis of head and neck cancer, other mechanisms such as binding of viral and cellular proteins to p53 are also likely to play a role.

Simultaneous expression of the ras p21 and p53 proteins in human endometrial carcinomas

The expression of ras-encoded p21 and p53 proteins was analyzed by immunohistochemical staining with monoclonal antibodies in 26 paraffin-embedded specimens (25 endometrial carcinomas and 1 uterine carcinosarcoma) taken from Polish women. The biotin-streptavidin-peroxidase detection system was employed. ras p21 protein was expressed in 68% of the specimens and p53 positive staining was noted in 36% of the carcinomas. Simultaneous expression of the ras p21 and p53 proteins was demonstrated in 8 (32%) out of the 25 specimens. Except one case, where the p53 protein was expressed, ras p21 protein was also detected. Both proteins were demonstrated in the sole case of carcinosarcoma. A difference between the detection of simultaneous expression of the ras p21 and p53 proteins in correlation with FIGO stages I to II-IV has been reported (22% v. 57% respectively). These data indicate, that ras p21 correlated with p53 positive staining in one-third of the endometrial cancers analyzed. The simultaneous detection of both proteins correlated with the advanced clinical stage of human endometrial carcinomas.

Retinoblastoma protein family in cell cycle and cancer: a review

Two genes, p107 and Rb2/p130, are strictly related to RB, the most investigated tumor suppressor gene, responsible for susceptibility to retinoblastoma. The products of these three genes, namely pRb, p107, and pRb2/p130 are characterized by a peculiar steric conformation, called "pocket," responsible for most of the functional interactions characterizing the activity of these proteins in the homeostasis of the cell cycle. The interest in these genes and proteins springs from their ability to regulate cell cycle processes negatively, being able, for example, to dramatically slow down neoplastic growth. So far, among these genes, only RB is firmly established to act as a tumor suppressor, because its lack-of-function is clearly involved in tumor onset and progression. It has been found deleted or mutated in most retinoblastomas and sarcomas, but its inactivation is likely to play a crucial role in other types of human cancers. The two other members of the family have been discovered more recently and are currently under extensive investigation. We review analogies and differences among the pocket protein family members, in an attempt to understand their functions in normal and cancer cells.

Tsg101: a novel tumor susceptibility gene isolated by controlled homozygous functional knockout of allelic loci in mammalian cells

Using a novel strategy that enables the isolation of previously unknown genes encoding selectable recessive phenotypes, we identified a gene (tsg101) whose homozygous functional disruption produces cell transformation. Antisense RNA from a transactivated promoter introduced randomly into transcribed genes throughout the genome of mouse 3T3 fibroblasts was used to knock out alleles of chromosomal genes adjacent to promoter inserts, generating clones that grew in 0.5% agar and formed metastatic tumors in nude mice. Removal of the transactivator restored normal growth. The protein encoded by tsg101 cDNA encodes a coiled-coil domain that interacts with stathmin, a cytosolic phosphoprotein implicated previously in tumorigenesis. Overexpression of tsg101 antisense transcripts in naive 3T3 cells resulted in cell transformation and increased stathmin-specific mRNA.

Hereditary cancer: two hits revisited

According to a "two-hit" model, dominantly inherited predisposition to cancer entails a germline mutation, while tumorigenesis requires a second, somatic, mutation. Non-hereditary cancer of the same type requires the same two hits, but both are somatic. The original tumor used in this model, retinoblastoma, involves mutation or loss of both are somatic. The original tumor used in this model, retinoblastoma, involves mutation or loss of both copies of the RB1 tumor-suppressor gene in both hereditary and non-hereditary forms. In fact, most dominantly inherited cancers show this relationship. New dominantly inherited cancers show this relationship. New questions have arisen, however. When a tumor-suppressor gene is ubiquitously expressed, why is there any specificity of tumor predilection? In some instances, it is clear that two hits produce only a benign precursor lesion and that other genetic events are necessary. As the number of necessary events increase, the impact of the germline mutation diminishes. The number of events is least for embryonal tumors, and relatively small for certain sarcomas. Stem-cell proliferation evidently plays a key role early in carcinogenesis. In some tissues it is physiological, as in embryonic development and in certain tissues in adolescence. In adult renewal tissues, the sites of the common carcinomas, mutation may be necessary to impair the control of switching between renewal and replicative cell divisions; the APC gene may be the target of such a mutation.

Role of oxygen free radicals in cancer development

In aerobic life, oxidative stress arises from both endogenous and exogenous sources. Despite antioxidant defence mechanisms, cell damage from oxygen free radicals (OFR) is ubiquitous. OFR-related lesions that do not cause cell death can stimulate the development of cancer. This review discusses the effects of oxidative stress at the different stages of carcinogenesis. Mutagenesis through oxidative DNA damage is widely hypothesised to be a frequent event in the normal human cell. A large body of evidence suggests important roles of OFR in the expansion of tumour clones and the acquisition of malignant properties. In view of these facts, OFR may be considered as an important class of carcinogens. Therefore, the ineffectiveness of preventive antioxidant treatments, as documented in several recent clinical trials, is surprising. However, the difficulties of antioxidant intervention are explained by the complexity of both free radical chemistry and cancer development. Thus, reducing the avoidable endogenous and exogenous causes of oxidative stress is, for the present, the safest option. In the near future, new insights in the action of tumour suppressor genes and the DNA repair mechanisms may lead the way to additional tools against carcinogenesis from OFR.

Some characteristics of neoplastic cell transformation in transgenic mice

The role of the expression of different cellular genes and viral oncogenes in malignant cell transformation is discussed. We pay special attention to the role of the genes for growth factors and their receptors and homeobox genes in oncogenesis. Based on both the literature and our own data, specific features of tumors developed in transgenic mice are discussed. All of these data are used to analyze current theories of multistep oncogenesis and the stochastic component in this process. We suggest that all known evidence about the mechanisms of oncogenesis be used in studying the problem at various structural and functional levels in an organism. The chapter shows that transgenic mice are a most suitable model for studying various aspects of malignant transformation from the molecular to the organismal and populational levels.

The effect of the JE (MCP-1) gene, which encodes monocyte chemoattractant protein-1, on the growth of HeLa cells and derived somatic-cell hybrids in nude mice

To investigate the effect of tumor-associated macrophages on the in vivo growth properties of cervical carcinoma cells, tumorigenic human papilloma virus (HPV) 18-positive HeLa cells were transfected with an expression vector harboring the cDNA for the macrophage chemoattractant protein-1 JE (MCP-1). Although the endogenous gene is present and not structurally rearranged, its expression seems to be negatively affected by a still unknown mechanism. Inoculation of JE (MCP-1)-negative HeLa cells into nude mice led to rapidly growing tumors, where macrophage infiltration into the inner tumor mass was not detectable immunohistochemically. The activity that attracted mononuclear cells under both in vitro and in vivo condition was reconstituted in HeLa cells after transfection with the JE (MCP-1) expression vector. Heterotransplantation of those cells into immunocompromised animals resulted in significant growth retardation that was accompanied by a strong infiltration of macrophages. On the other hand, in vivo selection of nonmalignant hybrids made between wild-type HeLa cells and normal human fibroblasts in nude mice resulted in tumorigenic segregants 4 mo after inoculation into the animals. Monitoring JE (MCP-1) expression directly within those nodules, we found that transcription was either absent or only weakly detectable. Recultivation of JE (MCP-1)-positive tissue grafts under in vitro conditions revealed that the gene was only marginally inducible by tumor necrosis factor-alpha, a cytokine that normally induces a very strong activation of transcription in nontumorigenic cells. These findings suggest that functional JE (MCP-1) expression and in turn activated macrophages may play a pivotal role in controlling the proliferation rate of HPV-positive cells in vivo.

Cytogenetics of 158 patients with regional or disseminated melanoma. Subset analysis of near-diploid and simple karyotypes

We report on the cytogenetic analyses of 158 cases of metastatic malignant melanoma, comprised of 63 cases with regional disease (RD) and 95 cases with distant (metastatic) disease (DD). Clonal structural abnormalities were identified in 126 (80%) cases and were significantly increased ( < 0.01 after adjusting for multiple comparisons) on chromosomes (in order of frequency of involvement) 1, 6, 7, 11, 9, and 3. Clustering of breakpoints occurred at 1p36, 1p22-q21, 6p11-q21, 9p, 11q23-qter, 13p (especially for cases with DD), and 19q13. The most common clonal numerical abnormalities, in a subset of 49 near-diploid cases were -10, -22, -9, +7, -19, and -Y. Analysis of chromosome segment gains and losses (CSRP) showed frequent loss of chromosomes 6 and 10, followed by equal rates of involvement of chromosomes 1, 7, and 9. Whole or segmental losses of chromosome 9 (especially 9p) correlate well with recent molecular genetic studies identifying putative suppressor genes, and are also likely important genetic abnormalities. However, based on the frequency of abnormalities in this large series of metastatic melanomas, it is likely that structural abnormalities of 1 and 6, and 10 are important in the pathogenesis of sporadic advanced melanoma.

The pathophysiology of angiogenesis

The formation of new capillary blood vessels, a process termed "angiogenesis", is one of the most pervasive and fundamentally essential biological processes encountered in mammalian organizations. Angiogenesis is an important event in a variety of physiological settings, such as embryonic development, chronic inflammation, and wound repair. It is a process that is tightly regulated in both time and space. Angiogenesis is driven by a cocktail of growth factors and pro-angiogenic cytokines and is tempered by an equally diverse group of inhibitors of neovascularization. Angiogenesis is also central to the etiology and pathogenesis of a number of pathological processes that include, among others, solid tumors, diseases of the eye, and chronic inflammatory disorders such as rheumatoid arthritis, psoriasis, and periodontitis. Based on recent work from several laboratories, it is now eminently clear that most if not all angiogenesis and vasoproliferative-dependent disease processes are not only a consequence of the unrestricted production of normal or aberrant forms of pro-angiogenic mediators but also the result of a relative deficiency in angiogenic-inhibitory molecules. In this review, I will describe how these multifunctional mediator systems function to coordinate and regulate the angiogenic response, and how disruption in the molecular controls that regulate the production of pro-angiogenic and angiostatic mediators leads to aberrant angiogenesis and disease. The implications of these findings in the development of novel therapeutic strategies for the treatment of diseases characterized by disregulated angiogenesis will also be discussed.

Familial and sporadic human renal cell carcinoma: evidence against a double-loss mechanism of carcinogenesis

It has been speculated that renal cell carcinoma (RCC) is an example of a double-loss mutation. We analyzed the age distribution of 71 cases of familial RCC and of 11 population-based cancer registries [German Democratic Republic, Denmark, Finland, Norway, Sweden, U.S.A. Whites, U.S.A. Blacks, Miyagi and Osaka Prefectures (Japan), Hong Kong, and Israeli Jews] according to the multi-hit and clonal growth models of carcinogenesis. The analysis rules out a double-loss mechanism for RCC. On both of the two models analyzed, carcinogenesis in the familial cases of RCC arises as a result of a three- to ten-fold increase in the average rate of mutation at the susceptible loci, as compared with the sporadic cases. In general, the clonal growth model provides a somewhat better fit to the age-distribution of RCC incidence than does the multi-hit model.

Induced terminal differentiation and tumorigenic suppression in murine keratinocyte somatic-cell hybrids

The development of malignancy has been associated with both the activation of oncogenes and the inactivation of tumor suppressor genes. Whereas recent data implicate tumor suppressor genes as cell-cycle check-points, the nature and timing of tumor suppressor gene inactivation during multistage carcinogenesis is still largely uncharacterized. To address this issue, we used a syngeneic mouse epidermal model system. By creating somatic-cell hybrids between nontumorigenic x benign (291 x 291.09RAT), nontumorigenic x malignant (291 x 291.05RAT and 291 x 291.03RAT), benign x malignant (291.09RAT x 291.03RAT) and malignant x malignant (291.03RAT x 291.05RAT) clones, multiple tumor suppressor activities were detected. Most importantly, we demonstrated the first example of the complete suppression of benign papillomas in vivo, thus implicating tumor suppressor gene activity loss an early event in skin carcinogenesis. In addition, the carcinoma phenotype was suppressed in vivo by nontumorigenic, benign, and heterologous malignant keratinocytes. The somatic-cell hybrids expressed the differentiation-specific keratins, K1 and K10, in response to high extracellular calcium concentrations (1.4 mM) in vitro. All of the hybrids had fewer local metastases than did the parental lines, and when tumor formation was not suppressed, the resulting tumors were highly differentiated. Polymerase chain reaction analysis of the neomycin-resistance gene at nontumorigenic injection sites indicated an absence of injected hybrids, and subsequent analyses failed to detect nontumorigenic 291 cells 1 wk after transplantation. These data demonstrate that distinct tumor suppressor gene activities are lost at discrete stages during multistage carcinogenesis and are consistent with the hypothesis that tumor suppression can occur through induction of terminal differentiation.

The role of the epidermal growth factor receptor in human gliomas: I. The control of cell growth

The epidermal growth factor receptor (EGFR) gene is amplified in over 40% of primary human glioblastomas and overexpressed in the majority. The authors' investigations demonstrate that the function of the EGFR in glioblastomas is distinct from that in other human cancers because it does not appear to mediate the primary growth-promoting effect of EGF. Findings show that the level of EGFR expression does not directly predict the growth response to EGF, with growth stimulated in some cells but inhibited in others when cells were cultured in plastic dishes. On the other hand, when human glioblastoma cells were placed in soft agar cultures, the cell line expressing the highest levels of the EGFR demonstrated considerable colony formation in response to EGF treatment. In addition, cell lines with the highest EGFR levels were also more resistant to the growth-suppressive effects of retinoic acid when maintained in soft agar. These observations suggest that even though the overexpression of the EGFR did not confer a distinct growth advantage to glioma cells cultured on flat culture dishes, the ability of these cells to maintain anchorage-independent growth in soft agar especially in response to EGF and retinoic acid is facilitated. Because anchorage-independent growth is the best in vitro correlate to tumorigenicity, amplification and overexpression of the EGFR in human glioblastoma cells may be in part responsible for the tumorigenic potential of these cells.

Gene-modified cells for the treatment of cancer

Gene therapy involves the insertion of a gene into an organism to treat a disease. Since its early development in the 1970s, gene therapy has expanded rapidly both in terms of the methods available and the number of candidate diseases for treatment. This report reviews gene therapy for cancer, including methodology, pre-clinical studies and experimental clinical trials.