Erythrodifferentiation and hemoglobin synthesis in dimethyl sulfoxide-stimulated Friend erythroleukemia cells were inhibited by hydrocortisone (HC) and four other steroids: dexamethasone, deoxycorticosterone, corticosterone, and aldosterone. The effect was specific, because no significant cytotoxicity occurred with any of these compounds at the concentrations that were inhibitory. The mechanism of action of HC was studied in detail. In the absence of dimethyl sulfoxide, it had no effect on hemoglobin levels; but, in the presence of this inducer, the synthesis of heme and globin were each inhibited by approximately 90%. There was no alteration in the synthesis of any major protein other than globin, as determined by gel electrophoresis of cell lysates. Alterations in DNA metabolism (1, 2) and structure (3) are among the many changes that occur in Friend leukemia (FL) cells undergoing dimethyl sulfoxide (Me2SO)-induced erythrodifferentiation (4). The increase in single-stranded breaks in DNA, detected early after Me2SO treatment (5, 6), before globin mRNA appeared (Scher, unpublished), suggested that these breaks might play a role in differentiation in this system as postulated in lens differentiation (7,8) and in transcription (9, 10). Since Me2SO is also known to affect the activity of lysosomes (11,12), the possibility that it was causing the release of specific DNases that might be involved in the production of these scissions was considered. Therefore, a study of the effect of lysosome-stabilizing agents on FL cells was undertaken. Since some compounds known to stabilize lysosomes were found to inhibit erythrodifferentiation of FL cells and others did not, this property did not appear to be correlated with the ability of an agent to inhibit the Me2SO effect.The inhibitory compounds were dexamethasone, hydrocortisone (HG), deoxycorticosterone, corticosterone and aldosterone. The most potent inhibitors were HC and dexamethasone. The mechanism of action of HC, a naturally occurring steroid, was studied further. It markedly inhibited both hemoglobin (Hb) synthesis and globin mRNA levels up to 90% without cytotoxicity, indicating that it acted at a pretranslational step(s). Me2SO-stimulated virus release was also reduced.The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. We studied in detail the effect of HG, the most potent of the naturally occurring steroids tested, in an effort to determine the level at which it exerted its inhibitory effect. HC, over a wide range of concentrations, was not cytotoxic and did not affect the cell saturation density (Fig. MATERIALS AND METHODS

A serially progagated cell line (L104) was established by co-cultivation of alung adenocarcinoma (L-1) from a patient with concurrent chronic lymphocytic leukemia and XC, a non-producer rat line, known to carry the Rous sarcoma virus (RSV) genome. Karyotype of the L104 cultures revealed predominantly rat-like patterns; however, about 5% of the cells reacted with HLA antibodies and demonstrated human isozyme patterns. Electron microscopy of L104 cells revealed the presence of C-type particles budding from the cell membranes and in cytoplasmic vacuoles. Virus was not detected in any of the other normal lung, lung tumor or XC cells examined after co-cultivation with XC cells. The particles isolated from tissue culture fluids had the biochemical and biophysical characteristics common to other known mammalian C-type particles and were serologically related to the woolly monkey virus (WMV)/gibbon ape leukemia virus (GaLV) complex. Cross-hybridization between viral 3H-DNA transcripts and cellular RNAs from virus-infected cells clearly show the presence of sequences in the L104 cellular RNA related to both the GaLV/WMV group of viruses and rat viruses. Hydroxyapatite chromatography reveals however that the primate-related sequences in the viral RNA are indistinguishable from WMV in thermal elution profile. The host range of L104 virus appears to vary greatly from WMV in being xenotropic and, in the cell lines thus far tested appears, to infect only rat cells. The virus gave positive KC but negative XC assays. Inoculation of whole cells or cell-free supernatants into weaning hamster did not result in either solid tumors or leukemia. Co-cultivation of appropriate cell lines may represent an approach to the detection of latent viruses in human neoplasia.

The rutc of D N A s)~iitlrcsis iii secotidarj. moii.rr embryo Jhrohlast ( MEF-2 j cultiircs was iircreased ,followirig iirfectiorr wirh Frierrd leukemai virus ( FL V ) cis compared to cotitrol cultirres which were iriitreuted or e.Ypo.wd to heat-deiraiirrc~l virirs, A peak MWS reached hetweeir 24 arid 48 h after irlfi.ctiorr. Radioautographic stirdies reveuled that the ii!fiwed criltirres had a higher perceiitage of cells which iircorporat~d tritiatcd thj~midirw into thair tiuclei as compared to coirtrols. This increase was appurerrtlj~ itideprircfctrr qf the abilit). of' the cells to divide, sirrce if was u!so observed iir irifcctcd stutioiiarj. cultures. The rates of crllular R N A arid proteiii synthesis did iiot appcar to he a#ected hy FL V iujkctioii. The time reyirired .for the cell populatiorr to doiible n u s orie-third shorter iii FL V-ii?fi.ctcd cultures as compared to coiitrols. The shortetiirig qf the geireratioii time. was foiiiid to be diir to a decrease iii the time required .for the cells to traverse the GI arid S phases of'the cell cycle. I n additioir, after 72 h oj'prowrh, the injected cultures reached grmtcv poprrlatioii derisities thaii did either of the cotrtvols.