Two levels of restriction by mouse or cat cells of murine sarcoma virus coated by endogenous xenotropic oncornavirus

Mouse and cat cells were each examined for the mode of restriction of endogenous xenotropic oncornavirus. Murine xenotropic helper virus (MuX) and its pseudo-type of Moloney murine sarcoma virus (MSV(MuX)) were grown in cat cells to high titre. MuX alone did not replicate in any mouse cell tested including normal or transformed outbred Swis 3T3 cells or SC-I cells, but did grow in a variety of other mammalian cells. MSV(MuX) was not able to achieve that intracellular state from which it could be rescued by mouse leukaemia virus (MuLV) in any mouse cell tested with the exception of SC-I cells. Detection of MSV(MuX) foci with appropriate helper virus was as sensitive in SC-I cells as in the cells of several other species. Sequential passage of MSV(MuX) virus complex in SC=I cells resulted in a loss of infectious sarcoma and helper viruses, but transformed, MSV rescuable cells were retained. If cat embryo cells were infected with either the feline endogenous xenotropic virus (FeX) or its MSV pseudotype (MSV(FeX), two analogous states of restriction were observed. FeX alone did not replicate in cat cells as measured by release of progeny virus or by FeX group-specific antigen induction. Cat cells could be susceptible or insusceptible to the entry of MSV(FeX) as measured by MSV rescue with appropriate ecotropic feline leukaemia virus. The sensitivity of detection of MSV(FeX) foci in some cat cells in the presence of feline ecotropic virus was comparable to that exhibited by cells of other mammalian species. A single strain of cat cells underwent a change in its restrictive capacity for MSV(FeX) on prolonged passage. Late passage cat cells became very insusceptible to MSV(FeX) but not to other pseudotypes of MSV. Infectious FeX or its group-specific antigens were not detected in the insusceptible cells. The major glycoprotein of FeX did appear as a surface antigen of the insusceptibel cells. It is apparent that two levels of cellular restriction can be distinguished in each of two mammalian cell systems by the susceptibility to penetration of MSV coated with endogenous xenotropic oncornavirus.

Reduced peripheral conversion of thyroxine to triiodothyronine in patients with hepatic cirrhosis

The role of liver in the peripheral conversion of thyroxine (T4) to triiodothyronine (T3) was studied in normal subjects and patients with alcoholic liver disease by measurement of thyrotrophin (TSH) and total and free T4 and T3 in randomand serial serum samples. Also, T4 to T3 conversion rates and T3 disposal rates were compared by noncompartmental analysis. While the mean total serum T4 values were similar for the two groups, 8.6 and 8.1 mug/kl, the mean free T4 value was significantly higher in the cirrhotic patients (3.3 ng/dl) than in the normal subjects (2.1 ng/dl, P less than 0.001). The mean serum T3 value, 85 ng/dl, was significantly reduced in the hepatic patients as compared to a mean serum T3 value of 126 ng/dl in the normal subjects (P less than 0.001), while the free T3 value was 0.28 ng/dl in both groups. The reduction of the serum total and free T3 values were closely correlated with the degree of liver damage, as indicated by elevation of serum bilirubin (r equal -0.547) and reduction of serum albumin (r equal 0.471). The mean serum TSH level was 3.1 muU/ml in the normals and 7.1 muU/ml in the cirrhotic aptients ( less than 0.001). 15% of the hepatic patients had serum TSH values above 10 muU/ml, which, however, did not correlate with any of the four liver function tests studied. Serial blood sampling from two convalescing patients with alcoholic hepatitis showed a gradual normalization of serum TSH and T3 levels as the liver function improved. After oral T4 administration, 0.25 mg/day for 10 days, three of four cirrhotic patients studied failed to raise their serum T3 values. The mean T4 to T3 conversion rate of seven normal subjects was 35.7%. The mean T4 to T3 conversion rate of four cirrhotic patients studied was significantly reduced to 15.6% (P less than 0.001). The mean disposal rates of T4 and T3 of the normal subjects were 114 and 34 mug/day, respectively. The ratio of T4 disposal to T3 disposal was 3.5. In contrast, the mean T4 disposal rate, 82 mug/day, and the mean T3 disposal rate, 10 mug/day, were both reduced in the cirrhotic patients. Their ratio of T4 disposal to T3 disposal was 7.9. These findings suggest that impairment of T4 conversion in patients with advanced hepatic cirrhosis may lead to reduced T3 production and lowered serum T3 level. Therefore, the liver is one of the major sites of T4 conversion to T3.

Electron microscopic demonstration of hormone-producing metastatic carcinoma of the choroid from the bronchus

Clinical, laboratory and pathological findings of a patient in bronchial carcinoma with choroidal metastasis were presented. X-ray examination of the chest suggested the tumor shadow in the posterior segmental bronchus of the right upper lobe of the lung (r-B2b), while funduscopy and fluorescein angiography revealed the presence of choroidal tumor. ACTH levels in tumor tissues at autopsy and in serum were measured and definitely demonstrated and elevated. Histopathologically, the primary lesion was r-B2b and diagnosed as a mucocellular type of adenocarcinoma. The choroidal lesion was metastatic carcinoma. Electron microscopic examination of the choroidal lesion reembedded for electron microscopy from celloidin-embedded materials for light microscopy could reveal the presence of characteristic cytoplasmic granules referred to as neurosecretory-type granules. It is extremely rare that a hormone-producing metastatic carcinoma of the choroid from the bronchus has been proved.

Mechanism of action of CM-55, a synthetic analogue of the antilipogenic antibiotic cerulenin

CM-55 is a synthetic analogue of the antibiotic cerulenin with the chemical structure of 2, 3-dodecenyl-4-oxo-dimethyl amide. This compound inhibited the growth of Saccharomyces cerevisiae ATCC 12341 and inhibited protein and lipid synthesis by 91 and 95%, respectively, at a concentration of 50 mug/ml (2.1 x 10(-4) M). The inhibition of protein synthesis was associated with the partial reduction of ribonucleic acid synthesis and leucine transport. The mechanism of inhibition of lipid synthesis was further investigated in a cell-free extract of the yeast. CM-55 inhibited the incorporation of [(14)C]acetyl Coenzyme A (CoA) into both fatty acid (FAF) and non-saponifiable fractions (NSF). However, it did not inhibit [(14)C]malonyl CoA incorporation into FAF and only slightly inhibited [(14)C]mevalonate incorporation into NSF. The activity of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) synthase was inhibited more strongly than the incorporation of [(14)C]3-hydroxy-3-methylglutaryl CoA into NSF; this could account for the CM-55 inhibition of [(14)C]acetyl CoA incorporation into NSF.

Simple, quantitative assay for both xenotropic murine leukemia and ecotropic feline leukemia viruses

A cat cell line carrying the genome of a murine sarcoma virus developed discrete foci in linear response to infection with feline leukemia virus or xenotropic murine C-type virus.

Revertants of mouse cells transformed by murine sarcoma virus. III. Metastable expression of virus functions in revertants retransformed by murine sarcoma virus

3T3FL cells transformed by the Moloney murine sarcoma virus (MSV) (sarcoma positive, leukemia negative, S+L- cells) segregate spontaneous flat revertants. These S-L- revertants do not release MSV upon superinfection with MuLV but are susceptible to a second cycle of single-hit MSV transformation. The behavior and nature of second-cycle MSV transformed revertants were followed by successive clonal generations. The second transformation by MSV resulted in a number of metastable states. The simplest of these was a tranformed S+L- like state, which in contrast to parental S+L- cells, was also inducible by halogenated pyrimidines. A second type consisted of a transformed S+L- clone which could give rise to a secondary flat S-L- clone, which when followed over several generations could turn again into a stable S+L- type cell. Thus an MSV genome can persist in a nontransformed cell in a nonrescuable state. A third condition has been found in which a previously S+L- type MSV retransformed revertant began to produce infectious MSV with or without an atypical murine leukemia virus (MuLV). Other clonal sublines from a second cycle MSV transformed cell resulted in both a stable S+L- type line and a spontaneous MSV releaser line. The S+L- type retransformed cell resembled parental single cycle MSV transformed S+L- cells in that it contained MuLV group specific antigen(s), and C type particles. Some second cycle MSV transformed S+L- cells produced infectious MSV on chemical induction. No second-cycle reversion was ever observed, if both the first and the second infecting genomes were Moloney-MSV. The nature of the atypical MuLV was examined in terms of host range, growth potential, and antigenicity. This MuLV was at times released with an apparent excess of MSV, yet if eleven weekly blind passages of such a virus stock were made in S+L- cells, replicating MuLV was found in titers similar to the MSV content. This atypical virus replicated in mouse cells, less in rat cells, but not at all in human or cat cells. Neutralization revealed that it was closely related to the Moloney type of MuLV. The above observations are compatible with the interpretation that the second cycle of MSV transformation destabilizes cellular controls over the transforming genome.

Isolation of RD-114-like oncornavirus from a cat cell line

A clone of cells derived from a continuous line of cat cells (CCC) spontaneously produced an RNA C-type virus (CCC virus) which did not have the group-specific antigen of the standard strains of feline leukemia viruses but did have that of the RD-114 virus. Single-hit infection of a virus yielding CCC cell with only the feline leukemia virus pseudotype of murine sarcoma virus [MSV(FeLV)] resulted in the release of a pseudotype of MSV coated with the CCC virus envelope. Host range, transmission of virus, helper functions, interference properties, and specific neutralization showed that the CCC and the RD-114 isolates as well as their respective MSV pseudotypes are closely similar if not identical. Parental, virus-negative cells frozen before the existence of RD-114 were chemically induced to yield CCC-like virus de novo. Infection of susceptible human cells with the chemically induced virus resulted in interference with the CCC virus pseudotype of MSV but not with the FeLV pseudotype of MSV.

Reversion of murine sarcoma virus transformed mouse cells: variants without a rescuable sarcoma virus

Murine sarcoma virus transformed mouse 3T3 cells, which are negative for murine leukemia virus and which yield sarcoma virus after superinfection with murine leukenmia virus, spotaneously give rise to flat variants front which murine sarcoma virus can no longer be rescued. The revertants support leukemia viruis growth and show an enhanced sensitivity to murine sarcoma superinfection and, like normal cells, do not release RNA-dependent DNA polymerase activity. Because revertants could be obtained with high frequency from progeny of single transformed cells, each cell that containts the sarconma virus genome seems to have the capacity to suppress or eliminate an RNA tumor virus native to its species of origin.

Replication of radiation-induced murine leukemia virus in normal and transformed mouse cells

Autonomous radiation-induced leukemia virus (RadLV) replication could be detected in mouse 3T3 cells by the development of interference with murine sarcoma virus (MSV), the appearance of covert helper activity for defective MSV, and by the induction of cytopathic effect type foci in MSV-transformed, leukemia virus-negative (S+L-) cells. A chronic infection of either 3T3 or S+L- cells with RadLV could be established. Both RadLV infectivity and helper activity were demonstrated in the same peak at a buoyant density of 1.16 g/cm(3). Additionally a soluble inhibitor of MSV focus formation was found which could be separated from infectious RadLV. Examination of cell clones derived from chronically infected 3T3 cells showed that essentially every cell was infected and produced both infectious RadLV and low levels of inhibitor. Quantitative comparisons of autonomously replicating RadLV in normal 3T3 and S+L- cells suggested that RadLV may consist of several populations of virus of varying replicative potential. Apparently 99% of RadLV can be assayed only as helper units in normal cells or as replicative units in S+L- cells. To explain the atypical results, a model for RadLV deficiency is proposed.

Rescue of murine sarcoma virus from a sarcoma-positive leukemia-negative cell line: requirement for replicating leukemia virus

The nature of murine sarcoma virus (MSV) "defectiveness" was investigated by employing an MSV-transformed mouse 3T3 cell line which releases noninfectious virus-like particles. Rescue kinetics of MSV, observed after murine leukemia virus (MuLV) superinfection of these "sarcoma-positive leukemia-negative (S + L -)" mouse 3T3 cells, consisted of a 9- to 12-hr eclipse period followed by simultaneous release of both MSV and MuLV with no evidence for release of infectious MSV prior to the production of progeny MuLV. Addition of thymidine to the growth medium of MuLV-superinfected S + L - cells at a concentration suppressing deoxyribonucleic acid synthesis inhibited the replication of MuLV and the rescue of MSV. MSV production closely paralleled MuLV replication under a variety of experimental conditions. These results suggest that replication of MuLV is required for the rescue of infectious MSV from S + L - cells and that one (or more) factor, produced late in the MuLV replicative cycle, is utilized by both viruses during virion assembly. During the course of these experiments, virus stocks were recovered which contained infectious MSV in apparent excess over MuLV. These stocks were used for generating new S + L - cell lines by simple end point dilution procedures.

Transformation of mouse 3T3 cells by murine sarcoma virus: release of virus-like particles in the absence of replicating murine leukemia helper virus

Small numbers of virus-like particles were observed by electron microscopy in each of two cloned lines of 3T3 cells transformed by murine sarcoma virus, even though these lines were free of detectable quantities of infectious leukemia and sarcoma virus. The morphology and occurrence of the particles were identical to those of the murine leukemia-sarcoma group. Moreover, the particles incorporated uridine and had a buoyant density of 1.16 g/ml in sucrose gradients. No evidence of sarcoma or leukemia virus infectivity was associated with the particles in cells of several susceptible species under various conditions, including both cosedimentation with leukemia virus and infection in the presence of inactivated Sendai virus. The particles may represent a form of murine sarcoma virus deficient in one or more of the viral components necessary for infectivity.