Specificity of the inflammatory response in viral encephalitis. I. Adoptive immunization of immunosuppressed mice infected with Sindbis virus.

The viral-induced perivascular inflammatory response in Sindbis virus encephalitis of mice was shown to be immunologically specific. Mice were inoculated intracerebrally with Sindbis virus, and 24 hr later a single dose of cyclophosphamide was given which ablated the inflammatory response. 3 days after virus inoculation, cells and/or sera from specifically and nonspecifically sensitized donor mice were given, and the inflammatory reactions, virus content, and antibody response of recipients were examined 5 days later. Reconstitution of the viral inflammatory response required virus-specific sensitized lymph node cells and was enhanced when these lymph node cells were combined with bone marrow cells. Reconstitution was not achieved with Sindbis virus immune serum even when combined with nonspecifically sensitized cells. Combination of immune serum with Sindbis virus-sensitized cells did not produce an accentuation of the reaction. In distinction, reconstitution of the inflammatory reaction surrounding the stab wound was reconstituted with bone marrow cells from mice inoculated with Sindbis virus or control antigens. Reconstitution of the perivascular reaction was associated with a reduction in brain virus content. Although the transfer of Sindbis virus-sensitized lymph node cells and bone marrow cells resulted in the limited production of neutralizing antibody in the immunosuppressed recipient, the reduction in virus was significantly greater with the transfers of Sindbis virus-sensitized lymph node cells than with the passive transfer of immune serum alone.

Caffeine overcomes a restriction point associated with DNA replication, but does not accelerate mitosis.

Mitotic chromosome condensation is normally dependent on the previous completion of replication. Caffeine spectacularly deranges cell cycle controls after DNA polymerase inhibition or DNA damage; it induces the condensation, in cells that have not completed replication, of fragmented nuclear structures, analogous to the S-phase prematurely condensed chromosomes seen when replicating cells are fused with mitotic cells. Caffeine has been reported to induce S-phase condensation in cells where replication is arrested, by accelerating cell cycle progression as well as by uncoupling it from replication; for, in BHK or CHO hamster cells arrested in early S-phase and given caffeine, condensed chromosomes appear well before the normal time at which mitosis occurs in cells released from arrest. However, we have found that this apparent acceleration depends on the technique of synchrony and cell line employed. In other cells, and in synchronized hamster cells where the cycle has not been subjected to prolonged continual arrest, condensation in replication-arrested cells given caffeine occurs at the same time as normal mitosis in parallel populations where replication is allowed to proceed. This caffeine-induced condensation is therefore "premature" with respect to the chromatin structure of the S-phase nucleus, but not with respect to the timing of the normal cycle. Caffeine in replication-arrested cells thus overcomes the restriction on the formation of mitotic condensing factors that is normally imposed during DNA replication, but does not accelerate the timing of condensation unless cycle controls have previously been disturbed by synchronization procedures.

A postprophase topoisomerase II-dependent chromatid core separation step in the formation of metaphase chromosomes.

Metaphase chromatids are believed to consist of loops of chromatin anchored to a central scaffold, of which a major component is the decatenatory enzyme DNA topoisomerase II. Silver impregnation selectively stains an axial element of metaphase and anaphase chromatids; but we find that in earlier stages of mitosis, silver staining reveals an initially single, folded midline structure, which separates at prometaphase to form two chromatid axes. Inhibition of topoisomerase II prevents this separation, and also prevents the contraction of chromatids that occurs when metaphase is arrested. Immunolocalization of topoisomerase II alpha reveals chromatid cores analogous to those seen with silver staining. We conclude that the chromatid cores in early mitosis form a single structure, constrained by DNA catenations, which must separate before metaphase chromatids can be resolved.

Visna virus infection of American lambs.

Random-bred fetal and 4-week-old American lambs, inoculated intracerebrally with visna virus, developed a persistent infection in the brain and sometimes in the lung. The pathologic changes present in these lambs were similar to the early lesions of visna in Icelandic sheep, thus providing a possible model for the study of virus-induced demyelinating disease.

Complementation analysis on virus-fused Chinese hamster cells with nutritional markers.

Cell fusion experiments have been carried out with Chinese hamster cell mutants with different nutritional growth requirements. Conditions have been devised in which approximately 1 to 2 percent of the cell population remaining after fusion are fused, hybrid cells. The all-or-none nature of the genetic markers employed and the extremely low reversion rates insure that no contamination of the hybrid population with parental forms occurs. Hybrids between glycine- and hypoxanthine-requiring mutants are prototrophic, which indicates that both mutations are recessive. Hybrids between a glycine-deficient mutant and a singlestep mutant which requires glycine, hypoxanthine, and thymidine are relieved of the glycine dependency, an indication that the two loci associated with glycine dependence are different. This mutation to the triple-supplement requirement as well as a proline deficiency were also shown to be recessive mutations. The system appears applicable to a variety of genetic problems.

Virus-induced hydrocephalus: development of aqueductal stenosis in hamsters after mumps infection.

Hydrocephalus developed as a sequela of mumps virus infections of suckling hamsters. The initial infection after intracerebral inoculation was limited largely to ependymal cells lining the ventricles. This infection was clinically inapparent but later resulted in a noninflammatory stenosis or occlusion of the aqueduct of Sylvius.

Virions from progressive multifocal leukoencephalopathy: rapid serological identification by electron microscopy.

Virions were extracted directly from the brain of a patient with progressive multifocal leukoencephalopathy (PML). They were treated with antiserum to SV40, with rabbit antiserum to previous PML isolates, or with serum from another patient with the same disease and observed directly by electron microscopy. This procedure could be used for the rapid identification of the antigenic nature of virions in cases of PML.

Brain endothelial cell infection in children with acute fatal measles.

Neurologic diseases are important complications of measles. The role of virus infection of the central nervous system as well as the route of virus entry has been unclear. Five autopsied cases of individuals who died with severe acute measles 3-10 d after the onset of the rash were studied for evidence of viral involvement of the central nervous system. In all cases, in situ hybridization and RT-PCR in situ hybridization techniques showed endothelial cell infection. Immunoperoxidase staining with an anti-ferritin antibody revealed a reactive microgliosis. These data suggest that endothelial cells in the brain are frequently infected during acute fatal measles. This site of infection may provide a portal of entry for virus in individuals who subsequently develop subacute sclerosing panencephalitis or measles inclusion body encephalitis and a target for immunologic reactions in post-measles encephalomyelitis.

Retroviruses and nervous system disease.

During the past decade retroviruses have been recognized as causes of human neurological disease. A wide clinical spectrum of neurological and neuromuscular diseases have been reported with HIV infections, and studies of these diseases have raised novel and exciting hypotheses of pathogenesis. As yet the full clinical spectrum of diseases associated with HTLV-1 has yet to be defined, and the pathogenesis of the chronic spastic paraparesis remains a mystery. Chronic neurological diseases in animals caused by both oncoviruses and lentiviruses can provide some clues to the pathogenesis of these newly recognized human neurological illnesses.

Slow DNA rejoining in ultraviolet-irradiated human diploid fibroblasts treated with the mitogens trypsin and insulin.

Normally in mammalian cells the postincision steps of UV-induced excision repair are much more rapid than the recognition of damage and incision. This means that at any one time the level of repair-generated single-stranded DNA breaks is very low. Here we report that detectable levels of DNA breaks accumulate in quiescent human fibroblasts which are UV irradiated a few hours after replating in conditions that stimulate progress through the cell cycle. Most DNA breaks accumulate in cultures trypsinized and seeded in medium supplemented with insulin, and irradiated in early G1. Because trypsin and insulin have no effect on UV-induced incision rates, as measured by DNA break accumulation in the presence of DNA synthesis inhibitors, we argue that our ability to detect incomplete repair-sites is due to a significant reduction in the rate of gap sealing indicative of a shift in the steady state of excision repair. Provision of DNA precursors prevents the enhancing effect of trypsin and insulin on the accumulation of DNA breaks, implying that these agents affect DNA precursor metabolism. Perturbation of the repair process, which leads to the accumulation of 1500-2000 DNA breaks/genome, is also associated with other effects including increased lethality, the appearance of double-strand breaks and the loss of NAD, the last effect presumably arising as a consequence of break-stimulated poly(ADPR) transferase activity. Addition of 3-amino-benzamide, an inhibitor of poly(ADPR) synthesis, completely blocks the decline in NAD levels, but does not change the rate of sealing of the accumulated DNA breaks. These results strongly suggest that ligation is largely, if not entirely, independent of ADP ribosylation in this system.

Correlations of DNA damage and repair with nuclear and chromosomal damage in HeLa cells caused by methylnitrosamides.

N-Methyl-N-nitrosourethan induces breaks or alkali-labile sites in cellular DNA, many if not all of which are repaired rapidly. Other DNA lesions are repaired by an excision process. Hydroxyurea and 1-beta-D-arabinofuranosylcytosine cause an accumulation of DNA breaks after N-methyl-N-nitrosourethan treatment, probably by inhibiting the DNA-synthetic (but not the nucleolytic) stage of excision repair. Chromosome damage (fragmentation or attenuation of interphase chromosomes and decondensation and radial rearrangement of metaphase chromosomes) is present soon after treatment with N-methyl-N-nitrosourethan and is not reversed during further incubation. It is apparently associated with the longer-lived DNA lesions, probably those which are removed by excision, and is enhanced by incubation with hydroxyurea and 1-beta-D-arabinofuranosylcytosine. N-Methyl-N-nitrosourethan also inhibits cellular protein and the loss of nucleolar structure. N-Methyl-N-nitrosourea is less potent than N-methyl-N-nitrosourethan in causing DNA or chromosome damage and is less cytotoxic.

Hypersensitivity of Cockayne's syndrome cells to camptothecin is associated with the generation of abnormally high levels of double strand breaks in nascent DNA.

We report that fibroblasts from individuals with Cockayne's Syndrome (CS), an autosomal recessive disease exhibiting hypersensitivity to UV, are also hypersensitive to the killing action of camptothecin (CPT). In normal and CS cell lines the level of the protein-linked single strand DNA breaks (SSBs) induced by equal doses of CPT is similar, and these DNA breaks disappear within minutes of the removal of CPT. Thus, the toxicity of CPT does not correlate with the primary DNA lesions induced by the drug, and the hypersensitivity of CS cells cannot be explained by excessive topoisomerase I activity or by a defect in the enzyme ligation step. We have reported that CPT toxicity in normal cells is closely associated with the generation of double-strand DNA breaks (DSBs), predominantly at sites of DNA replication. The hypersensitivity of CS cells to CPT correlates closely with the much higher level of DSBs in nascent DNA than in normal cells. These DSBs are long-lived in all cells, but in CS many more (about 10-fold) remain 24 h after CPT removal and are presumably responsible for the higher frequency of chromosome aberrations in these cells. In CS as in normal cells aphidicolin prevents the generation of replication-related DSBs, suggesting that the movement of the DNA polymerase is necessary for the induction by CPT of the cytotoxic DSBs. Resistance to CPT and UV is restored to wild type in proliferating hybrids constructed between CS lines from two different complementation groups as is the abundance of replication-related DSBs. On the basis of this complementation we conclude that the UV and CPT sensitivities are distinct phenotypic traits arising from mutations in the CS A and B genes.

Enhanced photoproduct repair: its role in the DNA damage-resistance phenotype of human malignant melanoma cells.

A fundamental issue in understanding melanoma is to seek the basis for the cellular resistance to DNA damaging agents, which is manifested in vivo as pronounced tumor resistance to therapeutic agents. The published consensus on melanoma has been that exaggerated postreplication recovery (PRR), rather than excision repair, underlies the unusual damage-resistance phenotype. We examined the resistance to the model DNA damaging agent, UV-C, of subclones derived from a human metastatic melanoma cell line. The clones essentially fall into two groups: one with normal and the other with enhanced resistance. We exploited this range to investigate the interrelationships between replication, transcription, and repair of DNA after UV irradiation. Subclones resistant to UV killing were indeed found to possess enhanced rates of PRR and were coresistant to cisplatin. However, we now report an overall elevation of photoproduct repair in both melanoma groups compared to nonmelanoma controls and conclude that this accounts for the resistant melanoma phenotype, including that of enhanced PRR. Repair enhancement may explain chemoresistance, while loss of efficiency of certain functions, such as PRR, due to the intrinsic genetic lability of tumor cells, may generate the class of melanoma subclones exhibiting only normal resistance.

Androgen receptor stabilization in recurrent prostate cancer is associated with hypersensitivity to low androgen.

The androgen receptor (AR) is highly expressed in androgen-dependent and recurrent prostate cancer (CaP) suggesting it has a role in the growth and progression of CaP. Previously proposed mechanisms for AR reactivation in recurrent CaP include altered growth factor signaling leading to protein phosphorylation and AR mutations that broaden ligand specificity. To further establish a role for AR in recurrent CaP, we compared several properties of AR in relation to the growth response to low levels of androgens in model systems of androgen-dependent and recurrent CaP. AR from all of the tumors and cell lines bound [3H]R1881 with similar high affinity (mean Kd, 0.12 nM). In the absence of androgen, AR in androgen-dependent LNCaP cells was unstable with a degradation half-time (t(1/2)) of 3 h at 37 degrees C. In contrast, AR was 2-4 times more stable in recurrent CWR22 tumors (t(1/2), >12 h) and CWR-R1 or LNCaP-C4-2 cell lines (t(1/2), 6-7 h) derived from recurrent prostate tumors. In the recurrent CWR22 tumor and its CWR-R1 cell line grown in the absence of androgen, AR immunostaining was entirely nuclear, whereas under the same conditions AR in LNCaP-C4-2 and LNCaP cells was predominantly nuclear but was also detected in the cytoplasm. High level expression, increased stability, and nuclear localization of AR in recurrent tumor cells were associated with an increased sensitivity to the growth-promoting effects of dihydrotestosterone in the femtomolar range. The concentration of dihydrotestosterone required for growth stimulation in CWR-R1 and LNCaP-C4-2 cells was four orders of magnitude lower than that required for androgen-dependent LNCaP cells. The results suggest that AR is transcriptionally active in recurrent CaP and can increase cell proliferation at the low circulating levels of androgen reported in castrated men.

A mechanism for androgen receptor-mediated prostate cancer recurrence after androgen deprivation therapy.

The development and growth of prostate cancer depends on the androgen receptor and its high-affinity binding of dihydrotestosterone, which derives from testosterone. Most prostate tumors regress after therapy to prevent testosterone production by the testes, but the tumors eventually recur and cause death. A critical question is whether the androgen receptor mediates recurrent tumor growth after androgen deprivation therapy. Here we report that a majority of recurrent prostate cancers express high levels of the androgen receptor and two nuclear receptor coactivators, transcriptional intermediary factor 2 and steroid receptor coactivator 1. Overexpression of these coactivators increases androgen receptor transactivation at physiological concentrations of adrenal androgen. Furthermore, we provide a molecular basis for this activation and suggest a general mechanism for recurrent prostate cancer growth.

Ultraviolet-induced DNA excision repair in human B and T lymphocytes. II. Effect of inhibitors and DNA precursors.

Despite their great sensitivity to ultraviolet light purified human B and T lymphocytes are capable of complete repair provided that the ultraviolet dose does not exceed 0.5 Jm-2. Their capacity to repair, as measured by the restoration of DNA supercoiling in preparations of nucleoids, and their survival are significantly increased in the presence of deoxyribonucleosides. Certain agents which inhibit semi-conservative DNA synthesis (hydroxyurea, 1-beta-D-arabinofuranosylcytosine (arafCyt) either stop or delay the repair process in lymphocytes. The effect of hydroxyurea is eventually overcome spontaneously, but changes in the sedimentation behaviour of ultraviolet-irradiated nucleoids caused by arafCyt can only be neutralized by addition of deoxycytidine. The effective inhibition of repair by arafCyt permits the detection of extremely small amounts of ultraviolet damage and also the estimation of when repair is complete.

Action of caffeine on DNA replication after ultraviolet irradiation in Indian muntjac cells: no connection with action on cell cycle delay.

Indian muntjac fibroblasts of the SV40-transformed line SVM are hypersensitivity to UV, and after UV irradiation have defective post-replication recovery and a high level of sister chromatid exchanges and chromosome aberrations. The lethal and clastogenic effects of UV on SVM have elsewhere been shown to be aggravated by caffeine, which overcomes the block to cycle traverse imposed by DNA damage; however, in DM cells, an Indian muntjac line of normal UV sensitivity, caffeine has no effect on cycle traverse, but nevertheless enhances UV killing and sister chromatid exchanges. In this paper, the effects of caffeine on irradiated DM cells are shown to be due to its inhibition of post-replication recovery, with subsequent formation of DNA double-strand breaks at the strand gaps thus produced. By contrast, in SVM cells the limited capacity for post-replication recovery is relatively insensitive to caffeine after UV fluences which permit significant cell survival; however, caffeine still strongly induces DNA double-strand breaks and chromosome aberrations, apparently by an alternative mechanism. The SVM and DM cell lines therefore exemplify separate actions of caffeine on mammalian cells, deficient in the caffeine effects on post-replication recovery and cell cycle progression, respectively.

New patterns of nuclear lamina induced by cell fusion.

During the eukaryote cell cycle the nuclear envelope displays a series of major morphogenetic changes, the most significant of which include its breakdown and reconstitution as cells move up to, pass through and emerge from division. The three polypeptides, lamins A, B and C, are major components of the nuclear pore complex-lamina fraction of the nuclear envelope and their association with the nuclear membrane or their dispersal in the cytoplasm reflects the existing balance between polymerization and depolymerization in the envelope. We have perturbed the lamina polymerization cycle by means of cell fusion between mitotic and interphase cells, following the redistribution of nuclear lamina protein by means of immunofluorescence techniques. In these heterophasic heterokaryons changes in the distribution of lamina occur as a function of (1) the time elapsed after fusion; (2) the ratio of mitotic to interphase elements in the cell, and (3) the stage in the cell cycle occupied by the interphase partner at the time of fusion. Depolymerization of nuclear lamina occurs most rapidly in cells with high ratios of mitotic to interphase elements, and especially in G1 rather than S-phase nuclei. While lamina depolymerization predominates early after fusion, at later times lamina is deposited around both the original metaphase and interphase nuclear masses and this is associated with the resumption of interphase activity in the form of limited DNA synthesis. These observations lead us to conclude that lamina depolymerization is under positive control mediated by diffusible factors in the cytoplasm of the metaphase partner. Repolymerization is likely to be associated with the inactivation of these factors as the heterokaryons age and, as a result, pass into an interphase-like state.

Competence for assembly of sister chromatid cores is progressively acquired during S phase in mammalian cells.

Condensed sister chromatids possess a protein scaffold or axial core to which loops of chromatin are attached. The sister cores are believed to be dynamic frameworks that function in the organization and condensation of chromatids. Chromosome structural proteins are implicated in the establishment of sister chromatid cohesion and in the maintenance of epigenetic phenomena. Both processes of templating are tightly linked to DNA replication itself. It is a question whether the structural basis of sister chromatid cores is templated during S phase. As cells proceed through the cell cycle, chromatid cores undergo changes in their protein composition. Cytologically, cores are first visualized at the start of prometaphase. Still, core assembly can be induced in G1 and G2 when interphase cells are fused with mitotic cells. In this study, we asked if chromatid cores are similarly able to assemble in S-phase cells. We find that the ability to assemble cores is transiently lost during local replication, then regained in chromosome regions shortly after they have been replicated. We propose that core templating occurs coincident with DNA replication and that the competence for the assembly of the sister chromatid cores is acquired shortly after passage of replication forks.

Pathogenesis of human poliovirus infection in mice. II. Age-dependency of paralysis.

The mechanism of resistance of newborn mice to poliovirus-induced paralysis was studied by comparing regional virus replication in the adult and in the newborn central nervous systems (CNS) after intracerebral (ic) and intraspinal inoculation. Initial virus replication in the brains was similar in both age groups. Paralysis correlated with replication of virus in the spinal cord to a constant threshold, and this replication in newborns was delayed. Intraspinal inoculation of newborns eliminated the delay, indicating that neonatal anterior horn motor neurons were fully susceptible to infection. Cordectomy prevented the spread of virus, despite patent cerebrospinal fluid (CSF) pathways. Thus, poliovirus appeared to spread within the CNS via an axonal transport system. Known maturational changes in the fast transport system may explain the relative resistance of immature mice to poliovirus-induced paralysis.