ERK1/2 is required for myoblast proliferation but is dispensable for muscle gene expression and cell fusion

Skeletal muscle satellite cells, which are found between the muscle fiber and the basal lamina, remain quiescent and undifferentiated unless stimulated to remodel skeletal muscle or repair injured skeletal muscle tissue. Quiescent satellite cells express c-met and fibroblast growth factor receptors (FGFR) 1 and 4, suggesting these receptors are involved in maintaining the undifferentiated quiescent state or involved in satellite cell activation. Although the signaling pathways involved are poorly understood, the mitogen activated protein kinase (MAPK) cascade has been implicated in the regulation of skeletal muscle growth and differentiation by FGFs. In this study, we investigated if activation of the Raf-MKK1/2-ERK1/2 signaling cascade plays a role in FGF-dependent repression of differentiation and proliferation of MM14 cells, a skeletal muscle satellite cell line. Inactivation ofthe Raf-MKK1/2-ERK1/2 pathway in myoblasts through the overexpression of dominant negative mutants of Raf-1 blocks ERK1/2 activity and prevents myoblast proliferation. Additionally, inhibition of MKK1/2 by treatment with pharmacological inhibitors also blocks FGF-mediated stimulation of ERK1/2 and blocks the G1 to S phase transition of myoblasts. Unexpectedly, we found that inactivation of the Raf-ERK pathway does not activate a muscle reporter, nor does inactivation of this pathway promote myogenic differentiation. We conclude that FGF-stimulated ERK1/2 signaling is required during the G1 phase of the cell cycle for commitment of myoblasts to DNA synthesis but is not required for mitosis once cells have entered the S-phase. Moreover, ERK1/2 signaling is not required either to repress differentiation, to promote skeletal muscle gene expression, or to promote myoblast fusion.

Viral-encoded cyclins

D-type cyclin homologs have been found in the genomes of herpesviruses associated with neoplasias. They appear to exploit features of G(1) cyclins but extend their properties to allow for deregulation of the cell cycle. Advances in the study of the molecular basis for these novel features as well as the potential role of viral cyclins in tumorigenesis are addressed.

Detection of an appropriate kinase activity in branchial arches I and II that coincides with peak expression of the Treacher Collins syndrome gene product, treacle

Treacher Collins syndrome (TCS) is an autosomal dominant craniofacial disorder involving the mid and lower face and, in particular, the tissues affected arise solely from embryonic branchial arches I and II. TCOF1, the gene involved in TCS, has been cloned and although the function of the encoded protein, treacle, has not yet been established, it exhibits peak expression in the branchial arches. Treacle contains a series of repeating units of acidic and basic residues, which are predicted to contain putative casein kinase II (CKII) and protein kinase C (PKC) phosphorylation site motifs. In addition, treacle has weak homology to two phosphorylation-dependent nucleolar proteins, which shuttle between the cytoplasm and nucleolus. Based on these observations, phosphorylation of treacle may be important for its function. In this study, GST-treacle fusion peptides were constructed using particular TCOF1 exons that contained potential CKII and PKC phosphorylation sites. These were used as substrates in in vitro kinase assays and showed that treacle fusion peptides can be phosphorylated by the appropriate kinases. Furthermore, using tissue extracts we have demonstrated that in avian embryonic branchial arches I and II there is a kinase activity that can phosphorylate treacle peptides that is consistent with CKII site recognition. This activity coincides with the reported high expression of treacle in these tissues at early developmental stages and declines later in development.

Regulation of myogenesis by fibroblast growth factors requires beta-gamma subunits of pertussis toxin-sensitive G proteins

Terminal differentiation of skeletal muscle cells in culture is inhibited by a number of different growth factors whose subsequent intracellular signaling events are poorly understood. In this study, we have investigated the role of heterotrimeric G proteins in mediating fibroblast growth factor (FGF)-dependent signals that regulate myogenic differentiation. Pertussis toxin, which ADP-ribosylates and inactivates susceptible G proteins, promotes terminal differentiation in the presence of FGF-2, suggesting that Galpha or Gbeta gamma subunits or both are involved in transducing the FGF-dependent signal(s) that inhibits myogenesis. We found that Gbetagamma subunits are likely to be involved since the expression of the C terminus of beta-adrenergic receptor kinase 1, a Gbetagamma subunit-sequestering agent, promotes differentiation in the presence of FGF-2, and expression of the free Gbeta gamma dimer can replace FGF-2, rescuing cells from pertussis toxin-induced differentiation. Addition of pertussis toxin also blocked FGF-2-mediated activation of mitogen-activated protein kinases (MAPKs). Ectopic expression of dominant active mutants in the Ras/MAPK pathway rescued cells from pertussis toxin-induced terminal differentiation, suggesting that the Gbeta gamma subunits act upstream of the Ras/MAPK pathway. It is unlikely that the pertussis toxin-sensitive pathway is activated by other, as yet unidentified FGF receptors since PDGF (platelet-derived growth factor)-stimulated MM14 cells expressing a chimeric receptor containing the FGF receptor-1 intracellular domain and the PDGF receptor extracellular domain were sensitive to pertussis toxin. Our data suggest that FGF-mediated signals involved in repression of myogenic differentiation are transduced by a pertussis toxin-sensitive G-protein-coupled mechanism. This signaling pathway requires the action of Gbeta gamma subunits and activation of MAPKs to repress skeletal muscle differentiation.

The FGF receptor-1 tyrosine kinase domain regulates myogenesis but is not sufficient to stimulate proliferation

Ligand-stimulated activation of FGF receptors (FGFRs) in skeletal muscle cells represses terminal myogenic differentiation. Skeletal muscle cell lines and subsets of primary cells are dependent on FGFs to repress myogenesis and maintain growth. To understand the intracellular events that transduce these signals, MM14 skeletal muscle cells were transfected with expression vectors encoding chimeric receptors. The chimeras are comprised of the PDGF beta receptor (PDGFbetaR) extracellular domain, the FGFR-1 intracellular domain, and either the PDGFbetaR or FGFR-1 transmembrane domain. The chimeric receptors were autophosphorylated upon PDGF-BB stimulation and are capable of stimulating mitogen-activated protein kinase activity. Activation of the tyrosine kinase domain of either chimera repressed myogenesis, suggesting intracellular responses regulating skeletal muscle differentiation are transduced by activation of the FGFR-1 tyrosine kinase. Unexpectedly, we found that activation of either chimeric receptor failed to stimulate cellular proliferation. Thus, it appears that regulation of skeletal muscle differentiation by FGFs requires only activation of the FGFR tyrosine kinase. In contrast, stimulation of proliferation may require additional, as yet unidentified, signals involving the receptor ectodomain, the FGF ligand, and heparan sulfate either alone, or in combination.

Differential control of cyclins D1 and D3 and the cdk inhibitor p27Kip1 by diverse signalling pathways in Swiss 3T3 cells

Quiescent Swiss 3T3 cells can be induced to re-enter the cell cycle by stimulation of a variety of growth factor-dependent signal transduction cascades. We have utilised this cell system to investigate the point of convergence of mitogenic signalling by analysing the changes that distinct mitogens induce in the components of the cell cycle regulatory machinery (the G1 cyclins, cdks and their inhibitors). In the presence of insulin, activation of cAMP-dependent protein kinase caused a dramatic post-transcriptional down-regulation of p27(Kip1), an increase in cyclin D3 but had little effect on cyclin D1 levels, whilst activation of protein kinase C had a more modest effect on cyclin D3 and p27(Kip1) but caused a striking elevation in the expression of cyclin D1. The neuropeptide bombesin, when combined with insulin, caused increased expression of cyclin D1 and down-regulation of p27(Kip1) mRNA and protein. Thus each combination of mitogenic agents had different effects on the components responsible for regulating the orderly progression of the cell cycle. This outcome is incompatible with a single route to mitogenesis and demonstrates that different mitogens remain distinct in the signalling responses they initiate, only converging at the levels of the expression of the D-type cyclins and the inhibitor p27(Kip1).

A comparison of prophylactic ondansetron and metoclopramide administration in patients undergoing major neurosurgical procedures

In a prospective, randomised, double-blind trial, we assessed the relative efficacy of prophylactic ondansetron and metoclopramide administration in the reduction of postoperative nausea and vomiting in 60 patients undergoing routine major neurosurgical procedures. The patients were randomly allocated into one of two groups. Both groups received a standardised anaesthetic. When the dura mater was closed, patients in group A received an intravenous injection of metoclopramide 10 mg whilst group B received ondansetron 8 mg intravenously. Patients who received metoclopramide experienced less postoperative nausea and vomiting than those who received ondansetron in the 48 h following surgery (17 (56%) versus 9 (30%) p = 0.038). In the light of these findings, we believe that ondansetron is an inappropriate agent for the prevention of postoperative nausea and vomiting in the neurosurgical population.

The addition of tenoxicam to prilocaine for intravenous regional anaesthesia

The analgesic effects of tenoxicam 20 mg added to prilocaine in a standard Bier's block (group 2) was studied in 45 patients who had their Colles' fractures reduced under intravenous regional anaesthesia, and compared both to a control group (group 1), and to a group who received a standard Bier's block combined with the same dose of tenoxicam given intravenously into the contralateral arm (group 3). Patients in group 2 obtained significantly better analgesia than group 1, as judged by a longer time before first additional analgesia was required (p < 0.05), less total analgesic consumption (p < 0.01), and lower pain scores (p < 0.01). These benefits were not obtained by patients in group 3.

E2F-1 but not E2F-4 can overcome p16-induced G1 cell-cycle arrest

BACKGROUND

The transition from G1 to S phase is the key regulatory step in the mammalian cell cycle. This transition is regulated positively by G1-specific cyclin-dependent kinases (cdks) and negatively by the product of the retinoblastoma tumour suppressor gene, pRb. Hypophosphorylated pRb binds to and inactivates the E2F transcription factor, which controls the expression of genes required for S-phase progression. Hyperphosphorylation of pRb in late G1 phase results in the accumulation of active E2F, a critical event in the progression to S phase. The E2F factor is not a single entity, but rather represents a family of highly related molecules, all of which bind to pRb or the pRb-related proteins p107 and p130.

RESULTS

In this study, we have used specific inhibitors of cdks to explore the requirements for cell-cycle progression from G1 to S phase. Expression of p16Ink4, which specifically inhibits cyclin D-directed cdks, blocks cells in G1 phase; this block can be overcome by expression of the viral proteins that inactivate pRb or by E2F-1. Importantly however, the G1 arrest is not overcome by overexpression of E2F-4. By using chimeric E2F proteins, containing amino-acid sequences from E2F-1 and E2F-4, we have shown that their differential abilities to overcome a p16-imposed arrest is determined by their respective amino-terminal regions. We also demonstrate that E2F-1 can promote entry into S phase without concomitant phosphorylation of pRb. In contrast to the p16-mediated G1 block, G1 arrest mediated by the cdk inhibitors p21Cip1 or p27Kip1 cannot be bypassed either by inactivation of pRb or overexpression of E2F family members.

CONCLUSIONS

These data demonstrate that the role of the cyclin D-directed cdks in promoting the progression of cells from G1 into S phase is wholly to activate an E2F-1-like activity through phosphorylation, thus preventing the formation of the E2F-pRb complex. The cyclin E-cdk2 complex is also required for the G1/S transition but has a different and as yet undefined role. We also provide evidence for a functional difference between E2F-1 and E2F-4, dependant upon the region that contains the DNA-binding and dimerization domains. These results indicate that these two E2F family members are likely to regulate the expression of different subsets of E2F-responsive promoters.

Massive arterial air embolism during cardiopulmonary bypass: antegrade blood cardioplegia delivered by the pump--an accident waiting to happen

Of the many possible causes of air embolism occurring in patients undergoing cardiopulmonary bypass (CPB), human error due to the perfusionist or the surgeon accounts for the vast majority. This case, however, presents a previously unreported, but recognized, cause of air embolism, due to a technical problem encountered during the administration of blood cardioplegia. The nature of some of the older CPB pumps allows the administration of cardioplegia at a time when the main CPB pump is not rotating. A situation may then arise whereby air may be entrained and delivered to the patient. The management of massive air embolism is discussed, and recommendations are made to prevent such an occurrence happening in the future.

The amino acid requirements of Staphylococcus aureus isolated from cases of bovine mastitis

The amino acid requirements of seven strains of Staphylococcus aureus isolated from cases of bovine mastitis were determined. Arginine, cystine, glycine, leucine, proline and valine were essential for the growth of all isolates. In addition, all isolates required one or more of the following: glutamic acid, histidine, isoleucine, lysine, methionine, phenylalanine, tryptophan and tyrosine.

Activating transcription factor-1 is a specific antagonist of the cyclic adenosine 3'.5'-monophosphate (cAMP) response element-binding protein-1-mediated response to cAMP

We have investigated the molecular basis of the variability of the somatostatin cAMP response element (CRE) function in different cell lines. All cells tested contain detectable levels of the CRE-binding protein CREB-1, which mediates transactivation in response to the cAMP-dependent protein kinase (protein kinase-A), in forms that can bind to a somatostatin CRE. Although both responsive and nonresponsive cells contain CREB-1 in heterodimers with activating transcription factor-1 (ATF-1), only cells that allow a cAMP response have a significant proportion of CREB-1 in a homodimeric form. Transfection experiments demonstrate that ATF-1 is capable of antagonizing CREB-1-dependent activation, suggesting that the ability of CREB-1 to mediate a cAMP response is down-regulated by heterodimer formation with ATF-1.

Different binding specificities and transactivation of variant CRE's by CREB complexes

The DNA binding specificities of CREB1 and CREB2 homodimers and the CREB2/cJun heterodimer were analyzed with a CASTing technique. All but one of the selected sequences varied from the consensus CRE (TGACGTCA) by three nucleotides or less. The profile of variations selected and the binding affinity for these sequences were unique for each CREB complex. The affinities were not effected by the palindromic nature of the sequences, but were strongly effected by flanking sequences. The strength of DNA binding in vitro correlated with the degree of transactivation observed in JEG-3 cells transfected with reporter plasmids harboring CRE variants, when hybrid CREB proteins fused to the VP16 activation domain were expressed. When native CREB proteins were expressed, the correlation was attenuated by the nature of the variant sequence. A CRE variant (TGACATCA) found in several natural promoters, exhibited the lowest basal transcription rate of the variants and a lower level of induction than expected when compared with the in vitro binding data. These results indicate that transactivation of DNA sequence elements is strongly effected by the strength of transcription factor binding, and that individual sequences can attenuate the level of induction.

Borrelia burgdorferi decreases hyaluronan synthesis but increases IL-6 production by fibroblasts

Despite the prevalence of clinical data on human Lyme disease, little is known about the immunopathologic effects of the causative organism on the host. We studied the effect of Borrelia burgdorferi on hyaluronan (hyaluronic acid, HYA) production and the effect on interleukin-6 (IL-6) synthesis by cultured fibroblasts. The cell line employed in this study produced an average of 1406 ng of hyaluronan/ml within 48 h. Using both a morphological staining protocol and a quantitative radiometric assay, we noted that in the presence of a low dose of Borrelia (9.4 x 10(5) cells/ml) the hyaluronan production decreased to an average of 1008 ng/ml, a significant difference (p < 0.05) from the amount of hyaluronan produced by the cells alone. The reduction was even more significant (p < 0.01) when a higher dose of Borrelia (9.4 x 10(6) cells/ml) was used giving an average hyaluronan concentration of 682 ng/ml. In contrast, we found that Borrelia stimulated the cells to produce IL-6 from a baseline of 293 pg/ml to a maximal value of 842 pg/ml (p < 0.01). The spirochetes had no significant effect on cell viability, nor were we able to demonstrate invasion of the cells by the bacteria. Both a decrease in hyaluronan and an increase in IL-6 may correlate with the pathogenicity of Lyme disease in man.

A case of Japanese encephalitis

We report a case of Japanese encephalitis that occurred in a woman who had spent only a few days in an area where she could have been exposed to the virus. The risks and protective efficacy of vaccination against Japanese encephalitis virus for travellers who visit endemic areas for only a short period are discussed.

Differential regulation of three members of the ATF/CREB family of DNA-binding proteins

The ATF/CRE binding site can mediate transcriptional activation by cAMP, the adenovirus E1A protein and the human T-cell leukaemia virus 1 (HTLV1) tax protein. A large number of different proteins bind specifically to this element either as homodimers or as heterodimers. Using GAL4-ATF/CREB fusions, we have investigated the regulatory functions of three members of this family. CREB1 (CREB) is strongly activated by cAMP and weakly activated by the E1A protein. In contrast, CREB2 (CRE-BP1, ATF2) is strongly activated by E1A but is insensitive to cAMP stimulation. ATF1 is weakly activated by cAMP but is not activated by E1A. All three proteins are insensitive to activation by the HTLV1 tax protein. The N-terminal region of CREB2, from amino acid residues 19 to 112, is both necessary and sufficient for E1A activation. This region contains a putative C2H2 metal-binding finger, and single amino acid substitutions of the cysteine residues severely decreased CREB2 activity. In contrast, mutations affecting a potential protein kinase A and casein kinase II phosphorylation site within this region had little effect.

Identification and functional characterisation of the cellular activating transcription factor 43 (ATF-43) protein

The promoter motif CGTCA binds multiple cellular factors that mediate a variety of inducible events, including positive responses to raised cellular levels of cAMP and to the Adenovirus E1a protein. To date, at least ten mammalian cDNA clones have been isolated that encode distinct proteins capable of binding to this motif. However, in most cases the precise stimuli that may regulate these different factors have yet to be determined. We have previously shown that the abundant Hela protein ATF-43 forms a complex in vivo with the cyclic AMP response element binding protein (CREB). In this report we definitively show that ATF-43 is the product of the two published cDNA clones, ATF1 and TREB 36. We confirm that ATF1 efficiently heterodimerises with CREB and demonstrate that even though ATF1 and CREB homodimers, as well as the ATF1/CREB heterodimer efficiently bind to the CGTCA motif, the resulting DNA-protein complexes have significantly different stabilities. A region outside the DNA binding domain of ATF1 contributes to the instability of its interaction with DNA. We further show that despite ATF1's homology to CREB, it responds poorly to activation by protein kinase A. In light of our finding that in Hela cells the majority of CREB protein is heterodimerised with ATF1, we speculate on the functional significance of such heterodimers.

Transformation by the human adenoviruses

Oncogenic transformation by the human adenoviruses involves the concerted action of two genes, E1A and E1B. Over the last few years the products of these genes have been characterised in considerable detail using genetic, immunological and biochemical means. The E1A gene by itself can immortalise primary cells and can cooperate to effect full morphological transformation not only with E1B but also with other known oncogenes. The immortalisation and cooperation activities of E1A require multiple functions that are directed by structurally and functionally independent regions of the E1A protein. These regions coincide with sites of protein: protein interaction between E1A and a variety of cellular polypeptides. One of these, the Rb protein, is a known regulator of the mammalian cell cycle. The E1B region encodes two proteins required for transformation, the larger of which binds to the p53 cellular protein. This protein has also been implicated as a negative regulator of cell growth. It appears therefore that E1A and E1B carry out their many functions associated with transformation at least in part by binding to and presumably modulating the activity of key cellular regulators.

The cellular transcription factor CREB corresponds to activating transcription factor 47 (ATF-47) and forms complexes with a group of polypeptides related to ATF-43

Promoter elements containing the sequence motif CGTCA are important for a variety of inducible responses at the transcriptional level. Multiple cellular factors specifically bind to these elements and are encoded by a multigene family. Among these factors, polypeptides termed activating transcription factor 43 (ATF-43) and ATF-47 have been purified from HeLa cells and a factor referred to as cyclic AMP response element-binding protein (CREB) has been isolated from PC12 cells and rat brain. We demonstrated that CREB and ATF-47 are identical and that CREB and ATF-43 form protein-protein complexes. We also found that the cis requirements for stable DNA binding by ATF-43 and CREB are different. Using antibodies to ATF-43 we have identified a group of polypeptides (ATF-43) in the size range from 40 to 43 kDa. ATF-43 polypeptides are related by their reactivity with anti-ATF-43, DNA-binding specificity, complex formation with CREB, heat stability, and phosphorylation by protein kinase A. Certain cell types vary in their ATF-43 complement, suggesting that CREB activity is modulated in a cell-type-specific manner through interaction with ATF-43. ATF-43 polypeptides do not appear simply to correspond to the gene products of the ATF multigene family, suggesting that the size of the ATF family at the protein level is even larger than predicted from cDNA-cloning studies.

Maintenance of cellular proliferation by adenovirus early region 1A in fibroblasts conditionally immortalized by using simian virus 40 large T antigen requires conserved region 1

Various mutants of adenovirus E1A were assayed for their ability to complement the growth defect at the nonpermissive temperature for the cell line tsa14 which was isolated by immortalizing rat embryo fibroblasts with the thermolabile large T antigen of tsA58. This cell line grows indefinitely at the permissive temperature but undergoes rapid growth arrest upon shift up to the nonpermissive temperature. Since this growth arrest can be overcome by introduction of wild-type simian virus 40 large T antigen, human papillomavirus 16 E7, and adenovirus E1A, the tsa14 cells provided an excellent system for defining regions of E1A necessary for complementation of the growth defect. We demonstrate that conserved region 1 (CR1) is the region of E1A required for complementation. While CR2 of E1A has been shown to be required for the immortalization of primary cells and is also necessary for the binding of the 105-kDa retinoblastoma protein, mutations within this region did not abrogate complementation of the growth defect. However, since both CR1 and CR2 have previously been shown to be absolutely required for immortalization of primary cells by adenovirus E1A, this evidence suggests that the tsa14 system assays for the maintenance of proliferation and that this requires CR1.

Activation in vitro of RNA polymerase II and III directed transcription by baculovirus produced E1A protein

The baculovirus expression system has been successfully used to overproduce a number of different protein products. In this report we describe the construction of a recombinant baculovirus containing the adenovirus E1A 13s cDNA sequence. Infection of insect cells with this virus results in the production of phosphorylated E1A protein. The phosphorylation pattern appears to be similar to the complex pattern associated with E1A protein synthesis in mammalian cells. Purified baculovirus generated E1A protein activated transcription of specific poIIII promoters both in microinjected Xenopus laevis oocytes and in HeLa cell in vitro transcription extracts. The protein also stimulates in vitro transcription of the poIIII transcribed VA1 gene.

Heterodimer formation between CREB and JUN proteins

DNA binding protein families have been identified that contain a leucine zipper dimerization motif preceded by a conserved, highly basic domain involved in direct specific interaction with DNA. Members of two of these families, the Jun and Fos related proteins, have been shown to directly interact and form heterodimeric complexes. A third such family known as the CREB or ATF proteins, bind to a sequence element present in promoters from a number of viral and cellular genes; this element can confer cAMP-inducibility and E1A-inducibility of transcription. In this report we show that one member of the CREB family can efficiently form a heterodimeric complex with the cJun protein. The DNA binding specificity of the heterodimer was indistinguishable from CREB alone. Transfection studies in undifferentiated F9 cells suggest that the CREB/cJun heterodimer can form in vivo, but that the complex does not activate transcription. The heterodimer formation between CREB and Jun proteins is highly specific; only one of the two CREB proteins would heterodimerize with cJun and it would not form dimers with JunB or cFos. The interaction of members of these two families of proteins increases the repertoire of possible regulatory complexes that could play an important role in the regulation of transcription of specific cellular genes.

Transactivation of the adenovirus EIIa promoter in the absence of adenovirus E1A protein is restricted to mouse oocytes and preimplantation embryos

Undifferentiated mouse embryonal carcinoma (EC) cells are capable of transactivating the adenovirus EIIa promoter in the absence of its normal transactivator, E1A protein, suggesting that EC cells contain an E1A-like activity. In an effort to identify where this activity appears during normal mouse development, mouse oocytes and preimplantation embryos were injected with plasmids containing the EIIa promoter coupled to various reporter genes. These expression vectors were fully active in human 293 cells where E1A is present, but were inactive in differentiated fibroblast cell lines unless cotransfected with the E1A gene. In mouse oocytes and preimplantation embryos, EIIa promoter activity in the absence of adenovirus E1A protein was equivalent to or greater than activity of the HSV thymidine kinase promoter coupled to a strong enhancer. Coinjection of the E1A gene failed to stimulate EIIa activity further, perhaps because c-myc protein, which has been reported to transactivate this promoter, was already present at high levels in mouse oocytes. Activation of the EIIa promoter in the absence of E1A was unique to mouse oocytes and preimplantation embryos because gene expression from an EIIa promoter introduced into transgenic mice was observed only in the adult ovary, and particularly in the oocytes. In addition, post-implantation transgenic embryos failed to express the E1A-activatable reporter gene, thereby indicating that expression from the EIIa promoter is restricted to the relatively undifferentiated stages of oogenesis and preimplantation development. These data suggest that cellular promoters of the class that can be transactivated by E1A may serve uniquely to initiate transcription of genes that are needed for preimplantation development.

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.