Susceptibility of human diploid fibroblast strains to transformation by SV40 virus

Cancer cells arise from bacteria

Background

The origin of cancer cells is the most fundamental yet unresolved problem in cancer research. Cancer cells are thought to be transformed from the normal cells. However, recent studies reveal that the primary cancer cells (PCCs) for cancer initiation and secondary cancer cells (SCCs) for cancer progression are formed in but not transformed from the senescent normal and cancer cells, respectively. Nevertheless, the cellular mechanism of PCCs/SCCs formation is unclear. Here, based on the evidences (1) the nascent PCCs/SCCs are small and organelle-less resembling bacteria; (2) our finding that the cyanobacterium TDX16 acquires its algal host DNA and turns into a new alga TDX16-DE by de novo organelle biogenesis, and (3) PCCs/SCCs formations share striking similarities with TDX16 development and transition, we propose the bacterial origin of cancer cells (BOCC).

Presentation of the hypothesis

The intracellular bacteria take up the DNAs of the senescent/necrotic normal cells/PCCs and then develop into PCCs/SCCs by hybridizing the acquired DNAs with their own ones and expressing the hybrid genomes.

Testing the hypothesis

BOCC can be confirmed by testing BOCC-based predictions, such as normal cells with no intracellular bacteria can not "transform" into cancer cells in any conditions.

Implications of the hypothesis

According to BOCC theory: (1) cancer cells are new single-celled eukaryotes, which is why the hallmarks of cancer are mostly the characteristics of protists; (2) genetic changes and instabilities are not the causes, but the consequences of cancer cell formation; and (3) the common role of carcinogens, infectious agents and relating factors is inducing or related to cellular senescence rather than mutations. Therefore, BOCC theory provides new rationale and direction for cancer research, prevention and therapy.

XYY Caryotype and Medulloblastoma

The case is described of a child who presented a slight psychomotor retardation and malformative signs, together with an XYY caryotype, and who died at the age of 7 years from a medulloblastoma, as could be later confirmed by autoptic examination.

The relations between chromosomal and neoplastic pathology are described.

Fanconi anemia patients are more susceptible to infection with tumor virus SV40

Fanconi anemia (FA) is a recessive DNA repair disease characterized by a high predisposition to developing neoplasms. DNA tumor polyomavirus simian virus 40 (SV40) transforms FA fibroblasts at high efficiency suggesting that FA patients could be highly susceptible to SV40 infection. To test this hypothesis, the large tumor (LT) antigen of SV40, BKV, JCV and Merkel Cell (MC) polyomaviruses were tested in blood samples from 89 FA patients and from 82 of their parents. Two control groups consisting of 47 no-FA patients affected by other genetic bone marrow failure diseases and 91 healthy subjects were also evaluated. Although JCV, BKV and MC were not found in any of the FA samples, the prevalence and viral load of SV40 were higher in FA patients (25%; mean viral load: 1.1×10² copies/10⁵cells) as compared with healthy individuals (4.3%; mean viral load: 0.8×10¹ copies/10⁵cells) and genetic controls (0%) (p<0.005). A marked age-dependent frequency of SV40 was found in FA with respect to healthy subjects suggesting that, although acquired early in life, the virus can widespread more easily in specific groups of population. From the analysis of family pedigrees, 60% of the parents of SV40-positive probands were positive for the virus compared to 2% of the parents of the SV40-negative probands (p<0.005). It is worthy of note that the relative frequency of SV40-positive relatives detected in this study was the highest ever reported, showing that asymptomatic FA carriers are also more susceptible to SV40. In conclusion, we favor the hypothesis that SV40 spread could be facilitated by individuals who are genetically more susceptible to infection, such as FA patients. The increased susceptibility to SV40 infection seems to be associated with a specific defect of the immune system which supports a potential interplay of SV40 with an underlying genetic alteration that increases the risk of malignancies.

DNA viruses and the cellular DNA-damage response

It is clear that a number of host-cell factors facilitate virus replication and, conversely, a number of other factors possess inherent antiviral activity. Research, particularly over the last decade or so, has revealed that there is a complex inter-relationship between viral infection and the host-cell DNA-damage response and repair pathways. There is now a realization that viruses can selectively activate and/or repress specific components of these host-cell pathways in a temporally coordinated manner, in order to promote virus replication. Thus, some viruses, such as simian virus 40, require active DNA-repair pathways for optimal virus replication, whereas others, such as adenovirus, go to considerable lengths to inactivate some pathways. Although there is ever-increasing molecular insight into how viruses interact with host-cell damage pathways, the precise molecular roles of these pathways in virus life cycles is not well understood. The object of this review is to consider how DNA viruses have evolved to manage the function of three principal DNA damage-response pathways controlled by the three phosphoinositide 3-kinase (PI3K)-related protein kinases ATM, ATR and DNA-PK and to explore further how virus interactions with these pathways promote virus replication.

Human polyomaviruses in skin diseases

Polyomaviruses are a family of small, nonenveloped viruses with a circular double-stranded DNA genome of ∼5,000 base pairs protected by an icosahedral protein structure. So far, members of this family have been identified in birds and mammals. Until 2006, BK virus (BKV), JC virus (JCV), and simian virus 40 (SV40) were the only polyomaviruses known to circulate in the human population. Their occurrence in individuals was mainly confirmed by PCR and the presence of virus-specific antibodies. Using the same methods, lymphotropic polyomavirus, originally isolated in monkeys, was recently shown to be present in healthy individuals although with much lower incidence than BKV, JCV, and SV40. The use of advanced high-throughput sequencing and improved rolling circle amplification techniques have identified the novel human polyomaviruses KI, WU, Merkel cell polyomavirus, HPyV6, HPyV7, trichodysplasia spinulosa-associated polyomavirus, and HPyV9. The skin tropism of human polyomaviruses and their dermatopathologic potentials are the focus of this paper.

Update on human polyomaviruses and cancer

Over 50 years of polyomavirus research has produced a wealth of insights into not only general biologic processes in mammalian cells, but also, how conditions can be altered and signaling systems tweaked to produce transformation phenotypes. In the past few years three new members (KIV, WUV, and MCV) have joined two previously known (JCV and BKV) human polyomaviruses. In this review, we present updated information on general virologic features of these polyomaviruses in their natural host, concentrating on the association of MCV with human Merkel cell carcinoma. We further present a discussion on advances made in SV40 as the prototypic model, which has and will continue to inform our understanding about viruses and cancer.

Multiple DNA damage signaling and repair pathways deregulated by simian virus 40 large T antigen

We demonstrated previously that expression of simian virus 40 (SV40) large T antigen (LT), without a viral origin, is sufficient to induce the hallmarks of a cellular DNA damage response (DDR), such as focal accumulation of gamma-H2AX and 53BP1, via Bub1 binding. Here we expand our characterization of LT effects on the DDR. Using comet assays, we demonstrate that LT induces overt DNA damage. The Fanconi anemia pathway, associated with replication stress, becomes activated, since FancD2 accumulates in foci, and monoubiquitinated FancD2 is detected on chromatin. LT also induces a distinct set of foci of the homologous recombination repair protein Rad51 that are colocalized with Nbs1 and PML. The FancD2 and Rad51 foci require neither Bub1 nor retinoblastoma protein binding. Strikingly, wild-type LT is localized on chromatin at, or near, the Rad51/PML foci, but the LT mutant in Bub1 binding is not localized there. SV40 infection was previously shown to trigger ATM activation, which facilitates viral replication. We demonstrate that productive infection also triggers ATR-dependent Chk1 activation and that Rad51 and FancD2 colocalize with LT in viral replication centers. Using small interfering RNA (siRNA)-mediated knockdown, we demonstrate that Rad51 and, to a lesser extent, FancD2 are required for efficient viral replication in vivo, suggesting that homologous recombination is important for high-level extrachromosomal replication. Taken together, the interplay of LT with the DDR is more complex than anticipated, with individual domains of LT being connected to different subcomponents of the DDR and repair machinery.

SV40: Cell transformation and tumorigenesis

The story of SV40-induced tumorigenesis and cellular transformation is intimately entwined with the development of modern molecular biology. Because SV40 and other viruses have small genomes and are relatively easy to manipulate in the laboratory, they offered tractable systems for molecular analysis. Thus, many of the early efforts to understand how eukaryotes replicate their DNA, regulate expression of their genes, and translate mRNA were focused on viral systems. The discovery that SV40 induces tumors in certain laboratory animals and transforms many types of cultured cells offered the first opportunity to explore the molecular basis for cancer. The goal of this article is to highlight some of the experiments that have led to our current view of SV40-induced transformation and to provide some context as to how they contributed to basic research in molecular biology and to our understanding of cancer.

Upregulated ATM gene expression and activated DNA crosslink-induced damage response checkpoint in Fanconi anemia: implications for carcinogenesis

Fanconi anemia (FA) predisposes to hematopoietic failure, birth defects, leukemia, and squamous cell carcinoma of the head and neck (HNSCC) and cervix. The FA/BRCA pathway includes 8 members of a core complex and 5 downstream gene products closely linked with BRCA1 or BRCA2. Precancerous lesions are believed to trigger the DNA damage response (DDR), and we focused on the DDR in FA and its putative role as a checkpoint barrier to cancer. In primary fibroblasts with mutations in the core complex FANCA protein, we discovered that basal expression and phosphorylation of ATM (ataxia telangiectasia mutated) and p53 induced by irradiation (IR) or mitomycin C (MMC) were upregulated. This heightened response appeared to be due to increased basal levels of ATM in cultured FANCA-mutant cells, highlighting the new observation that ATM can be regulated at the transcriptional level in addition to its well-established activation by autophosphorylation. Functional analysis of this response using gamma-H2AX foci as markers of DNA double-stranded breaks (DSBs) demonstrated abnormal persistence of only MMC- and not IR-induced foci. Thus, we describe a processing defect that leads to general DDR upregulation but specific persistence of DNA crosslinker-induced damage response foci. Underscoring the significance of these findings, we found resistance to DNA crosslinker-induced cell cycle arrest and apoptosis in a TP53-mutant, patient-derived HNSCC cell line, whereas a lymphoblastoid cell line derived from this same individual was not mutated at TP53 and retained DNA crosslinker sensitivity. Our results suggest that cancer in FA may arise from selection for cells that escape from a chronically activated DDR checkpoint.

The human papillomavirus type 16 E7 oncoprotein activates the Fanconi anemia (FA) pathway and causes accelerated chromosomal instability in FA cells

Fanconi anemia (FA) patients have an increased risk for squamous cell carcinomas (SCCs) at sites of predilection for infection with high-risk human papillomavirus (HPV) types, including the oral cavity and the anogenital tract. We show here that activation of the FA pathway is a frequent event in cervical SCCs. We found that FA pathway activation is triggered mainly by the HPV type 16 (HPV-16) E7 oncoprotein and is associated with an enhanced formation of large FANCD2 foci and recruitment of FANCD2 as well as FANCD1/BRCA2 to chromatin. Episomal expression of HPV-16 oncoproteins was sufficient to activate the FA pathway. Importantly, the expression of HPV-16 E7 in FA-deficient cells led to accelerated chromosomal instability. Taken together, our findings establish the FA pathway as an early host cell response to high-risk HPV infection and may help to explain the greatly enhanced susceptibility of FA patients to squamous cell carcinogenesis at anatomic sites that are frequently infected by high-risk HPVs.

deltaNp73 facilitates cell immortalization and cooperates with oncogenic Ras in cellular transformation in vivo

TP73, despite significant homology to TP53, is not a classic tumor suppressor gene, since it exhibits upregulation of nonmutated products in human tumors and lacks a tumor phenotype in p73-deficient mice. We recently reported that an N-terminally truncated isoform, DeltaNp73, is upregulated in breast and gynecological cancers. We further showed that DeltaNp73 is a potent transdominant inhibitor of wild-type p53 and TAp73 in cultured human tumor cells by efficiently counteracting their target gene transactivations, apoptosis, and growth suppression functions (A. I. Zaika et al., J. Exp. Med. 6:765-780, 2002). Although these data strongly suggest oncogenic properties of DeltaNp73, this can only be directly shown in primary cells. We report here that DeltaNp73 confers resistance to spontaneous replicative senescence of primary mouse embryo fibroblasts (MEFs) and immortalizes MEFs at a 1,000-fold-higher frequency than occurs spontaneously. DeltaNp73 cooperates with cMyc and E1A in promoting primary cell proliferation and colony formation and compromises p53-dependent MEF apoptosis. Importantly, DeltaNp73 rescues Ras-induced senescence. Moreover, DeltaNp73 cooperates with oncogenic Ras in transforming primary fibroblasts in vitro and in inducing MEF-derived fibrosarcomas in vivo in nude mice. Wild-type p53 is likely a major target of DeltaNp73 inhibition in primary fibroblasts since deletion of p53 or its requisite upstream activator ARF abrogates the growth-promoting effect of DeltaNp73. Taken together, DeltaNp73 behaves as an oncogene that targets p53 that might explain why DeltaNp73 upregulation may be selected for during tumorigenesis of human cancers.

Diffusion and directed motion in cellular transport

We study the motion of a probe driven by microtubule-associated motors within a living eukaryotic cell. The measured mean square displacement, <x(t)2> of engulfed 2 and 3 microm diameter microspheres shows enhanced diffusion scaling as t(3/2) at short times, with a clear crossover to ordinary or subdiffusive scaling, i.e., t(gamma) with gamma less than or equal to 1, at long times. Using optical tweezers we tried to move the engulfed bead within the cell in order to relate the anomalous diffusion scaling to the density of the network in which the bead is embedded. Results show that the larger beads, 2 and 3 microm diameter, must actively push the cytoskeleton filaments out of the way in order to move, whereas smaller beads of 1 microm diameter can be "rattled" within a cage. The 1 microm beads also perform an enhanced diffusion but with a smaller and less consistent exponent 1.2<gamma<1.45. We interpret the half-integer power observed with large beads based on two diverse phenomena widely studied in purified cytoskeleton filaments: (1) the motion of the intracellular probe results from random forces generated by motor proteins rather than thermal collisions for classical Brownian particles, and (2) thermal bending modes of these semiflexible polymers lead to anomalous subdiffusion of particles embedded in purified gel networks or attached to single filaments, with <x(t)2> approximately t(3/4). In the case of small beads, there may also be a Brownian contribution to the motion that results in a smaller exponent.

SV40 large T-antigen disturbs the formation of nuclear DNA-repair foci containing MRE11

The accumulation of DNA repair proteins at the sites of DNA damage can be visualized in mutagenized cells at the single cell level as discrete nuclear foci by immunofluorescent staining. Formation of nuclear foci in irradiated human fibroblasts, as detected by antibodies directed against the DNA repair protein MRE11, is significantly disturbed by the presence of the viral oncogene, SV40 large T-antigen. The attenuation of foci formation was found in both T-antigen immortalized cells and in cells transiently expressing T-antigen, indicating that it is not attributable to secondary mutations but to T-antigen expression itself. ATM-mediated nibrin phosphorylation was not altered, thus the disturbance of MRE11 foci formation by T-antigen is independent of this event. The decrease in MRE11 foci was particularly pronounced in T-antigen immortalized cells from the Fanconi anaemia complementation group FA-D2. FA-D2 cells produce essentially no MRE11 DNA repair foci after ionizing irradiation and have a significantly increased cellular radiosensitivity at low radiation doses. The gene mutated in FA-D2 cells, FANCD2, codes for a protein which also locates to nuclear foci and may, therefore, be involved in MRE11 foci formation, at least in T-antigen immortalized cells. This finding possibly links Fanconi anaemia proteins to the frequently reported increased sensitivity of Fanconi anaemia cells to transformation by SV40. From a practical stand point these findings are particularly relevant to the many studies on DNA repair which exploit the advantages of SV40 immortalized cell lines. The interference of T-antigen with DNA repair processes, as demonstrated here, should be borne in mind when interpreting such studies.

A new dimension in retrograde flow: centripetal movement of engulfed particles

Centripetal motion of surface-adherent particles is a classic experimental system for studying surface dynamics on a eukaryotic cell. To investigate bead migration over the entire cell surface, we have developed an experimental assay using multinuclear giant fibroblasts, which provide expanded length scales and an unambiguous frame of reference. Beads coated by adhesion ligands concanavalin A or fibronectin are placed in specific locations on the cell using optical tweezers, and their subsequent motion is tracked over time. The adhesion, as well as velocity and directionality of their movement, expose distinct regions of the cytoplasm and membrane. Beads placed on the peripheral lamella initiate centripetal motion, whereas beads placed on the central part of the cell attach to a stationary cortex and do not move. Careful examination by complementary three-dimensional methods shows that the motion of a bead placed on the cell periphery takes place after engulfment into the cytoplasm, whereas stationary beads, placed near the cell center, are not engulfed. These results demonstrate that centripetal motion of adhering particles may occur inside as well as outside the cell. Inhibition of actomyosin activity is used to explore requirements for engulfment and aspects of the bead movement. Centripetal movement of adherent particles seems to depend on mechanisms distinct from those driving overall cell contractility.

De novo formation of focal complex-like structures in host cells by invading Streptococci

Group A streptococcus (GAS) induces its own entry into eukaryotic cells in vitro and in vivo. Fibronectin (Fn) bound to protein F1, a GAS surface protein, acts as a bridge connecting the bacterium to host cell integrins. This triggers clustering of integrins, which acquire a polar pattern of distribution similar to that of protein F1 on the GAS surface. A unique and transient adhesion complex is formed at the site of GAS entry, which does not contain alpha-actinin. Vinculin is recruited to the site of GAS entry but is not required for uptake. The invading GAS recruits focal adhesion kinase (FAK), which is required for uptake and is tyrosine phosphorylated. The Src kinases, Src, Yes and Fyn, enhance the efficiency of GAS uptake but are not absolutely required for GAS entry. In addition, Rac and Cdc42, but not Rho, are required for the entry process. We suggest a model in which integrin engagement by Fn-occupied protein F1 triggers two independent signalling pathways. One is initiated by FAK recruitment and tyrosine phosphorylation, whereas the other is initiated by the recruitment and activation of Rac. The two pathways subsequently converge to trigger actin rearrangement leading to bacterial uptake.

Site-specific and temporally-regulated retinoblastoma protein dephosphorylation by protein phosphatase type 1

pRb is dephosphorylated at mitotic exit by the type 1 serine/threonine protein phosphatases (PP1). Here we demonstrate for the first time that mitotic pRb dephosphorylation is a sequential, temporally-regulated event. We also provide evidence that the three mammalian isoforms of PP1, alpha, gamma-1, and delta, differ in their respective preferences for site-specific pRb dephosphorylation and that the mitotic and G(1) PP1-isoform counterparts exhibit differential activities towards mitotic pRb. Finally, the physiological relevance of the striking contrast between the patterns of Thr821 and Thr826 dephosphorylation, sites known to be important for disrupting binding of LXCXE-containing proteins to pRb, is addressed.

Molecular analysis of selected cell cycle regulatory proteins during aerobic and hypoxic maintenance of human ovarian carcinoma cells

We have previously reported on the development of an in vitro model system for studying the effect of hypoxia on ovarian carcinoma cell proliferation and invasion (Krtolica and Ludlow, 1996). These data indicate that the cell division cycle is reversibly arrested during the G1 phase. Here, we have continued this study to include the proliferation properties of both aerobic and hypoxic human ovarian carcinoma cells at the molecular level. The growth suppressor product of the retinoblastoma susceptibility gene, pRB, appears to be functional in these cells as determined by SV40 T-antigen binding studies. Additional G1-to-S cell cycle regulatory proteins, cyclins D and E, cyclin-dependent kinases (cdks) 4 and 2, and cdk inhibitors p27 and p18, also appear to be intact based on their apparent molecular weights and cell cycle stage-specific abundance. During hypoxia, there is a decrease in abundance of cyclins D and E, with an increase in p27 abundance. cdk4 activity towards pRB and cdk2 activity towards histone H1 are also decreased. Co-precipitation studies revealed an increased amount of p27 complexing with cyclin E-cdk2 during hypoxia than during aerobic cell growth. In addition, pRB-directed phosphatase activity was found to be greater in hypoxic than aerobic cells. Taken together, a model is suggested to explain hypoxia-induced cell cycle arrest in SKA human ovarian carcinoma cells.

CD40 induces resistance to TNF-mediated apoptosis in a fibroblast cell line

CD40, a member of the TNF receptor family, has been characterized as an important T-B cell interaction molecule. In B cells it co-stimulates isotype switching, proliferation, adhesion and is involved in cell death regulation. In addition to B cells, CD40 expression was found on transformed cells and carcinomas. However, little is known about its functions in these cell types. Recent studies show that CD40 mediates the production of pro-inflammatory cytokines in non-hematopoietic cells, inhibits proliferation or induces cell death. In some cell types the apoptotic program triggered by CD40 is only executed when protein synthesis is blocked, suggesting the existence of constitutively expressed resistance proteins. Here we demonstrate that CD40, similar to the 55-kDa TNF receptor (p55TNFR), has a dual role in the regulation of apoptosis in such cells. In the fibroblast cell line SV80 both CD40 and the p55TNFR trigger apoptosis when protein synthesis is blocked with cycloheximide (CHX). Simultaneous activation of both receptors results in markedly enhanced cell death. However, CD40 activation more than 4 h prior to a challenge with TNF/CHX paradoxically conferred resistance to TNF-induced cell death. Protection correlated with NF-kappaB induction and up-regulation of the anti-apoptotic zinc finger protein A20. Overexpression of A20 in turn rendered SV80 cells resistant to TNF cytotoxicity. In conclusion, our data provide evidence that CD40 may regulate cell death in non-hematopoietic cells in a dual fashion: the decision upon apoptosis or survival of a CD40-activated cell seems to depend on its ability to up-regulate resistance factors.

Elevated homologous recombination activity in fanconi anemia fibroblasts

It is widely believed that Fanconi anemia cells possess a reduced ability to repair inter-strand DNA cross-links. While the mechanism through which inter-strand DNA cross-links are removed from mammalian chromosomes is unknown, these lesions are repaired via homologous recombination in lower eukaryotes and bacteria. Based on the hypothesis that a similar mechanism of DNA repair functions in mammalian somatic cells, we measured homologous recombination activity in diploid fibroblasts from healthy donors, and Fanconi anemia patients. Somewhat surprisingly, homologous recombination levels in nuclear protein extracts prepared from Fanconi anemia cells were nearly 100-fold higher than in extracts prepared from control cells. We observed a similar increase in the activity of a 100-kDa homologous DNA pairing protein in extracts from Fanconi anemia cells. Transfection studies confirmed that plasmid homologous recombination levels in intact Fanconi anemia cells were substantially elevated, compared with control cells. These results suggest that inappropriately elevated levels of homologous recombination activity may contribute to the genomic instability and cancer predisposition that characterize Fanconi anemia.

p300 family members associate with the carboxyl terminus of simian virus 40 large tumor antigen

Several cellular polypeptides critical for growth regulation interact with DNA tumor virus oncoproteins. p400 is a cellular protein which binds to the adenovirus E1A oncoprotein(s). The biological function of p400 is not yet known, but it is structurally and immunologically closely related to p300 and CREB-binding protein, two known E1A-binding transcription adapters. Like p300, p400 is a phosphoprotein that binds to the simian virus 40 large tumor antigen (T). In anti-T coimmunoprecipitation experiments, staggered deletions spanning the amino-terminal 250 amino acids of T did not abrogate T binding to either p400 or p300. A T species composed of residues 251 to 708 bound both p400 and p300, while a T species defective in p53 binding was unable to bind either detectably. Anti-p53 immunoprecipitates prepared from cells containing wild-type T also contained p400 and p300. Hence, both p400 and p300 can bind (directly or indirectly) to a carboxyl-terminal fragment of T which contains its p53 binding domain. Since the p53 binding domain of T contributes to its immortalizing and transforming activities, T-p400 and/or T-p300 interactions may participate in these functions.

Interaction between the mRNA of the 55-kDa tumor necrosis factor receptor and cellular proteins. Possible involvement in post-transcriptional regulation of receptor expression

Numerous effects of tumor necrosis factor are signaled by its 55-kDa receptors. Studying their expression we found that the level of receptor mRNA was decreased during the phorbol ester-induced differentiation of myelomonocytic cell lines. While only minor changes in transcription were noted, the half-life of receptor mRNA in the differentiated cells was markedly decreased, indicating the involvement of post-transcriptional regulation. In an electrophoretic mobility shift assay, formation of complexes between radiolabeled receptor mRNA and cellular proteins was observed. The decrease in receptor mRNA levels during phorbol ester-induced differentiation was paralleled by a change in the pattern of those complexes. Protein-RNA interaction was selective, as it was not competed by unrelated RNAs. Yet, certain mRNAs that contain AU-rich sequences, known to be involved in the control of their stability, did compete with the receptor mRNA, although the latter is devoid of such sequences. A region of 18 nucleotides within its coding region was found to contain an element essential for the formation of all complexes and sufficient for the formation of those with lower molecular mass. Adjacent bases were required in addition for the formation of the complexes with higher molecular mass. The results suggest that proteins interacting with this region of the 55-kDa tumor necrosis factor receptor mRNA contribute to the regulation of its expression.

A novel function of CD40: induction of cell death in transformed cells

CD40 is known as an important T-B cell interaction molecule which rescues B lymphocytes from undergoing apoptosis. Like other receptors of the tumor necrosis factor (TNF) receptor gene family, CD40 is expressed on cells of different tissue origins including some transformed cells. In contrast to its well-studied effects on B cells, the biological functions of CD40 in non-immune cells remain largely unknown. Here we show that CD40 ligation induces apoptotic cell death in transformed cells of mesenchymal and epithelial origin. This CD40-mediated cell death seems to use a preformed signaling pathway since it occurs even when protein synthesis is blocked. Notably, the CD40 cytoplasmic domain shares a structural homology with the recently defined "death domains" of the 55-kD TNF receptor (p55TNFR) and Fas. Despite these structural similarities, differences are seen in the way phorbol myristate acetate, interleukin 1, TNF, and various metabolic inhibitors influence the cellular responsiveness to CD40, p55TNFR, and Fas-mediated killing. Our study indicates that CD40 induces cell death by a distinct mechanism.

A casein-kinase-2-related protein kinase is tightly associated with the large T antigen of simian virus 40

The simian virus 40 (SV40) large T antigen is a multifunctional protein involved in SV40 cell transformation and lytic virus infection. Some of its activities are regulated by interaction with cellular proteins and/or by phosphorylation of T antigen by various protein kinases. In this study, we show that immuno-purified T antigen from SV40-transformed cells and from baculovirus-infected insect cells is tightly associated with a protein kinase that phosphorylates T antigen in vitro. In the presence of heparin or a peptide resembling a protein kinase CK2 recognition site, the phosphorylation of T antigen by the associated kinase is reduced whereas a p34cdc2-kinase-specific peptide has no influence. In addition, the T-antigen-associated protein kinase can use GTP and ATP as phosphate donors. These properties together with the observation that immunopurified T antigen can be phosphorylated by the addition of protein kinase CK2 suggest that at least one of the T-antigen-associated protein kinases is CK2 or a protein-kinase-CK2-related enzyme. The association of recombinant CK2 with T antigen was strongly confirmed by in vitro binding studies. Experiments with temperature-sensitive SV40-transformed cells provide evidence for a close correlation between cell transformation and phosphorylation of T antigen by the associated protein kinase.

Functional discrepancies between tumor necrosis factor and lymphotoxin alpha explained by trimer stability and distinct receptor interactions

Tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha) are closely related cytokines which bind with nearly identical affinities to the same pair of cell surface receptors, p55 and p75TNFR. Therefore it is assumed that TNF and LT alpha are redundant cytokines. This study, however, demonstrates that TNF and LT alpha differ significantly with regard to their mitogenic and cytotoxic potentials. LT alpha's superior mitogenic effect could be explained by its formation of a more stable trimer. In contrast to the TNF trimer, which disintegrated under physiological conditions into biologically inactive monomers, the LT alpha trimer remained stable for several days. Accordingly, LT alpha more effectively induced fibroblast growth which demands long-term presence of the cytokine. TNF's superior cytotoxicity, which requires only short-term impact of the cytokine, could be attributed to a distinct interaction with the human p55TNFR. This was demonstrated in NIH 3T3 cells transfected with the human p55TNFR, where cytotoxicity is mediated exclusively by the transfected receptor. Although the p55ATNFR had virtually identical affinities for TNF and LT alpha, as defined by Scatchard analysis, it nevertheless discriminated between binding of each cytokine and showed a 200-fold enhanced cytotoxicity mediated by TNF.

Squamous cell carcinoma of the tongue in a child with Fanconi anemia: a case report and review of the literature

This report documents a case of squamous cell carcinoma (SCC) of the tongue in a child with Fanconi anemia (FA). FA is an autosomal recessive syndrome defined by chromosomal breakage in response to diepoxybutane or mitomycin C in which many patients present with pancytopenia, hypoplastic bone marrow, hyperpigmentation of the skin, skeletal malformations, small stature, hypogonadism, and chromosomal aberrations. Such patients are prone to the development of hematological malignancies and squamous cell carcinoma, especially of the head and neck. Although FA appears to be genetically heterogeneous, all cases display abnormalities of DNA repair. A gene defective in one of the four subsets of FA patients has been defined. Defects in this gene are thought to play a role in the development of neoplasia in FA patients. However, many other factors may also contribute to the development of malignancies, including immune deficiencies, therapeutic strategies, and bone marrow transplantation. This report reviews the association of FA and SCC and highlights the many factors involved in the development of neoplasia within a single patient, including FA, cyclophosphamide, immunosuppression, X-irradiation, and chronic oral graft-versus-host disease. In addition, the human papillomavirus status, although negative, is documented for the first time in such a case.

A cytotoxic CD40/p55 tumor necrosis factor receptor hybrid detects CD40 ligand on herpesvirus saimiri-transformed T cells

The B cell activation molecule CD40 and the p55 tumor necrosis factor receptor (p55TNFR) belong to the same family of structurally conserved proteins. We constructed a chimeric receptor consisting of the CD40 extracellular and transmembrane domains and the p55TNFR intracellular domain. This receptor hybrid retained the biological activity and the ligand specificity of the respective wild-type receptor domains. Thus it exerted a marked cytotoxic effect in three different transfected cell lines after activation not only with anti-CD40 antibody but also with CD40 ligand (CD40L) in soluble and membrane-bound forms. Using hybrid-transfected baby hamster kidney cells we demonstrated that herpesvirus saimiri-transformed human CD4+ T lymphocytes constitutively express bioactive CD40 ligand on their surface. The hybrid receptor-based assay was highly specific for CD40 activating reagents and more sensitive than an assay measuring CD40-mediated B cell rescue from apoptosis. Hence CD40/p55TNFR transfectants may be useful for dissecting CD40L-mediated events in T-B cell interactions, and also to detect a defective CD40L molecule in putative hyper-IgM syndrome patients.

Head and neck carcinoma in Fanconi's anaemia--report of a case and review of the literature

Fanconi's anaemia (FA) is a rare autosomal recessive syndrome characterised by progressive lethal pancytopenia, skeletal abnormalities, hyperpigmentation and increased chromosomal aberrations. A high incidence of leukaemia and hepatocellular and squamous cell carcinomas (SCC) have been reported in FA patients. A rare case of SCC of the dorsum of the tongue in a FA patient is presented. A review of the reported cases of head and neck carcinoma in FA patients shows a different male:female ratio than previously reported, and a high incidence of carcinoma of the tongue.

Induction of cytoplasmic factors that bind to the 3' AU-rich region of human interferon beta mRNA during early development of Xenopus laevis

Certain endogenous Xenopus mRNAs, carrying a destabilizing 3' AU-rich sequence, are unusually very stable in oocytes and become unstable only after fertilization. In addition, heterologous short lived mRNA, containing 3' AU-rich sequences, appear to be very stable when injected into Xenopus oocytes. In the present study, a human interferon beta (hu-IFN beta) mRNA, carrying the destabilizing 3' AU-rich element, was used as a probe to identify Xenopus proteins that specifically bind to the 3' AU-rich element as well as to study their relative levels during early embryonic development. While three major proteins that specifically bind to the 3' AU-rich element were detected in human SV80 cells, that naturally express hu-IFN beta (proteins termed AU-F1, F2 and F3), only two proteins, migrating similarly to the SV80 AU-F1 and AU-F3, were detected in cytoplasmic extracts from Xenopus oocytes or eggs. Following fertilization, the intensity of the Xenopus AU-F1 and AU-F3 proteins increased considerably and a new protein, corresponding to SV80 AU-F2, was also detected. Cyclohexamide applied either at the morula or at the early blastula stages reduced the intensity of the AU-binding factors, while actinomycin D did not, indicating that the levels of these factors during these stages are regulated posttranscriptionally. In contrast, application of each of these metabolic inhibitors at the late blastula stage increased the intensity of the AU-binding proteins. The possible function of these AU-binding factors in regulating the expression and half life of AU-rich mRNAs is discussed.

Fanconi's anaemia associated with multicentric Bowen's disease and decreased NK cytotoxicity

We report a patient with Fanconi's anaemia and multiple lesions of vulvo-anal Bowen's disease. She was thrombocytopenic and lymphopenic, and NK-mediated cytotoxicity was undetectable. The vulvar lesions did not contain papillomavirus DNA. In vitro studies showed a possible benefit from acitretin treatment on bone marrow stem cells. However, low-dose acitretin given for 14 months did not prevent the development of an anal squamous carcinoma. Acitretin therapy was, however, associated with a sustained rise in the platelet count.

Translational regulation of human beta interferon mRNA: association of the 3' AU-rich sequence with the poly(A) tail reduces translation efficiency in vitro

The 3' AU-rich region of human beta-1 interferon (hu-IFN beta) mRNA was found to act as a translational inhibitory element. The translational regulation of this 3' AU-rich sequence and the effect of its association with the poly(A) tail were studied in cell-free rabbit reticulocyte lysate. A poly(A)-rich hu-IFN beta mRNA (110 A residues) served as an inefficient template for protein synthesis. However, translational efficiency was considerably improved when the poly(A) tract was shortened (11 A residues) or when the 3' AU-rich sequence was deleted, indicating that interaction between these two regions was responsible for the reduced translation of the poly(A)-rich hu-IFN beta mRNA. Differences in translational efficiency of the various hu-IFN beta mRNAs correlated well with their polysomal distribution. The poly(A)-rich hu-IFN beta mRNA failed to form large polysomes, while its counterpart bearing a short poly(A) tail was recruited more efficiently into large polysomes. The AU-rich sequence-binding activity was reduced when the RNA probe contained both the 3' AU-rich sequence and long poly(A) tail, supporting a physical association between these two regions. Further evidence for this interaction was achieved by RNase H protection assay. We suggest that the 3' AU-rich sequence may regulate the translation of hu-IFN beta mRNA by interacting with the poly(A) tail.

Translational regulation of human beta interferon mRNA: association of the 3' AU-rich sequence with the poly(A) tail reduces translation efficiency in vitro

The 3' AU-rich region of human beta-1 interferon (hu-IFN beta) mRNA was found to act as a translational inhibitory element. The translational regulation of this 3' AU-rich sequence and the effect of its association with the poly(A) tail were studied in cell-free rabbit reticulocyte lysate. A poly(A)-rich hu-IFN beta mRNA (110 A residues) served as an inefficient template for protein synthesis. However, translational efficiency was considerably improved when the poly(A) tract was shortened (11 A residues) or when the 3' AU-rich sequence was deleted, indicating that interaction between these two regions was responsible for the reduced translation of the poly(A)-rich hu-IFN beta mRNA. Differences in translational efficiency of the various hu-IFN beta mRNAs correlated well with their polysomal distribution. The poly(A)-rich hu-IFN beta mRNA failed to form large polysomes, while its counterpart bearing a short poly(A) tail was recruited more efficiently into large polysomes. The AU-rich sequence-binding activity was reduced when the RNA probe contained both the 3' AU-rich sequence and long poly(A) tail, supporting a physical association between these two regions. Further evidence for this interaction was achieved by RNase H protection assay. We suggest that the 3' AU-rich sequence may regulate the translation of hu-IFN beta mRNA by interacting with the poly(A) tail.

Pleomorphic adenoma cells vary in their susceptibility to SV40 transformation depending on the initial karyotype

Chromosomal aberrations involving 8q12 or 12q13-15 characterize two cytogenetic subgroups of salivary gland pleomorphic adenomas. As the tumors of the two groups differ in their clinical and histologic characteristics, we decided to determine their susceptibility to SV40 transformation. We transfected cell cultures from 13 adenomas with aberrations involving 8q12 and from seven adenomas with involvement of 12q13-15 using an SV40 plasmid coding for the early region of the viral genome. Whereas all cultures with aberrations of 12q13-15 showed transformed foci, only 4 of the 13 cultures with 8q12 abnormalities showed foci of transformed cells. We also observed a much higher immortalization rate in the first group (3/7 vs. 1/13). All successfully transformed tumor cell cultures showed a relatively stable karyotype in the pre-crisis stage and a high mitotic index, were T-antigen positive, and had an extended life span in vitro.

Depressed interferon synthesis in skin fibroblasts from lung cancer patients

Skin fibroblast cell cultures, derived from male adult lung cancer patients, an adult control population, and a newborn population were examined for their susceptibility to transformation with Kirsten murine sarcoma virus and their ability to respond to an interferon inducer (poly I.poly C). An association between sensitivity to viral transformation and induction of interferon was observed. Cultures derived from lung cancer patients demonstrated an increased sensitivity to virus transformation and a decreased ability to respond to interferon induction as compared with age-matched controls and newborns.

Coexpression of the cys E and cys M genes of Salmonella typhimurium in mammalian cells: a step towards establishing cysteine biosynthesis in sheep by transgenesis

The Salmonella typhimurium genes for serine acetyltransferase (cys E) and O-acetylserine sulphydrylase B (cys M) were isolated and characterized in order to express these as transgenes in sheep to establish a cysteine biosynthesis pathway and, thereby, to achieve an increased rate of wool growth. Comparison of the S. typhimurium and Escherichia coli genes showed considerable homology, both at the nucleotide and amino acid sequence levels. The in vitro and in vivo expression studies showed that both genes could be transcribed and translated in eukaryotic cells and that their products could function as active enzymes. The cys M gene of S. typhimurium possessed a GUG initiation codon, like its E. coli counterpart, but translation could be initiated using this codon in eukaryotic cells to give an active enzyme product. Chinese hamster ovary cells, stably transfected with a tandem arrangement of the two genes, showed a capacity to synthesize cysteine in vivo, indicating the establishment of a cysteine biosynthesis pathway in these cells. The measured levels of activity of the gene products suggest that improved wool growth is possible by transgenesis of sheep with these genes.

Collagenase production by immortalized human aortic endothelial cells infected with simian virus 40

Human aortic endothelial cells, isolated at autopsy from a 52-year-old male dying from lung cancer, were treated with simian virus 40 (SV40). One colony was isolated from the infected endothelial cell culture 4 weeks after infection. The cells expressed SV40 large T antigen and p53 protein (p53) in their nuclei but lacted the characteristics of a transformed phenotype. The cells grew well in a monolayer over the 97th passage and exhibited Factor VIII-related antigen, Ulex europaeus 1 agglutinin (UEA-1) as endothelial cell markers, and a well-developed fibronectin network. The amount of prostacyclin synthesized by the cells was less than the amount synthesized by normal aortic or umbilical cord vein endothelial cells. The cells produced relatively large amounts of procollagenase, and 12-o-tetradecanoyl-phorbol-13-acetate (TPA) augmented the ability of the cells to produce this enzyme. These immortalized human aortic endothelial cells, which have some characteristics of normal endothelial cells and, like capillary endothelial cells, have the ability to produce collagenase, will probably prove useful for studies of atherosclerosis and angiogenesis.

Detection and chromosomal assignment of SV40-DNA integration in Chinese hamster cell lines by chromosome sorting and dot blot hybridization

A combination of cytometric (chromosome sorting), molecular (dot blot hybridization using radio-active and/or biotinylated DNA probes) and cytogenetic (G-banding) evaluation is described which allows the rapid identification of single copy and repetitive viral integrates and their assignment to chromosome groups or even individual chromosomes. In the case of Chinese hamster cell line CO 631 it could be demonstrated that SV40 DNA was solely integrated into a submetacentric marker chromosome. Such a cytometric/molecular/cytogenetic "identogram" may prove to be a useful tool in many areas of cell and tumor biology. Furthermore, amounts of chromosomes sufficient for analysis as well as subsequent cloning experiments can be accumulated.

Loss of insulin binding and insulin receptor mRNA in a transformed human fetal fibroblast cell line

Insulin binding and insulin receptor gene expression have been assessed in cultured fetal (WI38) and SV40 transformed fetal (WI38/VA13) human fibroblasts to determine whether transformation influences the expression of insulin receptors. The transformed cell line had virtually no insulin binding and extremely low levels of insulin receptor mRNA. No apparent gene deletion or rearrangement was detected and therefore the marked decrease in insulin receptor gene expression seen in WI38/VA13 cells is an important example of negative regulation of insulin receptor gene expression. This cell line could serve as a model for studies of the mechanism for negative regulation of insulin receptor gene expression. Overexpression of the insulin receptor gene in these cells may reveal insights into the role of the insulin receptor in tumor biology.

Spontaneous losses of control of cytokeratin gene expression in transformed, non-epithelial human cells occurring at different levels of regulation

Intermediate filaments (IFs) of the cytokeratin (CK) type are cytoskeletal elements typical for epithelial differentiation. However, in diverse transformed culture lines of non-epithelial origin, rare cells emerge spontaneously, which synthesize, in addition to their vimentin IFs, CKs 8 and 18. We enriched such cells by cloning and studied the level(s) of regulation at which these changes occur. We found that in SV40-transformed fibroblasts the CK 18 gene is constitutively transcribed into translatable mRNA but that the protein is rapidly degraded in the absence of its complex partner, CK 8. In contrast, cells immunocytochemically positive for CK IFs contained both CKs 8 and 18, which apparently stabilized in heterotypic complexes. These findings and related observations of active genes for CKs 8 and/or 18 in several other transformed non-epithelial cell lines indicate that the genes for CKs 18 and, less frequently, 8 can be active in diverse different non-epithelial cell lines; synthesis of type I and type II CK pair partners can be uncoupled; control of CK IF formation can take place at different levels. We suggest that the intrinsic instability of the inactive state of these genes is responsible for the occurrence of CKs 8 and 18 in certain non-epithelial tissues and tumors, a caveat in tumor diagnosis.

Characterization of the human p53 gene promoter

Transcriptional deregulation of the p53 gene may play an important part in the genesis of some tumors. We report here an accurate determination of the transcriptional start sites of the human p53 gene and show that the majority of p53 mRNA molecules do not contain a postulated stem-loop structure at their 5' ends. Recombinant plasmids of the human p53 promoter-leader region fused to the bacterial chloramphenicol acetyltransferase gene (cat) were constructed. After transfection into rodent or human cells, a 350-base-pair fragment spanning the promoter region conferred 4% of the CAT activity mediated by the simian virus 40 early promoter/enhancer. We monitored the efficiency with which 15 3' and 5' promoter deletion constructs initiated transcription. Our results show that an 85-base-pair fragment, previously thought to have resided in exon 1, is all that is required for full promoter activity.

An N-terminal transformation-governing sequence of SV40 large T antigen contributes to the binding of both p110Rb and a second cellular protein, p120

In addition to Rb and p53, a third cellular protein, p120 in monkey and p118 in human cells, forms a specific complex with SV40 large T antigen (T). p118/120 is not a product of the Rb-gene. As was shown with T/Rb complex formation, the interaction between T and p120 is dependent on the intact nature of a ten residue, transformation-controlling domain in T (residues 105-114). In mouse cells, a readily detectable protein of 115 kd was detected, which, like murine Rb, also forms a stable complex with T. Like p118/120, p115 binding is also dependent on the intact nature of the 105-114 sequence. Given their similar size and T antigen binding sequence dependence, p115 and p118/120 may be products of the same gene in different species. These results suggest that interactions between T and p115/118/120, as well as T and Rb, contribute to the SV40 transforming mechanism.