Viral DNA in transformed cells. II. A study of the sequences of adenovirus 2 DNA IN NINE LINES OF TRANSFORMED RAT CELLS USING SPECIFIC FRAGMENTS OF THE VIRAL GENOME;

"Infectious tolerance" develops after the spontaneous acceptance of Lewis-to-Dark Agouti rat liver transplants

BACKGROUND

After monoclonal antibody or donor-specific transfusion treatment, infectious tolerance to rat or mouse heart or skin transplants can be passed on to naive recipients by adoptive transfer of tolerant lymphocytes. We examined whether similar regulatory cells develop after the spontaneous acceptance of Lewis-to-Dark Agouti (DA) rat liver transplants without immunomodulating agents.

METHODS

After Lewis-to-DA rat liver transplantation, 100 x 10(6) splenocytes were harvested and adoptively transferred into a 450 rad-irradiated naive DA rat 24 hours before Lewis heart transplantation. Adoptive transfer of CD4+ or CD8+ T cells was also examined. In some experiments, splenocytes from recipients with long-term accepted Lewis hearts induced by adoptive transfer were serially transferred to multiple generations of recipients before Lewis rat heart transplantation. In vitro mixed lymphocyte culture response and cytotoxic T lymphocyte generation were measured.

RESULTS

When splenocytes from a DA rat recipient >60 days after Lewis rat liver acceptance were transferred into irradiated DA rat recipients, all Lewis rat hearts were accepted, whereas third-party Brown-Norway rat hearts were rejected. However, splenocytes from DA rat recipients 30 days after liver transplantation did not prolong Lewis rat heart survival. Adoptive transfer of 40 x 10(6) CD4+, 10 x 10(6) CD4+ or 10 x 10(6) CD8+ cells from a DA rat bearing Lewis rat liver >60 days resulted in acceptance of 88%, 80%, or 57% acceptance of Lewis rat hearts, respectively. Serial second and third adoptive transfer of long-term survivor splenocytes resulted in the acceptance of all Lewis rat hearts. In mixed lymphocyte culture, splenocytes from a naive DA rat and a DA rat accepting a Lewis rat liver transplant for >60 days showed similar proliferative responses to both Lewis and Brown-Norway rat stimulators. An equivalent level of indirect cytotoxic T lymphocyte activity was exhibited by splenocytes from both a naive DA and a DA rat accepting a Lewis rat liver transplant for >60 days.

CONCLUSIONS

Regulatory cells developing after the spontaneous acceptance of a Lewis to DA liver transplant can serially adoptively transfer the acceptance of a Lewis rat cardiac graft in spite of the presence of in vitro antidonor reactivity. Both CD4+ and CD8+ populations have this regulatory activity, although the CD4+ population plays the dominant role.

Development of infectious tolerance after donor-specific transfusion and rat heart transplantation

Regulatory cells developed after donor-specific transfusion (DST)-induced acceptance of a LEW heart transplanted into a DA rat. Both DST and the cardiac transplant were necessary to generate the regulatory cells. This donor-specific tolerance can then be transferred into a new DA recipient by adoptive transfer of lymphocytes from the DST-treated long term survivor (LTS) in a dose-dependent manner. The effectiveness of tolerance did not diminish over five generations of adoptive transfer, thus supporting its infectious nature. Although both spleen and lymph node cells were equally effective, graft-infiltrating lymphocytes were more potent. A high level of indirect CTL activity and MLC proliferation were observed in lymphocytes from LTS. In vivo tracking of adoptively transferred CFSE-labeled splenocytes from LTS showed equivalent FACS proliferation and a higher percentage of graft-infiltrating lymphocytes 7 days after heart transplantation, compared with adoptively transferred naive splenocytes. Adoptive transfer of CD8(+)-depleted LTS splenocytes resulted in 100% subsequent LEW allograft acceptance; whereas CD4(+) depletion decreased acceptance to 40%, and depletion of both CD4 and CD8 resulted in 0% acceptance. When positively selected CD4(+) or CD8(+) cells were adoptively transferred, 100% or 62.5% of LEW cardiac allografts survived, respectively. In conclusion, DST alone promotes a donor-specific infectious tolerance of a heart graft that can be adoptively transferred to subsequent naive allograft recipients despite the undiminished in vitro immunological response to donor Ag. Although both CD4(+) and CD8(+) populations are responsible for the regulatory mechanism in DST-induced tolerance, the CD4(+) population appears to dominate.

Transactivation of human cdc2 promoter by adenovirus E1A

Expression of the adenovirus oncoprotein E1A 12S induces the heterotrimeric transcription factor, NF-Y. NF-Y binds to the two CCAAT motifs upstream of the transcriptional start site of the human cdc2 promoter and is required for activation of the promoter by E1A 12S in cycling cells. The observations that a number of eukaryotic cell cycle regulatory genes also contain the CCAAT motifs and NF-Y binds to them support the notion that E1A 12S could play an important role in deregulated expression of these genes through activation of NF-Y gene in cycling cells.

Portal venous ultraviolet B-irradiated donor alloantigen prevents rejection in circumferential rat tracheal allografts

BACKGROUND

Before tracheal transplantation can be considered as a method of reconstruction in patients with extensive circumferential tracheal defects, we must achieve a state of nontoxic, donor-specific tolerance so that the risks of such a transplant do not outweigh the benefits.

OBJECTIVE

Our objective was to determine whether a single intraportal injection of modified donor alloantigen achieves donor-specific immunosuppression for major histocompatibility complex-mismatched rat tracheal allografts.

STUDY DESIGN

Buffalo (recipient) rats were pretreated with either a single portal-vein administration of ultraviolet B (UVB)-irradiated donor splenocytes (n = 4) or an intraportal inoculation of nonirradiated donor splenocytes (n = 4). Major histocompatibility complex-mismatched Lewis (donor) tracheal allograft segments were then grafted into treatment groups 7 days after donor-cell pretreatment. Tracheal rejection was assessed by histologic analysis, mucosal cilia motility, and in vitro immunologic assessment.

RESULTS

The UVB-treated group demonstrated no acute or chronic rejection as well as complete functional recovery. In vitro immunologic assessment demonstrated a donor-specific hyporesponsiveness and donor allospecificity. Untreated animals and those receiving nonirradiated donor splenocytes showed acute rejection of their tracheal allografts.

CONCLUSION

Recipient pretreatment with intraportally administered UVB-irradiated donor splenocytes prevents rejection of circumferential rat tracheal allograft segments by inducing a donor-specific immune hyporesponsiveness.

Pretreatment with portal venous ultraviolet B-irradiated donor alloantigen promotes donor-specific tolerance to rat nerve allografts

OBJECTIVE

To determine if a single intraportal inoculation of ultraviolet B-irradiated (UVB) donor splenocytes can prevent nerve allograft rejection and confer donor-specific immunotolerance to rat nerve allograft segments.

METHODS

Age-matched, class I and class II major histocompatibility complex (MHC) mismatched Buffalo (RT1b) rats were transplanted with a syngeneic nerve isograft, a Lewis (RT1l) nerve allograft, or a Brown-Norway (RT1n) rat nerve allograft segment. Control Buffalo rats in group I received a 3.0-cm Lewis (RT11) sciatic-posterior tibial interposition nerve allograft without pretreatment; group II Buffalo rats received a syngeneic Buffalo nerve isograft without pretreatment. Group III Buffalo recipients were inoculated with 2.5 x 107 UVB-irradiated Lewis donor splenocyte cells by portal venous administration 7 days before transplantation with a 3.0-cm sciatic-posterior tibial nerve allograft from a Lewis (RT11) or a third party Brown-Norway rat (RT1n) donor (group IV). Nerve graft regeneration was assessed with walking track analysis, nerve conduction studies, retrograde neural tracing, nerve graft histology, and morphometry. Recipient immune tolerance was assessed through in vitro immunological assessment.

RESULTS

Pretreatment with UVB-irradiated donor splenocytes 7 days before transplantation prevented nerve allograft rejection. Pretreated animals receiving a nerve allograft recovered limb function, and demonstrated morphological, histological, and electrophysiologic parameters of nerve regeneration similar to that measured in rats receiving a nerve isograft. In vitro immunological assessment by mixed lymphocyte culture (MLC), cytotoxic T lymphocyte (CTL) assay, limiting dilution analysis (LDA) of helper (pTH) and cytotoxic (pCTL) precursor frequencies, and IL-2 production demonstrated a marked donor-specific suppression in allografted animals pretreated with intraportal UVB-irradiated donor splenocytes. These assessments correlated with indefinite acceptance of donor nerve allografts.

CONCLUSIONS

A single pretreatment with a single intraportal dose of UVB-modified donor antigen specifically induces tolerance to peripheral nerve allografts in rats.

The kinetics of tolerance induction by nondepleting anti-CD4 monoclonal antibody (RIB 5/2) plus intravenous donor alloantigen administration

BACKGROUND

CD4+ T cells play an essential role in allograft rejection. The monoclonal anti-rat CD4 antibody, RIB 5/2, has been shown to modulate the CD4 glycoprotein without eliminating the recipient T cells. We have successfully induced tolerance to rat heart allografts by recipient pretreatment with a single dose of RIB 5/2 plus intravenous administration of donor splenocytes. In this study, we explored whether this potent regimen could induce tolerance to the more resistant kidney and skin allografts. Furthermore, we examined the kinetics and requirements for tolerance to be met by a single dose of RIB 5/2 plus i.v. alloantigen.

METHODS

The efficacy of a single i.p. dose of 20 mg/kg RIB 5/2 plus i.v. donor antigen (25x10(6) splenocyte) pretreatment 0, 21, or 40 days before receipt of an MHC-mismatched Lewis (RT1l) to Buffalo (RT1b) rat cardiac, renal, or skin allograft was studied. Another group of Buffalo recipients treated with RIB 5/2 plus an i.v. alloantigen +/-thymectomy received kidney transplants after 40 days. Attempts to prevent tolerance used interleukin-2 or prior sensitization. Mixed lymphocyte cultures, cytotoxic assays, and precursor frequencies of helper and cytotoxic cells, by limiting dilution analysis, serially measured in vitro cell-mediated immunity.

RESULTS

RIB 5/2 administration combined with i.v. alloantigen 21 days before induced tolerance to heart and kidney allografts but did not prolong skin graft survival. In contrast, kidney allografts delayed for 40 days after pretreatment were acutely rejected and survival was not affected by the thymectomy. MLC, CTL, and pTH, and pCTL precursor frequencies from recipients of long-term grafts were specifically suppressed to donor, but not third party, alloantigen.

CONCLUSION

A single dose of the nondepleting anti-CD4 monoclonal antibody, RIB 5/2, plus i.v. alloantigen is a potent inducer of tolerance to heart and kidney, but not skin, allografts. The RIB 5/2-induced donor unresponsiveness to a delayed kidney or cardiac allograft is time dependent but can be prolonged if specific alloantigen is present. Suppression of cell-mediated allo-immune responsiveness correlates with allograft acceptance.

Brief cyclosporine treatment prevents intrathymic (IT) tolerance induction and precipitates acute rejection in an IT rat cardiac allograft model

BACKGROUND

Intrathymic (IT) alloantigen combined with administration of rabbit anti-rat anti-lymphocyte serum (ALS) intraperitoneally induces donor-specific tolerance to rat cardiac transplants. The purpose of this study was to examine the effect of a brief course (4 days) of cyclosporine (CsA) on the development of IT tolerance.

METHODS

Buffalo (BUF) (RT1b) rats were given 25x10(6) fully MHC-mismatched Lewis (LEW) (RT1l) splenocytes by IT injection plus 1.0 ml of ALS intraperitoneally. Twenty-one days later, IT donor-specific LEW (group 1) or third-party (ACI, RT1a) (group 2) hearts were heterotopically transplanted to the abdominal aorta A third group of BUF (group 3) were given daily CsA (10 mg/kg) by oral gavage for 4 days before administration of IT LEW cells and ALS. Rejection as defined by the cessation of a palpable heartbeat was confirmed by histology. Cytokine profiles of allografts from all groups were then analyzed using a multi-probe RNase protection assay.

RESULTS

Sixty-seven percent of IT/ALS-treated BUF recipients not pretreated with CsA accepted LEW heart grafts for greater than 90 days. However, 86% of animals treated with CsA for 4 days before IT injection and ALS rejected allografts at 10.7+/-3.2 days. Third-party allografts (ACI) were uniformly rejected (7.0+/-0.0 days). Histology confirmed cellular rejection in CsA-treated allografts and cytokine analysis detected increased interleukin (IL)-3, IL-5, and tumor necrosis factor-alpha when compared to increased IL-2 and interferon-gamma in rejecting untreated controls.

CONCLUSIONS

CsA can prevent the induction of intrathymic alloantigen tolerance. These results support the development of a CsA-sensitive, but IL-2-independent, active regulatory mechanism after intrathymic exposure to donor-specific alloantigen and depletion of mature peripheral T cells.

p53 status does not determine outcome of E1B 55-kilodalton mutant adenovirus lytic infection

The ability of the adenovirus type 5 E1B 55-kDa mutants dl1520 and dl338 to replicate efficiently and independently of the cell cycle, to synthesis viral DNA, and to lyse infected cells did not correlate with the status of p53 in seven cell lines examined. Rather, cell cycle-independent replication and virus-induced cell killing correlated with permissivity to viral replication. This correlation extended to S-phase HeLa cells, which were more susceptible to virus-induced cell killing by the E1B 55-kDa mutant virus than HeLa cells infected during G1. Wild-type p53 had only a modest effect on E1B mutant virus yields in H1299 cells expressing a temperature-sensitive p53 allele. The defect in E1B 55-kDa mutant virus replication resulting from reduced temperature was as much as 10-fold greater than the defect due to p53 function. At 39 degreesC, the E1B 55-kDa mutant viruses produced wild-type yields of virus and replicated independently of the cell cycle. In addition, the E1B 55-kDa mutant viruses directed the synthesis of late viral proteins to levels equivalent to the wild-type virus level at 39 degreesC. We have previously shown that the defect in mutant virus replication can also be overcome by infecting HeLa cells during S phase. Taken together, these results indicate that the capacity of the E1B 55-kDa mutant virus to replicate independently of the cell cycle does not correlate with the status of p53 but is determined by yet unidentified mechanisms. The cold-sensitive nature of the defect of the E1B 55-kDa mutant virus in both late gene expression and cell cycle-independent replication leads us to speculate that these functions of the E1B 55-kDa protein may be linked.

In vitro analysis of gadolinium chloride abrogation of the systemic tolerance induced by portal venous administration of ultraviolet B-irradiated donor cells

BACKGROUND

Normally, a Buffalo (BUF) recipient (RT1b) rejects a heterotopically transplanted Lewis (LEW) heart (RT1l) drained into the portal vein (PV) within 14 days. However, the addition of PV administration of 25x10(6) ultraviolet B (UVB)-treated LEW spleen cells (SC) to BUF recipients 7 days before cardiac transplantation results in 70% long-term allograft survival.

METHODS

In this study, we used gadolinium chloride (GdCl3) (7 mg/kg/day) to selectively block the phagocytosis of recipient hepatic Kupffer cells before PV injection of UVB-treated donor SC to examine the mechanism of tolerance induction, as measured by in vitro analysis of mixed lymphocyte culture (MLC), T cell cytotoxicity, T helper cell precursors (pTH), and cytotoxic T cell precursors (pCTL) by limiting dilution analysis.

RESULTS

A BUF recipient that received untreated or gamma-irradiated LEW SC intraportally reacted to in vitro stimulation by LEW alloantigen with increased MLC proliferation, T cell cytotoxicity, pTH and pCTL frequencies, and interleukin-2 production. In contrast, SC from BUF that received UVB-treated LEW SC were hyporesponsive on MLC stimulation by donor LEW alloantigen and exhibited markedly reduced cytotoxicity, pTH and pCTL frequency, and interleukin-2 production. However, normal in vitro responsiveness resulted with stimulation by third-party Brown-Norway (RT1n) SC, thus indicating that the systemic hyporesponsiveness was specific for the UVB donor alloantigen given PV. On the other hand, GdCl3 given by intravenous injection daily for 3 days before PV alloantigen blocked the induction of in vitro hyporesponsiveness.

CONCLUSION

Therefore, prevention of alloantigen sequestration by GdCl3 inhibition of hepatic Kupffer cell phagocytosis was pivotal in preventing the development of portal venous tolerance.

Induction of donor specific transplantation tolerance to cardiac allografts following treatment with nondepleting (RIB 5/2) or depleting (OX-38) anti-CD4 mAb plus intrathymic or intravenous donor alloantigen

The nondepleting monoclonal antirat CD4 antibody, RIB 5/2, has been shown to modulate, but not eliminate, the CD4+ T cells and to prolong survival of rat skin, renal, or cardiac allografts when serially administered after transplantation. In the present study, we compared the efficacy of recipient pretreatment with a single dose of nondepleting RIB 5/2 or depleting OX-38 anti-CD4 monoclonal antibody plus donor alloantigen given intravenously or intrathymically 21 days before transplantation on the survival of completely MHC-mismatched rat cardiac allografts. Intraperitoneal injection of a single dose (20 mg/kg) of RIB 5/2 resulted in a decrease in CD4 surface molecule expression on peripheral CD4+ T cells without cell elimination as shown by FACS analysis. The nonspecific effect of a single dose of RIB 5/2 mAb had resolved by 21 days after treatment as evidenced by the almost complete recovery of normal surface CD4 molecule expression. Cardiac allografts transplanted immediately or 21 days after a single dose of RIB 5/2 alone were uniformly acutely rejected. On the other hand, recipients treated with depleting anti-CD4 OX-38 (20 mg/kg) acutely rejected cardiac allografts transplanted 21 days later, but indefinitely accepted all grafts transplanted on the same day. In contrast, combined treatment with i.v. donor splenocytes (25 x 10(6)) plus nondepleting RIB 5/2, but not with depleting anti-CD4 mAb, OX-38, resulted in survival for more than 100 days in 75% of recipients of donor specific, but not third party, cardiac allografts transplanted 21 days later. Irradiation (3000 rads) of the i.v. donor splenocytes combined with RIB 5/2 abrogated their tolerizing effect. When donor antigen was given intrathymically, both RIB 5/2 and OX-38 resulted in indefinite tolerance to cardiac allografts transplanted 21 days later. The failure of exogenous administration of high dose (180,000 IU/injection) rIL-2 for 10 days to reverse the unresponsiveness of i.v. SC plus RIB 5/2 pretreatment suggests that this tolerant state is not due to a deficiency of IL-2. In vitro studies showed marked inhibition of MLC responsiveness and cytolytic T cell activity in tolerant recipients that cannot be reversed by the addition of IL-2. Thus, pretransplant intravenous donor alloantigen combined with a dose of nondepleting anti-CD4 mAb, RIB 5/2, which alone has no significant effect, induced donor specific cardiac allograft tolerance.

Induction of polyploidy in adenovirus E1-transformed cells by the mitotic inhibitor colcemid

Adenovirus-transformed cells were tested for their ability to synthesize DNA in the presence of cell cycle inhibitory drugs. We show that transformed cells are completely resistant to the mitotic inhibitor colcemid, partly resistant to lovastatin, mimosine, aphidicolin and genistein but not to hydroxyurea or thymidine. When treated with colcemid, AdE1-transformed cells continue to synthesize DNA but do not divide and, therefore, become highly polyploid. This effect is dependent on the presence of both E1A and E1B.

The adenoviral transcription factor, E1A 13S, trans-activates the human tumor necrosis factor-alpha promoter

The 1311 bp TNF-alpha promoter region fused to a luciferase reporter vector was used in a transient transfection system to study the regulation of TNF-alpha promoter activity by E1A 13S in the U937 macrophage cell line and the MLA 144 T cell line. Co-transfections of the TNF-alpha promoter with an E1A expression vector resulted in a strong trans-activation of the promoter in both cell lines. Sequential truncation of the promoter mapped the E1A responsive region to sequences contained between -120 bp and the transcription start site. Truncation to -95 bp caused a dramatic 87% reduction of E1A activation in MLA 144 cells and further truncation to -36 bp caused a complete loss of E1A activation. In U937 cells, each truncation lowered E1A responsiveness but activity was never completely abolished. Site-directed mutagenesis of putative cis-acting sequences in the TNF-alpha promoter identified the AP-1 site as important for E1A trans-activation in the U937 cell line; the AP-2 and CRE sites also appeared to contribute to a lesser degree. In contrast, only the CRE mutation caused a reduction in E1A induced activity in the MLA 144 cell line. Co-transfection of the E1A expression vector with expression vectors for the cellular transcription factors AP-1, AP-2 and CREB indicated that none of these transcription factors showed any co-operativity with E1A. Thus, cis-acting sequences which contribute to E1A trans-activation of the TNF-alpha promoter have been delineated.

Identification of functional domains of adenovirus tumor-specific transplantation antigen in types 5 and 12 by viable viruses carrying chimeric E1A genes

The adenovirus (Ad) E1A gene induces in immunized animals a strong tumor transplantation (TSTA) immunity against Ad tumors. Such immunity with group-A and group-C viruses is highly group-specific and no cross-protection is detected between serotypes 5 and 12. This fact was used to map the domains of the Ad5 and Ad12 E1A gene products, respectively, which control the TSTA. We constructed a library of 8 recombinant viruses (H5sub1101 through H5sub1108) which carry chimeric Ad5/Ad12 E1A genes in the background of Ad5. The chimeric genes are functional and these viruses are viable. Some of these constructs induce strong and highly specific tumor syngraft immunity in immunized rats. The viruses carrying the 5' terminus of the first E1A exon derived from Ad12 (viruses H5sub1101, H5sub1102 and H5sub1103) induce strong protection against Ad12 tumors irrespective of the rest of their E1A sequence. The viruses which carry the second exon of the Ad5 E1A gene (viruses H5sub1101, H5sub1102 and H5sub1106) protect against group-C tumors, regardless of the origin of the rest of their E1A gene. The 2 viruses that carry the 5' E1A terminus of the first exon of Ad12 and the second exon of Ad5 (H5sub1101 and H5sub1102) are thus effective in inducing immunity against Ad12 tumors as well as against Ad2 tumors. The viruses which carry the 5' terminus of the first exon derived from Ad5 and the second exon of Ad12 (H5sub1107 and H5sub 1108) fail to induce immunity against either tumor. Expression of only the truncated 5' terminus of the Ad12 E1A gene (viruses H5sub1104 and H5sub1105) is sufficient for induction of Ad12 TSTA. Our results provide direct and unequivocal in vivo evidence that TSTA activities of adenovirus groups A and C are controlled by different domains of their respective E1A genes. The Ad12 TSTA is a function of the 5' terminus of the first E1A exon, while the Ad5 TSTA is coded for by the 3' exon of its E1A gene.

A 9L gliosarcoma transplantation model for studying adoptive immunotherapy into the brains of conscious rats

A rat model for brain tumor immunotherapy is described that closely mimics the type of treatment that could be administered to humans. It involves surgical implantation of a permanent cannula in the brain, through which tumor cells and various effector cells and/or cytokines can be injected. The advantage of this system over more conventional animal surgical procedures is that conscious animals can be treated multiple times while avoiding morbidity and mortality associated with reoperative procedures. Using this system to study adoptive immunotherapy for brain tumors, we provide evidence that the 9L gliosarcoma tumor from the Fischer rat strain can be reduced or destroyed in situ following adoptive immunotherapy with specifically activated cytotoxic T lymphocytes.

MHC class II presenting cells are necessary for the induction of intrathymic tolerance

OBJECTIVE

This study determined the form of cellular donor MHC alloantigen necessary for the induction of intrathymic tolerance.

BACKGROUND

The authors have achieved indefinite donor-specific tolerance, to a fully MHC-disparate rat heterotopic cardiac allograft, after the pretransplant intrathymic injection of unfractionated donor splenocytes and a single injection of rabbit anti-rat lymphocyte serum (ALS), without subsequent immunosuppression.

METHODS

Male 4-12-week-old Buffalo (RT1b) rats underwent an intrathymic injection of either fractionated Lewis (RT1(1)) red blood cells (purified by Ficoll gradient) or T lymphocytes (purified by nylon wool column and plastic adherence), both of which express only MHC class I alloantigens, or B lymphocytes, macrophages, and dendritic cells (purified by plastic adherence) which express both MHC class I and class II alloantigens. At the completion of alloantigen injection the Buffalo recipient rats were given 1 ml of ALS intraperitoneally. Twenty-one days later a heterotopic Lewis heart was transplanted.

RESULTS

The intrathymic injection of the fractions of Lewis MHC class I and class II expressing B lymphocytes, macrophages, and dendritic cells induced a donor-specific tolerance that resulted in indefinite Lewis cardiac allograft survival (MST > 125 days) in all recipients without further immunosuppression, whereas groups receiving MHC class I expressing red blood cell or T lymphocyte injections plus ALS rejected Lewis cardiac allografts with a MST of 7.3 and 16.5 days, respectively, thus indicating that the MHC class II expressing cell is necessary for the induction of intrathymic tolerance. Buffalo recipients with a long-term surviving Lewis cardiac allograft, after Lewis MHC class II expressing cells were still able to reject a third-party heterotopic ACI (RT1a) cardiac allograft in normal time (MST = 7.0 days), but did not reject a second Lewis cardiac allograft (MST > 100 days). Additionally, the intrathymic injection of MHC class II expressing cells resulted in decreased interleukin-2 (IL-2) production and an 80% decrease in in vitro donor-specific cell mediated cytotoxicity, whereas the cytolytic response to a third party was unaltered.

CONCLUSION

Donor MHC class II, and not class I, expressing cells are the cells in donor splenocytes, injected intrathymically, responsible for the development of donor-specific allograft tolerance.

E2F: a link between the Rb tumor suppressor protein and viral oncoproteins

The cellular transcription factor E2F, previously identified as a component of early adenovirus transcription, has now been shown to be important in cell proliferation control. E2F appears to be a functional target for the action of the tumor suppressor protein Rb that is encoded by the retinoblastoma susceptibility gene. The disruption of this E2F-Rb interaction, as well as a complex involving E2F in association with the cell cycle-regulated cyclin A-cdk2 kinase complex, may be a common mechanism of action for the oncoproteins encoded by the DNA tumor viruses.

Transduction of the CHO aprt gene into mouse L cells using an adeno-5/APRT recombinant virus

An adenovirus-5 recombinant virus Adapt1 carrying the Chinese hamster ovary (CHO) adenine phosphoribosyltransferase (aprt) gene was constructed by insertion of a 2.5-kb fragment containing the complete CHO aprt structural gene linked to a Moloney murine sarcoma virus (MSV) promoter into the E3 region of adenovirus-5. The CHO aprt gene was in the opposite orientation to the adenovirus E3 promoter. Mouse Lapt- tk- (LAT) cells expressed the CHO aprt gene when infected with the virus, even at low MOI (O.1). APRT activity was detectable from approximately 20 h postinfection. At a low frequency, LAT cells were transformed to aprt+, and four stable transductants were selected in adenine, azaserine (AA) medium. Such cells expressed APRT at approximately 50% wild-type activity and the enzyme was shown to be CHO APRT by starch gel electrophoresis. DNA was isolated from the transductants and probed with CHO aprt-specific DNA and with viral DNA probes. The results indicated that the CHO aprt gene was integrated into the LAT cells at a site other than mouse aprt. Although neighboring viral sequences were integrated and maintained in the transductants, viral sequences further upstream and downstream of the aprt gene were absent.

Phosphorylation of transcriptional factors and cell-cycle-dependent proteins by casein kinase II

Casein kinase II is involved in the phosphorylation of several proto-oncogenes, anti-oncogenes, and oncogenes that are nuclear transcriptional regulatory factors. The potential functions of the phosphorylations in each of these proteins are evaluated. New findings indicate that casein kinase II is a critical component of the mechanisms regulating the cell cycle.

Dissection of functional domains in the adenovirus 2 early 1B 55K polypeptide by suppressor-linker insertional mutagenesis

To determine whether the viral replication functions of the adenovirus E1B 55K protein play a role in its ability to transform cloned rat embryo fibroblast cells in culture, we constructed an extensive series of insertion mutations throughout the 55K gene. The mutations were recombined into infectious virus and characterized for their abilities to produce stable 55K protein in HeLa cells, replicate virus in HeLa cells, express late viral proteins efficiently, and transform CREF cells following infection. Mutant 55K transforming activity in primary baby rat kidney cells was also assayed following DNA transfection. The functions required for viral replication are encoded in several patches of the 55K linear sequence, while the CREF transforming functions are sensitive to all of the insertions. An insertion at amino acid 380 created a mutant virus which was reduced in transforming activity, but was not reduced for viral replication. Therefore, a function required for efficient transformation of CREF cells can be separated from functions required for late gene expression and viral replication. Transformation of BRK cells following DNA transfection was reduced by complete disruption of the 55K protein gene, but was not significantly affected by any of the insertions.

Analysis of E1A-mediated growth regulation functions: binding of the 300-kilodalton cellular product correlates with E1A enhancer repression function and DNA synthesis-inducing activity

Adenovirus E1A transforming function requires two distinct regions of the protein. Transforming activity is closely linked with the presence of a region designated conserved domain 2 and the ability of this region to bind the product of the cellular retinoblastoma tumor suppressor gene. We have investigated the biological properties of the second transforming region of E1A, which is located near the N terminus. Transformation-defective mutants containing deletions in the N terminus (deletion of residues between amino acids 2 and 36) were deficient in the ability to induce DNA synthesis and repress insulin enhancer-stimulated activity. The function of the N-terminal region correlated closely with binding of the 300-kilodalton E1A-associated protein and not with binding of the retinoblastoma protein. These results indicate that transformation by E1A is mediated by two functionally independent regions of the protein which interact with different specific cellular proteins and suggest that the 300-kilodalton E1A-associated protein plays a major role in E1A-mediated cell growth control mechanisms.

Role of adenovirus E1B proteins in transformation: altered organization of intermediate filaments in transformed cells that express the 19-kilodalton protein

Cooperation of the nuclear oncogene E1A with the E1B oncogene is required for transformation of primary cells. Expression vectors were constructed to produce the 19-kilodalton (19K) and 55K E1B proteins under the direction of heterologous promoters in order to investigate the role of individual E1B proteins in transformation. Coexpression of E1A and either the 19K or 55K E1B gene products was sufficient for the formation of transformed foci in primary rat cells at half the frequency of an intact E1B gene, suggesting that the 19K and 55K proteins function via independent pathways in transformation. Furthermore, the effects of Ha-ras and the E1B 19K gene product were additive when cotransfected with E1A, suggesting that the 19K protein functions in transformation by a mechanism independent from that of ras as well. Although expression of E1A and either E1B protein was sufficient for the subsequent growth of cells in long-term culture, the 19K protein was required to support growth in semisolid media. As the 19K protein has been shown to associate with and disrupt intermediate filaments (IFs) when transiently expressed with plasmid vectors (E. White and R. Cipriani, Proc. Natl. Acad. Sci. USA, 86:9886-9890, 1989), the organization of IFs in transformed cells was investigated. Primary rat cells transformed by plasmids encoding E1A plus the E1B 19K protein showed gross perturbations of IFs, whereas cell lines transformed by plasmids encoding E1A plus the E1B 55K protein or E1A plus Ha-ras did not. These results suggest that an intact IF cytoskeleton may inhibit anchorage-independent growth and that the E1B 19K protein can overcome this inhibition by disrupting the IF cytoskeleton.

Cytotoxic T-cell precursors with low-level CD8 in the diabetes-prone Biobreeding rat: implications for generation of an autoimmune T-cell repertoire

Lymphocytes from diabetes-prone Biobreeding rats consistently fail to generate T-cell-mediated cytotoxicity under conditions where cytotoxic T lymphocyte activity is readily demonstrated in normal rats. The failure is associated with generalized T-cell lymphopenia and marked reduction in the frequency of CD8+ cells. The few remaining CD8+ cells are widely held to be natural killer cells rather than class I major histocompatibility complex-restricted T lymphocytes. In this report we show that a detectable percentage of CD8+ lymphocytes express the T-cell receptor for antigen, thus identifying them as part of the T-cell lineage. The failure of these CD8+ T-cell-receptor-positive T cells to lyse target cells that are susceptible to T-cell mediated cytotoxicity is associated with markedly reduced expression of cell-surface CD8. Targets expressing higher than normal levels of class I major histocompatibility complex target antigen could be lysed, suggesting that reduction in CD8 has decreased T-cell activity for target antigen. We discuss the derivation of T cells that express low levels of CD8 and the role they could play in generating autoimmune diabetes.

Role of adenovirus E1B proteins in transformation: altered organization of intermediate filaments in transformed cells that express the 19-kilodalton protein

Cooperation of the nuclear oncogene E1A with the E1B oncogene is required for transformation of primary cells. Expression vectors were constructed to produce the 19-kilodalton (19K) and 55K E1B proteins under the direction of heterologous promoters in order to investigate the role of individual E1B proteins in transformation. Coexpression of E1A and either the 19K or 55K E1B gene products was sufficient for the formation of transformed foci in primary rat cells at half the frequency of an intact E1B gene, suggesting that the 19K and 55K proteins function via independent pathways in transformation. Furthermore, the effects of Ha-ras and the E1B 19K gene product were additive when cotransfected with E1A, suggesting that the 19K protein functions in transformation by a mechanism independent from that of ras as well. Although expression of E1A and either E1B protein was sufficient for the subsequent growth of cells in long-term culture, the 19K protein was required to support growth in semisolid media. As the 19K protein has been shown to associate with and disrupt intermediate filaments (IFs) when transiently expressed with plasmid vectors (E. White and R. Cipriani, Proc. Natl. Acad. Sci. USA, 86:9886-9890, 1989), the organization of IFs in transformed cells was investigated. Primary rat cells transformed by plasmids encoding E1A plus the E1B 19K protein showed gross perturbations of IFs, whereas cell lines transformed by plasmids encoding E1A plus the E1B 55K protein or E1A plus Ha-ras did not. These results suggest that an intact IF cytoskeleton may inhibit anchorage-independent growth and that the E1B 19K protein can overcome this inhibition by disrupting the IF cytoskeleton.

C-terminal domain of the adenovirus E1A oncogene product is required for induction of cytotoxic T lymphocytes and tumor-specific transplantation immunity

Adenovirus genes required for the elicitation of adenovirus group C-specific cytolytic T lymphocytes (CTLs) and for the induction of adenovirus-specific transplantation antigen (TSTA) were identified by immunization with a library of adenovirus mutants. The group C Ad-specific CTL response was elicited by immunization with wild-type adenovirus type 5 (Ad5) or with recombinant adenoviruses containing Ad5 E1A gene. The specific CTL response was also elicited by Ad5 virus constructs which express only the 12 S or 13 S E1A early mRNA, but not with viruses unable to express E1A protein sequences normally encoded by the E1A early messages. The induction of transplantation immunity against tumorigenic Ad-transformed cells was studied next. The product encoded by either 13 S and 12 S E1A mRNA alone was sufficient for strong TSTA activity. A series of viruses with mutations within the first exon of the E1A message also induced strong TSTA, while Ad5 mutants with lesions within the second exon failed to induce syngraft immunity. These results provide strong evidence that amino acid sequence encoded by the second exon of the Ad5 E1A message is required, either directly or indirectly, for the induction of both Ad-specific CTL and Ad TSTA.

Transgenic mouse model for human gastric carcinoma

To understand the pathogenesis that may be induced by human adenovirus type 12 (Ad12), we have generated transgenic mice carrying the Ad12 early region 1 under control of the mouse mammary tumor virus long terminal repeat. Eleven of 11 male founder mice, but only 2 of 12 females, died between 3 to 4 mo of age. Death was associated with presence of tumors at or near the squamocolumnar junction of the stomach. Microscopically, these multifocal tumors appeared to arise from hyperplastic epithelium and showed features consistent with adenocarcinoma or adenosquamous carcinoma. High levels of expression of both the Ad12 E1A and E1B genes were seen in the tumor-bearing stomach. Various levels of expression were also detected in other tissues, although the stomach was the only organ with detectable pathology. These observations suggest an organ-specific action of the Ad12 early region 1 gene products. This transgenic mouse model provides an experimental system for studying the development of human carcinomas at sites of transition from squamous to columnar epithelium.

The p53 proto-oncogene can act as a suppressor of transformation

DNA clones of the wild-type p53 proto-oncogene inhibit the ability of E1A plus ras or mutant p53 plus ras-activated oncogenes to transform primary rat embryo fibroblasts. The rare clones of transformed foci that result from E1A plus ras plus wild-type p53 triple transfections all contain the p53 DNA in their genome, but the great majority fail to express the p53 protein. The three cell lines derived from such foci that express p53 all produce mutant p53 proteins with properties similar or identical to transformation-activated p53 proteins. The p53 mutants selected in this fashion (transformation in vitro) resemble the p53 mutants selected in tumors (in vivo). These results suggest that the p53 proto-oncogene can act negatively to block transformation.

Growth factor induction by the adenovirus type 5 E1A 12S protein is required for immortalization of primary epithelial cells

The 12S protein encoded by the adenovirus E1A region induces cellular DNA synthesis in and proliferation and immortalization of primary rat epithelial cells in the presence or absence of serum. It also induces the production of a growth factor(s) that stimulates epithelial cell proliferation. We have undertaken a mutational analysis of the 12S gene to determine the sequences required for these functions. We found that a region near the C-terminus of the 12S protein was required for growth factor induction. No activities have been defined previously for this region. Furthermore, we show that growth factor production was necessary for epithelial cells to survive past their normal life span in culture and to become immortalized. The ability to induce growth factor production required prior expression of E1A activities encoded by the N-terminus of the 12S protein, including activation of quiescent cells into the cell cycle, and an unknown activity that required expression of the first 13 amino acids of the gene. In addition, examination of the subcellular localization of mutant 12S polypeptides suggested new regions that affect the nuclear localization of E1A proteins.

Cellular targets for transformation by the adenovirus E1A proteins

Three cellular proteins, including species of 300,000 daltons and 107,000 daltons as well as p105-RB, the product of the retinoblastoma susceptibility gene, stably interact with the adenovirus E1A proteins. To help determine the functional basis of these interactions, the regions of E1A that participate in these interactions were mapped using a series of deletion mutants. The 300,000 dalton and the 107,000 dalton proteins interacted with sequences within amino acids 1 to 76 and 121 to 127, respectively. Interaction with the third cellular protein, p105-RB, required the presence of sequences from two noncontiguous regions of the E1A polypeptide chain, amino acids 30 to 60 and 121 to 127. The regions of E1A that are required for these interactions coincided precisely with the regions of E1A that are required for its transforming function. These results suggest that the interactions with these cellular proteins are fundamental to the transforming activity of E1A.

Growth factor induction by the adenovirus type 5 E1A 12S protein is required for immortalization of primary epithelial cells

The 12S protein encoded by the adenovirus E1A region induces cellular DNA synthesis in and proliferation and immortalization of primary rat epithelial cells in the presence or absence of serum. It also induces the production of a growth factor(s) that stimulates epithelial cell proliferation. We have undertaken a mutational analysis of the 12S gene to determine the sequences required for these functions. We found that a region near the C-terminus of the 12S protein was required for growth factor induction. No activities have been defined previously for this region. Furthermore, we show that growth factor production was necessary for epithelial cells to survive past their normal life span in culture and to become immortalized. The ability to induce growth factor production required prior expression of E1A activities encoded by the N-terminus of the 12S protein, including activation of quiescent cells into the cell cycle, and an unknown activity that required expression of the first 13 amino acids of the gene. In addition, examination of the subcellular localization of mutant 12S polypeptides suggested new regions that affect the nuclear localization of E1A proteins.

Interactions between cell growth-regulating domains in the products of the adenovirus E1A oncogene

Among the various biological activities expressed by the products of the adenovirus E1A gene are the abilities to induce cellular DNA synthesis and proliferation in quiescent primary baby rat kidney cells. The functional sites for these activities lie principally within two regions of the E1A proteins: an N-terminal region and a small second region of approximately 20 amino acids further downstream. To study the biological functions of the first domain, we constructed an in-frame deletion of amino acid positions 23 through 107 of the E1A products. This deletion did not impede the ability of the E1A products to transactivate the adenovirus early region 3 promoter in a transient-expression assay in HeLa cells. The ability to induce DNA synthesis in quiescent baby rat kidney cells was, however, lost in the absence of these sequences. Deletion of the small second region induced a form of S phase in which DNA synthesis occurred in the apparent absence of controls required for the cessation of DNA synthesis and progression through the remainder of the cell cycle. These cells did not appear to accumulate in or before G2, and many appeared to have a DNA content greater than that in G2. The functions of both domains are required for production of transformed foci in a ras cooperation assay. Focus formation occurred, however, even when the two domains were introduced on two separate plasmids. This complementation effect appeared to require expression of both of the mutant proteins and did not appear to result merely from recombination at the DNA level.

Interactions between cell growth-regulating domains in the products of the adenovirus E1A oncogene

Among the various biological activities expressed by the products of the adenovirus E1A gene are the abilities to induce cellular DNA synthesis and proliferation in quiescent primary baby rat kidney cells. The functional sites for these activities lie principally within two regions of the E1A proteins: an N-terminal region and a small second region of approximately 20 amino acids further downstream. To study the biological functions of the first domain, we constructed an in-frame deletion of amino acid positions 23 through 107 of the E1A products. This deletion did not impede the ability of the E1A products to transactivate the adenovirus early region 3 promoter in a transient-expression assay in HeLa cells. The ability to induce DNA synthesis in quiescent baby rat kidney cells was, however, lost in the absence of these sequences. Deletion of the small second region induced a form of S phase in which DNA synthesis occurred in the apparent absence of controls required for the cessation of DNA synthesis and progression through the remainder of the cell cycle. These cells did not appear to accumulate in or before G2, and many appeared to have a DNA content greater than that in G2. The functions of both domains are required for production of transformed foci in a ras cooperation assay. Focus formation occurred, however, even when the two domains were introduced on two separate plasmids. This complementation effect appeared to require expression of both of the mutant proteins and did not appear to result merely from recombination at the DNA level.

Normalization of epidermal growth factor receptor and transforming growth factor production in drug resistant variants derived from adenovirus transformed cells

Variants (G2, G5) resistant to the cancer chemotherapeutic drug methylglyoxal bis (guanylhydrazone) (MGBG) were isolated from adenovirus type 2 transformed rat brain cells (F4; Sircar et al., 1987). Although at least one of these variants continued to express the adenovirus Ela and Elb transforming proteins, they both exhibited a detransformed phenotype as witnessed by flat morphology, loss of anchorage independent growth, and tumor forming capacity. Reverse transformation suggested the possibility of changes in growth factor receptors and the production of transforming growth factors. To test this possibility, we investigated the status of epidermal growth factor receptors (EGF-r) and transforming growth factor alpha (TGF-alpha) production in F4, G2 and G5 cells. The level of 125I-labeled EGF binding to intact drug resistant cells increased by 2- to 3-fold compared to the transformed parental cell. Scatchard analysis suggests that increased binding was the result of increased receptor levels rather than altered affinity of receptor for ligand. The production of growth factors which compete with 125I-labeled EGF binding declined in the detransformed G2 and G5 cells to a level intermediate between transformed (F4) and normal cells (FR3T3). EGF-receptor increase and the complementary decrease in growth factor production in the drug resistant variants may be associated with detransformation.

Cellular transformation by adenovirus type 5 is influenced by the viral DNA polymerase

Early region 2B (E2B) of the group C adenoviruses encodes a number of proteins, including the 140-kilodalton DNA polymerase, which plays a role in the initiation of viral DNA replication. Temperature-sensitive (ts) mutants with mutations mapping to E2B are conditionally defective for both DNA replication in human cells and transformation of rat cells. Nucleotide sequence analysis shows that the E2B mutant ts36 possesses a single point mutation specific to the viral DNA polymerase; this transition of a C to a T at position 7623 changes leucine residue 249 in the polymerase to a phenylalanine. A wild-type (ts+) revertant possesses a codon specifying the original leucine at position 249. Phenotypic analysis of revertant and wild-type viruses derived by marker rescue from ts36 shows that these variants are wild type for both viral DNA replication and transformation. Thus, the single point mutation in the polymerase gene of ts36 is responsible for both defects.

Transformation of differentiated rat hepatocytes with adenovirus and adenovirus DNA

Primary cultures of hepatocytes isolated by collagenase perfusion of adult rats were transformed by infection with adenovirus type 5 or transfection with adenovirus DNA. Total virion DNA or recombinant plasmid DNA containing the adenovirus E1A and E1B genes transformed hepatocytes at comparable frequencies. No foci of replicating hepatocytes were detected after transfection with a plasmid containing the E1A gene alone. The frequency of transformation by the adenovirus E1A and E1B genes was dependent on the composition of the culture medium. Transformation occurred at a low frequency when the transfected hepatocytes were maintained in a chemically defined medium (CDM), but the frequency was enhanced 8- to 10-fold when the cells were maintained in (i) serum-supplemented medium or (ii) CDM supplemented with epidermal growth factor. Cell lines derived from the adenovirus-transformed colonies of hepatocytes expressed adenovirus E1A and E1B RNAs. When hepatocytes were maintained in CDM supplemented with dimethyl sulfoxide and transfected with plasmids containing the E1A and E1B genes, it was possible to derive cell lines that retained the ability to express several liver-specific genes, including albumin, transferrin, hemopexin, and the third component of complement. The amount of albumin secreted per cell varied from 1 to 5 pg per cell per 24 h, and in one cell line it was below detectable levels by passage 9. Adenovirus-transformed hepatocytes were not tumorigenic when inoculated subcutaneously into neonatal syngeneic rats. We conclude that the adenovirus E1A and E1B genes are capable of transforming adult rat hepatocytes, a differentiated epithelial cell type.

Growth factor(s) produced during infection with an adenovirus variant stimulates proliferation of nonestablished epithelial cells

Infection of primary baby rat kidney cells with an adenovirus variant that encodes only the 12S gene of the E1A region, adenovirus type 5 (Ad5) 12S, results in the production of a growth factor that stimulates primary epithelial cells to proliferate. Increased epithelial cell DNA synthesis and proliferation is detectable between 24 and 36 hr after the addition of conditioned medium from Ad5 12S infected cells and not from cells infected with an E1A deletion mutant virus, Ad5 dl312. This mitogenic factor(s) is effective in the absence of serum and can override the inhibitory effect of serum on primary epithelial cells. Furthermore, there is a requirement for the continued presence of the growth factor(s) in the Ad5 12S conditioned medium to maintain epithelial cell proliferation, and the conditioned medium can maintain these cells in a proliferative state for at least 6 wk. The stimulatory activity in Ad5 12S conditioned medium is associated with large molecular weight complexes, from which it can be released by 4 M NaCl. Several characteristics of the growth factor(s) indicate that it is a unique mitogen for epithelial cells.

Adenovirus E1A 12S protein induces DNA synthesis and proliferation in primary epithelial cells in both the presence and absence of serum

Infection of primary baby rat kidney (BRK) cells with an adenovirus that carries an E1A 12S cDNA in place of the normal E1A region (adenovirus 5 [Ad5] 12S) resulted in the induction of cellular DNA synthesis and proliferation of the epithelial cells in the population, even in the absence of serum. Increased cellular DNA synthesis was first detectable by 12 h after infection and was maintained at a 10- to 20-fold higher level than in mock-infected cells. By 5 days after infection there was a 10-fold-greater number of 12S virus-infected BRK cells. These infected BRK cells retained many of their normal epithelial cell characteristics and were not transformed. The expression of the E1A 12S protein(s) occurred early after infection. There was no induction of adenoviral gene expression or viral DNA replication in these cells. The early effects of a fully transforming gene product(s) were also examined. The Ad5-simian virus 40 hybrid virus, Ad5.SVR4, in which the early region of simian virus 40 has replaced the E1 region of Ad5, was used to infect BRK cells. The kinetics of expression of the T antigens were similar to those of the 12S polypeptides. Infection with Ad5.SV4 also resulted in the induction of cellular DNA synthesis and cell proliferation at levels similar to those observed with the 12S virus. However, infection with Ad5.SVR4 resulted in cells that had lost some of their epithelial cell characteristics and were fully transformed. Thus, although the early cellular events induced by the two genes were similar, they did not yield the same final cellular phenotype.

Adenovirus E1a proteins repress expression from polyomavirus early and late promoters

We have examined the effects of the E1a products of adenovirus types 5 and 12 on the expression of polyomavirus early and late promoters. In cotransfection experiments in HeLa cells, plasmids expressing the E1a region of adenovirus type 5 or 12 repressed both the early and late promoters of polyomavirus, and deletion analysis indicates that the polyomavirus enhancers were the target of the E1a repression. With mutants lacking enhancer sequences, the polyomavirus early promoter but not the late promoter was trans-activated by E1a. Chimeric mutant plasmids with deletions in the regulatory region that contained either the A enhancer or the B enhancer were repressed to the same extent, indicating that E1a can repress both elements. Polyomavirus variant plasmids with rearrangements in the regulatory region conferring activity in embryonal carcinoma stem cells were repressed by E1a as was the wild type, suggesting that the repressor function is quite general. We discuss a model in which the influence of E1a on the transcriptional activity of a gene is the sum of positive and negative effects on promoter and enhancer elements and discuss possible mechanisms of negative regulation of enhancer function.

Mutations in the E1a gene of type 5 adenovirus result in oncogenic transformation of Fischer rat embryo cells

Transformation of a specific clone of Fischer rat embryo (CREF) cells with wild-type 5 adenovirus (Ad5) or the E1a plus E1b transforming gene regions of Ad5 results in epithelioid transformants that grow efficiently in agar but that do not induce tumors when inoculated into nude mice or syngeneic Fischer rats. In contrast, CREF cells transformed by a host-range Ad5 mutant, H5hrl, which contains a single base-pair deletion of nucleotide 1055 in E1a resulting in a 28-kd protein (calculated) in place of the wild-type 51-kd acidic protein, display a cold-sensitive transformation phenotype and an incomplete fibroblastic morphology but surprisingly do induce tumors in nude mice and syngeneic rats. Tumors develop in both types of animals following injection of CREF cells transformed by other cold-sensitive Ad5 E1a mutants (H5dl101 and H5in106), which contain alterations in their 13S mRNA and consequently truncated 289AA proteins. CREF cells transformed with only the E1a gene (0-4.5 m.u.) from H5hrl or H5dl101 also produce tumors in these animals. To directly determine the role of the 13S E1a encoded 289AA protein and the 12S E1a encoded 243AA protein in initiating an oncogenic phenotype in adenovirus-transformed CREF cells, we generated transformed cell lines following infection with the Ad2 mutant pm975, which synthesizes the 289AA E1a protein but not the 243AA protein, and the Ad5 mutant H5dl520 and the Ad2 mutant H2dl1500, which do not produce the 289AA E1a protein but synthesize the normal 243AA E1a protein. All three types of mutant adenovirus-transformed CREF cells induced tumors in nude mice and syngeneic rats. Tumor formation by these mutant adenovirus-transformed CREF cells was not associated with changes in the arrangement of integrated adenovirus DNA or in the expression of adenovirus early genes. These results indicate, therefore, that oncogenic transformation of CREF cells can occur in the presence of a wild-type 13S E1a protein or a wild-type 12S E1a protein when either protein is present alone, but does not occur when both wild-type E1a proteins are present.

Multiple effects of the 72-kDa, adenovirus-specified DNA binding protein on the efficiency of cellular transformation

The early region 2A gene (E2A) of adenovirus types 2 and 5 encodes a 72-kDa DNA binding protein (DBP) which contains two physical domains comprising approximately the amino-terminal one-third and carboxyl-terminal two-thirds of the protein, respectively. Previous work has shown that some Ad5 mutants containing temperature-sensitive (ts) mutations in the carboxyl-terminal domain of DBP, such as Ad5ts125, show a 3- to 8-fold enhanced ability to transform rat cells. We have examined the transformation characteristics of a series of Ad5 E2A deletion mutants, Ad5dl801-5, which encode either no functional DBP or encode truncated, defective DBPs. The E2A deletion mutants transformed rat embryo cells at frequencies similar to wild-type (wt) Ad5. These results suggest that the high transformation phenotype of carboxyl-terminal E2A mutants like Ad5ts125 is not due to the simple inactivation of DBP function, but rather results from an activity possessed by an altered DBP. This hypothesis is supported by the fact that the transformation phenotype of Adsts125 and similar mutants is dominant over the wild-type phenotype. A number of additional Ad2 and Ad5 E2A mutants were examined with respect to their ability to transform primary rat embryo cells. It was found that a carboxyl-terminal E2A mutant, Ad2+ND1ts23, also showed the enhanced transformation phenotype. In contrast, several amino-terminal E2A host-range (hr) mutants, originally isolated on the basis of their ability to replicate in monkey cells, transformed rat embryo cells at a frequency similar to wild-type virus. Ad2ts400, and E2A mutant with alterations in both DBP domains, showed a wild-type frequency of transformation, while two similar mutants, Ad5ts125 X 405 and Ad5ts125 X 404, showed an enhanced frequency. Last, it was found that coinfection of primary rat embryo cells with the hr mutants plus Ad5ts125 or Ad2+ND1ts23 resulted in a wild-type frequency of transformation, demonstrating that the hr mutants are dominant to the ts mutants with regard to transformation phenotype. Thus, DBP can both positively and negatively affect viral transformation in this system.

Association of adenovirus early-region 1A proteins with cellular polypeptides

Extracts from adenovirus-transformed human 293 cells were immunoprecipitated with monoclonal antibodies specific for the early-region 1A (E1A) proteins. In addition to the E1A polypeptides, these antibodies precipitated a series of proteins with relative molecular weights of 28,000, 40,000, 50,000, 60,000, 80,000, 90,000, 110,000, 130,000, and 300,000. The two most abundant of these polypeptides are the 110,000-molecular-weight protein (110K protein) and 300K protein. Three experimental approaches have suggested that the 110K and 300K polypeptides are precipitated because they form stable complexes with the E1A proteins. The 110K and 300K polypeptides do not share epitopes with the E1A proteins, they copurify with a subset of the E1A proteins, and they bind to the E1A proteins following mixing in vitro. The 110K and 300K polypeptides are not adenoviral proteins, but are encoded by cellular DNA. Both the 12S and the 13S E1A proteins bind to the 110K and 300K species, and these complexes are found in adenovirus-transformed and -infected cells.