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Biomedical subjects

A Sonnenberg

Publications and source records attributed to A Sonnenberg.

At least 73 records · Page 4Linked to original sources
PubMed2000

The LIM-only protein DRAL/FHL2 binds to the cytoplasmic domain of several alpha and beta integrin chains and is recruited to adhesion complexes.

LIM proteins contain one or more double zinc finger structures (LIM domains) mediating specific contacts between proteins that participate in the formation of multiprotein complexes. We report that the LIM-only protein DRAL/FHL2, with four and a half LIM domains, can associate with alpha(3A), alpha(3B), alpha(7A), and several beta integrin subunits as shown in yeast two-hybrid assays as well as after overexpression in human cells. The amino acid sequence immediately following the conserved membrane-proximal region in the integrin alpha subunits or the C-terminal region with the conserved NXXY motif of the integrin beta subunits are critical for binding DRAL/FHL2. Furthermore, the DRAL/FHL2 associates with itself and with other molecules that bind to the cytoplasmic domain of integrin alpha subunits. Deletion analysis of DRAL/FHL2 revealed that particular LIM domains or LIM domain combinations bind the different proteins. These results, together with the fact that full-length DRAL/FHL2 is found in cell adhesion complexes, suggest that it is an adaptor/docking protein involved in integrin signaling pathways.

3T3 Cells↗
PubMed2000

Cost-effectiveness of colonoscopy in screening for colorectal cancer.

BACKGROUND: Fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy are used to screen patients for colorectal cancer. OBJECTIVE: To compare the cost-effectiveness of fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy. DESIGN: The cost-effectiveness of the three screening strategies was compared by using computer models of a Markov process. In the model, a hypothetical population of 100 000 persons 50 years of age undergoes annual fecal occult blood testing, sigmoidoscopy every 5 years, or colonoscopy every 10 years. Positive results on fecal occult blood testing or adenomatous polyps found during sigmoidoscopy are worked up by using colonoscopy. After polypectomy, colonoscopy is repeated every 3 years until no polyps are found. DATA SOURCES: Transition rates were estimated from U.S. vital statistics and cancer statistics and from published data on the sensitivity, specificity, and efficacy of various screening techniques. Costs of screening and cancer care were estimated from Medicare reimbursement data. TARGET POPULATION: Persons 50 years of age in the general population. TIME HORIZON: The study population was followed annually until death. PERSPECTIVE: Third-party payer. OUTCOME MEASURE: Incremental cost-effectiveness ratio. RESULTS OF BASE-CASE ANALYSIS: Compared with colonoscopy, annual screening with fecal occult blood testing costs less but saves fewer life-years. A screening strategy based on flexible sigmoidoscopy every 5 or 10 years is less cost-effective than the other two screening methods. RESULTS OF SENSITIVITY ANALYSIS: Screening with fecal occult blood testing is more sensitive to changes in compliance rates, and it becomes easily dominated by colonoscopy under most conditions assuming less than perfect compliance. Other assumptions about the sensitivity and specificity of fecal occult blood testing, screening frequency, efficacy of colonoscopy in preventing cancer, and polyp incidence have a lesser influence on the differences in cost-effectiveness between colonoscopy and fecal occult blood testing. CONCLUSIONS: Colonoscopy represents a cost-effective means of screening for colorectal cancer because it reduces mortality at relatively low incremental costs. Low compliance rates render colonoscopy every 10 years the most cost-effective primary screening strategy for colorectal cancer.

Colonoscopy↗
PubMed2000

The tetraspan molecule CD151, a novel constituent of hemidesmosomes, associates with the integrin alpha6beta4 and may regulate the spatial organization of hemidesmosomes.

CD151 is a cell surface protein that belongs to the tetraspan superfamily. It associates with other tetraspan molecules and certain integrins to form large complexes at the cell surface. CD151 is expressed by a variety of epithelia and mesenchymal cells. We demonstrate here that in human skin CD151 is codistributed with alpha3beta1 and alpha6beta4 at the basolateral surface of basal keratinocytes. Immunoelectron microscopy showed that CD151 is concentrated in hemidesmosomes. By immunoprecipitation from transfected K562 cells, we established that CD151 associates with alpha3beta1 and alpha6beta4. In beta4-deficient pyloric atresia associated with junctional epidermolysis bullosa (PA-JEB) keratinocytes, CD151 and alpha3beta1 are clustered together at the basal cell surface in association with patches of laminin-5. Focal adhesions are present at the periphery of these clusters, connected with actin filaments, and they contain both CD151 and alpha3beta1. Transient transfection studies of PA-JEB cells with beta4 revealed that the integrin alpha6beta4 becomes incorporated into the alpha3beta1-CD151 clusters where it induces the formation of hemidesmosomes. As a result, the amount of alpha3beta1 in the clusters diminishes and the protein becomes restricted to the peripheral focal adhesions. Furthermore, CD151 becomes predominantly associated with alpha6beta4 in hemidesmosomes, whereas its codistribution with alpha3beta1 in focal adhesions becomes partial. The localization of alpha6beta4 in the pre-hemidesmosomal clusters is accompanied by a strong upregulation of CD151, which is at least partly due to increased cell surface expression. Using beta4 chimeras containing the extracellular and transmembrane domain of the IL-2 receptor and the cytoplasmic domain of beta4, we found that for recruitment of CD151 into hemidesmosomes, the beta4 subunit must be associated with alpha6, confirming that integrins associate with tetraspans via their alpha subunits. CD151 is the only tetraspan identified in hemidesmosomal structures. Others, such as CD9 and CD81, remain diffusely distributed at the cell surface. In conclusion, we show that CD151 is a major component of (pre)-hemidesmosomal structures and that its recruitment into hemidesmosomes is regulated by the integrin alpha6beta4. We suggest that CD151 plays a role in the formation and stability of hemidesmosomes by providing a framework for the spatial organization of the different hemidesmosomal components.

Antigens, CD↗
PubMed2000

Timing of surgery for enterovesical fistula in Crohn's disease: decision analysis using a time-dependent compartment model.

OBJECTIVES: Previous decision analyses of inflam matory bowel diseases (IBD) have used decision trees and Markov chains. Occasionally IBD patients present with medical problems that are difficult or even impossible to phrase in terms of such established decision tools. This article aims to introduce modeling by a time-dependent compartment mode and demonstrate its feasibility for decision analysis in IBD METHODS: A Crohn's disease patient presented with a pelvic abscess and an enterovesical fistula. Being hesitant to operate in an acutely inflamed area, the surgeon recommended that the patient continue antibiotic therapy until the abscess had re solved. The gastroenterologist argued that the patient had already been treated with antibiotics for a prolonged time period and expressed concern that the patient's overall diminished health status would deteriorate by further delay of surgery. The occurrence of fistula, abscess, urinary tract infection, antibiotic therapy, surgical operation, and health-related quality of life were modeled as separate compartments, with time-dependent relationships among them. The simulation was carried out on an Excel spreadsheet. RESULTS: In the model, the surgeon's predictions were associated with rapid resolution of the pelvic abscess under antibiotic therapy and improvement of the patient's health status. The gastroenterologist's predictions resulted in a smaller decline in abscess size and further deterioration of the patient's health while waiting for a definitive treatment. The disagreement between surgery and gastroenterology arose from predicting different time courses for the individual disease events, in essence, from assigning different time constants to the time-dependent influences of the disease model. CONCLUSIONS: The compartment model provides a simple and generally applicable method to assess time dependent-changes of a complex disease. The present analysis also serves to illustrate the usefulness of such models in simulating disease behavior.

Abdominal Abscess↗
PubMed2000

The impact of colorectal cancer screening on life expectancy.

METHODS: The purpose of this study was to assess the effect of screening for colorectal cancer on life expectancy and estimate the number of colonoscopies needed per life year saved. The declining exponential approximation of life expectancy was used to calculate the effect of colorectal cancer screening on expected remaining lifetime. The annual number of deaths from colorectal cancer and the size of the population were obtained from the vital statistics of the United States. Published reports were consulted to determine the decrease in mortality from colorectal cancer achieved by fecal occult blood testing, screening sigmoidoscopy or colonoscopy. A Markov chain analysis was used to determine the endoscopic resources required to screen and survey the entire population of U.S. residents age 50 years until death or age 85 years. RESULTS: Colorectal cancer decreases the life expectancy of U.S. residents aged 50 to 54 years by 292 days and those aged 70 to 74 years by 70 days. Screening with fecal occult blood tests extends expected lifetime of the 2 age groups by 51 and 12 days, respectively, whereas screening with sigmoidoscopy leads to increases of 86 and 21 days. Colonoscopic screening increases expected lifetime by 170 and 41 days, respectively. The number of colonoscopies needed to save 1 year of expected life ranges from 2.9 to 6.0, depending on the type of screening regimen used. CONCLUSIONS: The extension of life through screening colonoscopy is two or three times longer than the extension achieved through flexible sigmoidoscopy or fecal occult blood test, respectively. Although a large number of colonoscopies are required to screen the U.S. population, relatively few colonoscopies need to be invested per year of life expectancy saved.

Aged↗
PubMed2000

Cost analysis of antibiotic prophylaxis for PEG.

BACKGROUND: There are conflicting recommendations regarding the prophylactic use of antibiotics in patients undergoing placement of percutaneous endoscopic gastrostomy tubes. The purpose of this decision analysis was to assess the cost-effectiveness of antibiotic prophylaxis in percutaneous endoscopic gastrostomy. METHODS: A decision tree was modeled using the data of 7 published prospective placebo-controlled trials. Infectious complications were classified as grade I (requiring local care), grade II (requiring intravenous antibiotics), or grade III (requiring surgery). Medication costs were estimated from the United States average wholesale prices of the 1998 Red Book. Physician and facility costs were estimated based on the 1998 Medicare costs. A one-way sensitivity analysis was performed by varying the probability rates of the complications associated with percutaneous endoscopic gastrostomy and the costs of their treatment. RESULTS: The average cost of prophylactic antibiotics was $13.10. Antibiotic prophylaxis led to expected cost savings of $76.72 per percutaneous endoscopic gastrostomy. A sensitivity analysis suggested that antibiotic prophylaxis for percutaneous endoscopic gastrostomy was the preferred strategy unless the average probability of grade III complications dropped below an improbably low threshold value of 0.09%. CONCLUSION: Antibiotic prophylaxis in percutaneous endoscopic gastrostomy is a cost-effective strategy.

Antibiotic Prophylaxis↗
PubMed2000

Special review: game theory to analyse management options in gastro-oesophageal reflux disease.

This study aims to demonstrate the applicability of linear programming to threshold analysis, using, as an example, patients with new onset of gastro-oesophageal reflux disease (GERD). The choice amongst competing management options is modelled as a decision tree, using threshold analysis, as well as an m x n matrix on an Excel spreadsheet. The different options of medical management correspond to the m rows, whilst the different disease states correspond to the n columns of the matrix. Each number at the intersection of a row and a column represents the outcome associated with that particular combination of management and disease state. The threshold values are calculated by the built-in functions for linear programming of Excel using its Solver tool. Varying the cost estimates in the sensitivity analysis translates into solving a set of different matrices. Threshold analysis provides a formalism to phrase problems of medical decision analysis in a concise fashion.

Cost-Benefit Analysis↗
PubMed2000

Defects in adhesion and migration, but not in proliferation and differentiation, of embryonic stem cells upon replacement of integrin subunit beta1A by beta1D.

Beta1D is a skeletal muscle-specific splice variant of the beta1 integrin subunit, while beta1A integrin subunit has a wide tissue distribution. We have previously shown that replacement of beta1A by beta1D by homologous recombination (knockin) in all mouse tissues was embryonic lethal. Through two successive rounds of homologous recombination, we have now produced embryonic stem (ES) cells expressing beta1D instead of beta1A, and analyzed the ability of beta1D to support ES cell differentiation in vitro and in teratomas in vivo. Beta1D knockin (KI) ES cells grew at a similar rate but as more compact colonies than the beta1A-expressing cells. Increased cell cohesiveness, however, did not appear to involve changes in cadherin activity. Although in both beta1A and beta1D-KI ES cells only one beta1 allele is active; the expression of beta1 integrins in the beta1D-KI ES cells was reduced by 50%, compared with that in the beta1A-expressing cells; this correlated with impaired adhesive and migratory capacities. It appeared that during in vitro cardiac differentiation, in spite of a slight delay in the induction of two cardiac-specific transcripts, the alpha- and beta-myosin heavy chains, contracting cardiomyocytes were detected in similar numbers and at the same time in embryoid bodies (EB) derived from beta1D-KI and from beta1A cells. Furthermore, replacement of beta1A by beta1D in ES cells did not affect neurite differentiation in embryoid bodies in the presence of retinoic acid suggesting that beta1D supports neurogenesis. However, the impaired migration of other cells from the EB, including endodermal cells, prevented the normal outgrowth of neurites in beta1D-KI EB. Finally, injection of beta1D-KI ES cells in the flank of syngeneic mice gave rise to fully developed teratomas containing simple and pluristratified epithelia, muscle, cartilage, blood vessels, and tissues from the neural lineage. These results show that the muscle-specific splice variant beta1D, in spite of its specific cytoplasmic domain, supports the differentiation of many cell types. This further suggests that the embryonic lethality in the beta1D-KI embryos was mainly due to the different ability of beta1 A and beta1D to mediate cell adhesion and migration.

Alternative Splicing↗
PubMed2000

Timing and scheduling of endoscopic procedures.

BACKGROUND: The aim of the present analysis is to compare the costs associated with different schemes of scheduling tests and to develop recommendations concerning the most cost-effective means for timing individual endoscopic procedures. METHODS: The diagnostic costs of three competing strategies to schedule various radiologic and endoscopic procedures in patients with jaundice or gastrointestinal hemorrhage are compared by computer models using a Monte Carlo simulation. In strategy 1, the evaluation is started with the most promising procedure and proceeds with the next most promising procedure in case of a normal finding. In strategy 2, physicians adhere to a rigid sequence of diagnostic tests that starts with the least expensive procedure and advances through progressively more expensive procedures. In strategy 3, all promising tests are scheduled at the onset without waiting for test results to decide in favor or against individual procedures. In the Monte Carlo simulation, two hypothetical populations of 5000 inpatients or outpatients are subjected to each strategy. RESULTS: Unless one particular diagnosis is suspected with a high a priori probability, a rigid sequence of advancing from less to more expensive and invasive procedures provides the cheapest diagnostic strategy. In case of limited access to endoscopy and long waiting times, the cheapest work-up may include simultaneous scheduling of complementary procedures without waiting for intermediate test results. Strategy 1 of starting with the most promising test procedure becomes the least expensive option, if the prior probability assigned to the most likely diagnosis exceeds a threshold between 40% and 70%, depending on the type of test needed to make the diagnosis. CONCLUSIONS: An expeditious diagnostic evaluation or an evaluation that is guided primarily by medical considerations is more likely to result in low healthcare costs.

Aged↗
PubMed2000

Waiting lines in the endoscopy unit.

BACKGROUND: The efficient management of the endoscopy unit involves issues of scheduling. The aim of this study was to assess efficient use of an endoscopy unit and its relationship to patient waiting. METHODS: Formulas of queueing theory are applied to patient scheduling in endoscopy. The M/M/n queueing model assumes exponential (Markovian) distributions underlying both patient arrival and endoscopy times with n as the number of endoscopists, while the D/M/n model assumes a constant (deterministic) patient arrival rate. RESULTS: As the use of the facility increases, so does the probability that patients will have to wait. It is impossible for an endoscopy facility to have a 100% rate of use without patients being forced to wait. Any increase in the use rate of an endoscopy unit results in a concomitant increase in waiting times. A facility with multiple endoscopists can reduce waiting probability at a higher rate of facility use. A table is included that physicians and administrators can use as a guide to estimate the use rate and waiting characteristics of different types of endoscopy facilities. CONCLUSIONS: Endoscopy units must find a balance between patient waiting and underuse of their resources. Endoscopists will occasionally find themselves idle at the benefit of providing patients with tolerable waiting times. It needs to be explained to patients that even under the best of circumstances some waiting cannot be prevented.

Appointments and Schedules↗
PubMed2000

Screening for high-grade dysplasia in gastroesophageal reflux disease: is it cost-effective?

OBJECTIVE: The present study aimed to assess the cost-effectiveness of endoscopic screening in patients with gastroesophageal reflux disease (GERD) to rule out high-grade dysplasia of Barrett's esophagus. METHODS: Using an incremental cost-effectiveness ratio as outcome measure, the cost-effectiveness of endoscopic screening was compared to not screening in a decision tree. It was assumed that GERD patients at age 60 yr undergo a one-time endoscopy with esophageal biopsies, targeting abnormal-appearing epithelium. Positive biopsies with respect to high-grade dysplasia or early esophageal adenocarcinoma result in esophagectomy. Transition rates were estimated from U.S. cancer statistics, as well as published data of endoscopic sensitivity, specificity, and surgical outcome. Costs of screening and cancer care were estimated from Medicare reimbursement data from the perspective of a third-party-payor. RESULTS: Compared with no screening, screening endoscopy cost $24,700 per life-year saved. The cost-effectiveness of screening is quite sensitive to the prevalence of Barrett's esophagus, high-grade dysplasia, and adenocarcinoma, as well as the sensitivity, specificity, and cost of screening endoscopy. A small drop in the health-related quality of life associated with postsurgical states markedly reduced the effectiveness of screening. Simultaneous variations of the prevalence, specificity, and health-related quality of life can easily change screening endoscopy from a life-saving into a life-losing strategy. CONCLUSIONS: Under favorable conditions, general screening by endoscopy of all patients with reflux symptoms to prevent death from esophageal adenocarcinoma may represent a cost-effective strategy; however, such conditions may be difficult to meet.

Cost-Benefit Analysis↗
PubMed2000

Sidetracks in the diagnosis of gastrointestinal disease.

Patients usually visit a physician for a particular reason, which medicine has termed the "chief complaint." As patients often have more than a single complaint, it is common for physicians to lose focus, get distracted, and venture down a path other than the one toward resolution of the chief complaint--in other words, to get sidetracked. The aim of the present review is to describe the nature of diagnostic sidetracking, why it occurs, mechanisms in action, and means to prevent it. During a regular diagnostic process, the physician's suspicions about a diagnosis advance from broad and general to narrow and specific concepts. Each step in the diagnostic process is potentially driven by its own hypothesis, and each individual hypothesis becomes verified or falsified by pointed questions during the history or by medical tests. If a diagnostic process were to focus on the correct diagnosis that eventually explained the chief complaint, the intersections among the consecutively refined diagnostic concepts would converge toward one specific set, with the final diagnosis located inside the nonzero intersection of all consecutive diagnostic concepts. In a faulty diagnostic process, consecutive diagnostic concepts fail to converge, and the final diagnosis and chief complaint do not intersect. In this regard, the physician has pursued a false path and has become sidetracked. The effects of sidetracking range from minimal to disastrous. Sidetracking can delay diagnosis, delay treatment, and waste resources investigating or treating irrelevant medical problems. To avoid sidetracking, physicians should focus on the main problem, avoid getting involved with complementary solutions to secondary medical problems, and verify repetitively during the diagnostic process the relationship between each current working hypothesis and the patient's major medical problem.

Decision Making↗
PubMed2000

A decision analysis of surveillance for colorectal cancer in ulcerative colitis.

BACKGROUND: Patients with long standing, extensive ulcerative colitis have an increased risk of developing colorectal cancer. AIMS: To assess the feasibility of surveillance colonoscopy in preventing death from colorectal cancer. PATIENTS: A hypothetical cohort of patients with chronic ulcerative colitis. METHODS: The benefits of life years saved were weighted against the costs of biannual colonoscopy and proctocolectomy, and the terminal care of patients dying from colorectal cancer. Two separate Markov processes were modelled to compare the cost-benefit relation in patients with or without surveillance. The cumulative probability of developing colorectal cancer served as a threshold to determine which of the two management strategies is associated with a larger net benefit. RESULTS: If the cumulative probability of colorectal cancer exceeds a threshold value of 27%, surveillance becomes more beneficial than no surveillance. The threshold is only slightly smaller than the actual cumulative cancer rate of 30%. Variations of the assumptions built into the model can raise the threshold above or lower it far below the actual rate. If several of the assumptions are varied jointly, even small changes can lead to extreme threshold values. CONCLUSIONS: It is not possible to prove that frequent colonoscopies scheduled at regular intervals are an effective means to manage the increased risk of colorectal cancer associated with ulcerative colitis.

Colitis, Ulcerative↗
PubMed2000

alpha3beta1 and alpha6beta4 integrin receptors for laminin-5 are not essential for epidermal morphogenesis and homeostasis during skin development.

Continuous regeneration and homeostasis of the stratified epidermis requires coordinated regulation of cell proliferation, cell differentiation, and cell survival. Integrin-mediated cell adhesion to the extracellular matrix has important roles in regulating each of these processes. Integrins alpha3beta1 and alpha6beta4 are both receptors on epidermal keratinocytes for the basement membrane protein laminin-5, the major ligand for epidermal adhesion in mature skin. Ablation in mice of either alpha3beta1 or alpha6beta4, through null mutation of the gene encoding the alpha3, alpha6, or beta4 integrin subunit, results in epidermal blistering of varying severity. Our previous studies showed that, despite blistering, differentiation and stratification of the epidermis appeared essentially normal in mice that lacked either alpha3beta1 or alpha6beta4. However, these studies did not definitively address the specific developmental importance of each integrin, since they may have overlapping and/or compensatory functions. Given the individual importance of alpha3beta1 or alpha6beta4 in maintaining the dermo-epidermal junction in mature skin, we sought to determine the importance of these integrins for embryonic skin development and epidermal morphogenesis. In the current study, we analyzed skin development in mutant embryos that completely lack both integrins alpha3beta1 and alpha6beta4. Although alpha3beta1/alpha6beta4-deficient embryos displayed epidermal blistering by stage E15.5 of development, they also retained regions of extensive epidermal adhesion to the basement membrane through stage E16.5, indicating alternative adhesion mechanisms. Apoptosis was induced in detached epidermis of alpha3beta1/alpha6beta4-deficient embryos, exemplifying vividly the importance of epithelial attachment to the basement membrane for cell survival. However, apoptotic cells were completely absent from attached epidermis of alpha3beta1/alpha6beta4-deficient embryos, showing that epithelial adhesion that occurred independently of alpha3beta1 and alpha6beta4 also protected cells from apoptosis. Remarkably, in the absence of the known laminin-5 binding integrins (alpha3beta1, alpha6beta4, and alpha6beta1), keratinocytes retained the capacity to proliferate in the epidermis, and epidermal stratification and skin morphogenesis appeared normal prior to blister formation. These findings show that while alpha3beta1 and alpha6beta4 are both required for integrity of the dermo-epidermal junction, neither one is essential for epidermal morphogenesis during skin development.

Animals↗
PubMed2000

Integrin binding specificity of laminin-10/11: laminin-10/11 are recognized by alpha 3 beta 1, alpha 6 beta 1 and alpha 6 beta 4 integrins.

Laminin-10/11, the laminin isoforms containing the alpha 5 chain, are major components of basement membranes of many fetal and adult tissues. Laminin-10/11 purified from the conditioned medium of human lung carcinoma cells were potent in mediating adhesion of the carcinoma cells in an integrin alpha 3 beta 1-dependent manner. To further define the type(s) of integrins involved in cell adhesion to laminin-10/11, we examined the effects of a panel of function-blocking anti-integrin antibodies on the adhesion of different cell types to laminin-10/11. Although anti-integrin beta 1 antibody inhibited the adhesion of all cell types tested, anti-alpha 3 antibody inhibited the adhesion of carcinoma and glioma cells but not fibroblastic cells. Adhesion of fibroblastic cells was inhibited, however, by a combination of anti-alpha 3 and anti-alpha 6 antibodies, suggesting that both alpha 3 beta 1 and alpha 6 beta 1 integrins function as laminin-10/11 receptors in these cells. To explore this possibility, we examined the adhesion of K562 leukemic cells transfected with integrin alpha 3 or alpha 6 subunit to laminin-10/11 or other laminin isoforms. Laminin-10/11 were potent adhesive ligands for both the alpha 3 beta 11 and alpha 6 beta 1 transfectants, whereas laminin-5 was the preferred ligand for the alpha 3 beta 1 transfectants. Upon stimulation with the activating anti-integrin beta 1 antibody, both transfectants became more adherent to the substratum regardless of the type of laminins coated, although their preference for laminin isoforms remained unaltered. K562 cells transfected with alpha 6 and beta 4 subunits were also capable of adhering to laminin-10/11, indicating that integrin alpha 6 beta 4 is another receptor for laminin-10/11. Even with lung carcinoma cells, the alpha 6-containing integrins partly contributed to adhesion to laminin-10/11 at higher coating concentrations, although non-integrin receptor(s) might also be involved under such conditions. These results indicated that laminin-10/11 are potent and versatile adhesive ligands in basement membranes capable of binding to both alpha 3 beta 1 and alpha 6 beta 1 integrins with high avidity and also to alpha 6 beta 4 integrin.

Antigens, CD↗
PubMed2000

Formation of hemidesmosome-like structures in the absence of ligand binding by the (alpha)6(beta)4 integrin requires binding of HD1/plectin to the cytoplasmic domain of the (beta)4 integrin subunit.

Hemidesmosomes are adhesion structures that mediate anchorage of epithelial cells to the underlying basement membrane. We have previously shown that the (alpha)6(beta)4 integrin can induce the assembly of these multi-protein structures independent of binding to its ligand laminin-5 (ligand-independent formation of hemidesmosomes). Our results suggested a role for HD1/plectin, which binds to the cytoplasmic domain of the (beta)4 integrin subunit, in controlling the clustering of hemidesmosomal components at the basal side of the cell. Using keratinocytes derived from patients lacking HD1/plectin, we now show that ligand-independent formation of hemidesmosomal clusters indeed requires HD1/plectin, in contrast to the ligand-dependent assembly of hemidesmosomes. No clustering of the (alpha)6(beta)4 integrin, or of the bullous pemphigoid antigens BP180 and BP230, was seen when HD1/plectin-deficient keratinocytes were plated on fibronectin or type IV collagen. In (&bgr;)4-deficient keratinocytes, expression of an interleukin 2 receptor (IL2R) transmembrane chimera containing the (beta)4 cytoplasmic tail with the mutation R1281W, which abrogates HD1/plectin binding, resulted in a diffuse distribution of the chimeric receptor. In contrast, a (beta)4(R1281W) mutant that can associate with (alpha)6 and bind ligand, was found to be directed to the basal surface of the cells, at sites where laminin-5 was deposited. In addition, this mutant induced clustering of BP180 and BP230 at these sites. Together, these results show that the formation of hemidesmosomes requires binding of either ligand or HD1/plectin to the (beta)4 integrin subunit. Intriguingly, we found that IL2R/(beta)4 chimeras become localized in pre-existing hemidesmosomes of HD1/plectin-deficient keratinocytes, and that this localization requires a domain in the (beta)4 cytoplasmic tail that is also required for HD1/plectin binding (residues 1115-1356). Because this part of (beta)4 lacks the BP180 binding site, and since we show in this study that it is unable to interact with the same part on another (beta)4 molecule, we suggest that the chimera becomes incorporated into hemidesmosomes of HD1/plectin-deficient keratinocytes by interacting with an as yet unidentified hemidesmosomal component.

Antigens, CD↗