Hemidesmosome formation is initiated by the beta4 integrin subunit, requires complex formation of beta4 and HD1/plectin, and involves a direct interaction between beta4 and the bullous pemphigoid antigen 180

Hemidesmosomes (HDs) are stable anchoring structures that mediate the link between the intermediate filament cytoskeleton and the cell substratum. We investigated the contribution of various segments of the beta4 integrin cytoplasmic domain in the formation of HDs in transient transfection studies using immortalized keratinocytes derived from an epidermolysis bullosa patient deficient in beta4 expression. We found that the expression of wild-type beta4 restored the ability of the beta4-deficient cells to form HDs and that distinct domains in the NH2- and COOH-terminal regions of the beta4 cytoplasmic domain are required for the localization of HD1/plectin and the bullous pemphigoid antigens 180 (BP180) and 230 (BP230) in these HDs. The tyrosine activation motif located in the connecting segment (CS) of the beta4 cytoplasmic domain was dispensable for HD formation, although it may be involved in the efficient localization of BP180. Using the yeast two-hybrid system, we could demonstrate a direct interaction between beta4 and BP180 which involves sequences within the COOH-terminal part of the CS and the third fibronectin type III (FNIII) repeat. Immunoprecipitation studies using COS-7 cells transfected with cDNAs for alpha6 and beta4 and a mutant BP180 which lacks the collagenous extracellular domain confirmed the interaction of beta4 with BP180. Nevertheless, beta4 mutants which contained the BP180-binding region, but lacked sequences required for the localization of HD1/plectin, failed to localize BP180 in HDs. Additional yeast two- hybrid assays indicated that the 85 COOH-terminal residues of beta4 can interact with the first NH2-terminal pair of FNIII repeats and the CS, suggesting that the cytoplasmic domain of beta4 is folded back upon itself. Unfolding of the cytoplasmic domain may be part of a mechanism by which the interaction of beta4 with other hemidesmosomal components, e.g., BP180, is regulated.

Ligand-independent role of the beta 4 integrin subunit in the formation of hemidesmosomes

Recently, we have shown that a region within the beta4 cytoplasmic domain, encompassing the second fibronectin type III (FNIII) repeat and the first 27 amino acids of the connecting segment, is critical for the localization of alpha6 beta4 in hemidesmosomes. In addition, this region was shown to regulate the distribution of HD1/plectin in transfected cells. In order to investigate the function of the beta4 extracellular and cytoplasmic domains in the assembly and integrity of hemidesmosomes, we have constructed chimeric receptors consisting of the extracellular and transmembrane domains of the interleukin 2 receptor (IL2R), fused to different parts of the beta4 cytoplasmic domain. These chimeras are expressed as single subunits at the plasma membrane. The results show that the first and the second FNIII repeat, together with the first part of the connecting segment (in total a stretch of 241 amino acids spanning amino acids 1,115 to 1,356) are both essential and sufficient for the localization of beta4 in pre-existing hemidesmosomes. Moreover, expression of the IL2R/beta4 chimeric constructs in COS-7 and CHO cells, which do not express alpha6 beta4 or the bullous pemphigoid (BP) antigens but do express HD1/plectin, revealed that the stretch of 241 amino acids is sufficient for inducing the formation of type II hemidesmosomes. Expression of the IL2R/beta4 chimeras in a keratinocyte cell line derived from a patient lacking beta4 expression, showed that amino acids 1,115 to 1,356 can also induce the formation of type I hemidesmosomes. We further demonstrate that type I and II hemidesmosomes can also be formed upon adhesion of alpha6 beta4-expressing cells to fibronectin. These findings establish that the beta4 extracellular domain is not essential for the induction of hemidesmosome assembly. Moreover, they demonstrate that binding of alpha6 beta4 to ligand, and heterodimerization of alpha6 with beta4, are not required for hemidesmosome formation. This indicates that the assembly of hemidesmosomes can be regulated from within the cell.

Empirical therapy versus diagnostic tests in gastroesophageal reflux disease: a medical decision analysis

Our objective was to describe the conditions that determine the costs of empirical therapy in gastroesophageal reflux disease (GERD). Our design was a threshold analysis using a decision tree. The costs of medications were estimated from the average wholesale prices. The costs of diagnostic procedures were expressed as the sum of physician and facility costs. A decision tree was modeled to calculate the threshold probability of GERD, for which empirical therapy became the preferred management strategy. Bayes' formula was used to transform the sensitivity and specificity of various symptoms and the joint occurrence of multiple symptoms into disease probabilities. The decision in favor of empirical therapy is influenced by four factors: the probability of GERD, the duration or costs of GERD therapy, the costs of erroneous empirical therapy in patients with diagnosis other than GERD, and the costs of diagnostic procedures. In general, the expected benefit of saving the costs of a diagnostic procedure outweighs the costs of occasional erroneous empirical therapy. However, if surgical therapy is considered or antisecretory therapy is administered for a time period of 10 or more years, diagnostic confirmation of GERD should be sought. In the long run, the failure to differentiate between peptic ulcer and GERD results in the highest cost associated with erroneous empirical therapy. In patients with multiple characteristic symptoms of GERD, the diagnosis can be ascertained with sufficient confidence to warrant empirical therapy.

Cost savings in duodenal ulcer therapy through Helicobacter pylori eradication compared with conventional therapies: results of a randomized, double-blind, multicenter trial. Gastrointestinal Utilization Trial Study Group

BACKGROUND

We hypothesized that treatment of duodenal ulcer disease with antibiotic therapy directed toward Helicobacter pylori infection is more cost-effective than therapy with antisecretory agents.

METHODS

A randomized, double-blind, multicenter clinical trial of adult patients with active duodenal ulcer and H. pylori infection was conducted. Patients were randomized to receive 500 mg of clarithromycin 3 times a day plus 40 mg of omeprazole daily for 14 days followed by 20 mg of omeprazole daily for an additional 14 days (group 1), 20 mg of omeprazole daily for 28 days (group 2), or 150 mg of ranitidine hydrochloride twice a day for 28 days (group 3). The use of ulcer-related health care resources was documented during monthly interviews for 1 year after the initial therapy. Clinical success was evaluated 4 to 6 weeks and 1 year after the end of therapy.

RESULTS

Of the 819 patients enrolled, 727 completed the study. Group 1 included 243 patients; group 2, 248 patients; and group 3, 236 patients. Patients in group 1 used fewer ulcer-related health care resources during the 1 year after therapy compared with groups 2 and 3 (comparisons are given as group 1 vs group 2 and group 1 vs group 3, respectively): the number of endoscopies performed, 28 vs 76 (P<.001) and vs 71 (P<.001); patients receiving drugs to treat an ulcer, 118 vs 180 (P<.001) and vs 168 (P<.001); clinic visits, 83 vs 135 (P=.05) and vs 161 (P<.001); hospitalizations, 0 vs 5 (P=.045) and vs 6 (P=.02); and length of hospital stay, 0 vs 24 days (P=.04) and vs 37 (P=.04). When ulcer-related costs were defined as the outcome variable in a multivariate linear regression analysis, therapy was determined to have a significant influence on costs (group 1 vs group 2, P<.001; group 1 vs group 3, P=.008). Clinical success rates at the end of the study and cure of H. pylori infection were significantly greater in group 1 compared with groups 2 and 3 (P<.001). Therapy with clarithromycin plus omeprazole provided savings of $1.94 and $2.96 (compared with therapy with omeprazole and with ranitidine hydrochloride, respectively) per dollar spent within the first year after therapy. This incremental cost-benefit translates to savings of $547 or $835 per patient in group 1 (compared with patients in group 2 or group 3, respectively) during the first year after therapy.

CONCLUSIONS

Combination therapy with clarithromycin and omeprazole resulted in significantly fewer uses of ulcer-related health care resources than conventional antisecretory therapy during a 1-year follow-up and significant savings in associated costs during the same period. Patients who received clarithromycin plus omeprazole also showed a significantly improved clinical outcome compared with patients who received only omeprazole or ranitidine.

Knockout and knockin of the beta1 exon D define distinct roles for integrin splice variants in heart function and embryonic development

The beta1D integrin is a recently characterized isoform of the beta1 subunit that is specifically expressed in heart and skeletal muscle. In this study we have assessed the function of the beta1D integrin splice variant in mice by generating, for the first time, Cre-mediated exon-specific knockout and knockin strains for this splice variant. We show that removal of the exon for beta1D leads to a mildly disturbed heart phenotype, whereas replacement of beta1A by beta1D results in embryonic lethality with a plethora of developmental defects, in part caused by the abnormal migration of neuroepithelial cells. Our data demonstrate that the splice variants A and D are not functionally equivalent. We propose that beta1D is less efficient than beta1A in mediating the signaling that regulates cell motility and responses of the cells to mechanical stress.

An endo-1,4-beta-xylanase-encoding gene from Agaricus bisporus is regulated by compost-specific factors

Compost is the preferred substrate for growth of the edible fungus Agaricus bisporus. Utilization of compost requires the production of enzymes involved in degradation of lignocellulolytic components. For molecular characterization of these processes we are isolating the encoding genes. By applying heterologous screening techniques, we have cloned such a gene, which is specifically induced on compost encoding an endo-1,4-beta-xylanase (xlnA) belonging to glycosyl hydrolase family 10. The gene encodes a pre-protein of 333 amino acid residues with a predicted molecular mass of 34,946 for the mature protein. The open reading frame is interrupted by ten introns of which introns 5 and 6 are separated by an exon of only two base-pairs. High expression of the xlnA gene was observed in vegetative mycelium grown on sterilized compost while xlnA messengers were not detected in fruit bodies. Addition of glucose or xylose to compost repressed xlnA expression. When glucose-grown colonies were transferred to a medium containing cellulose, xylan or xylose as sole carbon source, the organism responded by expressing xlnA at a high level for a short period. Transfer from glucose to compost yielded a much stronger and constant xlnA induction. A similar pattern of expression was found for the cel3 gene encoding a cellulase, suggesting that these genes are induced by compost-specific factors rather than by the substrates they act upon. Antiserum raised against XLNA protein, which was heterologously expressed in Escherichia coli, detected, when the fungus was grown on compost, an extracellular protein of 33 kDa with endo-xylanase activity.

Incidence and risk factors for self-reported peptic ulcer disease in the United States

Incidence and risk factors for peptic ulcer disease in the United States have not been well defined. During the 1989 National Health Interview Survey, a population-based sample of 42,392 individuals responded to questions regarding doctor-diagnosed ulcers with confirmation by either an upper gastrointestinal series or endoscopy. Ulcers present during the previous 12 months were considered either incident ulcers if diagnosed during this period or chronic active ulcers if diagnosed more than 12 months before the interview. The incidence of ulcers over the year prior to the interview was 5.27 per 1,000 adults. Whereas incident duodenal ulcer cases represented only 2.4 percent of all persons with a history of duodenal ulcer, the corresponding value for gastric ulcer was 8.7 percent. Risk factors for incident ulcers included increasing age, lower income and educational attainment, and musculoskeletal pain or headache. These were similar to risk factors for chronic active ulcers, except smoking was an additional important risk factor for chronic active ulcers. Thus, incident peptic ulcers are common in the United States but represent a small proportion of persons with a history of ulcer disease. Smoking may be a stronger risk factor for chronic ulcers than for new ulcers.

Role of the bullous pemphigoid antigen 180 (BP180) in the assembly of hemidesmosomes and cell adhesion--reexpression of BP180 in generalized atrophic benign epidermolysis bullosa keratinocytes

Bullous pemphigoid antigen 180 (BP180) is a transmembrane component of hemidesmosomes (HD), cell-substrate attachment complexes in stratified and complex epithelia. To determine the role of BP180 in the assembly of HD and cell adhesion, using SV40 virions we have immortalized BP180-deficient keratinocytes derived from a patient with the inherited skin blistering disorder generalized atrophic benign epidermolysis bullosa (GABEB). The GABEB keratinocytes form HD-like structures, which contain alpha 6 beta 4 integrin and HD1/plectin, but not the bullous pemphigoid antigen 230 (BP230). The expression of integrin subunits by GABEB keratinocytes was comparable to that of an immortalized normal human keratinocyte cell line (NHK), except for alpha 6 and beta 4, which were less strongly expressed in GABEB cells. In short-term adhesion assays, both GABEB keratinocytes and NHK bound strongly and to a similar extent to laminin-1, laminin-5, fibronectin, and type IV and V collagens, which suggests that BP180 is not involved in promoting the initial adhesion to these ligands. Transfection of GABEB keratinocytes with cDNAs for wild-type or a mutant of BP180 lacking the collagenous extracellular domain resulted in the expression of recombinant BP180 proteins that were correctly polarized at the basal cell surface together with alpha 6 beta 4. In addition, restored synthesis of BP180 affected the subcellular localization of BP230, which was no longer diffusely distributed in the cytoplasm, but was found in HD-like structures. In contrast, a BP180 mutant with a 36-amino-acid deletion from the amino terminus of the cytoplasmic domain failed to localize to HD-like structures. These results demonstrate that a region within the cytoplasmic domain of BP180 is essential for its localization into HD and that BP180 may play a critical role in coordinating the subcellular distribution of BP230.

Glomerular extracellular matrix components and integrins

It has become apparent that extracellular matrix components and their cellular receptors, the integrins, are important regulators of glomerular development and function. In this rapidly evolving field we studied the production of extracellular matrix components and integrins by rat glomerular visceral epithelial and mesangial cells, using molecular probes and antibodies that have recently become available. Special attention was paid to laminin isoforms and to splice variants of the integrin subunits alpha 3 and alpha 6. Results were compared to the in vivo expression in human fetal, newborn and adult kidneys. The mesangial cells were found to produce laminin-1, nidogen and two as yet unidentified laminin isoforms with putative alpha chains of about 395 (alpha x) and of 375 kDa (alpha y), tentatively described before as bovine kidney laminin. Furthermore, they expressed the integrins alpha 1 beta 1, alpha 2 beta 1, alpha 3A beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, and small amounts of alpha 6A beta 1 and alpha 6B beta 1. The glomerular visceral epithelial cells produced the two new laminin isoforms mentioned above, laminin-5, but no laminin-1 or nidogen. The integrins alpha 2 beta 1, alpha 3A beta 1, alpha 6A beta 4, alpha 6B beta 4 and the integrin subunit alpha v were found to be expressed. We show that during nephrogenesis, the laminin alpha 1 chain disappears and is replaced by another alpha chain, possibly one of the two as yet unidentified alpha chains mentioned above. The laminin beta 1 chain is replaced by the beta 2 chain somewhat later in glomerular development. In general, the integrins found to be expressed in glomeruli of adult kidney were consistent with those found in cultured glomerular visceral epithelial and mesangial cells. No splice variant switch of the integrin alpha 3 or alpha 6 subunits could be demonstrated during nephrogenesis. Our results suggest an important role for the mesangial cell in providing nidogen as a crucial component of the supramolecular structure of the glomerular basement membrane. Furthermore our results indicate that laminin alpha x beta 2 gamma 1 and alpha y beta 2 gamma 1 isoforms are important in the glomerulus of adult kidney and that the integrin alpha 3A beta 1 is the main integrin receptor for laminin isoforms on glomerular visceral epithelial and mesangial cells, both in vitro and in vivo.

Review article: Medical decision models of Helicobacter pylori therapy to prevent gastric cancer

The aim of the present article is to study the utility of Helicobacter pylori eradication programmes in decreasing the incidence of gastric cancer. Three types of decision models are employed to pursue this aim, i.e. decision tree, present value, and declining exponential approximation of life expectancy (DEALE). 1) A decision tree allows one to model the interaction of multiple variables in great detail and to calculate the marginal cost, as well as the marginal cost-benefit ratio, of a preventive strategy. The cost of gastric cancer, the efficacy of H. pylori therapy in preventing cancer, and the cumulative probability of developing gastric cancer exert the largest influence on the marginal cost of cancer prevention. The high cost of future gastric cancer and a high efficacy of therapy make screening for H. pylori and its eradication the preferred strategy. 2) The present value is an economic method to adjust future costs or benefits to their current value using a discount rate and the length of time between now and a given time point in the future. It accounts for the depreciation of money and all material values over time. During childhood, the present value of future gastric cancer is very low. Vaccination of children to prevent gastric cancer would need to be very inexpensive to be practicable. Cancer prevention becomes a feasible option, only if the time period between the preventive measures and the occurrence of gastric cancer can be made relatively short. 3) The DEALE provides a means to calculate the increase in life expectancy that would occur, if death from a particular disease became preventable. Life expectancy of the general population is hardly affected by gastric cancer. For life expectancy to increase appreciably by vaccination or antibiotic therapy directed against H. pylori infection, these interventions would need to be focused towards a sub-population with an a priori high risk for gastric cancer.

Spatial and temporal expression of the beta1D integrin during mouse development

The beta1D protein is a recently characterized isoform of the integrin beta1 subunit that is present in cardiac and skeletal muscles. In this study, we have examined the expression of beta1D in different types of skeletal muscle and in cardiac muscle and studied its distribution during mouse development, using new monoclonal antibodies specific for beta1D. Immunoprecipitation studies revealed that, while beta1A is strongly expressed in proliferating C2C12 myoblasts, beta1D is only expressed after their differentiation to myotubes. In these myotubes, beta1D is associated with different alpha subunits, namely alpha3A, alpha5, alpha7A, or alpha7B. Initially, during embryogenesis, the alpha1A subunit is the only beta1 variant expressed in skeletal and cardiac muscle. The beta1D subunit is first detected in skeletal muscle at E17.5, whereas in cardiac muscle its expression begins around the time of birth. Later the expression of beta1A in skeletal and cardiac muscle becomes restricted to capillary cells, whereas beta1D eventually becomes the only variant expressed in adult cardiac and skeletal muscle cells. The switch from the beta1A to the beta1D subunit in cardiac muscle cells coincides with the expression of alpha7. In adults there is a distinct concentration of beta1D at the myotendinous junctions of muscle fibers and at costameres in both cardiac and skeletal muscle. In addition, beta1D is present at intercalated discs in cardiac muscle and at neuromuscular junctions in skeletal muscle cells. The amount of beta1D in different types of skeletal muscle (fast, slow, and mixed-type) was similar, but cardiac muscle expressed almost five times as much of this protein. We suggest that beta1D plays a role in the maintenance of the cytoarchitecture of mature muscle and in the functional integrity of the muscle cells.

The two phenylalanines in the GFFKR motif of the integrin alpha6A subunit are essential for heterodimerization

The membrane-proximal domain of the integrin alpha subunit contains a conserved motif of five amino acid residues, GFFKR. We deleted this motif from the human alpha6A subunit and found that in COS-7 cells this mutant cannot associate with the beta1 subunit and is retained in the endoplasmic reticulum. Point mutations in the GFFKR motif of the glycine residue or the two highly charged amino acids, or deletion of the lysine and arginine residues, had no effect on the ability of alpha6 to interact with beta1 and to be expressed at the cell surface. In contrast, by replacing either of the two phenylalanines with alanine, or by deletion of both of these residues, alpha6 was incapable of associating with beta1. The alpha6 point mutants that associated with beta1 were expressed in K562 cells and their responsiveness to integrin-activating factors was determined. None of these transfectants bound spontaneously to laminin-1, but binding could be induced by either PMA or the stimulating anti-beta1 antibody TS2/16 to the same extent as that of the wild-type transfectant. The ability of these mutants to initiate focal-contact formation in CHO cells plated on laminin-1 substrates also appeared to be unaltered. Thus the behaviour of alpha6 mutants involving the glycine, lysine or arginine residues was indistinguishable from that of wild-type alpha6 both in inside-out and outside-in signalling. In contrast, deletion of the cytoplasmic domain of alpha6 C-terminal of the GFFKR motif resulted in a loss of responsiveness of alpha6beta1 to PMA stimulation and formation of focal contacts on laminin-1. However, this mutant was targeted to focal contacts formed by other integrins, even when they had not bound ligand. Together, these results suggest that the two phenylalanine residues of the GFFKR motif provide a site for interaction of the alpha6A subunit with beta1, whereas the cytoplasmic domain C-terminal of this motif is involved in the regulation of bidirectional signalling via alpha6Abeta1.

Associations between different forms of gastro-oesophageal reflux disease

AIMS

To study the epidemiology and natural history of gastro-oesophageal reflux disease (GORD).

METHODS

Retrospective cohort study involving all 172 hospitals of the Department of Veterans Affairs. A total of 194,527 patients with GORD were followed between 1981 and 1994. Distribution of oesophagitis, oesophageal ulcer, oesophageal stricture, strictured hiatus hernia, hiatus hernia, and pyrosis by age, sex, and ethnicity were determined. The comorbid occurrence of various forms of GORD in identical patients was analysed by an age and race standardised morbidity ratio. The population of all hospitalised veterans was used for comparison.

RESULTS

Severe forms of GORD associated with oesophageal erosions, ulcers, or strictures, affected elderly, white, male patients more often than their corresponding opposite demographic group. All forms of GORD clustered in the same patient population; on average, any form of GORD was 10 times more likely to occur in a patient with another form of GORD than without. The highest morbidity ratio (22) was found in oesophageal ulcer and stricture. About one third of all patients with oesophageal erosions, ulcers, or strictures also had hiatus hernia; 46% of patients with hiatus hernia were diagnosed as having other forms of GORD. While one third of all oesophageal strictures appeared in patients without other forms of GORD diagnosed at any time, oesophageal ulcers were always associated with some other form of GORD. No clear cut progression in different forms of GORD was found.

CONCLUSIONS

Older age, male sex, and white ethnicity are risk factors in the development of severe forms of GORD. The most severe grade of GORD is reached at the onset of the disease.

Cost-analysis of prophylactic antibiotics in spontaneous bacterial peritonitis

BACKGROUND & AIMS

Antibiotic prophylaxis has been shown to decrease the incidence of spontaneous bacterial peritonitis (SBP) in patients with cirrhosis and ascites. The aim of this study was to test whether antibiotic prophylaxis for SBP is cost-effective and to compare the costs associated with different patient groups and treatment strategies.

METHODS

A cost-effectiveness analysis was performed using a Markov chain model. The costs incurred during 1-year treatment with prophylactic antibiotics vs. no prophylaxis in patients with cirrhosis and ascites were calculated. The incidence rates of primary and recurrent SBP and the mortality rate of SBP were obtained from the literature. Total direct costs of SBP treatment were determined from the wholesale price of drugs and from disbursements by the Health Care Financing Administration.

RESULTS

Norfloxacin prophylaxis resulted in savings between $2216 and $8545 per patient per year, depending on the patient group studied. Trimethoprim-sulfamethoxazole prophylaxis resulted in savings between $2934 and $9251 per patient per year. The groups that benefited most from prophylaxis were patients with an ascitic fluid total protein concentration of < or = 1 g/dL and those with a previous history of SBP.

CONCLUSIONS

The use of prophylactic antibiotics to decrease the incidence of SBP is a cost-saving strategy in patients with cirrhosis and ascites.

Comorbid occurrence of laryngeal or pulmonary disease with esophagitis in United States military veterans

BACKGROUND & AIMS

It has been speculated that gastroesophageal reflux disease (GERD) represents a risk factor for the occurrence of extraesophageal complications. The aim of this study was to compare the comorbid occurrence of sinus, laryngeal, and pulmonary diseases in case subjects with and control subjects without reflux esophagitis.

METHODS

The case population consisted of all patients with erosive esophagitis (International Classification of Diseases code 530.1) or esophageal stricture (ICD code 530.3) who were discharged from hospitals of the Department of Veteran Affairs between 1981 and 1994. In multivariate logistic regressions, the occurrence of sinus, pharyngeal, laryngeal, or pulmonary disease was compared between cases with and an equal number of controls without esophagitis or stricture.

RESULTS

A total of 101,366 case subjects was analyzed. Erosive esophagitis and esophageal stricture were associated with sinusitis (odds ratio, 1.60; 95% confidence interval, 1.51-1.70), pharyngitis (1.48; 1.15-1.89), aphonia (1.81; 1.18-2.80), laryngitis (2.01; 1.53-2.63), laryngeal stenosis (2.02; 1.12-3.65), chronic bronchitis (1.28; 1.22-1.34), asthma (1.51; 1.43-1.59), chronic obstructive pulmonary disease (1.22; 1.16-1.27), pulmonary fibrosis (1.36; 1.25-1.48), bronchiectasis (1.26; 1.09-1.47), pulmonary collapse (1.31; 1.23-1.40), and pneumonia (1.15; 1.12-1.18).

CONCLUSIONS

Patients with reflux esophagitis are at an increased risk of harboring a large variety of sinus, pharyngeal, laryngeal, and pulmonary diseases.

A minimal region on the integrin beta4 subunit that is critical to its localization in hemidesmosomes regulates the distribution of HD1/plectin in COS-7 cells

The integrin alpha6 beta4 is a major component of hemidesmosomes, in which it mediates firm adhesion to laminin 5. Previous studies have shown that the incorporation of alpha6 beta4 into hemidesmosomes requires a 303 amino acid stretch of the cytoplasmic domain of beta4, comprising part of the first fibronectin type III (FNIII) repeat, the second FNIII repeat and the segment that connects the second to the third FNIII repeat (connecting segment). Now, we have further defined sequences within beta4 that are critical for its localization in hemidesmosomes and we demonstrate that these sequences also induce the redistribution of HD1/plectin into junctional complexes containing the integrin alpha6 beta4 in COS-7 cells, transfected with cDNAs encoding alpha6A and beta4. Truncation of the cytoplasmic domain of beta4 after amino acids 1,382 or 1,355 in the connecting segment, by which a potential tyrosine activation motif (TAM) is removed, does not prevent the localization of alpha6 beta4 in hemidesmosomes in the rat bladder carcinoma cell line 804G and neither did it eliminate the ability of alpha6 beta4 to change the subcellular distribution of HD1/plectin in COS-7 cells. In contrast, beta4 subunits in which the entire connecting segment had been deleted or which were truncated after amino acid 1,328, which removes almost the complete segment, had lost both of these functions. Furthermore, when beta4 subunits with either a deletion of the second FNIII repeat or a small deletion in this repeat were co-expressed with alpha6, the integrins were not localized in hemidesmosomes and did not induce the redistribution of HD1/plectin in COS-7 cells. Finally, the fourth FNIII repeat of beta4 could not replace the second in either of these activities. These findings establish that a region in beta4, which encompasses the second FNIII repeat and a stretch of 27 amino acids (1,329-1,355) of the connecting segment, is critical for the localization of alpha6beta4 in hemidesmosomes and that it regulates the distribution of HD1/plectin.

Implications of intragenic marker homozygosity and haplotype sharing in a rare autosomal recessive disorder: the example of the collagen type XVII (COL17A1) locus in generalised atrophic benign epidermolysis bullosa

Generalised atrophic benign epidermolysis bullosa (GABEB) is a form of junctional epidermolysis bullosa with a recessive mode of inheritance. The gene considered likely to be involved in this disease is COL17A1, since in the majority of GABEB patients the product of that gene, the 180-kD bullous pemphigoid antigen (BP180), is undetectable in skin. We have identified an intragenic COL17A1 microsatellite marker for which 83% of randomly selected control individuals are heterozygous. We observed homozygosity for different alleles of this marker in five out of six collagen type XVII-negative GABEB patients of different European descent. Five of the six COL17A1 alleles of three patients originating from the eastern part of the Netherlands were identical, as were the haplotypes including flanking markers. The 2342delG mutation was identified in all these five alleles. This confirms the expectation that due to genetic drift and hidden inbreeding for an autosomal recessive disorder with low gene frequency, such as collagen type XVII-negative GABEB, most disease alleles from a restricted geographical area will be "identical by descent". Our results demonstrate that involvement of a candidate gene can be confirmed by looking for identity by descent of highly informative intragenic markers.

Time trends of physician visits and treatment patterns of peptic ulcer disease in the United States

BACKGROUND

In the last 4 decades, the prevalence rates of peptic ulcer disease and our understanding of its pathophysiological features underwent major changes.

OBJECTIVE

To analyze how these trends affected physician visits and treatment of ulcer disease.

METHODS

The National Diseases and Therapeutic Index of IMS America Ltd, Plymouth Meeting, Pa, was used as the data source. Survey data were obtained from a representative sample of US physicians 4 times per year during a 48-hour period and extrapolated to a national level. Physician visits for gastric, duodenal, and all peptic ulcers were expressed as rates per 100,000 living US population.

RESULTS

Between 1958 and 1995, physician visits for duodenal ulcer showed a marked decline, while those for gastric ulcer remained largely unchanged. In 1995, 4 million patients visited a physician because of peptic ulcer, corresponding to a rate of 1500 per 100,000 US population. The predominant therapy changed from anticholinergics, tranquilizers, and antacids between 1958 and 1977 to histamine2 receptor antagonist from 1978 until 1988, which subsequently became replaced in part by sucralfate and proton pump inhibitors. In 1995, about 75% of ulcers were still treated primarily with antisecretory medications, and only 5% received antibiotic therapy.

CONCLUSIONS

Peptic ulcer is still common, although duodenal ulcer rates continue to decrease. The historical trends of treatment regimens show a steady change between various medications. No therapeutic class dominated ulcer therapy for more than 20 years. This trend is likely to continue, particularly, in light of the small fraction currently treated by antibiotics to eradicate Helicobacter pylori.

The unique cytoplasmic domain of the human integrin variant beta4E is produced by partial retention of intronic sequences

A novel cytoplasmic splice variant of the human beta4 integrin subunit has been identified by reverse transcription polymerase chain reaction using mRNA from cultured keratinocytes as the template. This fifth beta4 variant, called beta4E, is expressed in a wide variety of tissues including the epidermis, lung, duodenum, heart, spleen and stomach and in several human epithelial cell lines. The beta4E cDNA contains an insert of 37 base pairs which produces a frame shift in the sequence encoding the beta4 cytoplasmic domain and generates a new stop codon after a stretch of cDNA encoding a unique 114-amino acid peptide. Analysis of the genomic organization at the site of this insertion in the human beta4 gene reveals that beta4E is produced by partial retention of an intron in the final transcript.

Identification of the cleavage sites in the alpha6A integrin subunit: structural requirements for cleavage and functional analysis of the uncleaved alpha6Abeta1 integrin

The alpha6A and alpha6B integrin subunits are proteolytically cleaved during biosynthesis into a heavy chain (120 kDa) that is disulphide-linked to one of two light chains (31 or 30 kDa). Analysis of the structure of the alpha6A subunit on the carcinoma cell line T24 and human platelets demonstrated that the two light chains of alpha6 are not differentially glycosylated products of one polypeptide. Rather they possess different polypeptide backbones, which presumably result from proteolytic cleavage at distinct sites in the alpha6 precursor. Mutations were introduced in the codons for the R876KKR879, E883K884, R890K891 and R898K899 sequences, the potential proteolytic cleavage sites, and wild-type and mutant alpha6A cDNAs were transfected into K562 cells. The mutant alpha6A integrin subunits were expressed in association with endogenous beta1 at levels comparable to that of wild-type alpha6Abeta1. A single alpha6 polypeptide chain (150 kDa) was precipitated from transfectants expressing alpha6A with mutations or deletions in the RKKR sequence. Mutations in the EK sequence yielded alpha6A subunits that were cleaved once into a heavy and a light chain, whereas alpha6A subunits with mutations in one of the two RK sequences were, like wild-type alpha6A, cleaved into one heavy and two light chains. Thus a change in the RKKR sequence prevents the cleavage of alpha6. The EK site is the secondary cleavage site, which is used only when the primary site (RKKR) is intact. Microsequencing of the N-termini of the two alpha6A light chains from platelets demonstrated that cleavage occurs after Arg879 and Lys884. Because alpha6(RKKG), alpha6(GKKR) and alpha6(RGGR) subunits were not cleaved it seems that both the arginine residues and the lysine residues are essential for cleavage of RKKR. alpha6A mutants with the RKKR sequence shifted to the EK site, in such a way that the position of the arginine residue after which cleavage occurs corresponds exactly to Lys884, were partly cleaved, whereas alpha6A mutants with the RKKR sequence shifted to other positions in the alpha6A subunit, including one in which it was shifted two residues farther than the EK cleavage site, were not cleaved. In addition, alpha6A mutants with an alpha5-like cleavage site, i.e. arginine, lysine and histidine residues at positions -1, -2 and -6, were not cleaved. Thus both an intact RKKR sequence and its proper position are essential. After activation by the anti-beta1 stimulatory monoclonal antibody TS2/16, both cleaved and uncleaved alpha6Abeta1 integrins bound to laminin-1. The phorbol ester PMA, which activates cleaved wild-type and mutant alpha6Abeta1, did not activate uncleaved alpha6Abeta1. Thus uncleaved alpha6Abeta1 is capable of ligand binding, but not of inside-out signalling. Our results suggest that cleavage of alpha6 is required to generate a proper conformation that enables the affinity modulation of the alpha6Abeta1 receptor by PMA.

Health impact of peptic ulcer in the United States

OBJECTIVES

To assess the general outcome and impact of current and previous peptic ulcer disease on health status in the United States.

METHODS

During the National Health Interview Survey of 1989, a special questionnaire on digestive diseases was administered to 41,457 randomly selected individuals. Various measures of impaired health in ulcer patients were expressed by their age- and sex-standardized prevalence rates.

RESULTS

Ten to 15% of all subjects with a recent ulcer reported that they had been in poor health, incapable of major activity, or unable to work for some time during the 12 months preceding the interview. Twenty to 25% of the subjects with recent ulcers complained about restricted activity and had spent 7 or more days per year in bed. About 40% of all ulcer subjects had seen a physician five or more times within 12 months before the interview. These percentages were significantly lower in patients with previous ulcer histories but no active ulcer within 12 months, but they were still significantly higher than in subjects with no ulcer history at all. In the United States, expenditures attributed to recent ulcers amounted to $5.65 billion per year.

CONCLUSIONS

In the United States, peptic ulcer disease is associated with major morbidity. Ulcer cure would result in large economic and medical savings.

The A and B variants of the alpha 3 integrin subunit: tissue distribution and functional characterization

The alpha subunits of the laminin-binding integrins alpha 3 beta 1, alpha 6 beta 1, and alpha 7 beta 1 have homologous sequences and are similar in structure. Two cytoplasmic variants, A and B, have been identified for each of these alpha subunits, although the alpha 3B splice variant has been detected only at the mRNA level. We prepared a panel of mouse monoclonal antibodies specific for the A and B variants of the alpha 3 subunit to study their tissue distribution. Four monoclonal antibodies react with alpha 3A, one of which recognizes only the nonphosphorylated form; of the three anti-alpha 3B antibodies, one cross-reacts with alpha 6B. Reverse transcriptase-PCR analysis of various human tissues revealed the presence of alpha 3B mRNA in brain, heart, and skeletal muscle. Moreover, the alpha 3B protein was detected by immunoblotting in brain and heart tissue but not in skeletal muscle. In contrast, alpha 3A mRNA and protein were present in all tissues studied. Thus, the expression of alpha 3B in adult tissues is more restricted than that of alpha 3A. Immunohistochemical studies showed that in brain tissue, both variants are exclusively expressed on small blood-vessel endothelium, whereas in heart tissue their distribution patterns differ markedly. Although alpha 3A is strongly expressed on vascular smooth muscle cells, alpha 3B is detected only on endothelial cells of veins. Expression of the two variant forms of alpha 3 in K562 cells revealed that the ligand-binding specificities of alpha 3A beta 1 and alpha 3B beta 1 are identical: both bind human laminin-2 and -4, laminin-5, and laminins isolated from bovine kidney, but not bovine laminin-2 and -4, mouse laminin-1, or human fibronectin. In addition, adhesion mediated by both integrins is induced to the same extent by phorbol 12-myristate 13-acetate. The alpha 3A, but not the alpha 3B subunit, is phosphorylated; and phosphorylation of alpha 3A increases after phorbol 12-myristate 13-acetate stimulation. Thus, we found no differences between the adhesion functions of the A and B variants of alpha 3.

Integrin alpha 6 beta 4 forms a complex with the cytoskeletal protein HD1 and induces its redistribution in transfected COS-7 cells

The integrin alpha 6 beta 4 is a major component of hemidesmosomes, in which it is linked to intermediate filaments. Its presence in these structures is dependent on the beta 4 cytoplasmic domain but it is not known whether beta 4 interacts directly with keratin filaments or by interaction with other proteins. In this study, we have investigated the interaction of GST-cyto beta 4A fusion proteins with cellular proteins and demonstrate that a fragment of beta 4A, consisting of the two pairs of fibronectin type III repeats, separated by the connecting segment, forms a specific complex containing a 500-kDa protein that comigrates with HD1, a hemidesmosomal plaque protein. A similar protein was also bound by a glutathione S-transferase fusion protein containing the cytoplasmic domain of a variant beta 4 subunit (beta 4B), in which a stretch of 53 amino acids is inserted in the connecting segment. Subsequent immunoblot analysis revealed that the 500-kDa protein is in fact HD1. In COS-7 cells, which do not express alpha 6 beta 4 or the hemidesmosomal components BP230 and BP180, HD1 is associated with the cytoskeleton, but after transfecting the cells with cDNAs for human alpha 6 and beta 4, it was, instead, colocalized with alpha 6 beta 4 at the basal side of the cells. The organization of the vimentin, keratin, actin, and tubulin cytoskeletal networks was not affected by the expression of alpha 6 beta 4 in COS-7 cells. The localization of HD1 at the basal side of the cells depends on the same region of beta 4 that forms a complex containing HD1 in vitro, since the expression of alpha 6 with a mutant beta 4 subunit that lacks the four fibronectin type III repeats and the connecting segment did not alter the distribution of HD1. The results indicate that for association of alpha 6 beta 4 with HD1, the cytoplasmic domain of beta 4 is essential. We suggest that this association may be crucial for hemidesmosome assembly.

Economic analysis of dyspepsia

A variety of organic and non-organic diseases can present with symptoms of dyspepsia or upper abdominal pain, and a large diagnostic and therapeutic armamentarium is available to manage symptoms of dyspepsia. How extensively should a diagnostic search be conducted; and where does the best path run through the maze of potential combinations of tests and therapies? Physicians have hoped that economic and medical decision analyses would help them to find the most cost-effective and most efficacious means to deal with dyspepsia. Because of the large variety of potential diagnoses, diagnostic procedures and therapeutic means, however, it is very doubtful that a single most effective or least expensive strategy can ever be developed to apply to every patient with dyspepsia. Following the lines of common medical sense is probably more cost-effective than observing a rigid regimen derived from an economical analysis.