Utilization of mammalian 70S RNA by a purified reverse transcriptase from human myelocytic leukemic cells

The discovery of HTLV-1, the first pathogenic human retrovirus

After the discovery of retroviral reverse transcriptase in 1970, there was a flurry of activity, sparked by the "War on Cancer," to identify human cancer retroviruses. After many false claims resulting from various artifacts, most scientists abandoned the search, but the Gallo laboratory carried on, developing both specific assays and new cell culture methods that enabled them to report, in the accompanying 1980 PNAS paper, identification and partial characterization of human T-cell leukemia virus (HTLV; now known as HTLV-1) produced by a T-cell line from a lymphoma patient. Follow-up studies, including collaboration with the group that first identified a cluster of adult T-cell leukemia (ATL) cases in Japan, provided conclusive evidence that HTLV was the cause of this disease. HTLV-1 is now known to infect at least 4-10 million people worldwide, about 5% of whom will develop ATL. Despite intensive research, knowledge of the viral etiology has not led to improvement in treatment or outcome of ATL. However, the technology for discovery of HTLV and acknowledgment of the existence of pathogenic human retroviruses laid the technical and intellectual foundation for the discovery of the cause of AIDS soon afterward. Without this advance, our ability to diagnose and treat HIV infection most likely would have been long delayed.

Enzyme inhibition. VIII: Mode of inhibition of reverse transcriptase activity by analogues, isomers, and related alkaloids of coralyne

Coralyne analogues, isomers, and related alkaloids were examined as inhibitors of reverse transcriptase of RNA tumor viruses in the presence of polyriboadenylic acid-oligodeoxythymidylic acid (Poly rA.oligo dT), polydeoxyadenylic acid-oligodeoxythymidylic acid (Poly dA.oligo dT), polyribocytidylic acid-oligodeoxyguanylic acid (Poly rC.oligo dG), activated calf thymus DNA, and 70S RNA template primers. The inhibition of the reverse transcriptase exhibited by analogues, isomers, and related alkaloids of coralyne was due to the interaction of the alkaloids with the template primers and was competitive. Furthermore, the addition of the alkaloids stopped instantly the DNA polymerization processes. Comparison of the inhibition of reverse transcriptase, antileukemic activities exhibited by the alkaloids, and the structure-activity relationships have been published elsewhere.

Enzyme inhibition VI: Inhibition of reverse transcriptase activity by protoberberine alkaloids and structure-activity relationships

Protoberberine alkaloids such as palmatine (I), 13-methylpalmatine iodide (II), 2,3-methylenedioxy-10,11-dimethoxy-13-methylprotoberberine iodide (III), 2,3-methylenedioxy-9,10-dimethoxy-13-methylprotoberberine chloride (IV), and berberine (V) showed inhibition of reverse transcriptase activity of RNA tumor viruses in the presence of polyriboadenylic acid-oligodeoxythymidylic acid (VI), polydeoxyadenylic acid-oligodeoxythymidylic acid (VII), activated calf thymus deoxyribonucleic acid (IX), and 70S ribonucleic acid (X), but not in the presence of polyribocytidylic acid-oligodeoxyguanylic acid (VIII). These results indicated that the alkaloids caused inhibition of the enzyme activity by interacting with the template primer, particularly of the adenine-thymine base pair. Furthermore, the alkaloids competed with the template primer-binding site of the enzyme. The time course inhibition indicated that the alkaloids stopped the DNA synthesis instantly when added after the initiation of polymerization processes. Inhibition of reverse transcriptase activity was correlated with the structure and antileukemic activity of the protoberberine alkaloids.

Characterization of an RNA-directed DNA-polymerase from a cell line derived from a radiation-induced lymphoma in mice

An RNA-directed DNA polymerase was purified from a cell line derived from a radiation-induced lymphoma in NIH Swiss mice which produced non-infectious type C virus particles. The enzyme was isolated from a high speed particulate fraction which bands at a density of 1.16--1.19 g/ml in a sucrose gradient, and purified by successive chromatography on DEAE-cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a KCl optimum of 50 mM, and a Mn2+ optimum of 0.25 mM. It prefers (dT)15 . (A)n to (dT)15 . (dA)n as the primer template and transcribes the poly(C) strand of (dG)15 .(C)n and (dG)15 . (OMeC)n. It transcribes heteropolymeric regions of avian myeloblastosis virus 70 S RNA, and is inhibited by antiserum to Rauscher murine leukemia virus DNA polymerase. Comparison of the properties of DNA polymerase purified from radiation-induced lymphoma cells with the DNA polymerase purified from non-defective murine type C RNA tumor viruses shows that the mouse lymphoma enzyme is both biochemically and immunologically related to murine leukemia virus DNA polymerases.

Purification and characterization of baboon endogenous virus DNA polymerase

An RNA-directed DNA polymerase was purified from baboon endogenous type-C virus by successive column chromatography on DEAE cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 8.0, a Mn2+ optimum of 1 mM, and a KCl optimum of 40 mM. The purified enzyme transcribes heteropolymeric regions of viral 60--70 S RNA isolated from different type-C viruses. The purified enzyme is immunologically related to a similarly purified polymerase from the cat endogenous type-C virus RD114.

In vitro inhibition of viral DNA polymerase activity by litmomycin

Litmomycin, an antibiotic isolated from Streptomyces litmogenes, is highly active against Gram-positive bacteria and possesses antitumor activity. It inhibited viral DNA polymerase activity in vitro. The amount of litmomycin required to cause 50% inhibition of enzyme activity was 80-100 mug (180-225 nmoles)/ml of reaction mixture. The enzyme inhibition was observed when polyriboadenylate--oligodeoxythymidylate, polydeoxyadenylate-oligodeoxythymidyate, polyribocytidylate-oligodeoxyguanylate, activated DNA, and 70 S RNA were used as templates. Reaction kinetics and the mechanism of enzyme inhibition are discussed. The results suggest that litmomycin interacts with the template primer and not with the enzyme protein to stop the polymerization process.

Purification and characterization of gibbon ape leukemia virus DNA polymerase

An RNA directed DNA polymerase was purified over 2500 fold from gibbon ape leukemia virus by successive column chromatography on Sephadex G100, DEAE cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a Mn2+ optimum of 0.8 mM, and KCl optimum of 80 mM. The purified enzyme transcribes heteropolymeric regions of viral 60-70 S RNA isolated from avian myeloblastosis virus, Rauscher murine leukemia virus and simian sarcoma virus and it is inhibited by antiserum prepared against either gibbon ape leukemia virus or simian sarcoma virus DNA polymerases.

A comparative evaluation of methods for isolation of RNA-directed DNA polymerase from cells in a reconstituted system

We have compared the relative merits of several procedures for the isolation of RNA-directed DNA polymerase (EC 2.7.7.7.) from cells using a reconsituted model system consisting of a mixture of woolly monkey (simian) sarcoma virus and a cultured human lymphoblastoid cell line, NC-37. When the cell-virus mixture was gently disrupted and fractionated by differential centrifugation, most of the added polymerase was recovered associated with a particulate fraction obtained from the post-mitochondrial supernatant. Purification of the polymerase was best achieved starting from this fraction. The particulate fraction itself can be purified by gel filtration through a Sepharose 2 B column. This procedure did not significantly alter the composition of viral and cellular DNA polymerases. Whereas as little as 7.5 - 10(5) viral particles were sufficient for the detection of RNA-directed DNA polymerase activity, a minimum of about 10(11) particles were necessary for the isolation and unequivocal characterization of the enzyme from the cell-virus mixture by subcellular fractionation and chromatographic separation from cellular DNA polymerases. Purified RNA-directed DNA polymerase had the same primer-template characteristics, sedimentation properties, and immunological cross reactivity as the enzyme purified from density gradient-banded virions of simian sarcoma virus. Methods involving total extraction of the cell-virus mixture either by repeated freezing and thawing followed by detergent treatment or by Dounce homogenization and treatment with high salt and detergent failed to provide RNA-directed DNA polymerase free of cellular DNA polymerases. Because of this, low levels of cellular RNA-directed DNA polymerase may be missed when these approaches are used.

Low frequency of (5'-3') -C-G- connection in 70S RNA from simian sarcoma virus

The frequency of oligonucleotides obtained from simian sarcoma virus RNA by digestion with ribonuclease T1 was compared with the frequency expected of an RNA molecule in which nucleotides are arranged in random distribution. Oligonucleotides containing C-residue attached to 3'-Gp were found significantly less in simian sarcoma virus 70S RNA than expected by random distribution.

On the stimulation of viral DNA polymerase activity by nonionic detergent

Nonionic detergents stimulate purified RNA-directed DNA polymerase (reverse transcriptase) activity from various RNA tumor viruses ranging from avian to primate species. The stimulatory effect of the nonionic detergent is dependent on the type and amount of template-primer. The greatest stimulation is obtained when high concentrations of (dT)12-18-(rA)n or activated salmon sperm DNA are used as template-primers. Little stimulation is obtained with viral 70S RNA or with (dT)12-18- (dA)n. The detergent stimulation appears to be specific for viral reverse transcriptase since this effect is not observed with purified bacterial DNA polymerase or with three known mammalian cellular DNA polymerases. This finding may, therefore, be a useful additional criterion for distinguishing viral reverse transcriptase isolated from cells from other cellular DNA polymerases. Nonionic detergent also has a stabilizing effect on viral DNA polymerase against thermal inactivation. This stabilizing effect is further enhanced by the presence of template-primer.

Purification of avian myeloblastosis virus DNA polymerase by affinity chromatography on polycytidylate-agarose

Polycytidylic acid [poly(rC)] covalently linked to cyanogen bromide-activated agarose is an effective affinity matrix for the RNA-dependent DNA polymerase from avian myeloblastosis virus. Poly(rC)-agarose is capable of binding large quantities of avian myeloblastosis DNA polymerase, which is then eluted by using a linear KCl gradient of increasing concentration. The DNA polymerase isolated from crude, detergent-disrupted virions by a single pass through columns of poly(rC)-agarose appears nearly homogeneous (approximately 90% pure) as determined by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complete recovery of input enzymatic activity was obtained. Results suggest that polyribonucleotide columns may provide a high-yield, rapid method for the purification of oncornaviral DNA polymerase.

Mechanism of stimulation of murine type-C RNA tumor virus production by glucocorticoids: post-transcriptional effects

We have previously shown that dexamethasone stimulates production of type-C virus from seemingly normal murine fibroblasts (BALB/3T3) and from transformed (Kirsten sarcoma-leukemia virus) nonproducing cells (BALB/K3T3) induced by 5-iododeoxyuridine. In this report, we further examine the mechanism of this effect by using BALB/K3T3 cells. Several observations suggest that this effect is post-transcriptional. The optimal stimulation by dexamethasone is obtained when dexamethasone is given 24 to 48 h after 5-iododeoxyuridine induction. Although this effect is late, time course experiments suggest that dexamethasone does not act to promote release of preformed virions. The stimulation by dexamethasone is blocked when cells are treated with cordycepin (3'-deoxyadenosine) during the first 24 h of induction, but not when cordycepin is added later. Conversely, interferon, which inhibits virus production, interferes with dexamethasone when it is added late or after removal of the steroid. The results of molecular hybridization experiments show that there is no detectable increase in Kirsten sarcoma-leukemia virus-specific RNA in dexamethasone-treated cells (with or without 5-iododeoxyuridine). The results of the time course studies, and the cordycepin, interferon, and hybridization experiments, suggest that the effect of dexamethasone on type-C virus production in this system is post-transcriptional.

Relationship between RNA-directed DNA polymerase (reverse transcriptase) from human acute leukemic blood cells and primate type-C viruses

An RNA-directed DNA polymerase was isolated from the peripheral blood leukocytes of a patient with acute myelomonocytic leukemia by successive purification of a particulate cytoplasmic fraction with endogenous, ribonuclease-sensitive DNA polymerase activity. Like RNA-directed DNA polymerase from mammalian type-C virus, the human leukemic cell enzyme efficiently utilized (A)(n).(dT)(12-18) and (C)(n).(dG)(12-18) and had an approximate molecular weight of 70,000. Further, the leukemic cell enzyme was strongly inhibited by antisera to RNA-directed DNA polymerase of primate type-C virus in a fashion similar to that noted with an extensively purified RNA-directed DNA polymerase from a person with acute myelogenous leukemia [Todaro, G.J. & Gallo, R.C. (1973), Nature 244, 206]. By these biochemical and immunological results the leukemic cell enzyme could be differentiated from all other known cellular DNA polymerases but could not be distinguished from RNA-directed DNA polymerase of primate type-C virus. We interpret these data, combined with observations published elsewhere, to indicate that human acute myelogenous leukemia cells contain components related to primate type-C virus. The parameters used in this study may provide the specificity and sensitivity required for determining the presence or absence and (if present) the relatedness of RNA-directed DNA polymerase in other cases and types of human leukemia.

Primate RNA tumor virus-like DNA synthesized endogenously by RNA-dependent DNA polymerase in virus-like particles from fresh human acute leukemic blood cells

A particle of discrete biochemical composition was purified from fresh, unfrozen peripheral blood leukocytes of human patients with acute myeloblastic leukemia. This particle endogenously synthesized DNA by use of an RNA primer and template. About half of the DNA sequences synthesized in the presence of actinomycin D hybridized to RNA isolated from type-C sarcoma viruses of primates or mice; lower annealing values were obtained with RNA isolated from other sarcoma or leukemia viruses. The results confirm and extend previous results from molecular hybridization experiments related to the existence in human leukemia of components of RNA tumor viruses.