Peptide analogues compete with the binding of alpha-factor to its receptor in Saccharomyces cerevisiae

alpha-Factor, a secreted tridecapeptide pheromone, is required for mating between the a- and alpha-haploid mating types of Saccharomyces cerevisiae. An analogue of alpha-factor, [DHP8,DHP11,Nle12] tridecapeptide (where DHP represents 3,4-dehydro-L-proline and Nle represents norleucine), was catalytically reduced in the presence of 3H gas to produce a radiolabeled pheromone with high specific activity, purity, and biological activity. Association and dissociation kinetics indicated values of 4.9 x 10(4) M-1 s-1 for k1 and 1.1 x 10(-3) s-1 for k-1. Saturation binding studies gave an equilibrium dissociation constant equal to 2.3 x 10(-8) M, which approximated the kinetically derived KD of 2.2 x 10(-8) M. These values compare favorably to the previously determined KD of 6 x 10(-9) M (Jenness, D.D., Burkholder, A.C., and Hartwell, L.H. (1986) Mol. Cell. Biol. 6, 318-320). Scatchard analysis and dissociation in the presence of excess unlabeled ligand indicated interaction with a homogeneous population of noninteracting binding sites (13,000 sites/cell). A number of alpha-factor analogues, previously investigated for their structure-function relationships (Naider, F., and Becker, J.M. (1986) CRC Crit. Rev. Biochem. 21, 225-249), were used to compete with [3H]alpha-factor binding. Four tridecapeptides having conservative amino acid replacements bound strongly to the receptor. In contrast, [Phe3]alpha-factor and 10 des-Trp1-alpha-factor analogues bound to the receptor 1-3 orders of magnitude less effectively than did alpha-factor itself. The binding constants for all active pheromones correlated with biological activity. However, des-Trp1[Phe3]alpha-factor and des-Trp1-[Ala3]alpha-factor, which were not biologically active, still competed with alpha-factor binding, indicating that these analogues fail to induce a secondary signal necessary for biological response to the pheromone. One analogue, des-Trp1-[Cha3,L-Ala9]alpha-factor (where Cha represents cyclohexylalanine), was not biologically active and did not demonstrate binding to the receptor, whereas des-Trp1-[Cha3,D-Ala9]alpha-factor was active and bound to the receptor. This finding suggests that a type II beta-turn is necessary for binding of alpha-factor to its receptor and for subsequent biological activity.     

Pertussis toxin as a probe of neutrophil activation

In reviewing our own and other work, it is clear that pertussis toxin treatment of neutrophils causes a time- and concentration-dependent inhibition of granule enzyme secretion induced by formylmethionylleucylphenylalanine (fMet-Leu-Phe), C5a, leukotriene (LT) B4 and platelet-activating factor (PAF). Chemotaxis, O2- generation, aggregation, and arachidonic acid production induced by fMet-Leu-Phe are also inhibited by pertussis toxin. Granule enzyme release caused by A23187 or phorbol 12-myristate 13-acetate is not inhibited. The inhibition of neutrophil function correlates closely with the NAD-ribosylation of a 41,000-dalton protein in the neutrophil plasma membrane, presumably the GTP-binding regulatory protein Ni. Pertussis toxin treatment prevents or obtunds the increased influx of Ca2+ induced by fMet-Leu-phe and LTB4, but not that caused by stimulation of neutrophils with PAF. Pertussis toxin prevents the receptor-induced breakdown of polyphosphoinositides in intact neutrophils and isolated membrane and prevents or decreases the production of inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. The hypothesis advanced by us and others is that pertussis toxin interacts with a GTP-binding regulatory protein identical or similar to Ni, which couples receptor-chemotactic factor interaction to phospholipase C activation. Inhibition of the activation prevents the production of IP3 and the resulting release of Ca2+ from intracellular stores and of 1,2-diacylglycerol and thus, the activation of protein kinase C. The lack of these two mediators is the immediate cause of the depression of neutrophil activation resulting from pertussis toxin. Some of the limitations and uncertainties of our present knowledge with respect to this hypothesis are discussed.     

Bizarre atypia in gastric brushings associated with hepatic arterial infusion chemotherapy

Hepatic arterial infusion chemotherapy (HAIC) for unresectable hepatic neoplasms has been associated with gastric ulcers and epithelial atypia that may be misinterpreted as carcinoma. Gastric brushings were reviewed from six patients who developed gastric ulcers with histologically proven atypia following HAIC. Marked cytologic atypia, reminiscent of a pronounced radiation effect, was present in gastric epithelial cells in five patients. The atypical cells occurred singly or in small sheets. They were markedly enlarged but a low nuclear-cytoplasmic ratio was preserved. The abundant cytoplasm was vacuolated or foamy. Binucleation and multinucleation were common, and massive nucleoli were characteristic. The brushings also contained the reparative, inflammatory and necrotic changes associated with usual benign gastric ulcers. The bizarre atypia associated with HAIC can be a source of misdiagnosis of cancer in cytologic as well as in histologic specimens.     

Structural aspects and orientation mechanism of mitochondrial F1 adenosinetriphosphatase. Evidence for a negative electric birefringence due to a permanent moment perpendicular to the long axes of the particle

The electric birefringence technique was used to investigate the steady-state birefringence, the orientational relaxation time, and the orientation mechanism of pig heart mitochondrial F1 adenosine-5'-triphosphatase (F1-ATPase). The electrooptical properties of this enzyme in solution were studied as functions of pH, protein concentration, and applied electric field. The F1-ATPase exhibits a surprising negative electric birefringence with a specific Kerr constant of -1.5 X 10(-3) esu cgs. The field-independent relaxation time was found to be 0.65 +/- 0.05 microseconds, corresponding to a rotational diffusion constant of 2.55 X 10(5) s-1. The overall size and shape of F1-ATPase have been calculated from both translational and rotational diffusion constants. The enzyme may be assumed to be an oblate ellipsoid of revolution with dimensions of about 170 X 170 X 70 A. The orientation mechanism of F1-ATPase was analyzed by fitting experimental birefringence rising curves with theoretical rising functions. The ratio of the permanent to induced dipole moment is found to be very high; therefore, the birefringence of F1-ATPase is due to a strong permanent dipole moment in a direction perpendicular to the long axes of the particle. These particular electric properties can be explained by the oligomeric structure of the protein and seem likely to play a role in its mechanism of functioning.     

Is a rise in intracellular concentration of free calcium necessary or sufficient for stimulated cytoskeletal-associated actin?

The addition of the calcium ionophore A23187 to rabbit neutrophils increases the amount of actin associated with the cytoskeleton regardless of the presence or absence of calcium in the incubation medium. In the presence of extracellular calcium, the effect of A23187 is biphasic with respect to concentration. The action of the ionophore is rapid, transient, and is inhibited by pertussis toxin, hyperosmolarity, and quinacrine. On the other hand, the addition of pertussis toxin or hyperosmolarity has small if any, effect on the rise in intracellular calcium produced by A23187. While quinacrine does not affect the fMet-Leu-Phe-induced increase in cytoskeletal actin and the polyphosphoinositide turnover, its addition inhibits completely the stimulated increase in Ca-influx produced by the same stimulus. The results presented here suggest that a rise in the intracellular concentration of free calcium is neither necessary nor sufficient for the stimulated increase in cytoskeletal-associated actin. A possible relationship between the lipid remodeling stimulated by chemoattractants and the increased cytoskeletal actin is discussed.     

Biological activity and conformational isomerism in position 9 analogues of the des-1-tryptophan,3-beta-cyclohexylalanine-alpha-factor from Saccharomyces cerevisiae

Analogues of the des-1-tryptophan,3-beta-cyclohexylalanine-alpha-factor of Saccharomyces cerevisiae, where the glycyl residue of position 9 was replaced by D-Ala, L-Ala, D-Leu, and L-Leu, were synthesized and evaluated by morphogenesis assays and circular dichroism spectroscopy. Synthesis was accomplished in solution phase with mixed anhydrides and p-nitrophenyl active esters as the coupling agents. All crude dodecapeptides were purified to greater than 98% homogeneity by preparative high-performance liquid chromatography on a reversed-phase column. The Gly9, D-Ala9, and D-Leu9 analogues elicited morphogenic alterations in MATa strains of S. cerevisiae at concentrations of 1-2 micrograms/mL and exhibited similar CD patterns in both trifluoroethanol and tris(hydroxymethyl)aminomethane buffer, pH 7.4. In contrast, the L-Ala9 and L-Leu9 analogues were more than 200 times less active in the morphogenesis assay and had markedly different CD spectra. These results demonstrate that the position 9 residue plays an important role in determining the biological activity and solution conformation of alpha-factor. We suggest the presence of a type II beta-turn in the Lys7-Gln10 region when the alpha-factor assumes its biologically active conformation.     

The hepatic response to Ca2+ is inhibited by Mg2+ and enhanced by phenylephrine or ouabain

Net hepatic Ca2+ efflux, K+ uptake and glycogen breakdown in response to the alpha 1-adrenergic agonist phenylephrine were studied. Rat livers were perfused with CO2/bicarbonate-buffered solutions containing 10 microM Ca2+ and different amounts of Mg2+. K+-free medium and/or ouabain were used to block (Na+ + K+)-ATPase-dependent K+ uptake. In some experiments a sharp increase in extracellular Ca2+ concentrations was produced by infusing CaCl2 into the medium entering the liver. Perfusion with K+-free medium and ouabain enhanced the phenylephrine-induced Ca2+ efflux and diminished the glycogenolytic response, indicating a dissociation of Ca2+ release and glycogenolysis. Exogenous Ca2+ had practically no effect if livers were perfused with regular medium containing 1.2 mM Mg2+. In the presence of phenylephrine and if extracellular Mg2+ concentrations were lowered by omitting Mg2+ from the medium or by preperfusion with EGTA, exogenous Ca2+ was glycogenolytically effective and also produced a transient K+ uptake. Increased extracellular concentrations of Mg2+ inhibited the effects of exogenous Ca2+. In the presence of phenylephrine, higher concentrations of Mg2+ were needed than in the absence of alpha 1-adrenergic agonist to achieve a similar degree of inhibition. In one respect ouabain effects were comparable to those of phenylephrine: the glycoside also increased the metabolic response to exogenous Ca2+ and diminished the sensitivity towards Mg2+. Phenylephrine and ouabain may both enhance the permeability of plasma membranes for Ca2+.     

A variant form of the 1,25-dihydroxyvitamin D3 receptor with low apparent hormone affinity in cultured monkey kidney cells (LLC-MK2). A model for tissue resistance to vitamin D

Chandler et al. (Chandler, J.S., Chandler, S.K., Pike, J.W., and Haussler, M.R. (1984) J. Biol. Chem. 259, 2214-2222) previously demonstrated that 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) caused the induction of 25-hydroxyvitamin D3-24-hydroxylase (24-hydroxylase) in a rhesus monkey kidney cell line (LLC-MK2) apparently deficient in the high affinity 1,25-(OH)2D3 receptor. We have re-examined this phenomenon and report here that 24-hydroxylase induction is mediated by a receptor variant in LLC-MK2 cells with low hormone affinity. Dose response analysis showed that in contrast to LLC-PK1 (a typical receptor-positive cell line), the LLC-MK2 line was less sensitive to 1,25-(OH)2D3 by 2 orders of magnitude. Employing optimal concentrations of 1,25-(OH)2D3 for 24-hydroxylase induction in each cell type, the early time courses of this bioresponse were identical in LLC-MK2 and LLC-PK1 and were consistent with a nuclear action of hormone-receptor complexes. Moreover, the rank order of potency of vitamin D3 congeners as inducers of 24-hydroxylase activity in LLC-MK2 cells agreed well with their relative affinity for the 1,25-(OH)2D3 receptor. An examination of 1,25-(OH)2D3 receptor content via DNA-cellulose chromatography in LLC-MK2 cells incubated at ligand concentrations 10-25-fold higher than the normal 2 nM revealed a minimum of 1600 receptor-like molecules/LLC-MK2 cell. These results show that LLC-MK2 cells possess a variant receptor form with apparent low affinity for 1,25-(OH)2D3. This system should serve as a model for clinical syndromes characterized by the requirement for massive doses of vitamin D to prevent rickets.