During postnatal liver development, LAP (NF‐IL‐6, C/EBP beta) expression and hepatocyte proliferation are mutually exclusive. In addition to transactivating liver‐specific genes, LAP, but not C/EBP alpha, arrests the cell cycle before the G1/S boundary in hepatoma cells. LIP, a liver‐inhibitory protein, which is translated from LAP mRNA lacking the activation domain of LAP, is not only ineffective in blocking hepatoma cell proliferation but also antagonizes the effect of LAP on the cell cycle. Deletion analysis indicated that this effect of LIP required only the DNA‐binding and leucine zipper domains. In addition we found that integrity of the LAP dimerization and activation domains is indispensable for the arrest of cell proliferation induced by LAP. Thus, hepatocyte differentiation and its characteristic quiescent state may be modulated by the LAP/LIP ratio.

During the lytic infection of monkey and mouse cells with simian virus 40 and polyoma virus, respectively, the preferentially increased synthesis of two host proteins of 92,000 and 72,000 Mr was observed by 15 to 20 h after infection besides the general stimulation of most cellular proteins. In a variety of organisms and cell cultures, from bacteria and yeasts to humans, a mild heat shock was found to induce the vigorous synthesis of a few characteristic proteins. In Drosophila melanogaster, where this phenomenon has been extensively investigated, the induction of the heat shock proteins is paralleled by a strong reduction in the synthesis of most proteins made before the heat shock. In avian and mammalian cells, decreased protein synthesis is less evident, but the increased synthesis of at least two proteins in the range of 85,000 to 95,000 Mr and 70,000 to 75,000 Mr was observed; these proteins may be related to two of the major heat shock proteins in insects. The increased synthesis of the same or similar proteins has been reported for cells subjected to a variety of treatments, such as exposure to amino acid analogs, chelating drugs, heavy metal ions, arsenite, and other sulfhydryl reagents (for a review, see reference 19).The lytic infection of mouse and monkey cell cultures with polyoma virus or simian virus 40 (SV40), respectively, induces an increased synthesis of the majority of cellular proteins (9). Among these, two strongly stimulated host proteins fall into the same size range as the proteins mentioned above (E. W. Khandjian, P. Arrigo, T. Rose, and J.-M. Matter, Experientia 36:749, 1980). Here, we show that the two proteins that are stimulated by virus infection are also induced by thermal treatment of uninfected mouse and monkey cells. MATERIALS AND METHODSCell cultures, virus infections, and thermal treatment. Confluent primary mouse kidney cultures and confluent cultures of CV-1 (African green monkey) cells in 9-cm-diameter petri dishes were mock infected or infected with polyoma virus or SV40, respectively, and incubated at 37°C as described previously (9). For thermal treatment (heat shock), cultures were incubated at 43.5°C for 1 h before labeling at 37°C for 2 h with 100 iCi of [35S]methionine (500 to 1,000 Ci/mmol; The Radiochemical Centre, Amersham, United Kingdom) in 2 ml of methionine-free medium.Extraction of proteins. After [35S]methionine labeling, the cell monolayers were washed with cold phosphate-buffered saline, total proteins were solubilized by the addition of sodium dodecyl sulfate (SDS) sample buffer (68 mM Tris-hydrochloride [pH 6.8], 2% SDS, 2% 2-mercaptoethanol, 0.01% bromophenol blue, 15% glycerol) (10), and the viscous extract was sonicated. Alternatively, cultures put on ice were lysed with 0.5% Nonidet P-40 in 0.1 M Tris-hydrochloride (pH 9)-0.1 M NaCI-5 mM MgCI2 for 10 min, and the lysates were centrifuged at 30,000 x g for 30 min at 4°C. To the supernatant 0.5 volume of threefoldconcentrated SDS sample buffer was added, and the samples were heated in a boiling water ...

After injection of lipopolysaccharides (LPS) in mice, there is first a release of DNA into plasma and secondly an induction of anti-DNA antibodies. The circulating DNA was purified from plasma and physico-immunochemically characterized. This DNA has a similar density to mammalian cellular DNA,is 4--6S insize, and probably represents a mixture of single-stranded DNA (SSDNA) and double-stranded DNA (DSDNA) or DSDNA with some single-stranded regions. This purified DNA was shown to react with anti-DNA antibodies which appeared as early as 3 days after a single injection of LPS in mice. In serum, DNA-anti-DNA complexes were not detected, although unidentified circulating immune complex-like material was demonstrated 5-8 days after the injection of LPS. In tissues, particularly in renal glomeruli, fine granular immune complex-type immunoglobulin deposits appeared along the glomerular capillary walls and in the mesangium 3 days after the injection of LPS. There is a direct correlation between the level of anti-DNA antibodies and the intensity of glomerular deposits and about 40% of immunoglobulins eluted from kidneys are anti-DNA antibodies, indicating that some of the immune complexes localized in kidneys are DNA-anti-DNA complexes. Based on these observations, the following hypothetical mechanism for the glomerular localization of DNA-anti-DNA complexes after the injection of LPS in mice is proposed. First, DNA, which has been released in circulating blood after injection of LPS, might bind to renal glomeruli, probably on glomerular basement membranes (GBM) through a high affinity of GBM for DNA; secondly, circulating anti-DNA antibodies, which appear later, might react with the glomerular-bound DNA and form immune complexes independently of circulating immune complexes. However, the possibility of direct deposition of immune complexes is not ruled out.

We studied synthesis of viral and cellular RNA in the presence and absence of 5-fluorodeoxyuridine (FdU, an inhibitor of DNA synthesis) during lytic infection with polyoma virus in confluent, primary mouse kidney cell cultures. In the presence of FdU, synthesis of early 19S polyoma mRNA and of polyoma tumor (T)-antigen, i.e. expression of the early viral gene, is rapidly followed by a mitogenic reaction of the host cell; it leads to an increase of 30 +/- 5% in cellular, mainly 28S and 18S rRNA, followed by activation of the cellular DNA-synthesizing apparatus. Polyoma-induced cellular RNA synthesis is paralleled by increased production of early 19S mRNA and begin of expression of the late viral genes, leading to synthesis of small amounts of late 19S and 16S mRNAs. Changed expression of the viral genome occurs in the absence of detectable synthesis of polyoma DNA I. Infection in the absence of FdU induces the same sequence of events; it is followed, however, by duplication of the mouse cell chromatin (S-phase) and production of progeny virus.

Purified simian virus 40 and polyoma DNAs injected into nuclei of Xenopus Nuclei from various eukaryotic cells injected into frog oocyte nuclei (germinal vesicles) continue to direct synthesis of origin-specific proteins (1). In addition, genes that were not expressed in the donor cell may be activated after injection (2). Purified viral, phage, or plasmid DNAs injected into the nucleus of Xenopus oocytes serve as templates for the transcription of specific RNA sequences (3). The synthesis of 5S RNA (4) and tRNA (5) is greatly stimulated upon injection of the corresponding templates. It has been claimed that, after injection of simian virus 40 (SV40) DNA I (6), much of the virus-specific RNA synthesized in the Xenopus oocyte has the same size and is transcribed from the same region as the late viral mRNAs present in lytically infected monkey cells (7,8), and proteins that migrate on two-dimensional gels in the same manner as the SV40 capsid proteins VP 1 and VP 3 were detected (8).In this article we report that Xenopus oocytes transcribe and translate most or all of the genetic information contained in the SV40 genome. In particular, we observed the synthesis of large (T) and small (t) SV40 tumor antigens having the same characteristics as those synthesized in monkey cells undergoing lytic infection. Injection of polyoma DNA I (6) resulted in the synthesis of three polyoma-specific polypeptides comigrating, during gel electrophoresis, with two minor polypeptides related to polyoma tumor antigen and with the major capsid protein, respectively.MATERIALS AND METHODS SV40 DNA I (covalently closed circular) was isolated from SV40-infected CV-1 African green monkey cells (Flow Laboratories, Irvine, Scotland) 40-48 hr after infection by selective extraction, deproteinized with phenol, and purified by CsCl/ethidium bromide density gradient equilibrium centrifugation (9). Polyoma DNA I was isolated from polyomainfected mouse kidney cell cultures 30-35 hr after infection by the same procedure. For injection, the viral DNA was dissolved in 88 mM NaCl/1 mM KCI/15 mM Tris-HCl, pH 7.6 at concentrations between 300 and 500 Ag/ml. 24 hr in Barth's solution containing 50 units per ml each of streptomycin, penicillin, and kanamycin. Thereafter 1 ml of Barth's solution containing 300 ,uCi of [35S]methionine (500-1000 Ci/mmol, the Radiochemical Centre, Amersham, England) was added and incubation was continued for another 24 hr (1 Ci = 3.7 X 1010 becquerels). The surviving oocytes (60-90%) were washed first with Barth's solution, then with distilled water, and stored at -80'C after removal of the water.For extraction of viral proteins, the oocytes were disrupted in a small Dounce homogenizer in 2 ml of a buffer containing detergent (0.1 M Tris-HCl, pH 9/0.1 M NaCl/5 mM KCI/1 mM CaCl2/0.5 mM MgCl2/0.7 mM Na2HPO4/0.5% Nonidet P-40). The homogenate was sonicated in a MSE ultrasonic disintegrator (Mk 1) for 1 min with an amplitude of 10 Atm and kept on ice for 20 min. After centrifugation at 15,000 X g for 30 min at 40C the s...