The human and canine TERT promoters function equivalently in human and canine cells

Telomerase targeted cancer gene therapy is being exploited for treatment of human cancer. The high incidence and many comparative aspects of human and canine cancer and the compliance and dedication of dog owners to treat cancer makes the canine pet population a good clinical model for investigating and developing new cancer therapeutics. Here, we report that the human telomerase promoter operates in canine cells, suggesting that human telomerase promoter-driven cancer therapy can be used to treat cancer in canines. Therefore, the canine pet population can act as a clinical model for new drug development based on telomerase therapeutics.

INDUCED RESISTANCE OF THE CENTRAL NERVOUS SYSTEM TO EXPERIMENTAL INFECTION WITH EQUINE ENCEPHALOMYELITIS VIRUS : II. SEROTHERAPY IN WESTERN VIRUS INFECTION

Under none of the experimental conditions here described was treatment of the infection induced by the virus of Western equine encephalomyelitis in mice and guinea pigs with specific hyperimmune rabbit serum effective if begun after the onset of signs of encephalitis. In mice, after intracerebral inoculation of virus, serum was ineffective when given even before that stage. After peripheral introduction of virus in guinea pigs the disease was completely arrested in certain animals by single or multiple doses of antiserum if treatment was begun within 24 to 48 hours after virus inoculation. In others the incubation period was prolonged to 2 or even as long as 7 weeks. In untreated guinea pigs, injection of virus alone led to active immunity in those which survived. Antiserum blocked the antigenicity of active virus in the serum-treated animals. The decrease in titer in the sera of all antiserum-treated animals proceeded at the same rate as in those of control guinea pigs which received antiserum alone. Thus it was not possible to predict which ones would survive and which would succumb after a prolonged incubation period. Delayed fatal disease occurred at a time when the neutralizing antibody of the treated guinea pigs had fallen to a low titer. It is therefore likely that the virus which persisted throughout this long incubation period had been prevented from passing to and infecting other cells but reached them when antibody fell to an ineffective level in the surrounding medium. The relative frequency of such delayed reactions limits to a further extent the degree to which antiserum can be depended on for effective treatment of infection with the virus of equine encephalomyelitis.

INDUCED RESISTANCE OF THE CENTRAL NERVOUS SYSTEM TO EXPERIMENTAL INFECTION WITH EQUINE ENCEPHALOMYELITIS VIRUS : III. ABORTIVE INFECTION WITH WESTERN VIRUS AND SUBSEQUENT INTERFERENCE WITH THE ACTION OF HETEROLOGOUS VIRUSES

Although vaccination of guinea pigs with formalin-inactivated Western equine encephalomyelitis virus rendered them specifically immune to an intracerebral challenge dose of 1,000 M.L.D. of Western virus, it failed to protect their central nervous system against the initial effects of the virus: the intracerebral challenge dose was followed by an abortive infection of 20 to 30 hours' duration characterized by fever and histopathological changes which simulated the response at that early stage of non-vaccinated control animals. During the abortive infection of immune animals, virus could occasionally be demonstrated in their brains; indeed, it was detected with about the same frequency it was isolated from brains of similarly inoculated, non-immune guinea pigs during corresponding early phases of the infection. About one week after the abortive infection there was found a marked transitory accumulation of specific neutralizing antibody in the brain tissue. See PDF for Equation equalled at this time 1:1 to 1:10 instead of the value of about 1:300 found under physiological conditions. Guinea pigs which had recovered from an abortive infection with Western virus were resistant for a limited period of time to the effects of intracerebral inoculations of the immunologically distinct viruses of Eastern equine encephalomyelitis or vesicular stomatitis.

INDUCED RESISTANCE OF THE CENTRAL NERVOUS SYSTEM TO EXPERIMENTAL INFECTION WITH EQUINE ENCEPHALOMYELITIS VIRUS : I. NEUTRALIZING ANTIBODY IN THE CENTRAL NERVOUS SYSTEM IN RELATION TO CEREBRAL RESISTANCE

1. Neutralizing antibody to equine encephalomyelitis virus was found in the spinal fluid of rabbits sufficiently vaccinated with active or formalin-inactivated virus. Antibody was specific for the Western or for the Eastern virus. 2. Neutralizing capacity of spinal fluid was equivalent to that of a 1/300 dilution of serum of the same animal, and was of the same order of magnitude as that of perfused brain of a vaccinated animal. 3. Vaccinated rabbits which showed antibody in the spinal fluid resisted intracerebral or intracisternal injection of active virus. This immunity was specific, i.e., there was no cross-reaction between the Eastern and Western virus after vaccination with formalin-inactivated virus. On the other hand, lack of antibody in the spinal fluid, even when antibody was demonstrable in the undiluted serum, was associated with lack of cerebral resistance.

ALLERGIC ENCEPHALOMYELITIS IN MONKEYS IN RESPONSE TO INJECTION OF NORMAL MONKEY NERVOUS TISSUE

By subcutaneous injection of central nervous tissue emulsified with adjuvants according to Freund's technique it has been possible to induce in the majority of monkeys an acute disseminated encephalomyelitis which is interpreted as an isoimmunization to CNS tissue. Positive reactions occurred only in response to CNS tissue containing white matter; i.e., cerebral white matter, spinal cord (whether normal or poliomyelitis-infected), and cortical "gray" matter (with an estimated 10 per cent contamination with white matter). No reaction occurred when peripheral nerve or kidney suspension or saline alone was injected with adjuvants. The perivascular and extravascular infiltration induced was confined to the CNS.

INFLUENCE OF AGE ON SUSCEPTIBILITY AND ON IMMUNE RESPONSE OF MICE TO EASTERN EQUINE ENCEPHALOMYELITIS VIRUS

The experiments described in this paper were carried out with the Rockefeller Institute strain of albino mice and with the Eastern strain of the virus of equine encephalomyelitis. 1. The observation was confirmed that with increasing age of mice there occurred a decrease in susceptibility to intraperitoneal injection of active virus; also, the length of incubation period of those which succumbed increased with age. 2. The mice of various age groups which survived an intraperitoneal injection of active virus were indistinguishable in their antibody response. 3. Young mice, vaccinated with formalin-inactivated. virus when 2, 5, and 7 days old, gave an immune response to such a degree that they showed (a) measurable peritoneal immunity which increased with small increments of age, (b) no cerebral resistance, and (c) detectable amounts of neutralizing antibody in their sera which paralleled, though at a considerably lower level, their peritoneal resistance. 4. The peritoneal resistance induced as a result of vaccination was shown to be not local, but a general, systemic immunity, specific for the Eastern strain. Such a peritoneal resistance was demonstrable by the 4th day after beginning of vaccination of 10-days-old mice. 5. After intraperitoneal injection of active virus, large amounts of virus were recoverable from the blood of non-vaccinated young mice; none was found in the blood of vaccinated young mice; a minimal amount was detectable in the blood of non-vaccinated adult mice. 6. The bearing of age on the degree of immune response of which mice are capable and on their susceptibility to the virus has been discussed.

Oncolytic gene therapy for canine cancers: teaching old dog viruses new tricks

The use of viruses to treat cancer has been studied for decades. With the advancement of molecular biology, viruses have been modified and genetically engineered to optimize their ability to target cancer cells. Canine viruses, such as distemper virus and adenovirus, are being exploited for the treatment of canine cancer as the dog has proven to be a good comparative model for human cancer research and proof of concept investigations. In this review, we introduce the concept of oncolytic viruses and describe some of the preliminary attempts to use oncolytic viruses for the treatment of canine cancer.

Presence of beta human papillomaviruses in nonmelanoma skin cancer from organ transplant recipients and immunocompetent patients in the West of Scotland

BACKGROUND

Nonmelanoma skin cancer (NMSC) has been linked to cutaneous human papillomaviruses of the genus beta (betaPV).

OBJECTIVES

We sought to assess the presence of betaPV in NMSC biopsies from a group of Scottish skin cancer patients, both immunocompetent (IC) patients and immunosuppressed (IS) organ transplant recipients.

METHODS

One hundred and twenty-one paraffin-embedded skin tumours (27 actinic keratosis, 41 intraepidermal carcinoma, 53 squamous cell carcinoma) and 11 normal skin samples were analysed for the presence of betaPV by a polymerase chain reaction-reverse hybridization assay designed to detect the presence of the 25 known betaPV genotypes.

RESULTS

In IC patients, betaPV was detected in 30 of 59 (51%) tumours and two of 11 (18%) normal skin samples (P = 0.046). In IS patients, betaPV was found in 27 of 62 (44%) tumours; no normal skin samples were available for comparison. The most frequently found genotypes were HPV-24, HPV-15 and HPV-38. Of those tumours infected with betaPV, 28 of 57 (49%) were infected with more than one genotype (range 2-8). Tumours from IS patients were from a younger age group (mean age 57.4 years) than IC patients (mean age 73.8 years). Multiple infections were more common in tumours from IC patients (21 of 30; 70%) compared with those from IS patients (seven of 27; 26%) (P < 0.001). In the IC group, age did not appear to influence the distribution of single and multiple infections whereas in IS patients the proportion of multiple infections to single infections increased with age. There were no multiple infections in normal skin.

CONCLUSIONS

A wide spectrum of betaPV types was detected in our samples. Further characterization of betaPV in vivo is needed in order to determine the mechanisms by which the virus contributes to cutaneous carcinogenesis.

Aberrant expression of TopBP1 in breast cancer

AIMS

The TopBP1 protein includes eight BRCT domains (originally identified in BRCA1) and has homology with BRCA1 over the carboxyl terminal half of the protein. The aim of this study was to determine whether TopBP1 is aberrantly expressed in breast cancer.

METHODS AND RESULTS

Sixty-one breast carcinomas from an unselected consecutive patient cohort were studied along with 12 samples of breast tissue from cosmetic breast reduction surgery; these were analysed immunohistochemically for TopBP1 expression using a rabbit polyclonal antibody. This antibody was validated in immunoprecipitation and immunofluorescence experiments. Immunohistochemical analysis demonstrated that TopBP1 was expressed almost exclusively in the nuclei of the normal breast epithelium. However, in a significant number of breast carcinomas TopBP1 was aberrantly expressed, as it was detected in the cytoplasm and nucleus of some tumours and exclusively in the cytoplasm of others. In two out of 61 carcinomas investigated, no TopBP1 expression was detected.

CONCLUSIONS

For the first time this report demonstrates aberrant expression of the TopBP1 protein in breast carcinoma. We propose TOPBP1 as a breast cancer susceptibility gene.

Identification and functional analysis of sequence variants in the long control region and the E2 open reading frame of bovine papillomavirus type 1 isolated from equine sarcoids

BPV-1 DNA is the predominant viral type detected in equine sarcoids and represents the only reported natural cross species infection of papillomaviruses. In this study, nucleotide variations in the LCR and the E2 regions of equine sarcoid-associated BPV-1 were characterised by sequence analysis. Variants particular to sarcoid BPV-1 were identified in both the LCR and E2 sequence. The functionality of the most common LCR variant was examined in equine and bovine cells. These studies showed that the activity of the variant LCR was higher in equine cells than bovine cells; the activity of the variant LCR in the presence of the E2 variant was similar to the reference/wild-type sequences in equine cells, whereas in bovine cells the variant function was reduced by 50%. These data suggest the viral BPV variants commonly detected in sarcoids have an enhanced function in equine cells compared to their function in bovine cells.

Human papillomavirus 16 L2 inhibits the transcriptional activation function, but not the DNA replication function, of HPV-16 E2

In this study we analysed the outcome of the interaction between HPV-16 L2 and E2 on the transactivation and DNA replication functions of E2. When E2 was expressed on its own, it transactivated a number of E2-responsive promoters but co-expression of L2 led to the down-regulation of the transcription transactivation activity of the E2 protein. This repression is not mediated by an increased degradation of the E2 protein. In contrast, the expression of L2 had no effect on the ability of E2 to activate DNA replication in association with the viral replication factor E1. Deletion mutagenesis identified L2 domains responsible for binding to E2 (first 50 N-terminus amino acid residues) and down-regulating its transactivation function (residues 301-400). The results demonstrate that L2 selectively inhibits the transcriptional activation property of E2 and that there is a direct interaction between the two proteins, although this is not sufficient to mediate the transcriptional repression. The consequences of the L2-E2 interaction for the viral life cycle are discussed.

Quercetin, E7 and p53 in papillomavirus oncogenic cell transformation

Bovine papillomavirus type 4 (BPV-4) infects the upper alimentary canal of cattle causing benign papillomas which can progress to squamous carcinomas in cattle grazing on bracken fern (BF). We have previously shown that quercetin, a well characterized and potent mutagen found in BF, causes cell cycle arrest of primary bovine cells (PalF), but that a single exposure to quercetin can cause full oncogenic transformation of PalF cells partially transformed by BPV-4. Here we show that cell cycle arrest correlates with an increase in p53 protein levels and transcriptional activity. However, in cells transformed but non-tumorigenic, p53 protein is elevated and transcriptionally activated in response to quercetin or other DNA damaging stimuli, but the cells bypass quercetin-induced G1 arrest likely due to E7 expression. In transformed tumorigenic cells, p53 is elevated in response to quercetin but its transcriptional activity is inhibited due to mutation, and the cells fail to stop in G1 in the presence of quercetin.

A novel silencer element in the bovine papillomavirus type 4 promoter represses the transcriptional response to papillomavirus E2 protein

The long control regions (LCRs) of mucosal epitheliotropic papillomaviruses have similar organizations: a promoter region, an enhancer region, and a highly conserved distribution of E2 DNA binding sites (C. Desaintes and C. Demeret, Semin. Cancer Biol. 7:339--347, 1996). The enhancer of these viruses is epithelial cell specific, as it fails to activate transcription from heterologous promoters in nonepithelial cell types (B. Gloss, H. U. Bernard, K. Seedorf, and G. Klock, EMBO J. 6:3735--3743, 1987). Using the bovine papillomavirus type 4 (BPV-4) LCR and a bovine primary cell system, we have shown previously that a level of epithelial specificity resides in a papillomavirus promoter region. The BPV-4 promoter shows an enhanced response to transcriptional activators in epithelial cells compared with that of fibroblasts (K. W. Vance, M. S. Campo, and I. M. Morgan, J. Biol. Chem. 274:27839--27844, 1999). A chimeric lcr/tk promoter suggests that the upstream BPV-4 promoter region determines the cell-type-selective response of this promoter in fibroblasts and keratinocytes. Promoter deletion analysis identified two novel repressor elements that are, at least in part, responsible for mediating the differential response of this promoter to upstream activators in fibroblasts and keratinocytes. One of these elements, promoter repressor element 2 (PRE-2), is conserved in position and sequence in the related mucosal epitheliotropic papillomaviruses, BPV-3 and BPV-6. PRE-2 functions in cis to repress the basal activity of the simian virus 40 promoter and binds a specific protein complex. We identify the exact nucleotides necessary for binding and correlate loss of binding with loss of transcriptional repression. We also incorporate these mutations into the BPV-4 promoter and demonstrate an enhanced response of the mutated promoter to E2 in fibroblasts. The DNA binding protein in the detected complex is shown to have a molecular mass of approximately 50 kDa. The PRE-2 binding protein represents a novel transcriptional repressor and regulator of papillomavirus transcription.

An enhanced epithelial response of a papillomavirus promoter to transcriptional activators

Mucosal epitheliotropic papillomaviruses have a similar long control region (LCR) organization: a promoter region, an enhancer region, and a highly conserved distribution of E2 DNA binding sites. The enhancer of these viruses is epithelial-specific, as it fails to activate transcription from heterologous promoters in nonepithelial cell types (Gloss, B., Bernard, H. U., Seedorf, K., and Klock, G. (1987) EMBO J. 6, 3735-3743; Morgan, I. M., Grindlay, G. J., and Campo, M. S. (1999) J. Gen. Virol. 80, 23-27). Studies on E2 transcriptional regulation of the human mucosal epitheliotropic papillomaviruses have been hindered by poor access to the natural target cell type and by the observation that some of the human papillomavirus promoters, including human papillomavirus-16, are repressed in immortalized epithelial cells. Here we present results using the bovine papillomavirus-4 (BPV-4) LCR and a bovine primary cell system as a model to study the mechanism of E2 transcriptional regulation of mucosal epitheliotropic papillomaviruses and the cell type specificity of this regulation. E2 up-regulates transcription from the BPV-4 LCR preferentially in epithelial cells (Morgan, I. M., Grindlay, G. J., and Campo, M. S. (1998) J. Gen. Virol. 79, 501-508). We demonstrate that the epithelial-specific enhancer element of the BPV-4 LCR is not required for the enhanced activity of E2 in epithelial cells and that the BPV-4 promoter is more responsive, not only to E2, but to other transcriptional activators in epithelial cells. This is the first time a level of epithelial specificity has been shown to reside in a papillomavirus promoter region.

The bovine papillomavirus type 4 long control region contains an epithelial specific enhancer

Bovine papillomavirus type 4 (BPV-4) is a mucosal epitheliotropic virus that is a causative agent in alimentary carcinoma of cattle. The long control region (LCR) of this virus controls expression of the transforming proteins, E8 and E7. Deletion mutants of the LCR were prepared and assayed for their ability to activate transcription from the LCR promoter in primary bovine palate keratinocytes (the natural target cell for BPV-4) and fibroblasts. The LCR was at least an order of magnitude more active in keratinocytes than in fibroblasts. An epithelial specific enhancer was identified that activated transcription from the SV40 promoter to levels identical to the full-length LCR. One of the active sites in the enhancer is 100% conserved in the LCR of human papillomavirus type 16. The results demonstrate that the BPV-4 LCR has an epithelial specific enhancer, which offers the opportunity to study epithelial specific transcriptional regulation of papillomavirus promoters.

The BPV-4 co-carcinogen quercetin induces cell cycle arrest and up-regulates transcription from the LCR of BPV-4

Bracken fern is the environmental co-carcinogen of BPV-4 in the induction of neoplasias of the upper alimentary canal of cattle. The flavonoid quercetin is one of the most potent and best characterised mutagens present in the fern. We have shown that transfection with BPV-4 DNA and exposure to a single dose of quercetin leads to tumorigenic transformation of primary bovine cells. We now show that quercetin induces cell cycle arrest and up-regulates transcription from the BPV-4 long control region (LCR). This up-regulation is mediated by a 21 nucleotide-long cis-element in the LCR, designated QRE-1, which is located immediately downstream of the TATA box. Cellular proteins bind to QRE-1 and removal or substitution of QRE-1 lead to the abrogation of the response to quercetin. As expression of the viral oncogenes is controlled by the LCR, perturbation in this control and increased oncoprotein expression are likely to contribute to fully malignant cell transformation by overcoming the cell cycle arrest induced by quercetin, thus forcing damaged cells to proliferate.

Epithelial specific transcriptional regulation of the bovine papillomavirus 4 promoter by E2

Bovine papillomavirus 4 (BPV-4) is a mucosal epitheliotropic papillomavirus. It encodes a transcriptional regulator, E2, which acts on the BPV-4 transcriptional control region (the long control region or LCR) to regulate transcription. The distribution of E2 binding sites within the LCR of BPV-4 is identical to that of the human papillomaviruses HPV-16 and HPV-18, indicating that the mechanism of transcriptional control by E2 of mucosal epitheliotropic papillomaviruses is conserved. In this study it has been shown that E2 activates transcription through the BPV-4 LCR promoter in primary bovine palate keratinocytes but not in primary bovine palate fibroblasts. The epithelial specific transcriptional activation of the BPV-4 LCR by E2 is promoter-specific because following binding to the BPV-4 LCR placed in an enhancer mode, E2 can activate transcription from heterologous promoters, such as SV40, in both keratinocytes and fibroblasts. Chimaeric VP16-E2 molecules suggest that the epithelial specific transcriptional activation of the BPV-4 LCR promoter is mediated by the E2 transactivation domain. Although low to intermediate levels of E2 can activate transcription from the BPV-4 LCR promoter, high levels of E2 result in down-regulation of transcription from this promoter in keratinocytes. Mutation of E2 binding site 1 (BS1), which is 3 bp upstream from the TATA box, abrogates down-regulation of transcription by high levels of E2. The results present a model system for studying transcriptional regulation of mucosal epitheliotropic papillomavirus LCRs by E2.

Efficient induction of fibrosarcomas by v-jun requires mutations in the DNA binding region and the transactivation domain

v-jun is the transforming gene of ASV 17, a retrovirus isolated from a spontaneous chicken fibrosarcoma. There are three mutations in the viral Jun protein (v-Jun) as compared to its cellular progenitor c-Jun: a deletion in the transactivation domain (called delta) and two amino acid substitutions in and near the DNA binding region. The effect of each of these mutations on fibrosarcoma development is described. All three mutations contribute towards tumor formation, and their cumulative effect makes v-Jun more tumorigenic compared to Jun proteins that carry only one or two of the mutations. Viruses rescued from tumors induced by c-Jun carrying the two amino acid substitutions in the DNA binding region have increased transforming and tumorigenic potential. These increases are probably due to further mutations that result in the expression of a rearranged Jun protein. Taken together the results show that the evolution of the c-Jun oncoprotein to an efficient carcinogen requires mutations in the transactivation and DNA binding regions.

Amino acid substitutions modulate the effect of Jun on transformation, transcriptional activation and DNA replication

The retroviral oncogene v-jun and its cellular counterpart code for proteins that function as major components of the transcription factor complex AP-1. Jun proteins bind to the AP-1 consensus sequence as homodimers or heterodimers with members of the Fos protein family. This report compares the ability of viral and cellular Jun proteins (v-Jun and c-Jun) to activate transcription and to stimulate DNA synthesis. The effect of amino acid substitutions on cellular transformation is also described. In F9 cells c-Jun is a more effective transactivator than v-Jun, which carries two amino acid substitutions in the carboxy-terminal region that together down-regulate transactivation. The delta deletion, present in the amino-terminal region of v-Jun, does not affect transactivation in F9 cells; however, it does modulate the stimulation of DNA synthesis. When delta is deleted, the amino acid substitutions are without consequence on DNA synthesis. In the presence of delta the amino acid substitutions down-regulate DNA synthesis. Deletion of the Jun transactivation domain, which is required for cellular transformation, abolishes both transactivation and stimulation of DNA synthesis. We conclude that transformation, transactivation and stimulation of DNA synthesis all depend on the presence of the transactivation domain. The three functions are, however, not tightly correlated, and further work is needed to define the role of the biochemical activities of Jun in oncogenesis.

c-Jun causes focus formation and anchorage-independent growth in culture but is non-tumorigenic

The RCAS retroviral vector was used to express chicken and mouse cellular Jun proteins in chicken embryo fibroblasts. Both mouse and chicken proteins induced foci of transformed cells with low to moderate efficiency compared with viral Jun, but were as effective as the viral protein in promoting anchorage-independent growth. Viral Jun and a recombinant between viral and cellular Jun induced tumors in 1-day-old chicks; the cellular Jun proteins were uniformly non-tumorigenic.

Transformation by Jun: requirement for leucine zipper, basic region and transactivation domain and enhancement by Fos

Mutants in the leucine zipper and basic regions of mouse c-jun were tested for transformation in chicken embryo fibroblast cultures. Reduction or elimination of the ability of Jun to dimerize or to bind to DNA severely decreased transformation. A chicken v-jun gene from which the major transactivation domain was deleted also failed to transform. We conclude that an intact leucine zipper, basic region and transactivation domain are required for Jun-induced oncogenic transformation. Coexpression of chicken c-Fos increased formation of transformed foci by Jun proteins of moderate to low oncogenic potency but had no effect on highly transforming Jun. Chicken c-Fos could also transform chicken embryo fibroblasts on its own, albeit after prolonged culture and at a low efficiency.

The serum response element and an AP-1/ATF sequence immediately downstream co-operate in the regulation of c-fos transcription

Transcription of the c-fos gene is activated in response to a wide variety of extracellular stimuli and several cis-acting transcriptional control elements have been characterized. One of these elements is called the serum response element (SRE) and here we investigate an interaction between this element and an AP-1/ATF-like sequence immediately downstream from the SRE. In growing cells these sequences activate transcription in an additive fashion whereas in quiescent cells they co-operate to repress transcription. This co-operation is disrupted upon separation of the elements which also alters the response of the elements to serum or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulation of quiescent cells. This separation also results in an increase of transcription in growing cells. A consensus AP-1 DNA-binding site can substitute for the AP-1/ATF-like sequence present in the c-fos promoter to activate transcription in an additive fashion with the SRE in growing cells, and co-operate in repression in quiescent cells. These observations show that any interaction that may be occurring between proteins binding to these elements results in a different pattern of transcriptional control in growing and quiescent cells. Alternatively, different proteins (or modified proteins) may complex with these sequences in the two different states of cell growth.

Mutations in the Jun delta region suggest an inverse correlation between transformation and transcriptional activation

The viral Jun protein (v-Jun) transforms chicken embryo fibroblasts (CEF) more effectively than its cellular counterpart (c-Jun). In certain cell types v-Jun is also a stronger transcriptional activator than c-Jun. These functional differences between v-Jun and c-Jun result from a deletion in v-Jun (referred to as "delta deletion") that seems to weaken the interaction of Jun with a negative cellular regulator molecule. These observations suggested that the oncogenicity of v-Jun may be due to an enhanced ability to activate transcription of target genes. To test this hypothesis, we constructed several deletions in the delta domain of chicken c-Jun and determined their transforming and transactivating properties. Surprisingly, we found an inverse correlation between the ability of the mutants to transform CEF and to transactivate the collagenase and transin promoters in CEF. In contrast, there was no significant effect of the delta mutations in c-Jun on transactivation in F9 murine embryonal carcinoma cells. The function of the delta region is therefore cell-type specific. The inverse correlation between transformation and transactivation in CEF suggests that the strong growth-promoting effect of v-Jun may be related to a failure to activate the transcription of growth attenuating genes.

Histopathological changes produced in rabbits by experimental inoculation with hemolytic streptococci, certain of their component factors and saponin: A preliminary report

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