cDNA-derived molecular characteristics and antibodies to a new centrosome-associated and G2/M phase-prevalent protein

Differential screening of a murine RNA-based cDNA library with cell cycle phase-specific transcripts released a cDNA clone (lambda CCD41) to a mRNA (1.349 kb) which, according to the mode of its detection, increases as expected during the cell cycle. The molecular characteristics of the protein (27 × 10(3) M(r)) encoded by this mRNA were deduced from the cDNA sequence and antibodies were prepared against the recombinant protein. Immunofluorescence studies performed with PtK2 cells revealed that the amount of the antigen specified by the CCD41 sequence increases during the cell cycle out of proportion with the DNA content. In G1 phase cells, the antigen is exclusively located at the site of the centrosome. During cell cycle progression the antigen becomes also detectable in perinuclear vesicles that increase in number and size, reaching a maximum in G2 phase cells. The centrosomal location of the CCD41 antigen was investigated in relation to another centrosomal antigen, centrosomin A. Since the latter antigen is detected by a monoclonal antibody reacting specifically and permanently with the centrosomes in PtK2 cells throughout the cell cycle it was possible to investigate the relative positions of the two proteins at the site of the centrosome and to add new information about the general architecture of the organelle and its changes during the cell cycle. While the centrosomin A antibody detects the pronounced cell cycle stage-dependent shape changes of the centrosome, the CCD41-encoded protein appears to be localized as a compact structure inside the centrosome. Its epitopes are exposed throughout the cell cycle except during a brief period immediately after the formation of the daughter centrosome.

Studies on the attachment and penetration of hepatitis B virus

There are two identified liver-specific attachment sites in the preS2 domain and one in the preS1 domain. Which mechanism leads to attachment in vivo is not known. The subsequent penetration seems to require proteolysis which does not occur spontaneously in HepG2 cells, but presumably in vivo. The role of the small HBs protein for attachment remains enigmatic so far, but it must have a function because an escape mutant exists against a monoclonal antibody which binds to an epitope of the small protein. The occurrence of this escape mutant in vaccinated persons proves that the standard hepatitis B vaccine does induce neutralizing antibodies, but it also suggests very strongly that the neutralizing preS epitopes be included in future hepatitis B vaccines.

Effect of multidrug-resistant P-glycoprotein gene expression on chloroaluminum tetrasulfonate phthalocyanine concentration

The effect of multidrug-resistant P-glycoprotein gene expression (MDR1) in 3T3 cells on cellular concentrations and cytotoxicity induced by the photodynamic agent chloroaluminum tetrasulfonate phthalocyanine (AlSPc) was evaluated. 3T3 cells transfected with a retroviral vector expressing human MDR1 cDNA were resistant to colchicine. Resistant cells incubated with daunomycin accumulated only 40-50% of the quantity of daunomycin accumulated in control cells. Resistant cells incubated with daunomycin in the presence of verapamil had intracellular daunomycin concentrations approximately equal to control cells without verapamil. When these MDR1 3T3 cells were incubated with AlSPc, cellular concentrations of AlSPc did not differ between cells resistant to colchicine and those that were not. Similarly, there was little difference in cytotoxicity demonstrated by 51Cromium release in the two cell lines exposed to AlSPc and light (675 nm; 6 J/cm2). This study suggests photodynamic therapy using AlSPc may be a useful treatment modality for tumors in which the MDR1 P-glycoprotein confers resistance to cancer chemotherapeutics.

Evidence for the regulation of guinea-pig heart microsomal phosphatidylcholine-hydrolysing phospholipase A1 by guanosine 5'-[gamma-thio]triphosphate

We have recently characterized lysophospholipase A2 activities in guinea-pig heart microsomes and postulated that these enzymes act sequentially with phospholipases A1 to release fatty acids selectively from phosphatidylcholine (PC) and phosphatidylethanolamine, thus providing an alternative route to the phospholipase A2 mode of release. In a further investigation of the postulated pathway, we have characterized the PC-hydrolysing phospholipase A1 in guinea-pig heart microsomes. Our results show that the enzyme may have a preference for substrates with C16:0 over C18:0 at the sn-1 position. In addition, although the enzyme cleaves the sn-1 fatty acid, the rate of hydrolysis of PC substrates with C16:0 at the sn-1 position was influenced by the nature of the fatty acid at the sn-2 position. The order of decreasing preference was C18:2 > C20:4 = C18:1 > C16:0. The hydrolyses of the molecular species were differentially affected by heating at 60 degrees C. An investigation into the effect of nucleotides on the activity of the enzyme showed that guanosine 5'-[gamma-thio]triphosphate (GTP[S]) inhibited the hydrolysis of PC by phospholipase A1 activity, whereas GTP, guanosine 5'-[beta-thio]diphosphate (GDP[S]), GDP, ATP and adenosine 5'-[gamma-thio]triphosphate (ATP[S]) did not affect the activity. The inhibitory effect of GTP[S] on phospholipase A1 activity was blocked by preincubation with GDP[S]. A differential effect of GTP[S] on the hydrolysis of different molecular species was also observed. Taken together, the results of this study suggest the presence of more than one phospholipase A1 in the microsomes with different substrate specificities, which act sequentially with lysophospholipase A2 to release linoleic or arachidonic acid selectively from PC under resting conditions. Upon stimulation and activation of the G-protein, the release of fatty acids would be inhibited.

Regulation of Hsp70 function by a eukaryotic DnaJ homolog

We report that a purified cytoplasmic Hsp70 homolog from Saccharomyces cerevisiae, Hsp70SSA1, exhibits a weak ATPase activity, which is stimulated by a purified eukaryotic dnaJp homolog (YDJ1p). Stable complex formation between Hsp70SSA1 and the permanently unfolded protein carboxymethylated alpha-lactalbumin (CMLA) was assayed by native gel electrophoresis. The affinity of Hsp70SSA1 for CMLA appeared to be regulated by YDJ1p. Significant reduction in both CMLA-Hsp70SSA1 complex formation and the release of CMLA pre-bound to Hsp70SSA1 was observed only in the presence of both YDJ1p and ATP. Thus, Hsp70SSA1 and YDJ1p interact functionally in the execution of Hsp70SSA1 chaperone activities in the eukaryotic cell.

Enhanced self-pumped phase conjugation from 16 degrees -cut KNSBN:Cu

With the maximum coupling coefficient and high internal reflection conditions, the self-pumped phase-conjugation reflectivity of copper-doped potassium sodium strontium barium niobate (KNSBN:Cu) is increased with 16 degrees -cut samples. The response time is also shortened. The resolution property of 16 degrees -cut KNSBN:Cu is determined and a distorted image is corrected by using the 16 degrees -cut sample.

The relationship between cellular ether glycerophospholipid content and sensitivity of cancer cells to 1-O-octadecyl-2-O-methyl-glycerophosphocholine

Cancer cells are more susceptible to the growth-inhibitory effects of alkyl lysophospholipids than normal cells, but the mechanism of this selectivity is unknown. In this study we have investigated the hypothesis that the sensitivity of cells to alkyl lysophospholipids is related to the cellular ether lipid content. The order of decreasing sensitivity of the cells to the growth-inhibitory effect of 1-O-octadecyl-2-O-methyl-glycerophosphocholine (ET-18-OCH3) was MCF 7 > T84 > Malme 3M > A427 > A549, while the order of decreasing ether phospholipid content as a proportion of the total phospholipid was T84 > A427 = A549 = Malme 3M > MCF7. There was also no correlation between ET-18-OCH3-sensitivity and the proportion of ether lipid in the cholineglycerophospholipid or ethanolamineglycerophospholipid classes. Our results clearly indicate that the postulated relationship between ether phospholipid content and ET-18-OCH3-susceptibility may have very limited applicability and is unlikely to be the underlying reason for the selective effects of alkyl lysophospholipids.

Ras-induced hyperplasia occurs with mutation of p53, but activated ras and myc together can induce carcinoma without p53 mutation

Using a reconstituted mouse prostate organ, the effects on endogenous p53 expression of the ras oncogene or of the ras + myc oncogenes were investigated. In this system the ras gene alone causes mild hyperplasia, but the combination of ras and myc leads to the formation of carcinomas. Surprisingly, while p53 mutations were found in cells derived from the reconstituted organs containing ras alone, no such mutations were found in the ras + myc-transformed cells. Their growth, unlike that of the cells containing ras alone, was not inhibited by transfection with plasmids encoding wild-type human p53. We suggest that expression of both activated ras and myc genes bypasses the need for p53 mutation by neutralizing the tumor suppressor activity of normal p53.

Differentiation of HT-29 human colonic adenocarcinoma cells correlates with increased expression of mitochondrial RNA: effects of trehalose on cell growth and maturation

The HT-29 human adenocarcinoma cell line has been used extensively in the study of colonic cell differentiation and colon cancer. We report here that substitution of glucose with trehalose (alpha-D-glucopyranosyl-alpha-D-glucopyranoside) depresses growth and promotes mucin-producing, goblet-like maturation of HT-29. An initial characterization of this process was made by analyzing several cDNA clones whose RNA templates were differentially expressed at elevated levels in cells grown in trehalose-containing medium. Seven of the 9 clones examined corresponded to 6 mitochondrial genes whose expression levels, relative to those from glucose-grown cells, ranged from approximately 3-fold for 16S rRNA to 8-23-fold for NADH dehydrogenase subunit 4. On the other hand, levels of mitochondrial DNA copy, measured by using NADH dehydrogenase subunit 4 cDNA as probe, were shown to be unaffected by trehalose treatment. Elevation of cellular NADH dehydrogenase subunit 4 RNA in HT-29 cultures grown in medium containing different components (sodium butyrate, galactose, no-sugar, glucose, cellobiose) generally correlated with depressed growth levels and specifically with increased numbers of mucin-producing cells present. Like butyrate, the sugar, trehalose, is an effective inducer of HT-29 differentiation, and may prove useful as a dietary therapeutic, and as a probe for elucidating mitochondrial involvement in colonic cell differentiation and transformation.

Hsp60/chaperonin gene expression and differentiation of human colon adenocarcinoma and multipotent leukaemic cells

Elevated mitochondrial gene expression is an early event in the switch from proliferation to differentiation of the human colon adenocarcinoma cell line, HT29, promoted by trehalose replacement of exogenous glucose. Here we report the isolation and elevated expression of hsp60, the gene encoding chaperonin, a mitochondrial protein required for assembly of mitochondrial and cellular proteins. In contrast to HT29, leukaemic cells (HL60 and K562) neither differentiated nor altered their mitochondrial gene expression after treatment with trehalose. However, differentiation of these cells, as promoted by 12-O-tetradecanoylphorbol-13-acetate actually resulted in decreased levels of hsp60 mRNA expression as well as mitochondrial RNA expression, suggesting significant differences in involvement of mitochondria in the differentiation of these cell lineages.

Perturbations of cellular acylation processes by the synthetic alkyl-lysophospholipid 1-O-octadecyl-2-O-methylglycero-3-phosphocholine do not correlate with inhibition of proliferation of MCF7 and T84 cell lines

We have investigated the hypothesis that the antiproliferative effect of 1-O-octadecyl-2-O-methylglycero-3-phosphocholine (ET-18-OCH3) is mediated through the inhibition of cellular acylation processes that control the unsaturated fatty acid complement of phospholipids. The effect of ET-18-OCH3 on the incorporation of radiolabeled oleic, linoleic, and arachidonic acids into MCF7 and T84 phospholipids was investigated. Incubation of MCF7 cells with fatty acids and 2.75 micrograms/ml ET-18-OCH3, which inhibited the proliferation of the cells after 8 h, resulted in decreased incorporation of fatty acids into a number of phospholipids, notably phosphatidylcholine; however, increased incorporation of fatty acids into other phospholipids was also observed. After 12 h incubation with the alkyl-lysophospholipid, differences in the distribution of newly incorporated fatty acids into the phospholipid classes were observed without any effect on the total amount of fatty acid incorporated. Incubation of MCF7 cells with 5 micrograms/ml ET-18-OCH3, which caused a cessation in proliferation, had a similar effect on the incorporation of the fatty acids into the phospholipids, but the redistribution of newly incorporated fatty acids in the phospholipids was accompanied by a decrease in the amount of associated radiolabeled fatty acid. Incubation of T84 cells with the labeled fatty acids and 3.5 micrograms/ml ET-18-OCH3, which significantly decreased proliferation after 8 h, resulted in decreased incorporation of oleic acid into phosphatidylcholine and increased incorporation of oleic, linoleic, and arachidonic acids into phosphatidylethanolamine, prior to the decrease in proliferation. After 12 h incubation with alkyl-lysophospholipid, significant increases in the total amount of labeled oleic and arachidonic acids incorporated in the phospholipid fraction were observed. These results clearly indicate that the antiproliferative effect of ET-18-OCH3 in MCF7 and T84 cells is not dependent on inhibition of acylation processes and the above hypothesis may not be applicable to all alkyl-lysophospholipid-sensitive cells.

The differential susceptibility of A427 and A549 cell lines to the growth-inhibitory effects of ET-18-OCH3 does not correlate with the relative effects of the alkyl-lysophospholipid on the incorporation of fatty acids into cellular phospholipids

Proliferation of A427, a lung cancer cell line, was significantly decreased 10 h after incubation with 5 micrograms/ml 1-O-octadecyl-2-O-methylglycero-3-phosphocholine (ET-18-OCH3) while the proliferation of A549, another lung cancer cell line, was unaffected until 15 h after incubation with the alkyl-lysophospholipid (ALP). The relative sensitivity of cells to the antiproliferative effect of ET-18-OCH3 has been postulated to be due to the degree of inhibition of cellular acylation processes. We therefore investigated the effect of 5 micrograms/ml ET-18-OCH3 on the incorporation of fatty acids for up to 12 h, into A427 and A549 phospholipids. Significant changes observed in the incorporation of fatty acids into A427 phospholipids by the ALP were a decreased incorporation of oleic acid into PC after 8 h, an increased incorporation of linoleic acid into PE after 12 h, decreased incorporation of arachidonate into PE after 3 h, and increased incorporation into PA after 5 h. Although the above changes affected the distribution of newly esterified fatty acids in the phospholipids, there was no effect on the total quantity of label incorporated in the phospholipid fraction between the experimental and control cells after 12 h. Incubation of A549 cells with ET-18-OCH3 resulted in decreased esterification of oleic acid into PC, SM, and LPC after 5 h; decreased incorporation of linoleic into PE after 12 h; and a decreased incorporation of arachidonate into SM after 1.5 h. After 12 h incubation with ET-18-OCH3, changes in the distribution of radiolabeled fatty acids were observed in the quantitatively minor phospholipids, SM and LPC. A 20% decrease in the quantity of oleic acid incorporated into the phospholipids was observed in cells incubated with the ALP; however, no differences were observed in the quantity of linoleic or arachidonic acid incorporated into the phospholipids. The lack of common effects of the ALP on the incorporation of fatty acids into A427 and A549 phospholipids, coupled with the absence of changes that were more severe or manifested earlier in the more sensitive A427 cell line, suggests that the effect of ET-18-OCH3 on the acylation processes depends on the cell type and the fatty acid species and is unlikely to be responsible for the relative sensitivities of the cells to the compound. Radiolabeled ET-18-OCH3 was used to examine the correlation between the amount of the compound accumulated in A427, A549, MCF7, T84, and LS174T cells and the relative susceptibilities of the cells to the ALP.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure of HIV-1 reverse transcriptase/DNA complex at 7 A resolution showing active site locations

AIDS, caused by human immunodeficiency virus (HIV), is one of the world's most serious health problems, with current protocols being inadequate for either prevention or successful long-term treatment. In retroviruses such as HIV, the enzyme reverse transcriptase copies the single-stranded RNA genome into double-stranded DNA that is then integrated into the chromosomes of infected cells. Reverse transcriptase is the target of the most widely used treatments for AIDS, 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI), but resistant strains of HIV-1 arise in patients after a relatively short time. There are several nonnucleoside inhibitors of HIV-1 reverse transcriptase, but resistance to such agents also develops rapidly. We report here the structure at 7 A resolution of a ternary complex of the HIV-1 reverse transcriptase heterodimer, a monoclonal antibody Fab fragment, and a duplex DNA template-primer. The double-stranded DNA binds in a groove on the surface of the enzyme. The electron density near one end of the DNA matches well with the known structure of the HIV-1 reverse transcriptase RNase H domain. At the opposite end of the DNA, a mercurated derivative of UTP has been localized by difference Fourier methods, allowing tentative identification of the polymerase nucleoside triphosphate binding site. We also determined the structure of the reverse transcriptase/Fab complex in the absence of template-primer to compare the bound and free forms of the enzyme. The presence of DNA correlates with movement of protein electron density in the vicinity of the putative template-primer binding groove. These results have important implications for developing improved inhibitors of reverse transcriptase for the treatment of AIDS.

Conserved residues flanking the thiol/disulfide centers of protein disulfide isomerase are not essential for catalysis of thiol/disulfide exchange

Protein disulfide isomerase (PDI) catalyzes the oxidative folding of proteins containing disulfide bonds by increasing the rate of disulfide bond rearrangements which normally occur during the folding process. The amino acid sequences of the N- and C-terminal redox active sites (PWCGHCK) in PDI are completely conserved from yeast to man and display considerable identity with the redox-active center of thioredoxin (EWCGPCK). Available data indicate that the two thiol/disulfide centers of PDI can function independently in the isomerase reaction and that the cysteine residues in each active site are essential for catalysis. To evaluate the role of residues flanking the active-site cysteines of PDI in function, a variety of mutations were introduced into the N-terminal active site of PDI within the context of both a functional C-terminal active site and an inactive C-terminal active site in which serine residues replaced C379 and C382. Replacement of non-cysteine residues (W34 to Ser, G36 to Ala, and K39 to Arg) resulted in only a modest reduction in catalytic activity in both the oxidative refolding of RNase A and the reduction of insulin (10-27%), independent of the status of the C-terminal active site. A somewhat larger effect was observed with the H37P mutation where approximately 80% of the activity attributable to the N-terminal domain (approximately 40%) was lost. However, the H37P mutant N-terminal site expressed within the context of an inactive C-terminal domain exhibits 30% activity, approximately 70% of the activity of the N-terminal site alone.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo molecular analysis of lymphokines involved in the murine immune response during Schistosoma mansoni infection. II. Quantification of IL-4 mRNA, IFN-gamma mRNA, and IL-2 mRNA levels in the granulomatous livers, mesenteric lymph nodes, and spleens during the course of modulation

Parasite egg-induced granulomas are the primary pathogenic lesions in murine schistosomiasis mansoni. This cell-mediated granulomatous response is specific for soluble egg Ag and appears to be mediated predominantly by CD4+ Th2 cells. As infection progresses from the acute to the chronic phase, the cell-mediated anti-soluble egg Ag responses attenuate in a process termed modulation. In this study the hypothesis that modulation is effected by a chronic phase increase in Th2-inhibiting Th1 cell activity was investigated. Northern blot quantification of mRNA specific for the Th2 lymphokine, IL-4, and the Th1 lymphokines, IFN-gamma and IL-2, in the spleens, mesenteric lymph nodes, and granulomatous livers of mice infected for various lengths of time over the course of modulation was performed. Also, the capacity of mitogen- and Ag-stimulated spleen cells to produce message for these lymphokines was compared. Peak tissue levels of both IL-4 mRNA and IFN-gamma mRNA were seen in acutely infected mice, and levels of both messages declined as infection became chronic. Stimulated spleen cells from acutely infected mice also produced higher levels of IL-4 and IFN-gamma mRNA than cells from chronically infected mice. IL-2 mRNA was never detected in any tissue sample but was detected in the stimulated spleen cells, again with acute phase levels higher than chronic phase levels. Hence, this study shows no evidence for increased Th1 cell activity during chronic infection and suggests that modulation may be effected by a generalized suppression of lymphokine synthesis.

In vivo molecular analysis of lymphokines involved in the murine immune response during Schistosoma mansoni infection. II. Quantification of IL-4 mRNA, IFN-gamma mRNA, and IL-2 mRNA levels in the granulomatous livers, mesenteric lymph nodes, and spleens during the course of modulation

Parasite egg-induced granulomas are the primary pathogenic lesions in murine schistosomiasis mansoni. This cell-mediated granulomatous response is specific for soluble egg Ag and appears to be mediated predominantly by CD4+ Th2 cells. As infection progresses from the acute to the chronic phase, the cell-mediated anti-soluble egg Ag responses attenuate in a process termed modulation. In this study the hypothesis that modulation is effected by a chronic phase increase in Th2-inhibiting Th1 cell activity was investigated. Northern blot quantification of mRNA specific for the Th2 lymphokine, IL-4, and the Th1 lymphokines, IFN-gamma and IL-2, in the spleens, mesenteric lymph nodes, and granulomatous livers of mice infected for various lengths of time over the course of modulation was performed. Also, the capacity of mitogen- and Ag-stimulated spleen cells to produce message for these lymphokines was compared. Peak tissue levels of both IL-4 mRNA and IFN-gamma mRNA were seen in acutely infected mice, and levels of both messages declined as infection became chronic. Stimulated spleen cells from acutely infected mice also produced higher levels of IL-4 and IFN-gamma mRNA than cells from chronically infected mice. IL-2 mRNA was never detected in any tissue sample but was detected in the stimulated spleen cells, again with acute phase levels higher than chronic phase levels. Hence, this study shows no evidence for increased Th1 cell activity during chronic infection and suggests that modulation may be effected by a generalized suppression of lymphokine synthesis.

Thermal Conductivity of Monolithic Organic Aerogels

The total thermal conductivity lambda of resorcinol-formaldehyde aerogel monoliths has been measured as a function of density rho in the range from rho = 80 to 300 kilograms per cubic meter. A record-low conductivity value in air at 300 K of lambda approximately 0.012 watt per meter per kelvin was found for rho approximately 157 kilograms per cubic meter. Caloric measurements under variation of gas pressure as well as spectral infrared transmission measurements allowed the determination of solid conductivity, gaseous conductivity, and radiative conductivity as a function of density. The development of such low conductivity materials is of great interest with respect to the substitution of environmentally harmful insulating foams made from chlorofluorocarbons.