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Biomedical subjects

A Sonnenberg

Publications and source records attributed to A Sonnenberg.

At least 127 records · Page 7Linked to original sources
PubMed1998

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.

Autoantigens↗
PubMed1998

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.

Adult↗
PubMed1998

Associations between hemorrhoids and other diagnoses.

PURPOSE: The risk factors and mechanisms that contribute to the occurrence of hemorrhoids are not well understood. The study of the comorbid occurrences of hemorrhoids with other diagnoses in identical patients may point to a common underlying pathophysiology. The present study was undertaken to determine which diagnoses are associated with the occurrence of hemorrhoids. METHODS: A case-control study compared the occurrence of comorbid diseases in case subjects with hemorrhoids with that of control subjects without hemorrhoids. The case population comprised all patients with hemorrhoids (International Classification of Diseases codes 455.0-455.9), who were discharged from hospitals of the U.S. Department of Veterans Affairs between 1986 and 1996. In a multiple logistic regression analysis, the occurrence of hemorrhoids served as outcome variable, and age, gender, ethnicity, and the comorbid occurrence of other diagnoses served as predictor variables. RESULTS: A total of 96,314 individual patients with hemorrhoids and the same number of control subjects were identified. In a chart review of a random sample of 100 cases, the diagnosis of hemorrhoids could be confirmed in 97 percent of all instances checked. The variety of diagnoses associated with hemorrhoids could be broken down into five large categories: 1) diseases associated with diarrhea (odds ratio, 1.30; 95 percent confidence interval, 1.27-1.33); 2) spinal cord injuries (odds ratio, 1.17; 95 percent confidence interval, 1.09-1.26); 3) constipation and related diseases (odds ratio, 1.48; 95 percent confidence interval, 1.43-1.54); 4) various types of anorectal diseases (odds ratio, 4.71; 95 percent confidence interval, 4.44-5.0); and 5) conditions that could be considered manifestations or sequelae of the hemorrhoidal disease itself (odds ratio, 3.41; 95 percent confidence interval, 3.30-3.51). CONCLUSIONS: The types and spectrum of comorbid diagnoses associated with hemorrhoids suggest that an increased tone of the anal sphincter constitutes a common pathophysiologic mechanism for the development of hemorrhoids.

Adult↗
PubMed1998

Integrin laminin receptor profile of pulmonary squamous cell and adenocarcinomas.

The differential expression of laminin receptors has been shown to modulate the invasive capability of malignant cells. We have investigated the reactivity of human pulmonary squamous carcinomas (SSC, n = 20) and adenocarcinomas (ADC, n = 20) with monoclonal antibodies to the cytoplasmic and extracellular domains of the integrin subunits alpha3 and alpha6. Integrins containing these subunits are laminin receptors. Monoclonal antibodies to beta1 and beta4 subunits, the beta1C splice variant of beta1, as well as to Ki-67, were also used. Reverse transcription polymerase chain reaction (PCR) single-strand conformational polymorphism analysis was done to detect possible mutations in the cytodomains. All carcinomas expressed alpha3 extensively; alpha3 expression predominated (40 of 40) over alpha6 (25 of 40). In all alpha6-positive carcinomas, alpha6A was expressed, whereas alpha6B was weakly expressed only in some of them. No mutations of the intracytoplasmic domain A of alpha3 and of the A or B intracytoplasmic domains of alpha6 were shown. Notably, in normal bronchial epithelium, alpha6 colocalized with beta4, whereas in the tumors, alpha6A frequently overlapped with beta1 in a circumferential pattern; alpha6beta1 coexpression was also shown by coprecipitation experiments. Strong and extensive beta4 reactions were invariably polarized at the cell/stroma interface in SCC and ADC. An inverse correlation was found between the expression of beta1C and Ki-67. The prevalence of alpha6A in pulmonary SCC and ADC is in contrast with previous results in colonic ADC in which alpha6B prevails, and alpha6 predominates over alpha3. The absence of mutations of the cytodomains suggests that the integrin subunits of these carcinomas are potentially active. Predominance of alpha3 over alpha6 and of alpha6A over alpha6B may contribute to explain the aggressive and metastatic behavior of lung carcinomas.

Adenocarcinoma↗
PubMed1998

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 of Illness↗
PubMed1998

Economic constraints in the diagnosis of peptic ulcer disease.

BACKGROUND: The discovery of Helicobacter pylori and its role in upper gastrointestinal disease has changed the outlook on diagnosis of peptic ulcer disease. OBJECTIVES: To address the questions of what types of diagnostic tests and how many of each type are needed to diagnose among patients with dyspepsia as many ulcers as possible at least cost. METHODS: Bayes' formula and a decision tree were used to follow the outcomes of alternative test combinations for ulcer diagnosis. RESULTS: Assuming unlimited resources, only endoscopy of all subjects results in the correct diagnoses of all ulcers, but costs $5600 per diagnosis. Barium swallow followed by endoscopy is less expensive ($2980), but misses 5% of all ulcers. Serology for H. pylori followed by endoscopy or barium meal provides relatively high diagnostic yields (85 or 81% of all ulcers detected) at lower costs ($2900 or $1050 per ulcer diagnosis, respectively). In general, a higher number of ulcers is found at a lower cost if the cheap tests are used to screen patients before subjecting them to the more expensive tests. CONCLUSIONS: The ideal work-up depends on the urgency of a correct diagnosis, the willingness to miss some ulcer diagnoses and the availability of resources. H. pylori serology followed by endoscopy or barium meal represents two cost-effective strategies.

Diagnostic Techniques, Digestive System↗
PubMed1998

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.

Decision Support Techniques↗
PubMed1998

The impact of peptic ulcer disease and infection with Helicobacter pylori on life expectancy.

OBJECTIVE: Knowledge about the influence of H. pylori-related disease on life expectancy might affect physician behavior in dealing with such disease. The aim of this study was to assess how life expectancy is influenced by H. pylori infection and peptic ulcer disease. METHODS: The declining exponential approximation of life expectancy was used to model the effects of H. pylori and various peptic ulcer disease conditions on life expectancy. Deaths from peptic ulcer and gastric cancer were determined from the Vital Statistics of the United States. H. pylori prevalence rates were derived from the existing literature. RESULTS: Cure of active peptic ulcer increases life expectancy by 2.3 yr in persons aged 40-44 yr and 121 days in persons aged 70-74 yr. More substantial impact occurs in complicated ulcer, with increases in life expectancy ranging between 26.1 and 6.3 yr. Primary prevention of H. pylori could increase life expectancy by 190 days in those aged 40-44 yr and 26 days in 70-74-yr-old subjects. CONCLUSION: The benefit of ulcer cure or H. pylori prevention diminishes as age advances. Cure of ulcers in young patients or in those who have sustained complications results in an appreciable increase in life expectancy. Successful primary prevention of H. pylori in selected populations could substantially increase life expectancy.

Adult↗
PubMed1998

Military history of patients with inflammatory bowel disease: an epidemiological study among U.S. veterans.

OBJECTIVES: The military history of patients with inflammatory bowel disease (IBD) contains types of exposure that are not available through other sources and may provide clues about the as-yet unknown etiology of IBD. We therefore sought to describe the epidemiology of IBD among veterans, with particular emphasis on their military history. METHODS: A case-control study compared 10,544 IBD patients and 42,026 controls with respect to age, gender, ethnicity, time period of military service, military duty in Vietnam, status as prisoner of war, and exposure to Agent Orange. RESULTS: Subjects with Crohn's disease were younger than those with ulcerative colitis or without IBD (odds ratio: 0.85; 95% confidence interval [CI]: 0.83-0.87). Both types of IBD affected female veterans significantly more often than male veterans, the relative female predominance being more pronounced in Crohn's disease than ulcerative colitis (0.70; 0.61-0.81 vs 0.83; 0.71-0.96). Whites were more prone to develop both types of IBD than nonwhites (2.46; 2.27-2.68 vs 2.11; 1.95-2.27). Military duty in Vietnam and a status as prisoner of war both exerted a protective influence against Crohn's disease (0.84; 0.75-0.96 and 0.60; 0.41-0.87, respectively), but not ulcerative colitis. CONCLUSIONS: The results are consistent with the hypothesis that exposure to poor sanitation decreases the future risk of developing Crohn's disease.

Adult↗
PubMed1998

Opposing time trends of peptic ulcer and reflux disease.

BACKGROUND: Gastritis associated hypochlorhydria may be protective against gastro-oesophageal reflux disease. It was hypothesised that the historic decline in Helicobacter pylori infection resulted in a decline in peptic ulcer and a concomitant risk in reflux disease. AIMS: To study the time trends of peptic ulcer and reflux disease. METHODS: Hospitalisation rates were analysed using the computerised database of the US Department of Veterans Affairs from 1970 until 1995. Death rates were calculated from the Vital Statistics of the United States. RESULTS: From 1970 to 1995, hospitalisation rates for gastric and duodenal ulcer, as well as gastric cancer fell, while the hospitalisation rates for gastro-oesophageal reflux disease and those for oesophageal adenocarcinoma rose significantly. Similar time trends were observed with respect to the death rates. There were notable ethnic differences. White subjects incurred higher rates of reflux disease and oesophageal adenocarcinoma and lower rates of gastric ulcer or cancer compared with non-whites. CONCLUSIONS: The ethnic variations and the opposing time trends of gastroduodenal versus oesophageal disease are consistent with the hypothesis that the declining infection rates of H pylori in the general population have led to a rise in the occurrence of gastro-oesophageal reflux disease and associated oesophageal adenocarcinoma.

Adenocarcinoma↗
PubMed1998

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.

Animals↗
PubMed1998

Threshold analysis of Helicobacter pylori therapy.

OBJECTIVE: Conflicting recommendations have been made on whom to treat with antibacterials to eradicate Helicobacter pylori. The present analysis aims to explain the basis of such discrepancies. DESIGN AND SETTING: The decision in favour of or against antibacterial therapy in patients with upper gastrointestinal symptoms is modelled as a threshold analysis. The threshold is the lowest probability for a given diagnosis at which the decision in favour of antibacterial therapy yields a higher expected outcome than the decision against it. A strong indication for antibacterial therapy is shown by a low threshold value. MAIN OUTCOME MEASURES AND RESULTS: In patients with suspected peptic ulcer disease, both the high success rate of antibacterial therapy and its low cost make it the most favourable treatment option, its threshold being less than 35%. In ulcer patients receiving nonsteroidal anti-inflammatory drugs, the threshold is 73% if based on success rates of different treatment modalities, but only 7% if treatment costs are considered. The relatively poor success rate of antibacterial therapy in non-ulcer dyspepsia raises the diagnostic threshold for antibacterial therapy to 76% if based on therapeutic success rates. The small marginal cost of antibacterial therapy lowers the diagnostic threshold to 16%. CONCLUSION: If therapeutic success is the primary concern, patients with vague abdominal symptoms should not be given antibacterial therapy, unless H. pylori has been established as a probable cause of their symptoms. If healthcare costs are the driving force for choosing one type of therapy over another, a trial of antibacterials appears indicated irrespective of any firm validation of H. pylori playing a role in the patient's disease.

Anti-Bacterial Agents↗
PubMed1998

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.

Adult↗
PubMed1997

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.

Amino Acid Sequence↗
PubMed1997

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.

Adolescent↗
PubMed1997

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.

Alternative Splicing↗
PubMed1997

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.

Amino Acid Sequence↗