Induction of HL-60 cells to undergo apoptosis is determined by high levels of wild-type p53 protein whereas differentiation of the cells is mediated by lower p53 levels

The observation that wild-type p53 may induce cells to undergo either apoptosis or differentiation raises the question of whether these two events share similar p53-dependent pathways. To evaluate the interrelationship between these two p53-dependent processes, our study focused on the human HL-60, a promyelocytic p53 nonproducer cell line in which p53 expression was introduced and the induction of apoptosis and differentiation was followed under controlled conditions. p53 expression was induced in the HL-60 cell line by infection with the recombinant wild-type p53 (p53WT) vaccinia virus. Viral infection gave rise to cells expressing various levels of wild-type p53 protein. High levels of p53 protein induced cells to undergo rapid apoptosis, whereas lower levels of p53 protein induced cells to undergo cell differentiation at a more moderate rate of kinetics. These results suggest that p53 protein levels may determine whether a given cell should prefer one pathway over the other to exit the cell cycle. Accordingly, we propose that the p53 vaccinia virus may be used as a potential vector for cell therapy leading toward the exit of p53 null human primary hematopoetic tumors from the malignant state in vivo via the apoptotic or cell differentiation pathways.

Inhibition of human immunodeficiency virus by N-methylisatin-beta 4':4'-diethylthiosemicarbazone and N-allylisatin-beta-4':4'-diallythiosemicarbazone

N-methylisatin-beta 4':4'-diethylthiosemicarbazone(M-IBDET) and N-allylisatin-beta-4':4'-diallylthiosemicarbazone(A-IBDAT ) inhibit the production of Human Immunodeficiency virus (HIV). Virus inhibition was related to the thiosemicarbazone derivative (TSCD) concentrations and time of treatment. Inhibition of HIV production was confirmed by various parameters of virus assay employing reverse transcriptase activity, plaque forming units (PFU) and levels of viral structural proteins. Effective antiviral TSCD concentrations ranged from 0.17 microM to 2.04 microM for M-IBDET, and from 1.45 microM to 17.4 microM for A-IBDAT. Treatment of the chronic HIV-infected cells for 48 h with 0.34 microM M-IBDET or 2.9 microM A-IBDAT caused about 50% inhibition in as virus yield ED50 as assayed by the PFU method. Almost 2 logs of virus infectivity (PFU) was suppressed after 48 h of treatment with 17.4 microM A-IBDAT. Therapeutic index values of 20 and 30 were found for M-IBDET and A-IBDAT, respectively. A significant selective inhibition of HIV structural protein synthesis was shown by both M-IBDET and A-IBDAT.

Transformation, growth rate, and the heme biosynthetic pathway in V-abl-transfected fibroblasts

The relationship between growth rate and various parameters of the heme biosynthetic pathway was studied in two cell lines of rat fibroblasts (REabl-1 and REabl-3) transfected with v-abl oncogene, coded by the Abelson murine leukemia virus, and subjected to glucocorticoid dependent transformation. In the REabl-1 cell line, whose growth rate was only slightly affected by dexamethasone (DX), almost no change was noticed either in heme content or in the enzymatic activities of aminolevulinate synthase (ALAS), porphobilinogen deaminase (PBGD), and ferrochelatase (FC) in the presence of various concentrations of DX. In the REabl-3 cell line, exhibiting a growth rate highly sensitive to DX, a significant reduction in intracellular heme concomitantly with decreases in ALAS and FC activities and a threefold increase in PBGD were noted. The fact that incubation with 10(-5)M hemin did not result in a decrease in ALAS activity raised the possibility that REabl cells lack a negative feedback control mechanism. The relationships between transformation, growth rate, and heme biosynthetic pathway are discussed.

Relationships between structure and antiretroviral activity of thiosemicarbazone derivatives

In an attempt to develop anti-AIDS drugs, the compound isatin beta-thiosemicarbazone has been subjected to systematic structural modifications. The resulting synthesized thiosemicarbazone derivatives (TSCDs) were examined for their ability to act as antiretrovirus agents in a model system--2M3/M cell system--consisting of B lymphocytes transformed by the v-abl oncogene and chronically infected with a retrovirus, the Moloney leukemia virus (M-MuLV). The efficacy of the synthesized TSCDs against retroviruses was determined by assaying the therapeutic index (TI) values of the compounds. The results enabled the classification of TSCD groups based on the relationship between chemical structure and antiretroviral activity. The compound N-allylisatin-beta':4'-diallylthiosemicarbazone showed the highest TI value and efficiently suppressed the chronic infection of M-MuLV in continuous long-term treatment.

Selective repression of v-abl-encoded protein by N-methylisatin-beta-4',4'-diethylthiosemicarbazone and N-allylisatin-beta-4',4'-diallylthiosemicarbazone

N-Methylisatin-beta-4',4'-diethylthiosemicarbazone (M-IBDET) and N-allylisatin-beta-4',4'-diallylthiosemicarbazone (A-IBDAT) selectively inhibited v-abl protein (P120), an oncogene product associated with tyrosine kinase activity. Concentrations of M-IBDET ranging between 0.17 and 0.64 microM and concentrations of A-IBDAT from 1.45 to 2.9 microM reduced tyrosine kinase activity significantly, whereas 0.64 microM M-IBDET and 2.9 microM A-IBDAT blocked P120 production. Cellular growth rate, protein production, and synthesis of p45 actin and p53 nuclear oncogene were not affected at these conditions. M-IBDET and A-IBDAT selectively suppress the v-abl oncogene as well as Moloney murine leukemia virus production.

Expression of wild-type and mutant p53 proteins by recombinant vaccinia viruses

To facilitate the purification of wild type p53 protein, we established a recombinant p53 vaccinia viral expression system. Using this efficient eukaryotic expression vector, we found that the expressed p53 proteins retained their specific structural characteristics. A comparison between wild type and mutant p53 proteins showed the conservation of the typical subcellular localization and the expression of specific antigenic determinants. Furthermore, wild type p53 exhibited a typical binding with large T antigen, whereas no binding was detected with mutant p53. Both wild type and mutant p53 proteins were highly stable and constituted 5-7% of total protein expressed in the infected cells. These expression recombinant viruses offer a simple, valuable system for the purification of wild type and mutant p53 proteins that are expressed abundantly in eukaryotic cells.

Accelerated heme synthesis and degradation in transformed fibroblasts

Various parameters of the heme biosynthetic pathway were studied in two cell lines, one nontransformed and the other malignantly transformed (MLV/MS), both replicating at the same rate. Using the above system enabled us to distinguish between phenomena characteristic of the malignant transformation per se and those due to accelerated growth rate. Heme synthesis and degradation as well as the activities of ALAS, ALAD, PBGD, and FC were found to be increased in the transformed cells. However, the concentration of intracellular heme was markedly reduced from 30.4 +/- 4.4 pmole/mg protein in nontransformed cells to 10.5 +/- 2.6 pmole/mg protein in transformed cells. These observations show that malignant transformation leads to changes in heme metabolism unrelated to growth rate in this cell line.

Growth rate determines activity of porphobilinogen deaminase both in nonmalignant and malignant cell lines

PBGD activity and growth rate were determined in cultures of rat embryo fibroblasts, nontransformed and MLV/MS transformed fibroblastic cell lines; NIH-3T3 cells, and in a mouse lymphosarcoma cell line [L-929]. The two parameters examined correlate positively (P less than 0.001). The results of this investigation would seem to indicate clearly that porphobilinogen deaminase activity is related to growth. However, these experiments do not rule out the possibility that malignant transformation per se also causes changes in porphobilinogen deaminase activity.

N-methylisatin-beta-4',4'-diethylthiosemicarbazone, an inhibitor of Moloney leukemia virus protein production: characterization and in vitro translation of viral mRNA

The mode of inhibition of N-methylisatin-beta-4',4'-diethylthiosemicarbazone (M-IBDET) on Moloney leukemia virus production was studied. Drug treatment of infected cells did not alter the amounts or sizes of the 35S and 22S subgenomic viral RNAs. The translation abilities of poly(A)+ RNA derived from M-IBDET-treated cells was also unaffected, as judged by cell-free translation analysis. Poly(A)+ RNA derived from M-IBDET-treated cells directed translation of equal amounts of viral gag precursors, gPr-80gag and Pr-65gag, as did poly(A)+ RNA prepared from untreated cells. The addition of M-IBDET to a cell-free translation system programmed with either total poly(A)+ RNA extracted from infected cells or hybrid-selected viral RNA inhibited the synthesis of viral protein precursors. An examination of the effect of M-IBDET on polysomes engaged in the translation of viral proteins revealed a fourfold accumulation of polysomal virus-specific RNA in drug-treated cells. These results suggest that the inhibition of Moloney leukemia virus by M-IBDET involves a block in the translation of viral RNA rather than interference with viral RNA transcription.

Effect of N-methylisatin-beta-4':4'-diethylthiosemicarbazone on intracellular Moloney leukemia virus constituents

N-Methylisatin-beta-4':4'-diethylthiosemicarbazone (M-IBDET) inhibits intracellular production of viral constituents in a mouse cell line, 3T3/MLV, chronically infected with Moloney leukemia virus. Electron microscopic observations confirmed that inhibition of virus production by the drug was not associated with any structural changes in the cell morphology or any damage to the plasma membrane, the site of viral assembly and 'budding'. Treatment of the cells with 17 microM M-IBDET for 6 h inhibited extracellular virus production by 80% but did not affect the level of viral RNA in the cytoplasm or in the plasma membrane. Intracellular reverse transcriptase activity and levels of viral structural proteins were significantly inhibited. Thus, although the drug did not affect viral RNA, it reduced viral protein synthesis.

Studies on cell binding and internalization of human lymphoblastoid (Namalva) interferon

The binding of iodinated human lymphoblastoid Namalva interferon to Namalva cells, to a human fibroblast cell strain (FS11), and to a bovine kidney cell line (MDBK) was characterized. Scatchard analysis of the binding data indicated the presence of about 1000-2000 receptors per cell and dissociation constants of the order of 0.1 to 0.01 nM. Two subspecies of Namalva interferon (16 K and 20 K), which differ in their antiviral activity toward bovine and human cells, were found to bind with the same affinity toward bovine MDBK cells but to differ in their affinity to human cells. Experimental results indicated that at 37 degrees C the bound interferon is internalized within 15 min after binding to Namalva cells, and then degraded in the lysosomes. Exposure of Namalva cells to interferon resulted in a 40% reduction of the number of cell surface receptors (down-regulation).

Inhibition of the synthesis of Moloney leukemia virus structural proteins by N-methylisatin-beta-4',4'-diethylthiosemicarbazone

The mechanism of inhibition of Moloney leukemia virus by N-methylisatin-beta-4',4'-diethylthiosemicarbazone was studied. Experiments that used [3H]leucine for short-pulse labeling in the presence of the drug resulted in a 71% inhibition in the synthesis of Pr-80, the polypeptide precursor of the gag viral proteins. The radioactive pulse products of the polypeptide precursors after a further 2-h chase period showed a normal cleavage of the precursors, with the formation of a reduced amount of final mature viral structural proteins. The experimental evidence indicated that at the inhibitory concentration of 17 microM N-methylisatin-beta-4',4'-diethylthiosemicarbazone, the amount of intracellular viral RNA was not affected, whereas the activities of reverse transcriptase and the other viral protein syntheses were suppressed.

Glycoprotein enrichment in Moloney leukemia virus structural proteins released from interferon-treated cells

Interferon treatment of Moloney-leukemia-virus-infected cells (3T3/MLV) leads to the formation of virus particles enriched with viral structural glycoproteins, in addition to the inhibition of virus production. A preferential inhibitory effect on incorporation of RNA and proteins rather than glycoproteins was found in the released virus particles from interferon-treated cells. Enrichment in 70,000- and 45,000-dalton glycoprotein (gP-70, gP-45) in these particles was further demonstrated by polyacrylamide analysis of viral proteins pulse-labeled with [3H]-leucine. Viral glycoproteins released as soluble antigens were also determined. A 40% reduction was found in gP-70 and gP-45 released from interferon-treated cells. Radioimmunoprecipitation of pulse-chase-labeled cellular viral proteins showed no effect of interferon on the formation of viral structural 30,000-, 15,000- to 12,000-dalton proteins, and gP-70 and gP-45 from their respective precursors. The uncoordinate effect of interferon inhibition on viral 30,000-dalton protein and gP-70 is discussed.

Localization of reverse-transcriptase in interferon-treated mouse cells chronically infected with Moloney leukemia virus

Interferon treatment of mouse cells chronically infected with Moloney leukemia virus (3T3/MLV) resulted in 97 per cent inhibition of infective virus release. The intracellular localization and distribution of virus reverse-transcriptase and group specific (gs) antigen were determined in interferon treated and control cells. Cytoplasm of infected cells was fractionated by isopycnic centrifugation on discontinuous sucrose gradients. Fractions were analysed for their chemical composition and characterized by the activity of membranal marker enzymes. The association and levels of viral antigens were determined in each fraction. Fractions enriched with 5' nucleotidase, specific enzyme marker for plasma membrane, were also enriched with viral proteins. In interferon treated cells, intracellular accumulation of viral proteins was specifically localized in the plasma membrane. Threefold increase in reverse-transcriptase level was the maximal accumulation found in purified plasma membranes. Intracellular enzyme levels in interferon treated cells were in accordance with the amount of cell associated infective virus particles. The small accumulation of viral proteins and infective virus particles was not sufficient to account for the great reduction in virus yield observed in the supernatants of the interferon treated cells. A possible role for interferon in modification of plasma membrane associated with virus assembly is postulated.

Inhibition of Moloney leukaemia virus production by N-methylisatin-beta-4':4-diethylthiosemicarbazone

N-methylisatin-beta-4':4'-diethylthiosemicarbazone (M-IBDET) inhibited the production of Moloney leukaemia virus (MLV). Virus inhibition was related to drug concentrations and time of treatment. The effective antiviral drug concentrations ranged between 3.4 muM and 34 muM. Virus reverse transcriptase activity even at concentrations of 34 muM-M-IBDET was not inhibited. At virus inhibitory concentrations the drug reduced RNA synthesis only very slightly and did not affect protein synthesis at all, although growth and DNA synthesis of host cells were suppressed. The inhibition of cellular DNA synthesis was reversible. Comparison of M-IBDET with actinomycin D, cycloheximide and alpha-amanitin in terms of their inhibitory effect on the release of MLV into the culture medium showed that M-IBDET was comparable to the other antimetabolites. The inhibition of MLV production by M-IBDET was confirmed by various parameters of virus assay. It was concluded from the experimental evidence that M-IBDET specifically inhibits MLV-production.