Cold-stable microtubules from Antarctic fishes contain unique alpha tubulins

The cytoplasmic microtubules of Antarctic fishes assemble from their tubulin subunits at physiological body temperatures in the range -2 to +2 degrees C. Our objective is to determine the structural features that enhance the assembly of Antarctic fish tubulins at low temperatures. Here we compare the structures of tubulin subunits from three Antarctic fishes (Notothenia gibberifrons, Notothenia coriiceps neglecta, and Chaenocephalus aceratus), from three temperate fishes (the dogfish shark Mustelus canis, the channel catfish Ictalurus punctatus, and the goosefish Lophius americanus), and from a mammal (the cow Bos taurus). When reduced, carboxymethylated, and examined by polyacrylamide gel electrophoresis, multiple alpha chains were observed in tubulins from the Antarctic fishes, the catfish, and the goosefish; dogfish and bovine alpha tubulins migrated as single components on this gel system. Prominent in the Antarctic fish tubulins was an alpha variant that migrated more rapidly than the bovine alpha chain; smaller amounts of a rapidly migrating alpha chain were also present in catfish and goosefish tubulins. The beta tubulins of the fishes, with the exception of the goosefish, resolved into major and minor variants with mobilities similar to those of beta 1 and beta 2 tubulins from bovine brain. Peptide mapping demonstrated that the alpha tubulins of Antarctic fishes were similar in structure, yet differed from the alpha chains of the dogfish and the cow (which, in turn, were similar to each other). In contrast, the beta tubulins from these organisms gave peptide patterns of near identity. Finally, the alpha chains of native tubulins from N. coriiceps neglecta and the cow differed in the sensitivity of their C-terminal domains to digestion by subtilisin. These results demonstrate that the alpha tubulins of Antarctic fishes (but not their beta chains) differ structurally from those of temperate fishes and a mammal.

Splice acceptor site for the env message of Moloney murine leukemia virus

We report the isolation and sequence of a cDNA clone containing part of the env message of the Moloney murine leukemia virus (MoMuLV). This clone was derived from a rat thymic lymphoma induced by MoMuLV. The AG acceptor site employed in this message is located at position 5490 in the MoMuLV genome. This splice site is detectable at the cDNA level by the creation of a novel SacI restriction site not present in the viral genome. In the -1 to -40 region, this AG acceptor site is preceded by four conserved heptanucleotides (PyXPyTPuAPy) that may function as acceptors for removal of the 5' end of the intron.

Effects of ATP and cyclic AMP on the in vitro assembly and stability of mammalian brain microtubules

The relevance of protein phosphorylation, transphosphorylation and binding phenomena in the kinetics of the ATP-induced assembly of cycle-purified microtubule protein from mammalian brain were studied. ATP was able to induce the polymerization of microtubules of normal appearance. However, the assembled structures, were unstable and microtubules depolymerized after achievement of a transitory maximum. Cyclic AMP reduced the amplitude of the polymerization maximum in a concentration-dependent manner, correlating with the stimulation of the endogenous phosphorylation reaction. When microtubule assembly was induced by GTP, in the presence of various concentrations of ATP, the slope of the depolymerization phase was found to depend on the concentration of ATP. Fluoride ion inhibited the endogenous phosphorylation reaction and reduced the disassembly rate, in a concentration-dependent manner. Evidence is also presented indicating that ATP did not bind to phosphocellulose-purified tubulin. These results further contribute to indicate that ATP and cyclic AMP, acting coordinately to control the phosphorylation extent of microtubule proteins are important factors to determine microtubule stability within the cell. Some implications of this mechanism for the regulation by cAMP of the initiation of DNA synthesis and mitosis are considered.

Mechanism of endogenous phosphorylation of microtubule proteins during GTP-induced microtubule assembly and implications for stability of the assembled structures

Cycle-purified microtubule protein from mammalian brain incorporated [32P]Pi upon incubation with [gamma-32P]GTP under the conditions used to promote assembly. This phosphorylation also occurred in the same proteins when phosphorylated with [gamma-32P]ATP and was only slightly stimulated by cAMP. GTP was a much less effective substrate than ATP. The transfer of phosphoryl groups from [gamma-32P]GTP to endogenous proteins followed a linear time-course and was stimulated by low concentrations of ATP and, more efficiently, by ADP. These data are in agreement with the predictions derived from a mechanism of phosphorylation by which [gamma-32P]GTP does not act as a phosphoryl donor for the protein kinase activity but, instead, only as a repository of high group transfer potential phosphoryl groups used to make [gamma-32P]ATP, from contaminating ADP, by means of the nucleoside diphosphate kinase activity. Using 100 mM fluoride, which suppressed protein phosphorylation without inhibiting the nucleoside diphosphate kinase activity, formation of [gamma-32P]ATP was detected. Fluoride was also able to protect microtubules from a slow depolymerization which was found to occur during long-term incubation of microtubules. This indicates that the phosphorylation observed in the presence of GTP is sufficient to destabilize microtubules.

Tau microheterogeneity: an immunological approach with monoclonal antibodies

The family of tau polypeptides purified from mammalian brain exhibit both extensive heterogeneity and large similarities in their chemical, physical, and functional properties. All the tau isoforms generated at a transcriptional or posttranscriptional level share the property of interacting with tubulin dimers in a specific manner. They strengthen longitudinal interactions between tubulin dimers and thus may stabilize microtubules once they are formed. Mild proteolysis or phosphorylation does not remove but only modulates the tau specific function that is probably related to the conserved sequences of the molecules. Monoclonal antibodies raised against tau were found to recognize epitopes conserved not only between species but also in different tissues. Using indirect immunofluorescence, a specific staining pattern was observed on rat neuronal cells and also on human skin fibroblasts. The same antibodies did not recognize glial cells, suggesting that these cells either do not contain detectable levels of tau or contain tau molecules different from the neuronal ones. These data suggest that tau protein is widely distributed, highly conserved, and may be preferentially associated with special subclasses of microtubules.

Effects of Tau and MAP2 on the interaction of maytansine with tubulin: inhibitory effect of maytansine on vinblastine-induced aggregation of tubulin

Maytansine, a potent inhibitor of mitosis and in vitro microtubule assembly, was used to demonstrate a striking difference in the mechanism by which two of the main groups of brain microtubule-associated proteins, Tau and MAP2, interact with tubulin. At the low concentrations of 0.5 to 2 microM, maytansine inhibited Tau-catalyzed tubulin assembly more effectively than it did MAP2-catalyzed assembly. This effect differed markedly from that of vinblastine, although both drugs bind competitively to tubulin. At the same low concentrations, vinblastine almost completely inhibited Tau- and MAP2-mediated tubulin assembly. At higher concentrations of 10 to 40 microM, a more striking difference was observed between the actions of the two drugs. Maytansine very effectively inhibited tubulin assembly promoted by either Tau or MAP2. Vinblastine also had this effect on MAP2-mediated tubulin assembly but in the presence of Tau induced extensive tubulin aggregation into spirals. In addition maytansine strongly inhibited vinblastine-induced Tau-dependent tubulin aggregation into spiral polymers. Even at very low concentrations, maytansine completely inhibited the effect of very high concentrations of vinblastine. These results very strongly suggest that the binding sites of maytansine and vinblastine on the tubulin molecule overlap and that the changes that they probably induce in the conformation of this molecule are markedly different, at least in the presence of microtubule-associated proteins.

Bis(1,8-anilinonaphthalenesulfonate). A novel and potent inhibitor of microtubule assembly

Two related compounds, 1,8-anilinonaphthalenesulfonate (1,8-ANS) and bis(1,8-anilinonaphthalenesulfonate) (Bis-ANS), are useful fluorescent probes for hydrophobic areas on protein molecules. Using fluorescence, we examined the binding of these compounds to bovine brain tubulin and found that Bis-ANS and 1,8-ANS bound to tubulin with Ki values of 2 and 25 microM, respectively. Bis-ANS potently inhibited the polymerization of tubulin into microtubules in vitro. In the presence of microtubule-associated protein 2, half-maximal inhibition of assembly was obtained at 3 microM Bis-ANS. In the presence of tau protein, half-maximal inhibition was obtained at 15 microM Bis-ANS. Surprisingly, 1,8-ANS, even at 200 microM, did not inhibit assembly. Scatchard analysis indicated one binding site for Bis-ANS on tubulin. Previous reports of 1,8-ANS binding to tubulin may have been influenced by the presence of Bis-ANS which until recently was a common contaminant of commercial supplies. Because of its intense fluorescence in addition to its potent inhibitory effects, Bis-ANS appears to be a useful probe to study microtubule assembly and other interactions involving tubulin.

Propranolol-induced psychosis

A 53-year-old black male with no history of neuropsychiatric behavioral problems was treated successfully with propranolol, furosemide, and minoxidil for previously uncontrolled hypertension. However, paranoid ideations, illusions, severe combativeness, and visual hallucinations developed shortly after initiation of the listed therapy. When atenolol was substituted for propranolol, all psychotic behavior resolved.

Synergistic effect of propranolol and quipazine on desipramine enhanced shock-elicited fighting in rats

Changes in shock-elicited fighting (SEF) were measured following single or repeated injections (IP) of dl-propranolol (5 mg/kg, 20 mg/kg) or quipazine (1.25 mg/kg, 2.5 mg/kg) given either alone or in combination to saline or desipramine (DMI) (10 mg/kg) treated rats. DMI + propranolol (20 mg/kg) caused a greater increase in fighting than DMI + saline 18 hours after last dose. Propranolol (20 mg/kg) produced an equal inhibition in both of these groups at 15 min. Propranolol (5 mg/kg) had no effect. Quipazine (2.5 mg/kg) failed to alter DMI induced increase in SEF. The combination of propranolol (5 mg/kg) + quipazine (1.25 mg/kg) blocked the enhanced SEF significantly in DMI treated rats in comparison to DMI + saline treated group. This combination of propranolol + quipazine produced no significant change in SEF in saline treated group in comparison to the pretest level. These results suggested that propranolol + quipazine act synergistically at low doses to inhibit the increased SEF seen in DMI treated rats and might have therapeutic implications for the management of irritable aggression or mania.

Competitive ability, effectiveness, and succinate – triphenyl tetrazolium chloride reductase activity of mutant strains of chick-pea (Cicer arietinum L.) Rhizobium sp

Chick-pea Rhizobium strain RG 4 was treated with 200 μg/mL of N-methyl-N-nitro-N′-nitrosoguanidine and 14 mutant strains isolated. Two mutant strains were found to be nonnodulating in the absence of certain amino acids. On the basis of nodulation, two mutant strains (M 38 and M 46) were found to be equally competitive against each other. Mutant strains M 38 and M 46 when applied together produced the maximum nodulation, nitrogenase activity, phenanthroline-reactive iron, and least tetrazolium reductase activity as compared to other pairwise combinations of mutant strains. It was also observed that the correlation between tetrazolium reductase and nitrogenase activity was highly negative.

beta 2-Tubulin, a form of chordate brain tubulin with lesser reactivity toward an assembly-inhibiting sulfhydryl-directed cross-linking reagent

Beta 1 and beta 2 are the designations given to two forms of beta-tubulin that have different electrophoretic mobilities on discontinuous polyacrylamide gels in the presence of sodium dodecyl sulfate [Little, M. (1979) FEBS Lett. 108, 283-286]. Beta 1 and beta 2 constitute respectively 75% and 25% of the total beta-tubulin in bovine brain. Although beta 1 appears to be ubiquitous in animals, beta 2 has so far only been found in the brains of cows, pigs, deer, rats, chicks, and dogfish but not in squid brain. Beta 2 is not found in bovine kidneys, in porcine lungs, or in any nonchordate tubulin that has been examined. When tubulin is reacted with the sulfhydryl-directed reagent N,-N'-ethylenebis(iodoacetamide) (EBI), beta 1, but not beta 2, is converted to a faster moving form, beta. The yield of beta 2 in this reaction is not altered by the presence of drugs. When [14C]EBI is used as a probe, most of the label is incorporated into beta 1 rather than beta 2. Tubulin molecules that have reacted with EBI to form beta are much less likely to polymerize into microtubules than are molecules that have not formed beta. In view of the observation that only beta 1, and not beta 2, can form beta, it is possible that beta 1 represents a form of tubulin whose assembly may be regulated by a mechanism involving sulfhydryls. In contrast, beta 2 may represent a form of tubulin whose assembly is regulated by some other mechanism.

Effect of lithium upon desipramine enhanced shock-elicited fighting in rats

Rats were tested for changes in shock-elicited fighting (SEF) following the chronic administration of saline (IP); lithium (Li+) (20 mEq./l tap water) + saline (IP); desipramine (DMI) (15 mg/kg, IP); and DMI + Li+ for 14 days. The repeated test trials indicated a significant decrease in SEF in Li+-saline group (p less than 0.05), a significant increase (p less than p.05) in the DMI group, but no difference in the DMI + Li+ group in comparison to saline controls. Combined treatment with DMI + Li+ significantly reduced (p less than 0.05) SEF in comprison to the DMI group. These results suggest that enhanced aggressivity resulting from chronic DMI administration and measured by SEF can be a useful behavioral model to study the action of lithium.

The effect of cyproterone acetate on shock elicited aggression in rats

The aggressive behavior of male rats treated chronically with cyproterone acetate was measured following electric footshock. Shock elicited fighting behavior and body weight was recorded once every week for 4 weeks. The level of plasma testosterone, brain 5-HT and 5-HIAA and weight of testes were measured 24 hours after the last injection. No significant change was observed in the level of testosterone or brain 5-HT and 5-HIAA. A trend towards an increase in plasma testosterone and shock elicited fighting in rats treated with a higher dose of CA (10 mg/kg) may be indicative of some androgenic property of CA. On the other hand a slower gain in the body weight and a significant reduction in the testes weight of CA treated rats corroborate the well known antiandrogen property of this steroid. The balance of these androgenic and antiandrogenic properties of CA may account for the absence of significant changes in behavioral and biochemical measures.