Surface Phosphorylation by Ecto-Protein Kinase C in Brain Neurons: A Target for Alzheimer's β-Amyloid Peptides

Abstract: The powerful regulatory machinery of protein phosphorylation operates in the extracellular environment of the brain. Enzymatic activity with the catalytic specificity of protein kinase C (PKC) was detected on the surface of brain neurons, where it can serve as a direct target for neurotrophic and neurotoxic substances that control neuronal development and cause neurodegeneration. This activity fulfilled all the criteria required of an ectoprotein kinase (ecto-PK). Detailed analysis of surface protein phosphorylation in cultured brain neurons using specific exogenous substrates (casein, histones, and myelin basic protein), inhibitors (PKC-pseudosubstrate 19–36; K252b) and antibodies (anti-PKC catalytic region M.Ab.1.9, antibodies to the carboxy-terminus of eight PKC isozymes) revealed several types of ecto-PK activity, among them ecto-PKs with catalytic specificity of the PKC isozymes ζ and δ. The activity of the neuronal ecto-PKC is constitutive and not stimulated by phorbol esters. The phosphorylation of a 12K/13K surface protein duplex by ecto-PKC-δ was found to be developmentally regulated, with peak activity occurring during the onset of neuritogenesis. Alzheimer's amyloid peptides β1–40 and β25–35 applied at neurotrophic concentrations stimulated the phosphorylation of endogenous substrates of ecto-PKC activity in brain neurons but inhibited specifically this surface phosphorylation activity with the same dose-response relationships that cause neurodegeneration. As may be expected from a relevant pathophysiological activity, β-amyloid peptide 1–28 did not inhibit this surface phosphorylation. The discovery that ecto-PKC-mediated protein phosphorylation serves as a target for β-amyloid peptides at the very site they operate, i.e., at the neuronal cell surface, opens a new research direction in the investigation of molecular events that play a role in the etiology of developmental disabilities and neurodegenerative disorders.     

Characterization ofH-2 congenic strains using DNA markers

Congenic mouse strains are widely used in mapping traits to specific loci or short chromosomal regions. The precision of the mapping depends on the information available about the length of the differential segment—the segment introduced from the donor into the background strain. Until recently, very few markers flanking the differential locus were known and consequently the length of the foreign segment could only be determined imprecisely. Now, in an attempt to construct a map of the mouse chromosome 17, we have produced a set of DNA markers distributed along the chromosome. These markers provide a new opportunity to measure the length of the differential segment of the congenic strains and thus increase their usefulness for gene mapping. Here we examined the DNA of 96H-2 congenic strains using 30 DNA markers; of these, the most proximal is located roughly 1.5 centiMorgans (cM) from the centromere and the most distal is about 20 cM telomeric from theH-2 complex (the complex itself being some 20 cM from the centromere). The mapping depends on polymorphism among the input strains and can therefore establish only the minimal length of the differential segment. This point is emphasized by the fact that the average observed length of the differential segment is only about one half of the expected values. Offprint requests to: V. Vincek.     

Response of net photosynthesis in bean (Phaseolus vulgaris) leaves to the elevation of the partial pressures of oxygen and carbon dioxide

Bean ( Phaseolus vulgaris L. cv. Golden Saxa) plants were grown under low artificial light or under natural daylight. The rate of net photosynthesis (P_N) was measured at: CO₂ partial pressure, p(CO₂), of 0.03, 0.09 or 0.15 kPa; O₂ partial pressure, p(O₂), of 2, 21 or 31 kPa and at light intensities of 350 or 1000 μmol m⁻² s⁻¹ (photosynthetically active radiation). In plants which had been grown under natural light, stimulation of P_N at 21 kPa p(O₂) was found only at elevated p(CO₂) and high light. It is proposed that this phenomenon is dependent on a high capacity of the photosynthetic apparatus to regenerate ribulose 1.5-bisphosphate.     

Comparison of temperature effects on the in vitro growth and disease development in potato tubers inoculated with bacteria Pectobacterium atrosepticum,P carotovorum subsp. carotovorum and Dickeya solani

The relationship between the rate of in vitro growth of bacterial isolates of Pectobacterium atrosepticum, P. carotovorum subsp. carotovorum and Dickeya solani and their pathogenicity was investigated in tubers of two potato cultivars at four temperatures ranging from 18°C to 30°C. The rate of in vitro growth was highly positively correlated with the number of rotted tubers (r ranged from 0.91 to 0.93) and with the weight of macerated potato tissue, which, however, was only found for P. carotovorum and D. solani (r = 0.76; r = 0.91, respectively) and not for P. atrosepticum. The weight of macerated tissue increased with the temperature, but significant differences between species of bacteria were observed only at 26°C and above, at which temperatures D. solani was the most aggressive, followed by P. carotovorum and P. atrosepticum. Almost all potato tubers inoculated with bacteria showed symptoms of soft rot at 26°C and 30°C, but the number of rotting tubers at lower temperatures (22°C and 18°C) decreased significantly. The lowest disease incidence, 11% of tubers with symptoms, was observed for the D. solani and cultivar Sonda at 18°C, what was also confirmed in a separate experiment with tubers from four potato cultivars inoculated with the highly aggressive isolate of D. solani. At temperatures from 18°C to 30°C, the differences in disease severity between potato cultivars with various resistance to bacteria increased in line with temperature, while the differences in disease incidence decreased.     

Molecular polymorphism and phenotypic variation in Aspergillus carbonarius

Thirteen collection strains and field isolates of Aspergillus carbonarius were examined by using various genotypic and phenotypic approaches. Restriction fragment length polymorphism analysis of the ribosomal RNA gene cluster and the mitochondrial DNA of the strains revealed only slight variations, except for one field isolate (IN7), which exhibited completely different ribosomal RNA gene cluster and mitochondrial DNA patterns. The mitochondrial DNAs of these strains were found to be much larger (45 to 57 kb) than those found earlier in the A. niger aggregate. Strain-specific characters could be detected by the random amplified polymorphic DNA technique. Isoenzyme analysis and examination of carbon source utilisation patterns of the strains also revealed some intraspecific variability, though much smaller than that observed by using DNA-based techniques. The dendrograms constructed based on genotypic and phenotypic data suggest that strain IN7 might represent a new subspecies of A. carbonarius.Abbreviations kb kilobase pair - mtDNA mitochondrial DNA - RAPD random amplified polymorphic DNA - rDNA ribosomal RNA gene cluster - RFLP restriction fragment length polymorphisms     

Differences in Gene-Gene Interactions in Graves’ Disease Patients Stratified by Age of Onset

Background

Graves’ disease (GD) is a complex disease in which genetic predisposition is modified by environmental factors. Each gene exerts limited effects on the development of autoimmune disease (OR = 1.2–1.5). An epidemiological study revealed that nearly 70% of the risk of developing inherited autoimmunological thyroid diseases (AITD) is the result of gene interactions. In the present study, we analyzed the effects of the interactions of multiple loci on the genetic predisposition to GD. The aim of our analyses was to identify pairs of genes that exhibit a multiplicative interaction effect.

Material and Methods

A total of 709 patients with GD were included in the study. The patients were stratified into more homogeneous groups depending on the age at time of GD onset: younger patients less than 30 years of age and older patients greater than 30 years of age. Association analyses were performed for genes that influence the development of GD: HLADRB1, PTPN22, CTLA4 and TSHR. The interactions among polymorphisms were analyzed using the multiple logistic regression and multifactor dimensionality reduction (MDR) methods.

Results

GD patients stratified by the age of onset differed in the allele frequencies of the HLADRB1*03 and 1858T polymorphisms of the PTPN22 gene (OR = 1.7, p = 0.003; OR = 1.49, p = 0.01, respectively). We evaluated the genetic interactions of four SNPs in a pairwise fashion with regard to disease risk. The coexistence of HLADRB1 with CTLA4 or HLADRB1 with PTPN22 exhibited interactions on more than additive levels (OR = 3.64, p = 0.002; OR = 4.20, p < 0.001, respectively). These results suggest that interactions between these pairs of genes contribute to the development of GD. MDR analysis confirmed these interactions.

Conclusion

In contrast to a single gene effect, we observed that interactions between the HLADRB1/PTPN22 and HLADRB1/CTLA4 genes more closely predicted the risk of GD onset in young patients.     

Effect of cadmium and Phytophthora infestans on polyamine levels in potato leaves

Changes in putrescine, spermidine and spermine concentrations in potato ( Solanum tuberosum L.) leaves stressed either with cadmium, with the fungal pathogen Phytophthora infestans Mont. (de Bary) or with both simultaneously were investigated. The leaves of two cultivars, Bintje and Bzura, respectively susceptible and resistant to P. infestans were examined. The level of of putrescine did not change under any stress conditions. Cadmium stress caused at least a 2-fold increase in spermidine and spermine concentrations in susceptible leaves. In resistant leaves there was a 4-fold increase in spermidine and a decrease in spermine. The pathogenic stress produced similar changes in polyamine concentrations, i. e. with differences between the cultivars. The double stress induced antagonistic alterations in the concentrations of spermidine and spermine.     

Free sterols,steryl esters,glucosides, acylated glucosides and water-soluble complexes in Calendula officinalis

In 3- and 14-day-old seedlings and in the leaves of Calendula officinalis the following sterols were identified: cholestanol, campestanol, stigmastanol, cholest-7-en-3-β-ol, 24-methylcholest-7-en-3β-ol, stigmast-7-en-3β-ol, cholesterol, campesterol, sitosterol, 24-methylcholesta-5,22-dien-3β-ol, 24-methylenecholesterol, stigmasterol and clerosterol. Sitosterol was predominant in young and stigmasterol in old tissues. Young tissues contained relatively more campesterol but in old tissues a C₂₈Δ^5,22 diene was present suggesting transformation of campesterol to its Δ^5,22 analog, similar to that of sitosterol to stigmasterol. All the identified sterols were present as free compounds and also in the steryl esters, glucosides, acylated glucosides and water-soluble complexes. The variations in the amounts of these fractions in the embryo axes and cotyledons of 3- and 14-day-old seedlings and the distribution of individual sterols among the fractions are discussed.