Phosphorylation of the beta-amyloid precursor protein at the cell surface by ectocasein kinases 1 and 2

The beta-amyloid precursor protein (betaAPP) is one of the rare proteins known to be phosphorylated within its ectodomain. We have shown previously that betaAPP can be phosphorylated within secretory vesicles and at the cell surface (Walter, J., Capell, A., Hung, A. Y. , Langen, H., Schnölzer, M., Thinakaran, G., Sisodia, S. S., Selkoe, D. J., and Haass, C. (1997) J. Biol. Chem. 272, 1896-1903). We have now specifically characterized the phosphorylation of cell surface-located betaAPP and identified two ectoprotein kinases that phosphorylate betaAPP at the outer face of the plasma membrane. By using selective protein kinase inhibitors and by investigating the usage of ATP and GTP as cosubstrates, we demonstrate that membrane-bound betaAPP as well as secreted forms of betaAPP can be phosphorylated by casein kinase (CK) 1- and CK2-like ectoprotein kinases. The ectodomain of betaAPP was also phosphorylated by purified CK1 and CK2 in vitro, but not by protein kinases A and C. Phosphorylation of betaAPP by ectoprotein kinases and by purified CK1 and CK2 occurred within an acidic domain in the N-terminal half of the protein. Heparin strongly inhibited the phosphorylation of cell-surface betaAPP by ecto-CK1 and ecto-CK2, indicating a regulatory role of this extracellular matrix component in betaAPP phosphorylation.

Rad51 accumulation at sites of DNA damage and in postreplicative chromatin

Rad51, a eukaryotic RecA homologue, plays a central role in homologous recombinational repair of DNA double-strand breaks (DSBs) in yeast and is conserved from yeast to human. Rad51 shows punctuate nuclear localization in human cells, called Rad51 foci, typically during the S phase (Tashiro, S., N. Kotomura, A. Shinohara, K. Tanaka, K. Ueda, and N. Kamada. 1996. Oncogene. 12:2165-2170). However, the topological relationships that exist in human S phase nuclei between Rad51 foci and damaged chromatin have not been studied thus far. Here, we report on ultraviolet microirradiation experiments of small nuclear areas and on whole cell ultraviolet C (UVC) irradiation experiments performed with a human fibroblast cell line. Before UV irradiation, nuclear DNA was sensitized by the incorporation of halogenated thymidine analogues. These experiments demonstrate the redistribution of Rad51 to the selectively damaged, labeled chromatin. Rad51 recruitment takes place from Rad51 foci scattered throughout the nucleus of nonirradiated cells in S phase. We also demonstrate the preferential association of Rad51 foci with postreplicative chromatin in contrast to replicating chromatin using a double labeling procedure with halogenated thymidine analogues. This finding supports a role of Rad51 in recombinational repair processes of DNA damage present in postreplicative chromatin.

Sequence conservation and variability of imprinting in the Beckwith-Wiedemann syndrome gene cluster in human and mouse

In human and mouse most imprinted genes are arranged in chromosomal clusters. This linked organization suggests coordinated mechanisms controlling imprinted expression. We have sequenced 250 kb in the centre of the mouse imprinting cluster on distal chromosome 7 and compared it with the orthologous Beckwith-Wiedemann gene cluster on human chromosome 11p15.5. This first comparative imprinting cluster analysis revealed a high structural and functional conservation of the six orthologous genes identified. However, several striking differences were also discovered. First, compared with the mouse the human sequence is approximately 40% longer, mostly due to insertions of two large repetitive clusters. One of these clusters encompasses an additional gene coding for a homologue of the ribosomal protein L26. Second, pronounced blocks of unique direct repeats characteristic of imprinted genes were only found in the human sequence. Third, two of the orthologous gene pairs Tssc4/TSSC4 and Ltrpc5/LTRPC5 showed apparent differences in imprinting between human and mouse, whereas others like Tssc6/TSSC6 were not imprinted in either organism. Together these results suggest a significant functional and structural variability in the centre of the imprinting cluster. Some genes escape imprinting in both organisms whereas others exhibit tissue- and species-specific imprinting. Hence the control of imprinting in the cluster appears to be a highly dynamic process under fast evolutionary adaptation. Intriguingly, whereas imprinted genes within the cluster contain CpG islands the non-imprinted Ltrpc5 and Tssc6/TSSC6 do not. This and additional comparisons with other imprinted and non-imprinted regions suggest that CpG islands are key features of imprinted domains.

Igf2 imprinting in development and disease

Igf2 is one of the first imprinted genes discovered and occupies a centre stage in the study of imprinting. This is because it has dramatic effects on the control of fetal growth, it is involved in growth disorders and in cancer, it interacts with products of other imprinted genes, and its imprinting status is under complex regulation in a cluster of tightly linked imprinted genes. Here we review briefly the key features of Igf2 imprinting in normal development and in disease, and hope to show what a fascinating subject of study this gene and its biology provides.

Genetics of atopy in a mouse model: polymorphism of the IL-5 receptor alpha chain

To study the genetics of atopy systematically we established a mouse model that provides the general phenotype of atopy: the early response characteristic of IgE-dependent eczema or atopic dermatitis, and the diagnostic test of atopy, the skin-prick test. Using an immediate cutaneous hypersensitivity test (ICHS) against birch pollen extract we could classify A/J and C57BL/6 (B6) inbred mouse strains respectively as high responder and low responders. The F1 hybrids were found to be high responders with incomplete penetrance. Backcrossing F1 mice to the low responder B6 strain yielded three classes of responders, high, intermediate, and low. A genome-wide microsatellite screen of the backcross progeny disclosed suggestive linkage to a microsatellite marker on chromosome 6 close to the locus of the IL-5 receptor alpha chain. Its allelic variation in A/J and B6 strains was investigated and two major differences were detected. Firstly, a nucleotide exchange in the 5' untranslated region of B6 mRNA resulted in increased transcription/translation of a reporter construct. Higher expression of the receptor on the cell surface would be expected to favor an allergic immune response. Secondly, the two alleles are differentially spliced so as to yield two soluble isoforms in A/J mice versus one in B6 mice. Higher expression of soluble IL-5R would be expected to reduce the level of allergy through capture of IL-5. Thus both findings conform to the expectation based on susceptibility to atopy and thus identify the IL-5R alpha chain as a likely contributor to the genetics of atopy.

Cognitive rehabilitation for traumatic brain injury: A randomized trial. Defense and Veterans Head Injury Program (DVHIP) Study Group

CONTEXT

Traumatic brain injury (TBI) is a principal cause of death and disability in young adults. Rehabilitation for TBI has not received the same level of scientific scrutiny for efficacy and cost-efficiency that is expected in other medical fields.

OBJECTIVE

To evaluate the efficacy of inpatient cognitive rehabilitation for patients with TBI.

DESIGN AND SETTING

Single-center, parallel-group, randomized trial conducted from January 1992 through February 1997 at a US military medical referral center.

PATIENTS

One hundred twenty active-duty military personnel who had sustained a moderate-to-severe closed head injury, manifested by a Glasgow Coma Scale score of 13 or less, or posttraumatic amnesia lasting at least 24 hours, or focal cerebral contusion or hemorrhage on computed tomography or magnetic resonance imaging.

INTERVENTIONS

Patients were randomly assigned to an intensive, standardized, 8-week, in-hospital cognitive rehabilitation program (n=67) or a limited home rehabilitation program with weekly telephone support from a psychiatric nurse (n=53).

MAIN OUTCOME MEASURES

Return to gainful employment and fitness for military duty at 1-year follow-up, compared by intervention group.

RESULTS

At 1-year follow-up, there was no significant difference between patients who had received the intensive in-hospital cognitive rehabilitation program vs the limited home rehabilitation program in return to employment (90% vs 94%, respectively; P=.51; difference, 4% [95% confidence interval ¿CI¿, -5% to 14%]) or fitness for duty (73% vs 66%, respectively; P=. 43; difference, 7% [95% CI, -10% to 24%]). There also were no significant differences in cognitive, behavioral, or quality-of-life measures. In a post-hoc subset analysis of patients who were unconscious for more than 1 hour (n = 75) following TBI, the in-hospital group had a greater return-to-duty rate (80% vs 58%; P=. 05).

CONCLUSIONS

In this study, the overall benefit of in-hospital cognitive rehabilitation for patients with moderate-to-severe TBI was similar to that of home rehabilitation. These findings emphasize the importance of conducting randomized trials to evaluate TBI rehabilitation interventions. JAMA. 2000;283:3075-3081

Separation of presenilin function in amyloid beta-peptide generation and endoproteolysis of Notch

Most of the genetically inherited Alzheimer's disease cases are caused by mutations in the presenilin genes, PS1 and PS2. PS mutations result in the enhanced production of the highly amyloidogenic 42/43 amino acid variant of amyloid beta-peptide (Abeta). We have introduced arbitrary mutations at position 286 of PS1, where a naturally occurring PS1 mutation has been described (L286V). Introduction of charged amino acids (L286E or L286R) resulted in an increase of Abeta42/43 production, which reached almost twice the level of the naturally occurring PS1 mutation. Although pathological Abeta production was increased, endoproteolysis of Notch and nuclear transport of its cytoplasmic domain was significantly inhibited. These results demonstrate that the biological function of PS proteins in the endoproteolysis of beta-amyloid precursor protein and Notch can be separated.

A cytokeratin profile of canine epithelial skin tumours

The reactions of a number of epithelial skin tumours in dogs to a panel of monoclonal antibodies against different human cytokeratins (CKs) were examined immunohistochemically, the purpose being to detect a specific CK profile. CK 6 was present in all epithelial skin tumours with the exception of pilomatrixoma. CK 14 was found in basal cell-derived neoplasias and in sebaceous and perianal gland tumours. CK 10/11 was restricted to spinous cell-derived tumours and CK 8/18 was limited to sweat gland tumours.

Active demethylation of the paternal genome in the mouse zygote

DNA methylation is essential for the control of a number of biological mechanisms in mammals [1]. Mammalian development is accompanied by two major waves of genome-wide demethylation and remethylation: one during germ-cell development and the other after fertilisation [2] [3] [4] [5] [6] [7]. Most previous studies have suggested that the genome-wide demethylation observed after fertilisation occurs passively, that is, by the lack of maintenance methylation following DNA replication and cell division [6] [7], although one other study has reported that replication-independent demethylation may also occur during early embryogenesis [8]. Here, we report that genes that are highly methylated in sperm are rapidly demethylated in the zygote only hours after fertilisation, before the first round of DNA replication commences. By contrast, the oocyte-derived maternal alleles are unaffected by this reprogramming. They either remain methylated after fertilisation or become further methylated de novo. These results provide the first direct evidence for active demethylation of single-copy genes in the mammalian zygote and, moreover, reveal a striking asymmetry in epigenetic methylation reprogramming. Whereas paternally (sperm)-derived sequences are exposed to putative active demethylases in the oocyte cytoplasm, maternally (oocyte)-derived sequences are protected from this reaction. These results, whose generality is supported by findings of Mayer et al. [9], have important implications for the establishment of biparental genetic totipotency after fertilisation, the establishment and maintenance of genomic imprinting, and the reprogramming of somatic cells during cloning.

Cell/adsorbent interactions in expanded bed adsorption of proteins

Expanded bed adsorption (EBA) is an integrated technology for the primary recovery of proteins from unclarified feedstock. A method is presented which allows a qualitative and quantitative understanding of the main mechanisms governing the interaction of biomass with fluidized resins. A pulse response technique was used to determine the adsorption of various cell types (yeast, Gram positive and Gram negative bacteria, mammalian cells and yeast homogenate) to a range of commercially available matrices for EBA. Cells and cell debris were found to interact with the ligands of agarose based resins mainly by electrostatic forces. From the adsorbents investigated the anion exchange matrix showed the most severe interactions, while cation exchange and affinity adsorbents appeared to be less affected. Within the range of biologic systems under study E. coli cells had the lowest tendency of binding to all matrices while hybridoma cells attached to all the adsorbents except the protein A affinity matrix. The method presented may be employed for screening of suitable biomass/adsorbent combinations, which yield a robust and reliable initial capture step by expanded bed adsorption from unclarified feedstock.

Initiation of eukaryotic DNA replication: origin unwinding and sequential chromatin association of Cdc45, RPA, and DNA polymerase alpha

We report that a plasmid replicating in Xenopus egg extracts becomes negatively supercoiled during replication initiation. Supercoiling requires the initiation factor Cdc45, as well as the single-stranded DNA-binding protein RPA, and therefore likely represents origin unwinding. When unwinding is prevented, Cdc45 binds to chromatin whereas DNA polymerase alpha does not, indicating that Cdc45, RPA, and DNA polymerase alpha bind chromatin sequentially at the G1/S transition. Whereas the extent of origin unwinding is normally limited, it increases dramatically when DNA polymerase alpha is inhibited, indicating that the helicase that unwinds DNA during initiation can become uncoupled from the replication fork. We discuss the implications of these results for the location of replication start sites relative to the prereplication complex.

Constitutive phosphorylation of the Parkinson's disease associated alpha-synuclein

alpha-Synuclein has been implicated in the pathogenesis of Parkinson's disease, since rare autosomal dominant mutations are associated with early onset of the disease and alpha-synuclein was found to be a major constituent of Lewy bodies. We have analyzed alpha-synuclein expression in transfected cell lines. In pulse-chase experiments alpha-synuclein appeared to be stable over long periods (t((1)/(2)) 54 h) and no endoproteolytic processing was observed. alpha-Synuclein was constitutively phosphorylated in human kidney 293 cells as well as in rat pheochromocytoma PC12 cells. In both cell lines phosphorylation was highly sensitive to phosphatases, since okadaic acid markedly stabilized phosphate incorporation. Phosphoamino acid analysis revealed that phosphorylation occurred predominantly on serine. Using site-directed mutagenesis we have identified a major phosphorylation site at serine 129 within the C-terminal domain of alpha-synuclein. An additional site, which was phosphorylated less efficiently, was mapped to serine 87. The major phosphorylation site was located within a consensus recognition sequence of casein kinase 1 (CK-1). In vitro experiments and two-dimensional phosphopeptide mapping provided further evidence that serine 129 was phosphorylated by CK-1 and CK-2. Moreover, phosphorylation of serine 129 was reduced in vivo upon inhibition of CK-1 or CK-2. These data demonstrate that alpha-synuclein is constitutively phosphorylated within its C terminus and may indicate that the function of alpha-synuclein is regulated by phosphorylation/dephosphorylation.

Detection and identification of gastrointestinal Lactobacillus species by using denaturing gradient gel electrophoresis and species-specific PCR primers

Denaturing gradient gel electrophoresis (DGGE) of DNA fragments obtained by PCR amplification of the V2-V3 region of the 16S rRNA gene was used to detect the presence of Lactobacillus species in the stomach contents of mice. Lactobacillus isolates cultured from human and porcine gastrointestinal samples were identified to the species level by using a combination of DGGE and species-specific PCR primers that targeted 16S-23S rRNA intergenic spacer region or 16S rRNA gene sequences. The identifications obtained by this approach were confirmed by sequencing the V2-V3 region of the 16S rRNA gene and by a BLAST search of the GenBank database.

Posttranslational modifications of amyloid precursor protein : ectodomain phosphorylation and sulfation

The amyloid precursor protein (APP) is a type I transmembrane protein with a large ectodomain, a single transmembrane domain and a small cytoplasmic tail (1). Translation of APP occurs at the endoplasmic reticulum (ER) and the protein is translocated into the ER lumen. The N-terminal domain of APP is directed towards the luminal compartment of the ER, whereas the C-terminal domain faces the cytoplasm. After synthesis, APP passes from the ER to the Golgi compartment. APP can then be transported in secretory vesicles to the cell surface, where the large ectodomain faces the extracellular milieu. Cell surface APP can be reinternalized into endosomes and lysosomes (for review see refs. 2 and 3). During its passage through the secretory pathway, APP is subjected to a variety of posttranslational modifications, including proteolytic processing, glycosylation, sulfation, and phosphorylation. Immediately on translocation into the ER, the signal peptide of APP is removed from the N-terminus by signal peptidase. APP is then modified cotranslationally by N-glycosylation on NH(2)-groups of asparagine residues. After passage into the Golgi compartment, the ectodomain of APP is subjected to O-glycosylation. In late Golgi compartments, e.g., the trans Golgi network, APP is subjected to sulfation on tyrosine residues within its ectodomain (4).

Inhibition of cyclin-dependent kinases, GSK-3beta and CK1 by hymenialdisine, a marine sponge constituent

BACKGROUND

Over 2000 protein kinases regulate cellular functions. Screening for inhibitors of some of these kinases has already yielded some potent and selective compounds with promising potential for the treatment of human diseases.

RESULTS

The marine sponge constituent hymenialdisine is a potent inhibitor of cyclin-dependent kinases, glycogen synthase kinase-3beta and casein kinase 1. Hymenialdisine competes with ATP for binding to these kinases. A CDK2-hymenialdisine complex crystal structure shows that three hydrogen bonds link hymenialdisine to the Glu81 and Leu83 residues of CDK2, as observed with other inhibitors. Hymenialdisine inhibits CDK5/p35 in vivo as demonstrated by the lack of phosphorylation/down-regulation of Pak1 kinase in E18 rat cortical neurons, and also inhibits GSK-3 in vivo as shown by the inhibition of MAP-1B phosphorylation. Hymenialdisine also blocks the in vivo phosphorylation of the microtubule-binding protein tau at sites that are hyperphosphorylated by GSK-3 and CDK5/p35 in Alzheimer's disease (cross-reacting with Alzheimer's-specific AT100 antibodies).

CONCLUSIONS

The natural product hymenialdisine is a new kinase inhibitor with promising potential applications for treating neurodegenerative disorders.

Immunization outreach in an inner-city housing development: reminder-recall on foot

OBJECTIVE

To determine rates of immunization coverage among children 3 to 72 months of age in a large public housing development, to develop a community-based outreach program to increase coverage, and to evaluate the effect of the program.

DESIGN

A door-to-door canvass of the development by specially trained emergency medical technicians to enroll families, to determine immunization status from written records, and to follow-up to encourage immunizations and well-child care. The program was evaluated, comparing rates of immunization by age with an expectation based on the immunization histories before enrollment.

SETTING

A Chicago public housing development, October 1993 through December 1996.

OUTCOME VARIABLES

Antigen-specific and series-specific coverage based on written records.

RESULTS

Of the caregivers, 92% were able to identify a primary care provider. At the time of enrollment, 37% of 1075 children were up-to-date, but that proportion varied by age with 27% of children 19 to 35 months of age being up-to-date. The program increased rates of immunization compared with the expectation from the preenrollment rates. At their final assessment, 50% of the children were up-to-date. For individual vaccines, there was a positive program effect. For example, before enrollment, 22% of children 15 months of age had received measles, mumps, and rubella vaccine. However, 39% of children who were enrolled in the program before they were 12 months of age had received their first immunizations by 15 months of age.

CONCLUSIONS

Children in the housing development had very low rates of immunization before enrollment. An in-person intervention was effective in reaching families and determining immunization status. In the 3-year enrollment and observation period, rates of immunization increased.

Appropriateness of medication selection for older persons in an urban academic emergency department

OBJECTIVES

To determine the frequency of potentially inappropriate medication selection for older persons presenting to the ED, the most common problematic drugs, risk factors for suboptimal medication selection, and whether use of these medications is associated with worse outcomes.

METHODS

The authors performed a prospective cohort study of 898 patients 65 years or older who presented to an urban academic ED in 1995 and 1996. Seventy-nine percent of the patients were African-American and 43% did not graduate from high school. Potentially inappropriate medications and adverse drug-disease interactions were identified using the 1997 Beers explicit criteria for elders. During the three months after the initial visit, revisits to the ED or hospital, death, and changes in health-related quality of life were analyzed as measured by validated questions adapted from the Medical Outcomes Study.

RESULTS

Upon presentation, 10.6% of the patients were taking a potentially inappropriate medication, 3.6% were given one in the ED, and 5.6% were prescribed one upon discharge from the ED. The most frequently prescribed potentially inappropriate medications in the ED were diphenhydramine, indomethacin, meperidine, and cyclobenzaprine. Emergency physicians added potentially inappropriate medications most often to patients with discharge diagnoses of musculoskeletal disorder, back pain, gout, and allergy or urticaria. Potentially adverse drug-disease interactions were relatively uncommon at presentation (5.2%), in the ED (0.6%), and on discharge from the ED (1.2%). Potentially inappropriate medications and adverse drug-disease interactions prescribed in the ED were not associated with higher rates of revisit to the ED, hospitalization, or death, but were correlated with worse physical function and pain. However, confidence intervals were wide for analyses of revisits and death.

CONCLUSIONS

Suboptimal medication selection was fairly common and was associated with worse patient-reported health-related quality of life.

Older patients' health-related quality of life around an episode of emergency illness

STUDY OBJECTIVES

We sought to describe older patients' health-related quality of life during a 4-month period surrounding a visit to the emergency department and to identify factors associated with less recovery.

METHODS

We prospectively studied 983 patients 65 years or older who presented to an urban academic ED in 1995 and 1996. Eighty percent of the patients were African American, and 63% were women. The primary outcome measures were the Katz Index of Activities of Daily Living and revised validated questions from the Medical Outcomes Study Health Survey at 1 month before the ED visit, the time of the ED visit, and 2-week and 3-month follow-up periods.

RESULTS

In general, patients worsened markedly during the illness and then improved, although not to baseline levels. After adjustment for demographic and social factors, the most consistently powerful predictors of poor recovery were more deficiencies in activities of daily living at baseline, reports of needing more help with everyday tasks, increasing Charlson Comorbidity Index scores, and requiring a proxy for the initial survey.

CONCLUSION

Emergency physicians and primary care physicians should consider inquiring about functional status and the adequacy of help at home in addition to comorbid conditions for their acutely ill older patients to target those at greatest risk for poor recovery. Future work needs to test interventions that may improve the health-related quality of life of these vulnerable patients.

Laser therapies in dermatology

BACKGROUND

Early lasers used in dermatology were continuous wave, with high energy focused in a small area, and did not utilise target specific wavelengths. They caused significant thermal injury to the skin surrounding the target. Over the past 8 years the safety of dermatological lasers has been enhanced by addressing these problems.

OBJECTIVE

To discuss the advances in laser technology and the clinical uses of these new devices.

DISCUSSION

Modern lasers are designed with a wavelength specific for thermally destroying a particular target without significantly damaging surrounding tissues (selective thermolysis). Electronic systems have been developed which deliver short pulse duration energy sufficient to damage target tissue but limiting thermal conduction to surrounding tissues. These advances have made treatment of vascular and pigmented lesions and resurfacing techniques safer.

Zebrafish (Danio rerio) presenilin promotes aberrant amyloid beta-peptide production and requires a critical aspartate residue for its function in amyloidogenesis

Alzheimer's disease (AD) is characterized by the invariable accumulation of senile plaques composed of amyloid beta-peptide (Abeta). Mutations in three genes are known to cause familial Alzheimer's disease (FAD). The mutations occur in the genes encoding the beta-amyloid precursor protein (betaAPP) and presenilin (PS1) and PS2 and cause the increased secretion of the pathologically relevant 42 amino acid Abeta42. We have now cloned the zebrafish (Danio rerio) PS1 homologue (zf-PS1) to study its function in amyloidogenesis and to prove the critical requirement of an unusual aspartate residue within the seventh putative transmembrane domain. In situ hybridization and reverse PCR reveal that zf-PS1 is maternally inherited and ubiquitously expressed during embryogenesis, suggesting an essential housekeeping function. zf-PS1 is proteolytically processed to produce a C-terminal fragment (CTF) of approximately 24 kDa similar to human PS proteins. Surprisingly, wt zf-PS1 promotes aberrant Abeta42 secretion like FAD associated human PS1 mutations. The unexpected pathologic activity of wt zf-PS1 may be due to several amino acid exchanges at positions where FAD-associated mutations have been observed. The amyloidogenic function of zf-PS1 depends on the conserved aspartate residue 374 within the seventh putative transmembrane domain. Mutagenizing this critical aspartate residue abolishes endoproteolysis of zf-PS1 and inhibits Abeta secretion in human cells. Inhibition of Abeta secretion is accompanied by the accumulation of C-terminal fragments of betaAPP, suggesting a defect in gamma-secretase activity. These data provide further evidence that PS proteins are directly involved in the proteolytic cleavage of betaAPP and demonstrate that this function is evolutionarily conserved.