Regulation of fibrinogen assembly. Transfection of Hep G2 cells with B beta cDNA specifically enhances synthesis of the three component chains of fibrinogen

Previous studies indicated that synthesis of B beta chain may be a rate-limiting factor in the production of human fibrinogen since Hep G2 cells contain surplus pools of A alpha and gamma but not of B beta chains, and fibrinogen assembly commences by the addition of preformed A alpha and gamma chains to nascent B beta chains attached to polysomes. To test whether B beta chain synthesis is rate limiting Hep G2 cells were transfected with B beta cDNA, and its effect on fibrinogen synthesis and secretion was measured. Two sets of stable B beta cDNA-transfected Hep G2 cells were prepared, and both cell lines synthesized 3-fold more B beta chains than control cells. The B beta-transfected cells also synthesized and secreted increased amounts of fibrinogen. Transfection with B beta cDNA not only increased the synthesis of B beta chain but also increased the rate of synthesis of the other two component chains of fibrinogen and maintained surplus intracellular pools of A alpha and gamma chains. Transfection with B beta cDNA did not affect the synthesis of albumin, transferrin, or anti-chymotrypsin and had a small inhibitory effect on the synthesis of C-reactive protein. Taken together these studies demonstrate that increased B beta chain synthesis specifically causes increased production of the other two component chains of fibrinogen and that unequal and surplus amounts of A alpha and gamma chains are maintained intracellularly.     

Involvement of calcium, calmodulin and protein phosphorylation in morphogenesis of Candida albicans

N-Acetyl-D-glucosamine-induced germ tube formation in Candida albicans at 37 degrees C was accompanied by an increase in the rate of protein phosphorylation. The calmodulin antagonist trifluoperazine and the Ca2+ ionophore A23187, which inhibited germ tube formation, also reduced the rate of phosphorylation. The rate of phosphorylation was also reduced when cells were incubated at 25 degrees C, which favoured yeast-phase growth. Two-dimensional SDS-PAGE analysis of phosphoproteins from germ-tube-forming and yeast cells revealed two germ-tube-specific and three yeast-specific phosphoproteins. Germ tubes and hyphae had more calmodulin activity than yeast cells, irrespective of the germ-tube-inducing condition used. As a first step towards understanding the inhibitory effect of trifluoperazine on germ tube formation, calmodulin from C. albicans was purified to homogeneity. It was heat stable, and displayed a pronounced Ca2(+)-induced shift in electrophoretic mobility.     

Structure of testicular angiotensin-converting enzyme. A segmental mosaic isozyme

The complete amino acid sequence of rabbit testicular angiotensin-converting enzyme has been deduced from the sequence of the corresponding cDNA clone. A protein of the expected molecular weight of 84,000 was translated in vitro from the mRNA encoded by this cDNA. All of the previously determined sequences of seven tryptic peptides from the enzyme are present in the deduced sequence, thus confirming the identity of the protein. From the deduced sequence it appears that the protein contains a signal peptide at the amino terminus and a hydrophobic anchoring domain near the carboxyl terminus. Northern analysis with oligonucleotide probes, whose sequences represented different regions of the cDNA, revealed not only the regions of extensive homology between the mRNAs encoding the testicular and the pulmonary isozymes but also a stretch of sequence near the 5' end unique to the testicular mRNA.     

Evaluation of genotoxicity of clofazimine, an antileprosy drug, in mice in vivo. II. Micronucleus test in bone marrow and hepatocytes

The antileprosy drug, clofazimine, was tested for its possible genotoxicity using micronucleus (MN) tests in mice. A significantly higher incidence of MN in bone marrow erythrocytes, particularly in polychromatic erythrocytes, as well as in regenerated hepatocytes revealed a positive clastogenic effect of the drug. The drug also had a marked antimitotic effect as indicated by a negative correlation with the dose.     

Lipoproteins: carriers of dehydroepiandrosterone fatty acid esters in human serum

The association between lipoproteins, cholesterol and cholesteryl esters is very well known to facilitate both the transport in plasma and the entry of these non-polar compounds into the cellular compartment. However, recent observations suggest that in addition to cholesterol, lipoproteins contain several other steroids in their lipoidal metabolite forms which may be transported in the very low, low and high density lipoproteins in human serum. Using the important androgen and oestrogen precursor, dehydroepiandrosterone (DHEA), the biosynthetic formation of lipoidal DHEA was demonstrated in human serum. Serum was also fractionated into its lipoprotein components during the course of its incubation with tritiated DHEA. A progressive movement of the label from the fraction containing the conventional steroid binding-proteins to the lipoproteins was observed with the fraction containing the low density lipoproteins demonstrating the greatest incorporation of the label. This displacement occurred simultaneous to an extensive esterification of the labelled DHEA in serum. After 6 h of incubation, approx. 90% of the radioactivity in all the lipoprotein fractions was in the lipoidal form. Very little labelled lipoidal DHEA was associated with the serum protein fraction throughout the duration of incubation. These data suggest that lipoproteins act as the carriers of lipoidal DHEA following its formation from the non-conjugate parent steroid in serum.     

Formation of lipoidal steroids in follicular fluid

The presence of high levels of lipoidal pregnenolone in follicular fluid has recently been established although no evidence has been presented concerning its possible origin. The following investigation focuses on the enzymatic conversion of non-conjugated steroids into their lipoidal derivatives in preovulatory follicular fluid obtained from women undergoing in vitro fertilization. Our observations indicated that pregnenolone, an important precursor steroid, was acylated at a similar rate as cholesterol in follicular fluid. Similar studies were subsequently conducted with serum obtained from a pool of normal women and women undergoing follicular stimulation which showed little difference to the results obtained in follicular fluid. Further studies using dehydroepiandrosterone, androst-5-ene-3 beta,17 beta-diol, estradiol and dihydrotestosterone were were also performed to monitor their respective lipoidal conversion percentages in follicular fluid which revealed a marked difference of conversion rates between steroids. The indirect identification of the lipoidal pregnenolone derivatives formed in follicular fluid was also conducted by incubating radiolabelled pregnenolone in follicular fluid. The fatty acid components of the resulting lipoidal pregnenolone derivatives showed a marked resemblance to those of cholesteryl esters formed in plasma by the enzymatic activity of lecithin:cholesterol acyltransferase. The pregnenolone derivatives were comprised predominantly of unsaturated fatty acids such as linoleate, palmitoleate, oleate, linolenate and arachidonate while saturated fatty acids, namely palmitate, constituted 20% of the total lipoidal pregnenolone.     

Catalysis of the oxidation of steroid and stilbene estrogens to estrogen quinone metabolites by the beta-naphthoflavone-inducible cytochrome P450 IA family.

Diethylstilbestrol (DES) or catecholestrogens are metabolized by microsomal enzymes to quinones, DES Q or catecholestrogen quinones, respectively, which have been shown to bind covalently to DNA and to undergo redox cycling. The isoforms of cytochrome P450 catalyzing this oxidation of estrogens to genotoxic intermediates were not known and have been identified in this study by (a) using microsomes of rats treated with various inducers of cytochrome P450; (b) using purified cytochrome P450 isoforms; and (c) examining the peroxide cofactor concentrations necessary for this oxidation by microsomes or pure isoenzymes. The highest rate of oxidation of DES to DES Q was obtained using beta-naphthoflavone-induced microsomes (14.0 nmol DES Q/mg protein/min) or cytochrome P450 IA1 (6.4 pmol DES Q/min/pmol P450). Isosafrole-induced microsomes or cytochrome P450 IA2 oxidized DES to quinone at one-third or one-fifth of that rate, respectively. Low or negligible rates of oxidation were measured when oxidations were catalyzed by microsomal rat liver enzymes induced by phenobarbital, ethanol, or pregnenolone-16 alpha-carbonitrile or by pure cytochromes P450 IIB1, IIB4, IIC3, IIC6, IIE1, IIE2, IIG1, or IIIA6. Cytochrome P450 IA1 also catalyzed the oxidation of 2- or 4-hydroxyestradiol to their corresponding quinones. The beta-naphthoflavone-induced microsomes and cytochrome P450 IA1 had the highest "affinity" for cumene hydroperoxide cofactor (Km = 77 microM). Cofactor concentrations above 250 microM resulted in decreased rates of oxidation. The other cytochrome P450 isoforms required much higher cofactor concentrations and were not inactivated at high cofactor concentrations. The data demonstrate that beta-naphthoflavone-inducible cytochrome P450 IA family enzymes catalyze most efficiently the oxidation of estrogenic hydroquinones to corresponding quinones. This oxidation may represent a detoxification pathway to keep organic hydroperoxides at minimal concentrations. The resulting quinone metabolites may be detoxified by other pathways. However, in cells with decreased detoxifying enzyme activities, quinones metabolites may accumulate and initiate carcinogenesis or cell death by covalent arylation of DNA or proteins.