Possible effect of pneumoperitoneum on the spreading of colon cancer tumor cells

PURPOSE

By using a murine hepatic metastatic model, we tried to investigate the possible influence of gas insufflation in colon cancer cells spreading from the portal system to the liver.

METHODS

After transducing the human placental ALP gene into murine colon cancer cell line CT26, we successfully selected a clone of CT26/DAP that would yield a specific color following histochemical staining. Fifty mice were assigned into two groups, receiving either an intrasplenic injection of 10(6) CT26/DAP cells alone or the cells followed by intra-abdominal helium insufflation with the pressure of 15 cm H2O for ten minutes. Five mice in each group were used to observe their survival and the other mice were killed at four different time periods: 10 minutes, 24 hours, 48 hours, and 72 hours following cell injection. The livers and spleens were removed for histochemical staining. By counting the numbers of specific dark reddish spots of CT26/DAP cells, we could estimate the number of tumor cells on the hepatic surface.

RESULTS

At the very beginning following tumor cell injection, we found a significantly greater number of tumor cells on the hepatic surface in mice with gas insufflation (6354 +/- 1072 vs. 2133 +/- 223, respectively; P = 0.012). But the difference of these two groups became smaller and smaller as time went by. The number of tumor cells on the hepatic surface would reach the lowest level at postoperative 48 hours, and the tumor foci then began to grow both in size and number. The above patterns of dynamic change in tumor cell distribution were similar in mice both with and without gas insufflation. Average survival was slightly shorter in mice with gas insufflation, but the difference was not statistically significant.

CONCLUSION

Pneumoperitoneum caused by gas insufflation may increase tumor cell spread from the portal system to the liver at the very beginning stage; however, there was no significant difference in long-term survival between mice with and without gas insufflation in this murine animal model.

Protein tyrosine phosphatase activities are involved in apoptotic cancer cell death induced by GL331, a new homolog of etoposide

GL331 is a semisynthetic topoisomerase II inhibitor derived from a plant toxin podophyllotoxin. In 72-h exposure assays, LD50 values of GL331 range from 0.5 to 2 microM, which are three- to ten-fold lower than those of its homologous compound etoposide (VP-16), depending on different cancer cell lines including nasopharyngeal, hepatocellular, gastric, cervical and colon cancer types. Apoptotic DNA ladders could be detected when cancer cells were treated with GL331 for 24 h even if the Bcl-2 and Bax protein levels were not altered during the period. Besides acting as topoisomerase II inhibitors, both GL331 and VP-16 decrease the cellular protein tyrosine kinase (PTK) activities in cancer cells. The activities of protein tyrosine phosphatase (PTP) are significantly increased after GL331 treatment but are not affected by VP-16. GL331-induced internucleosomal cleavage can be efficiently prevented by two inhibitors of PTP, sodium orthovanadate and zinc chloride, but not by okadaic acid, which inhibits serine/threonine phosphatase activity. These results indicate that GL331 may induce apoptotic cell death, and that activation of protein tyrosine phosphatases may be involved in this process.

Interleukin-3 increases the incidence of 5-azacytidine-induced thymic lymphomas in pBOR-Il-3 mice

Interleukin-3 (Il-3) is a glycoprotein produced by a CD4+CD8- subpopulation of T-lymphocytes. Il-3 has been associated with the proliferation of bone marrow stem cells and their differentiation to granulocytes, macrophages, basophil/mast cells, megakaryocytes, erythroid cells, and neutrophils. The pBOR-Il-3 transgenic mice were developed by pronuclear microinjection to study how chemical insults modulate transcription of the Il-3 gene driven by a long-terminal repeat (LTR) of an endogenous retrovirus and to determine the biological consequences of interleukin-3 expression. We injected 5-azacytidine, a demethylating agent, to increase the LTR-driven expression of Il-3. Upon 5-azacytidine treatment, both the pBOR-Il-3 and the FVB/N nontransgenic controls developed thymic lymphomas. The pBOR-Il-3 mice developed thymic lymphomas at a higher frequency than the FVB/N mice. The thymic lymphoma cells were of a T-cell origin, as determined by T-cell receptor gene rearrangement analysis, and, in most cases, were of monoclonal origin. According to flow cytometric analysis of CD3, CD4, and CD8 cell surface markers, the thymic lymphoma cells did not lose their ability to differentiate, but the differentiation process was aberrant. Flow cytometric analyses also revealed that in pBOR-Il-3 mice the thymic lymphomas are mostly of a CD8+CD4- origin, whereas in the FVB/N group, the predominant type of thymic lymphoma is of a CD4+CD8- origin.

Lack of NK cells and related cytokines in pleural effusion

BACKGROUND

Relatively low number and activity of natural-killer (NK) cells have been reported in malignant pleural effusions. However, there has been no report on NK cells related cytokines.

METHODS

Lymphocyte subpopulations were studied in 30 cases of pleural effusion with various etiologies, along with peripheral blood, by using flow cytometry. The related cytokine levels in peripheral blood and pleural fluid, including IL-1 alpha, IL-4 and IL-12, were also analyzed with ELISA assays.

RESULTS

The results showed significant increase of T-helper cell subpopulation in pleural effusion of various etiologies. No obvious change of B-lymphocyte subpopulation between peripheral blood and pleural effusion was found. IL-4 was undetectable in both peripheral blood and pleural fluid in most cases. IL-1 alpha was detectable in some cases and the level was highest in pleural fluid of empyema. Decreased NK cells were found in most cases of pleural effusion and accompanied by undetectable IL-12 both in pleural fluid and peripheral blood. The only one case with detectable IL-12 concentration in pleural fluid was the one with tuberculous pleurisy.

CONCLUSIONS

Increased T-helper cell subpopulation and decreased NK cell subpopulation were found in pleural effusion of various etiologies. In spite of the small series of our patients, the decrease of NK cell subpopulation and the undetectable IL-12 concentration in pleural effusion deserves further investigations.

Distinct p53-mediated G1/S checkpoint responses in two NIH3T3 subclone cells following treatment with DNA-damaging agents

N3T3 and P-3T3 cells, originally isolated from a NIH3T3 cell clone on the basis of their negative and positive transformation by v-Abl, v-Src and Bcr-Abl, were previously found to show distinct cyclin activity changes following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, which is anti-mitogenic for N-3T3 cells and mitogenic for P-3T3 cells. We have found in this study that, while the G1/S arrest and cell death induced by serum starvation and TPA treatment in N-3T3 cells did not involve p53-mediated checkpoint or apoptosis, N-3T3 and P-3T3 cells evidently responded differently in these aspects of cell cycle regulation to DNA-damaging agents, methylmethane sulfonate (MMS) and gamma-radiation. In N-3T3 cells, DNA damages elicit cell growth arrest at G1/S transition with concomitant accumulation of p53 and p53-inducible Waf1/Cip1 proteins and also signs of apoptosis such as DNA ladder patterns and apoptotic (subgenomic) peak in flow cytograph. Conversely, P-3T3 cells treated with the DNA-damaging agents showed no cell cycle interruption nor accumulation of p53 or Waf1/Cip1. However, both P-3T3 and N-3T3 cells showed the same p53 protein half-life of 40 min or less, the same wild-type p53 DNA sequence and the same co-immunoprecipitable cellular proteins in complexes with p53, suggesting that an alteration in a signal transduction pathway upstream of p53 might account for the evasion of p53-mediated G1 checkpoint in P-3T3 cells.

Elevation of interleukin-10 levels in malignant pleural effusion

STUDY OBJECTIVE

Human immunity has been found to have two major components, cellular and humoral immunity. T-helper type 1 (Th1) pathway favors cellular immunity and Th2 pathway favors humoral immunity. Early determination toward Th1 and Th2 cells in the immune response is dependent on the balance between interleukin-12 (IL-12), which favors Th1 responses, and IL-4, which favors Th2 responses. IL-2 and interferon-gamma (IFN-gamma) are produced in the Th1 pathway, and IL-4 and IL-10 are produced in the Th2 pathway. Lack of cellular immunity, IL-2, and IFN-gamma had been reported in malignant pleural effusions. However, to our knowledge, there are no previous reports on other cytokine components involving Th1 or Th2 pathway. The present study was designed to answer these questions.

DESIGN

Cytokine levels in peripheral blood and pleural fluid of 21 patients with malignant pleural effusion, including IL-4, IL-10, and IL-12, were analyzed with enzyme-linked immunosorbent assays. Lymphocyte subpopulations of peripheral blood and pleural effusion were also studied by using flow cytometry.

MEASUREMENTS AND RESULTS

The results showed a significant increase in IL-10 level as compared with blood samples. IL-4 and IL-12 were below minimal detectable concentrations both in the blood and the effusion. The ratio of pleural helper T cells was significantly higher than in the blood (p = 0.0002). The ratio of pleural natural killer (NK) cells was significantly lower than in the blood (p = 0.0001). The ratio of pleural suppressor T cells was lower than blood with borderline significance (p = 0.0522). No significant change in B-lymphocyte ratio between blood and pleural effusion was found (p = 0.2471). There was no correlation between difference in IL-10 level and lymphocyte subpopulation of pleural effusion and blood samples.

CONCLUSIONS

Helper T-cell subpopulations were increased while NK and suppressor T-cell subpopulations were decreased in malignant pleural effusions. The decrease in NK cell subpopulations with elevated IL-10 and minimal IL-12 concentration in neoplastic pleural effusion would suggest the usage of IL-12 or antibody of IL-10 to improve local cellular immunity. Further study is needed.

Cloning and characterization of the endogenous retroviral-tRNA(Glu) multigene family from human genomes of different racial backgrounds

An 8.3-kb human endogenous retroviral-tRNA(Glu) (HERV-E)-encoding cDNA clone and a 1.5-kb genomic clone were isolated from a Chinese-derived cervical cancer cell line, CC7T, and their sequences determined. The former is a full-length endogenous retroviral cDNA containing corresponding u5-gag-pol-env-u3-r regions. The latter is a partial retroviral DNA segment, covering the gag and pol genes. Analysis of normal human DNA by Southern blot hybridization with three specific HERV-E molecular DNA probes revealed complex restriction-fragment length polymorphisms (RFLP), implying that the human genome contains diverse proviral structures and dispersed integration sites. The complex patterns were virtually identical between DNAs from African-Americans, Asians and Caucasians, with only a few minor variations. The data suggest that these proviral sequences were mostly incorporated into the human genome before racial divergence and, hence, may serve as markers for distinct chromosomal sites.

Differential expression of microsomal epoxide hydrolase gene by azole heterocycles in rats

The effects of heterocycles including imidazole (IM), 1,2,4-triazole (TR) and thiazole (TH) on the expression of microsomal epoxide hydrolase (mEH) gene were examined in rats (200 mg/kg body weight/day, i.p.). Hepatic microsomes prepared from rats treated with IM for 3 days failed to exhibit an increase in mEH protein level whereas TR treatment resulted in an approximately 2- to 3-fold elevation in hepatic mEH levels relative to control, as assessed by both SDS-PAGE and immunoblot analyses. In contrast, thiazole-induced hepatic microsomes resulted in a substantial increase in mEH levels (i.e. approximately 5-fold). Slot and northern blot analyses, probed with an mEH cDNA, showed that the hepatic mEH mRNA levels in the animals treated with IM for 3 days were marginally increased by approximately 2-fold, as compared with untreated animals, whereas TR caused an approximately 8-fold increase in hepatic mEH mRNA levels after three consecutive daily treatments. TH treatment resulted in an approximately 22-fold increase in the mEH mRNA levels, demonstrating that TH is the most efficacious among these three azole heterocycles. Because TH was the most effective in increasing hepatic mEH protein and mRNA levels, the agent was chosen for further evaluation. Time course of mEH gene expression at early times after a single treatment with TH was determined and compared with that caused by pyrazine (PZ), a strong mEH inducer. Hepatic mEH mRNA levels were increased approximately 1-, 3-, 20- and 16-fold at 3, 6, 12 and 24 hr, respectively, following TH treatment, relative to control, whereas mEH mRNA levels were elevated approximately 1-, 1-, 22- and 18-fold, respectively, at the same time points after PZ treatment, as monitored by slot RNA hybridization analyses. Northern blot analyses using either total RNA or poly(A)+ RNA fractions exhibited comparable time courses in increasing mEH mRNA levels after TH or PZ treatment with maximal mRNA increases being noted at 12 hr post treatment. Although neither IM or TR failed to affect renal mEH gene expression to a notable extent, TH treatment caused 6- to 8-fold increases in kidney mEH mRNA levels, with a 2-fold increase in mEH protein detected. These results demonstrated that the azole heterocyclic compounds IM, TR and TH differentially induce mEH with TH as the most efficacious azole; and that the changes in mEH levels are primarily associated with increases in mRNA levels.

Effect of maternal aging on transgene heritability in transgenic founder mice derived from zygotes microinjected with retroviral long terminal repeat-containing recombinant deoxyribonucleic acid

To determine the stability of artificially introduced recombinant DNA in the mouse germline throughout the reproductive life, founder mice derived from fertilized eggs injected with retroviral long-terminal-repeat-containing recombinant DNAs were mated with congenic FVB/N mice. Tail DNA of all progeny were screened and restriction fragment patterns of the transgenes were examined. Litter size and percentage of transgene transmission at various reproductive age periods were analyzed. Microinjection of 1737 eggs with four different recombinant DNAs resulted in 12 female and 11 male transgenic mice; 2 males were sterile and the remaining 21 mice served as founders to produce 1087 F1 progeny. With increasing parental age, litter size decreased generally. The percentage of progeny inheriting the transgenes declined markedly with increasing aging of 4 female founders; this aging effect was not observed in male founders (p < 0.005). No apparent change in transgenes was detected in progeny from late reproductive stages.

Carbon tetrachloride induction of rapid changes in liver nuclear protein factors capable of sequence-specific binding to regulatory elements in the long terminal repeat of polytropic-class endogenous murine leukemia virus-related proviruses

Treatment of mice with hepatic carcinogens, including CCl4, has been shown to rapidly enhance the transcription of endogenous murine leukemia virus-related proviral sequences in the liver. To understand the mechanism for this transcriptional stimulation, we used nuclear protein preparations from mouse livers to perform DNase I protection analyses and identified nuclear protein binding on approximately 20 individual sequences within the regulatory regions of the long terminal repeat (LTR) of a polytropic-class endogenous provirus clone. From 3 to 144 h after treatment with CCl4, the livers of FVB/N mice were analyzed for specific nuclear protein binding to the LTR DNA. Three to nine hours after CCl4 treatment, decreased protection was seen at potential regulatory cis-elements throughout the LTR, including specific sites within the putative negative regulatory element (located 5' of the consensus enhancer sequences) and the 3' terminal portion of the polytropic class-specific enhancer-like inserted sequence element and around the CCAA(C/T) box in the promoter region. In addition, by 3-6 h after treatment, a transient increase in protection activity for the transcription initiation site occurred. The loss of cis-element protection expanded to other binding sites and became most marked by 48 h after treatment. As the regenerating liver recovered, the nuclear protein binding activities for these LTR sequences also recovered, but protection at the TATAA and transcription initiation sites remained deprotected at 144 h after treatment. Nuclear protein protection of other sites, particularly in the conserved LTR enhancer sequences, was minimally affected by CCl4 treatment. Three nuclear protein binding sites that showed rapid CCl4-induced kinetic changes were homologous to the consensus sequence for the binding of the transcription factor families MEF-2, HNF-1, and C/EBP. The complex kinetic changes in factors that may contribute to the rapid and transient induction of endogenous retroviral gene expression in the liver after CCl4 exposure are discussed.

A simple and economical procedure for large-scale plasmid DNA isolation

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Negative regulatory element associated with potentially functional promoter and enhancer elements in the long terminal repeats of endogenous murine leukemia virus-related proviral sequences

Three series of recombinant DNA clones were constructed, with the bacterial chloramphenicol acetyltransferase (CAT) gene as a quantitative indicator, to examine the activities of promoter and enhancer sequence elements in the 5' long terminal repeat (LTR) of murine leukemia virus (MuLV)-related proviral sequences isolated from the mouse genome. Transient CAT expression was determined in mouse NIH 3T3, human HT1080, and mink CCL64 cultured cells transfected with the LTR-CAT constructs. The 700-base-pair (bp) LTRs of three polytropic MuLV-related proviral clones and the 750-bp LTRs of four modified polytropic proviral clones, in complete structures either with or without the adjacent downstream sequences, all showed very little or negligible activities for CAT expression, while ecotropic MuLV LTRs were highly active. The MuLV-related LTRs were divided into three portions and examined separately. The 3' portion of the MuLV-related LTRs that contains the CCAAC and TATAA boxes was found to be a functional promoter, being about one-half to one-third as active as the corresponding portion of ecotropic MuLV LTRs. A MboI-Bg/II fragment, representing the distinct 190- to 200-bp inserted segment in the middle, was found to be a potential enhancer, especially when examined in combination with the simian virus 40 promoter in CCL64 cells. A PstI-MboI fragment of the 5' portion, which contains the protein-binding motifs of the enhancer segment as well as the upstream LTR sequences, showed moderate enhancer activities in CCL6 cells but was virtually inactive in NIH 3T3 cells and HT1080 cells; addition of this fragment to the ecotropic LTR-CAT constructs depressed CAT expression. Further analyses using chimeric LTR constructs located the presence of a strong negative regulatory element within the region containing the 5' portion of the enhancer and the immediate upstream sequences in the MuLV-related LTRs.

Specific sequence deletions in two classes of murine leukemia virus-related proviruses in the mouse genome

Characteristic long terminal repeats (LTR) of approximately 700 and 750 bp were found, respectively, in the two classes (polytropic and modified polytropic) of murine leukemia virus (MuLV)-related nonecotropic nonxenotropic proviral sequences in eight individual molecular clones of RFM/Un mouse chromosomal DNA fragments. Three proviral clones, two polytropic and one modified polytropic, contained sequence deletions in the viral structural genes. Nucleotide sequence analysis revealed that 7-bp direct repeats occur at both ends of deleted sequences in intact structures and one of the repeats remains in genomes with the deletion. Specifically, the deleted sequences were a 1487-bp gag-pol sequence with ACTGCCC repeat, a 113-bp mid-pol sequence with CAGGCAA repeat, and a 1811-bp env sequence with GGTCCAG repeat. The same specific sequence deletions were found in both classes of MuLV-related proviral structures. Examination of chromosomal DNA from eight inbred laboratory mouse strains and six wild mouse species showed that a minor population of proviruses with these specific deletions were present in Mus musculus and Mus spretus, all of which contain prominent 700-bp LTR polytropic proviral structures. The 750-bp LTR modified polytropic proviral structures were phylogenetically more restricted, being equally predominant in Mus musculus domesticus mice, but minor to undetectable in Mus spretus subspecies, and absent in other wild mouse populations.

Fv-1 N- and B-tropism-specific sequences in murine leukemia virus and related endogenous proviral genomes

Oligonucleotide probes specific for the Fv-1 N- and B-tropic host range determinants of the gag p30-coding sequence were used to analyze DNA clones of various murine leukemia virus (MuLV) and endogenous MuLV-related proviral genomes and chromosomal DNA from four mouse strains. The group of DNA clones consisted of ecotropic MuLVs of known Fv-1 host range, somatically acquired ecotropic MuLV proviruses, xenotropic MuLV isolates, and endogenous nonecotropic MuLV-related proviral sequences from mouse chromosomal DNA. As expected, the prototype N-tropism determinant is carried by N-tropic viruses of several different origins. All seven endogenous nonecotropic MuLV-related proviral sequence clones derived from RFM/Un mouse chromosomal DNA, although not recognized by the N probe, showed positive hybridization with the prototype B-tropism-specific probe. The two xenotropic MuLV clones derived from infectious virus (one of BALB:virus-2 and one of AKR xenotropic virus) failed to hybridize with the N- and B-tropic oligonucleotide probes tested and with one probe specific for NB-tropic Moloney MuLV. One of two endogenous xenotropic class proviruses derived from HRS/J mouse chromosomal DNA (J. P. Stoye and J. M. Coffin, J. Virol. 61:2659-2669, 1987) also failed to hybridize to the N- and B-tropic probes, whereas the other hybridized to the B-tropic probe. In addition, analysis of mouse chromosomal DNA from four strains indicates that hybridization with the N-tropic probe correlates with the presence or absence of endogenous ecotropic MuLV provirus, whereas the B-tropic probe detects abundant copies of endogenous nonecotropic MuLV-related proviral sequences. These results suggest that the B-tropism determinant in B-tropic ecotropic MuLV may arise from recombination between N-tropic ecotropic MuLV and members of the abundant endogenous nonecotropic MuLV-related classes including a subset of endogenous xenotropic proviruses.

Characterization of two solitary long terminal repeats of murine leukemia virus type that are conserved in the chromosome of laboratory inbred mouse strains

Twenty molecular clones containing sequences homologous to the long terminal repeats (LTRs) of the endogenous ecotropic murine leukemia virus (MuLV) of the RFM/Un mouse were isolated from a library of RFM/Un mouse spleen DNA in phage lambda. Three of these LTRs were not associated with any viral structural genes. Nucleotide sequence analysis demonstrated that they were solitary LTRs which were flanked by 4-bp directly repeated cellular sequences and which lacked primer binding sites. Two of the three subclones were found to be identical except for their orientations in the vector pBR322. Unique-sequence regions on either side of the two nonidentical elements were used to characterize their integration sites in genomic DNA. The solitary LTRs and their flanking regions were found to be conserved in a number of inbred mouse strains, including three strains known not to harbor endogenous ecotropic MuLV-type proviruses. Comparison of cleavage by the methylation-sensitive restriction enzyme SmaI and methylation-insensitive KpnI at the characteristic LTR SmaI/KpnI site suggested that at least one of these solitary LTRs is methylated to a lesser extent than are most endogenous proviral LTRs. These particular solitary LTRs, like endogenous proviral sequences, appear to be stably transmitted genetic elements.

Characterization of a molecular clone of RFM/Un mouse chromosomal DNA that contains a full-length endogenous murine leukaemia virus-related proviral genome

A 12.4 kbp HindIII chromosomal DNA fragment harbouring an apparently intact 9.2 kbp endogenous murine leukaemia virus (MuLV)-related proviral genome was isolated from an RFM/Un strain mouse by molecular cloning and designated pRFM #6. Nucleotide sequence analysis revealed the following characteristic features in the pRFM #6 provirus: a distinct 200 bp sequence in the long terminal repeat (LTR) mid-U3 region, a primer binding site for glutamine tRNA, a 3' pol region encoding an 'endonuclease' protein of 390 amino acids, and the mink cell focus-forming virus type-specific sequence at the 5' portion of the env gene. The 699 bp 5' LTR and 700 bp 3' LTR of pRFM #6 provirus were identical except for three base changes in the U3 'enhancer' region. At the cell-provirus DNA junction, 4 bp direct repeats were present. The proviral genome was found at the same chromosomal DNA site in BALB/c, AKR, C3H, CBA and RFM strain mice, but not in NFS/N or C57BL/6 strain mice.

Hematopoietic neoplasias of the RFM/Un mouse contain somatic re-integration of the restriction endogenous ecotropic provirus

We have examined the spleen DNA of individual mice of the RFM/Un strain for evidence of re-integration of the endogenous ecotropic provirus in radiation-induced and spontaneous neoplasms. The ecotropic env specific probe detects only a single 19 kb EcoRI or a single 7.0 kb HindIII fragment in all DNA preparations from normal tissues of RFM mice, corresponding to the endogenous provirus. Additional DNA restriction fragments containing the ecotropic virus (eco) specific sequence, corresponding to somatically acquired provirus, are detected in two out of five spleen DNA samples from animals with myeloid leukemia and one of three with thymic lymphoma. In addition somatically acquired eco-specific fragments are also detected in greater than 85% of DNA samples from reticulum cell sarcomas, a late occurring spontaneous hematopoietic neoplasm in this mouse strain. These results are consistent with a 'promoter/enhancer insertion' model of leukemogenesis involving the endogenous ecotropic provirus and are of particular interest since the RFM/Un mouse possesses a locus that restricts exogenous infection of cells by the endogenous virus.

Nucleotide sequences of gag-pol regions that determine the Fv-1 host range property of BALB/c N-tropic and B-tropic murine leukemia viruses

Previously, in vitro recombinant DNA studies demonstrated that genetic determinants of N-tropism and B-tropism, or Fv-1-related host range properties of murine leukemia viruses, were located in a BamHI-HindIII DNA segment derived from the 5' portion of the cloned viral genome. We sequenced this segment and its immediate 5' region from cloned DNA of two BALB/c mouse C-type viruses (WN1802N and WN1802B) and found base differences at 12 positions out of the otherwise identical 1,390-base-pair sequences. Analysis of the most likely reading frame showed that 6 of the 12 base differences would result in four encoded amino acid changes, three of which occur at positions 109 (glutamine in WN1802N versus threonine in WN1802B), 110 (arginine in WN1802N versus glutamic acid in WN1802B), and 159 (glutamic acid in WN1802N versus glycine in WN1802B) of the p30 protein. The remaining one is located at position 36 (threonine in WN1802N versus isoleucine in WN1802B) of the viral polymerase protein. Significant conformational alteration of the p30 protein could be predicted from these amino acid changes.

Reversal of Fv-1 host range by in vitro restriction endonuclease fragment exchange between molecular clones of N-tropic and B-tropic murine leukemia virus genomes

We molecularly cloned unintegrated viral DNA of the BALB/c endogenous N-tropic and B-tropic murine leukemia retroviruses and in vitro passaged N-tropic Gross (passage A) murine leukemia retroviruses. Recombinant genomes were constructed in vitro by exchanging homologous restriction enzyme fragments from N- or B-tropic parents and subsequent recloning. Infectious virus was recovered after transfection of these recombinant genomes into NIH-3T3 cells and cocultivation with the Fv-1 nonrestrictive SC-1 cells. XC plaque assays of recombinant virus progeny on Fv-ln and Fv-lb cells indicated that the Fv-l host range was determined by sequences located between the BamHI site in the p30 region of the gag gene (1.6 kilobase pairs from the left end of the map) and the HindIII site located in the pol gene (2.9 kilobase pairs from the left end of the map).

A novel sequence segment and other nucleotide structural features in the long terminal repeat of a BALB/c mouse genomic leukemia virus-related DNA clone

A recombinant DNA clone, named AL10, that contains murine leukemia virus (MuLV) related sequences was isolated from BALB/c mouse chromosomal DNA and examined in detail. Restriction endonuclease mapping revealed that the 10.5 kbp EcoRI insert consists of a 3.6 kbp left flanking cellular DNA region and a 6.9 kbp MuLV-related region that has a typical proviral LTR-gag-pol-env structure up to the EcoRI site in the env gene region. Comparison of the AL10 map with ecotropic and xenotropic virus isolates revealed many common restriction sites in the LTR and pol gene regions, but much fewer in the leader and gag regions. A stretch of 1,700 nucleotides containing the cellprovirus junctional region was sequenced and revealed transcriptional consensus signals and other structural features characteristic of MuLV LTRs, as well as two distinctive features: (a) a sequence of approximately 170 bp with direct and inverted terminal repeats not seen in infectious MuLV LTRs was identified in the U3 region between the "enhancer" region and the "CAT" box. This novel segment or its homologous sequences appear to be present in most of the endogenous MuLV-related LTRs and in other chromosomal locations of the mouse (b) The tRNA primer binding site is not complementary to proline tRNA, the primer for all known MuLVs, but is a 17/18 match with rat glutamine tRNA. The integration site of AL10 provirus was in a unique DNA region but contained an "Alu"-like short interdispersed repeat in the 5' adjacent cellular region. The AL10 proviral integration found in BALB/c was also apparent in RFM, AKR and SENCAR mouse cells but not in cells of NFS/N, C3H, HRS/J, SC-1, and a California Lake Casitas wild mouse.

Molecular cloning and analysis of the endogenous retrovirus chemically induced from RFM/Un mouse cell cultures

We molecularly cloned and analyzed an N-tropic ecotropic retrovirus induced with iododeoxyuridine from RFM/Un mouse cell cultures. Based on the restriction map, the RFM/Un virus appears to be indistinguishable from other induced N-tropic retroviruses. A nucleotide sequence analysis of the long terminal repeat of an infectious clone revealed structural features characteristic of murine type C retrovirus long terminal repeats. The U3 region of the RFM/Un virus long terminal repeat, however, contained no short sequence duplication or insertion found in other murine leukemia virus isolates.