Involvement of potassium ions in the action of various antineoplastic drugs on the growth of Saccharomyces cerevisiae

The involvement of potassium ions in the action of some antineoplastic drugs on the growth of Saccharomyces cerevisiae was studied by incubating yeast cells in the presence of drugs at various concentrations and KC1 at concentrations of 50 mmol 1^-1 and 100 mmol 1^-1. The presence of 6.25–50 μg m1^-1 amsacrine or melphalan alone in the culture medium had no significant effect on yeast growth. Addition of KC1 significantly increased the sensitivity to these drugs. On the contrary, incubation of yeast cells with KC1 had no effect on the cytotoxic action of doxorubicin, methotrexate or 5-fluorouracil.     

Stimulation of purified DNA polymerase alpha by various basic proteins which interact with activated DNA

Extensive purification of DNA polymerase alpha-primase resulted in a marked loss of the DNA polymerase alpha activity. This loss is due partly to the elimination of some basic proteins from the enzyme preparation since the activity of purified enzyme was stimulated 10- to 15-fold by the addition of various basic proteins, including all five classes of histones, protamine, poly-L-lysine, and poly-L-arginine, at a concentration of 2 micrograms/0.2 ml in the presence of 20 micrograms/0.2 ml of activated DNA. The optimum concentration of the basic proteins and the maximum activity attained at that concentration varied with varying concentrations of the template primer used, indicating that the observed stimulation is caused by an interaction between these basic proteins and activated DNA. The enzyme activity with an optimal concentration of activated DNA was markedly inhibited by the addition of denatured DNA. The suppressed enzyme activity could be restored by an appropriate concentration of histone H1. These results suggest that histone H1 and other basic proteins protect the enzyme from forming an abortive complex with single-stranded DNA or with a long stretch of the single-stranded part of activated DNA as single-stranded DNA-specific binding proteins do (M. Sapp, H. K?nig, H. D. Riedel, A. Richter, and R. Knippers (1985) J. Biol. Chem. 260, 1550-1556). Spermine also showed a similar stimulatory effect. All acidic proteins tested were ineffective.     

Effect of various lysosomotropic agents and microtubule disrupting drugs on the lactogenic and the mammogenic action of prolactin

Various drugs added to the culture medium of rabbit mammary gland were assayed for their capacity to affect the lactogenic and the mammogenic activities of prolactin. Three lysosomotropic agents NH4Cl, chloroquine and methylamine which were previously demonstrated to inhibit the degradation of the hormone-receptor complex after its internalization (down-regulation) did not prevent the initiation of casein synthesis, of lactose synthetase activity and of DNA synthesis. Five microtubule disrupting drugs, colchicine, colcemid, vinblastin, podophyllotoxin and nocodazole inhibited the induction of casein and DNA synthesis by prolactin whereas two inactive analogues, trimethylcolchicinic acid and lumicolchicine had no effect. None of these drugs exhibited any general cytotoxic effect as judged by the capacity of the tissue to incorporate 14C aminoacids into total proteins and 3H-uridine into total RNA. The microtubule disrupting drugs did not greatly reduce the rate of casein synthesis in the cultured mammary tissue explanted from lactating rabbits. The data suggest that the down-regulation of prolactin receptor is not strictly required for the two considered prolactin activities. By contrast, the integrity of microtubules, or at least of structures in which tubulin is involved, is necessary to ensure a normal transmission of the prolactin information responsible for the initiation of milk and DNA synthesis. In addition, the fact that the lactogenic and the mammogenic activities of prolactin are affected by the same drugs suggests that these two properties of the hormone are mediated by cellular mechanisms which have at least one common step.     

Hemostasis in larvae of Manduca sexta: formation of a fibrous coagulum by hemolymph proteins

Little is known of the participation of insect hemolymph proteins in wound healing and clot formation. We describe the assembly of purified hemolymph protein from the tobacco hornworm into an extended fibrous coagulum in the absence of hemocytes. This coagulum resembles the clot formed from bovine fibrinogen and thrombin. Structural components of the coagulum are present in hemolymph, however, spontaneous assembly occurs only in hemolymph collected through a wound. The fibrous coagulum assembles from purified structural protein(s) following addition of a non-protein factor from hemolymph, which is also present in Grace's insect cell culture medium.     

Peptides released by physiological cleavage of semen coagulum proteins form amyloids that enhance HIV infection

Semen serves as a vehicle for HIV and promotes sexual transmission of the virus, which accounts for the majority of new HIV cases. The major component of semen is the coagulum, a viscous structure composed predominantly of spermatozoa and semenogelin proteins. Due to the activity of the semen protease PSA, the coagulum is liquefied and semenogelins are cleaved into smaller fragments. Here, we report that a subset of these semenogelin fragments form amyloid fibrils that greatly enhance HIV infection. Like SEVI, another amyloid fibril previously identified in semen, the semenogelin fibrils exhibit a cationic surface and enhance HIV virion attachment and entry. Whereas semen samples from healthy individuals greatly enhance HIV infection, semenogelin-deficient semen samples from patients with ejaculatory duct obstruction are completely deficient in enhancing activity. Semen thus harbors distinct amyloidogenic peptides derived from different precursor proteins that commonly enhance HIV infection and likely contribute to HIV transmission.     

Effect of various antimicrotubular drugs on the osmotic water flow through the wall of frog's urinary bladder]

The action of antimicrotubular drugs (colchicine, vinblastine and copper) on the osmotic water flow through the wall of the urinary bladder of Rana temporaria has been studied. The osmotic gradient was made by five- or tenfold dilution of the internal Ringer solution. The water flow was estimated gravimetrically. The water flow was induced by pituitrin (50 milliunits/ml), cyclic AMP (cAMP, 0.5-10(-3) M) and nystatine (3.5-10(-5) M). Pituitrin and cAMP and all the antimicrotubular drugs were added from the serosal surface of the bladder. Nystatine was introduced with the help of a fixed polyethylene tube. Preincubation with colchicine lasted 4 hours and that with vinblastine and copper (CuSO4), 1 hour. The drug concentrations varied between 10(-5)--10(-4) M. All the drugs studied showed a significant inhibitory effect toward pituitrin. The action of cAMP on the water flow was seen inhibited in the presence of colchicine and copper. The nystatine induced water flow was supressed by copper, colchicine being in this case inactive. A conclusion is drawn that the inhibition of cAMP formation does not cause a decreased pituitrine effect in the presence of antimicrotubular drugs. It has been assumed that the microtubules may be involved in the directed water flow within the cell.