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Biomedical subjects

E Fuchs

Publications and source records attributed to E Fuchs.

At least 127 records · Page 7Linked to original sources
PubMed1996

Beta4 integrin is required for hemidesmosome formation, cell adhesion and cell survival.

The integrin heterodimer alpha 6 beta 4 is expressed in many epithelia and in Schwann cells. In stratified epithelia, alpha 6 beta 4 couple with BPAG1-e and BPAG2 to form hemidesmosomes, attaching externally to laminin and internally to the keratin cytoskeleton. To explore the function of this atypical integrin, and its relation to conventional actin-associated integrins, we targeted the removal of the beta 4 gene in mice. Tissues that express alpha 6 beta 4 are grossly affected. Stratified tissues are devoid of hemidesmosomes, display only a very fragile attachment to the basal lamina, and exhibit signs of degeneration and tissue disorganization. Simple epithelia which express alpha 6 beta 4 are also defective in adherence, even though they do not form hemidesmosomes. In the absence of beta 4, alpha 6 is dramatically downregulated, and other integrins do not appear to compensate for the loss of this heterodimer. These data have important implications for understanding integrin function in cell-substratum adhesion, cell survival and differentiation, and for understanding the role of alpha 6 beta 4 in junctional epidermolysis bullosa, an often lethal human disorder with pathology similar to our mice.

Animals↗
PubMed1996

Genetic analysis of a severe case of Dowling-Meara epidermolysis bullosa simplex.

The epidermis serves an important protective function, which it manifests by producing an extensive cytoskeletal architecture, the unique feature of which are keratin filaments. Through studies that began with epidermolysis bullosa simplex (EBS) and now extend to a group of autosomal dominant human blistering skin disorders it was discovered that defects in the keratin genes lead to cell fragility and degeneration upon mechanical trauma. In most cases of EBS, point mutations occur in the keratin 5 (K5) and K14 genes expressed in the basal layer of the epidermis. The precise location of the mutation and the degree to which it causes perturbations in filament assembly correlate with disease severity. In the present study, we examine a case of EBS, which clinically lies at the severe end of the spectrum of Dowling-Meara EBS and which shows keratin filament clumping in suprabasal as well as basal cells. We show that one of the two K14 alleles has a single point substitution, giving rise to a Y129D mutation. This mutation resides 4 residues internal to the R125C/H hotspot known to account for the majority of Dowling-Meara cases. We provide functional and structural evidence to suggest why the Y129D mutation may be capable of creating such a severe form of EBS.

Adult↗
PubMed1996

Tumors of the respiratory tract observed at the German Primate Center, 1978-1994.

Eight spontaneous pulmonary tumors (four bronchiolar tubular adenomas, two bronchiolar adenocarcinomas, two squamous-cell carcinomas) occurred in a total of 54 adult tree shrews (Tupaia belangeri) of the GPC colonies between 1978 and 1994. The adenomas and adenocarcinomas consisted of tubularly or trabecularly arranged cuboidal to cylindrical cells interspersed with some PAS-positive goblet cells, thus resembling the epithelial lining of respiratory bronchioles of tree shrews. The two squamous-cell carcinomas probably originated from the pulmonary alveoles. Three more pulmonary tumors (one small-cell carcinoma, one bronchial adenoma, one squamous-cell carcinoma) developed in 409 adult callitrichids of the GPC colonies during the same period, and one more bronchial adenoma was observed in a common marmoset (Callithrix jacchus) of another colony located in Göttingen. With regard to the adenomas and squamous-cell carcinomas, a similar cellular origin with the three shrews is assumed. The small-cell carcinoma possibly developed from the bronchial epithelium, provided a pathogenesis parallel to that of human small-cell carcinoma is suggested. Four of the tree shrew pulmonary adenomas/adenocarcinomas and the small-cell Ca were macroscopically visible as yellowish-grey nodules of 1 mm x 1 mm to 15 mm x 15 mm diameter, predominantly involving the main lobes (2 x right main lobes, 2 x left main lobes, 1 x all lobes). The pulmonary tumors of the other animals were below macroscopical detectability.

Adenocarcinoma↗
PubMed1996

The cytoskeleton and disease: genetic disorders of intermediate filaments.

Specialized cytoskeletons play many fascinating roles, including mechanical integrity and wound-healing in epidermal cells, cell polarity in simple epithelia, contraction in muscle cells, hearing and balance in the inner ear cells, axonal transport in neurons, and neuromuscular junction formation between muscle cells and motor neurons. These varied functions are dependent upon cytoplasmic networks of actin microfilaments (6 nm), intermediate filaments (10 nm) and microtubules (23 nm), and their many associated proteins. In this chapter, I review what is known about the cytoskeletons of intermediate filaments and their associated proteins. I focus largely on epidermal cells, which devote most of their protein-synthesizing machinery to producing an extensive intermediate filament network composed of keratin. Recent studies have shown that many of the devastating human disorders that arise from degeneration of this cell type have as their underlying basis either defects in the genes encoding keratins or abnormalities in keratin IF networks. I discuss what we know about the functions of IFs, and how the link to genetic disease has enhanced this understanding.

Amino Acid Sequence↗
PubMed1996

Retinoic acid receptor- and retinoid X receptor-selective retinoids activate signaling pathways that converge on AP-1 and inhibit squamous differentiation in human bronchial epithelial cells.

Human bronchial epithelial (HBE) cells undergo squamous differentiation in response to a variety of conditions in tissue culture, and retinoid treatment has been shown to reverse this process. Retinoids mediate their effects through the retinoic acid and retinoid X nuclear receptors (RAR and RXR, respectively), which form RAR-RXR heterodimers, RXR homodimers, and heterodimers of RXR and certain orphan receptors. These receptor dimers bind to distinct response elements, activating separate pathways. In this study, we investigated the roles of RAR and RXR signaling pathways in the inhibition of HBE squamous differentiation. After induction of squamous differentiation by confluent growth, HBE cells were treated with retinoids that selectively activate RARs (E-4-[2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthaienyl)-1- propenyl] benzoic acid), RXRs (4-[1-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthyl)ethenyl]benzoic acid), or both RARs and RXRs (9-c/s retinoic acid). These retinoids inhibited the mRNA expression of the squamous differentiation markers transglutaminase type I, involucrin, keratin 5, and keratin 13, suggesting that inhibition of HBE squamous differentiation could be mediated by activation of either RAR or RXR signaling pathways. We examined the role of AP-1 as a potential effector of these retinoid pathways. AP-1 transcriptional activity was reduced markedly by these retinoids, and a concomitant, but proportionally smaller, reduction in AP-1 DNA binding was observed. Furthermore, treatment of squamous HBE cells with the retinoid SR11238, which inhibited AP-1 without activating retinoid receptor transcriptional properties, reduced the expression of transglutaminase type I and involucrin. These findings support the hypothesis that, in HBE cells, RAR and RXR signaling pathways inhibit AP-1 transcriptional activity, and this contributes to retinoid-induced reversal of HBE squamous differentiation.

Alitretinoin↗
PubMed1995

Gene targeting of BPAG1: abnormalities in mechanical strength and cell migration in stratified epithelia and neurologic degeneration.

BPAG1 is the major antigenic determinant of autoimmune sera of bullous pemphigoid (BP) patients. It is made by stratified squamous epithelia, where it localizes to the inner surface of specialized integrin-mediated adherens junctions (hemidesmosomes). To explore the function of BPAG1 and its relation to BP, we targeted the removal of the BPAG1 gene in mice. Hemidesmosomes are otherwise normal, but they lack the inner plate and have no cytoskeleton attached. Though not affecting cell growth or substratum adhesion, this compromises mechanical integrity and influences migration. Unexpectedly, the mice also develop severe dystonia and sensory nerve degeneration typical of dystonia musculorum (dt/dt) mice. We show that in at least one other strain of dt/dt mice, BPAG1 gene is defective.

Animals↗
PubMed1995

Lymphoid enhancer factor 1 directs hair follicle patterning and epithelial cell fate.

T cell-specific transcription factor (TCF-1) and lymphoid enhancer factor 1 (LEF-1) have been implicated exclusively in the regulation of T cell-specific genes. The only adult tissue other than thymus known to express these factors is spleen and lymph node, which contain low levels of LEF-1 and no TCF-1. We noticed that genes involved in hair-specific gene expression possess LEF-1/TCF-1 consensus motifs located in similar positions relative to their TATA box. We show that of the two factors only LEF-1 is expressed in hair follicles; it can be cloned in both splice forms from human skin keratinocytes and it can bind to these sites in the hair promoters. We show that LEF-1 mRNA is present in pluripotent ectoderm, and it is up-regulated in a highly restricted pattern just before the formation of underlying mesenchymal condensates and commitment of overlying ectodermal cells to invaginate and become hair follicles. New waves of ectodermal LEF-1 spots appear concomitant with new waves of follicle morphogenesis. To test whether LEF-1 patterning might be functionally important for hair patterning and morphogenesis, we used transgenic technology to alter the patterning and timing of LEF-1 over the surface ectoderm. Striking abnormalities arose in the positioning and orientation of hair follicles, leaving a marked disruption of this normally uniform patterning. This provides the first direct evidence that ectodermal cues are critical in establishing these developmental processes, which at later stages are known to be influenced by underlying mesenchyme. Remarkably, elevated LEF-1 in the lip furrow epithelium of developing transgenic animals triggered these cells to invaginate, sometimes leading to the inappropriate adoption of hair follicle and tooth cell fates. Collectively, our findings demonstrate that ectodermal expression of LEF-1 plays a central role in gene expression, pattern formation, and other developmental processes involving epithelial-mesenchymal associations.

Alternative Splicing↗
PubMed1995

Inhibition of skin development by targeted expression of a dominant-negative retinoic acid receptor.

Although pharmacological doses of retinoic acid (RA) have a wide variety of actions in vivo, experimental difficulties have prevented a definitive assignment of its physiological functions. We recently made a dominant-negative retinoic acid receptor (RAR) by a single amino-acid substitution which creates a dominant-negative thyroid hormone receptor. The mutated RAR efficiently inhibited the endogenous activities of RARs (alpha, beta, gamma). Thus, targeted expression of the mutated receptor should reveal RA functions during organogenesis by blocking RA signalling in the tissues concerned. To address this possibility, we expressed the dominant-negative RAR in the epidermis, a potential target organ of RA. We report here that the resultant transgenic mice exhibited dramatic suppression of epidermal maturation, demonstrating the requirement of RA in normal skin development.

Animals↗
PubMed1995

Chronic psychosocial stress induces morphological alterations in hippocampal pyramidal neurons of the tree shrew.

The effect of sustained psychosocial stress on the morphology of hippocampal pyramidal neurons was analysed in male tree shrews after 14, 20, and 28 days of social confrontation. A variety of physiological changes such as constantly elevated levels of urinary cortisol and norepinephrine and reduced body weight, which are indicative of chronic stress were observed in the subordinate, but not in the dominant males. Light microscopic analysis of Nissl-stained hippocampal sections showed that the staining intensity of the nucleoplasm in the CA1 and CA3 pyramidal neurons was increased after prolonged psychosocial stress, indicating a change in the nuclear chromatin structure. These alterations were observed only in subordinate animals and increased in a time dependent manner in accordance with the length of the stress period. There was, however, neither a reduction in density nor a degeneration of pyramidal neurons in chronically stressed animals. Mechanisms which may possibly account for the observed alterations are discussed.

Age Factors↗
PubMed1995

The importance of intramolecular ion pairing in intermediate filaments.

Nuclear and cytoskeletal networks of 10-nm intermediate filaments (IFs) are probably ubiquitous in multicellular eukaryotes. They likely play a role in maintaining the mechanical integrity of a cell. With the exception of the nuclear lamins, IF proteins can form IFs in vitro in the absence of cofactors or associated proteins. Below we present data suggesting that the large alpha-helical "rod" domains of IF proteins are stabilized by large numbers (up to 50) of intra-helical ion pairs formed by residues of opposite charge situated four residues apart. These many ion pairs, sometimes involving up to 30% of the residues within a coiled-coil IF segment, can potentially contribute as much as 10-25 kcal/mol (1 kcal = 4.18 kJ) to the stability of a single alpha-helical rod. Such stabilization is likely to play a major role in the chemical and physical stability of IF networks in vitro and in vivo. An investigation of other coiled-coil proteins shows that selection for intrahelical ion pairing is not simply a property intrinsic to coiled-coil proteins. Rather, there is a correlation between the degree to which there is selection for intrahelical ion pairs and the extent to which a coiled-coil protein participates in highly ordered multimolecular interactions--e.g., as in IFs and myosin thick filaments. The propensity of putative ion pairs in some IF proteins--e.g., epidermal keratins--suggests that an underlying structural stability at the level of the monomer may play an important role in the extraordinary stability of dimers and higher ordered structures in cytoplasmic IFs.

Amino Acid Sequence↗
PubMed1995

Modulation of binding sites for corticotropin-releasing hormone by chronic psychosocial stress.

This study was conducted to determine whether long lasting psychosocial stress would affect corticotropin-releasing hormone (CRH) binding sites in the brain, the pituitary, and the adrenal gland. As a model for sustained emotional stress we used chronic psychosocial conflict in male tree shrews. In subordinate tree shrews, repeated confrontation with a dominant conspecific results in constant hyperactivity of the HPA-axis and an elevated neurosympathetic tone. After 24 days of psychosocial conflict, CRH binding sites were quantified by in vitro-autoradiography with 125I-ovine CRH in 23 discrete brain regions, the pituitaries, and the adrenal glands of subordinate and control animals. Chronic stress significantly reduced the number of binding sites (Bmax) in the anterior lobe of the pituitary, the dentate gyrus, the CA1-CA3 areas of the hippocampus, and in both the stratum griseum superficiale and the stratum opticum of the superior colliculus. In cortical area 17, the reduction of Bmax was counterbalanced by an increase in the affinity (Kd) of the radioligand for the binding sites. A significant stress-induced enhancement of Bmax was observed in the frontal cortex, cingulate cortex, claustrocortex, the central and lateral nucleus of the amygdala, and in the choroid plexus. This increase was accompanied by a significant decrease of Kd-values in the frontal and cingulate cortex, the lateral nucleus of the amygdala, and the choroid plexus. These findings represent the first in vivo demonstration of a modulation of extrahypothalamic CRH receptors by a naturally occurring form of stress. The different response patterns of the central CRH binding sites reflect distinct neuroendocrine processes which are presumed to coordinate behavioral, autonomic, endocrine, and immune responses to long-lasting psychosocial conflict.

Adrenal Glands↗
PubMed1995

The basal keratin network of stratified squamous epithelia: defining K15 function in the absence of K14.

Keratin 5 and keratin 14 have been touted as the hallmarks of the basal keratin networks of all stratified squamous epithelia. Absence of K14 gives rise to epidermolysis bullosa simplex, a human blistering skin disorder involving cytolysis in the basal layer of epidermis. To address the puzzling question of why this disease is primarily manifested in skin rather than other stratified squamous epithelia, we ablated the K14 gene in mice and examined various tissues expressing this gene. We show that a key factor is the presence of another keratin, K15, which was hitherto unappreciated as a basal cell component. We show that the levels of K15 relative to K14 vary dramatically among stratified squamous epithelial tissues, and with neonatal development. In the absence of K14, K15 makes a bona fide, but ultrastructurally distinct, keratin filament network with K5. In the epidermis of neonatal mutant mice, K15 levels are low and do not compensate for the loss of K14. In contrast, the esophagus is unaffected in the neonatal mutant mice, but does appear to be fragile in the adult. Parallel to this phenomenon is that esophageal K14 is expressed at extremely low levels in the neonate, but rises in postnatal development. Finally, despite previous conclusions that the formation of suprabasal keratin filaments might depend upon K5/K14, we find that a wide variety of suprabasal networks composed of different keratins can form in the absence of K14 in the basal layer.

Amino Acid Sequence↗
PubMed1995

Keratins and the skin.

Keratins are the major structural proteins of the vertebrate epidermis and its appendages, constituting up to 85% of a fully differentiated keratinocyte. Together with actin microfilaments and microtubules, keratin filaments make up the cytoskeletons of vertebrate epithelial cells. Traced as far back in the evolutionary kingdom as mollusks, keratins belong to the superfamily of intermediate filament (IF) proteins that form alpha-helical coiled-coil dimers which associate laterally and end-to-end to form 10-nm diameter filaments. The evolutionary transition between organisms bearing an exoskeleton and those with an endoskeleton seemed to cause considerable change in keratin. Keratins expanded from a single gene to a multigene family. Of the approximately 60 IF genes in the human genome, half encode keratins, and at least 18 of these are expressed in skin. Vertebrate keratins are subdivided into two sequence types (I and II) that are typically coexpressed as specific pairs with complex expression patterns. The filament-forming capacity of a pair is dependent upon its intrinsic ability to self-assemble into coiled-coil heterodimers, a feature not required of the invertebrate keratins (Weber et al 1988). Approximately 20,000 heterodimers of type I and type II keratins assemble into an IF. Mutations that perturb keratin filament assembly in vitro can cause blistering human skin disorders in vivo. From studies of these diseases, an important function of keratins has been unraveled. These filaments impart mechanical strength to a keratinocyte, without which the cell becomes fragile and prone to rupturing upon physical stress. In this review, studies on the pattern of expression, structure, and function of skin keratins are summarized, and new insights into the functions of these proteins and their involvement in human disease are postulated.

Amino Acid Sequence↗
PubMed1995

Expression of vascular endothelial growth factor and its receptors in human renal ontogenesis and in adult kidney.

Vascular endothelial growth factor (VEGF) may modulate vascular permeability, chemotaxis for monocytes, and protease activity. In addition, VEGF may play a role in embryonic and tumor angiogenesis. In fetal mouse kidney, VEGF mRNA and protein expression have been demonstrated. This finding led to the hypothesis that VEGF might be involved in renal growth and development. To further elucidate the role of VEGF in human kidney, expression of VEGF and its receptors, the specific tyrosine kinase receptors, fit-1 and KDR, were studied. In fetal (6-24 gestational wk; mesonephros and metanephros) and adult kidney, VEGF mRNA and protein could be colocalized in glomerular epithelia and collecting duct cells by in situ hybridization and immunohistology. By reverse transcription-polymerase chain reaction, mRNA of three VEGF isoforms, VEGF121, VEGF165, and VEGF189, were found in fetal kidney and cortex, isolated glomeruli, and medulla of adult human kidney. KDR and flt-1 mRNA were coexpressed in endothelia of glomeruli and in peritubular capillaries in fetal and adult kidney. These data support the assumption that VEGF and its receptors may influence renal ontogenesis. We speculate that the constitutive expression of VEGF in adult kidney may be required for the function of VEGF receptor positive-fenestrated endothelia in glomeruli and postglomerular vessels. The expression of VEGF in collecting duct and of its receptors in medullary capillaries may in addition be relevant for maintaining medullary osmolality.

Aged↗
PubMed1995

The A/B domain of truncated retinoic acid receptors can block differentiation and promote features of malignancy.

Recently, we discovered that stable introduction of a carboxyl-terminally truncated retinoic acid receptor gamma (tRAR gamma) into an epidermal keratinocyte line blocked the ability of these cells to differentiate, as judged by their failure to express late markers of squamous differentiation. We now demonstrate a correlation between the level of residual endogenous RAR activity of tRAR gamma-expressing keratinocyte lines and degree of terminal differentiation. Mutagenesis studies localize the effects to the A/B subdomain of the truncated receptor. Despite tRAR gamma's capacity to interfere with RAR-mediated transactivation of retinoic acid response elements (RAREs) in keratinocytes, the effects of the truncated receptor are independent of its ability to bind DNA and directly interact with endogenous RARs. tRAR alpha also inhibits RARE-mediated gene expression in keratinocytes, even though its full-length counterpart enhances RARE activity in these cells. Intriguingly, both tRAR gamma and RAR gamma suppress keratin promoter activity in epidermal cells, although for tRAR gamma, the effect is mediated through the A/B domain whereas for RAR gamma, the effects require DNA binding. Taken together, these findings suggest that the truncation allows for new and aberrant interactions with transcriptional proteins/cofactors that participate in governing RARE activity. This discovery may have relevance in tumorigenesis, where genetic lesions can result in mutant RARs or in loss of receptor expression.

Base Sequence↗
PubMed1995

Intestinal trichomoniasis due to Tritrichomonas mobilensis in tree shrews (Tupaia belangeri).

Intestinal trichomoniasis was observed in 156 of 202 Tupaia belangeri (77.2%). The parasites were located principally in the cecum (75%) and were far less common in the proximal portion of the colon (19%) or terminal portion of the ileum (6%). Advanced trichomoniasis was associated with liquid cecal contents but not diarrhea. The trichomonads had a tendency to penetrate the mucosal epithelial layer, causing desquamation of entire crypts. They never penetrated the epithelial basement membrane and never triggered inflammatory responses. The trichomonads were characterized by three anterior flagella and one trailing flagellum that extended over the entire parasite body, connected to it by an undulating membrane. The capitulum of the straight axostyle formed a small but well defined pelta, and the stout costa had distinct banding. The parasites thereby matched the description of Tritrichomonas mobilensis.

Animals↗
PubMed1994

Genetic and clinical mosaicism in a type of epidermal nevus.

BACKGROUND: Many skin disorders are characterized by a mosaic pattern, often with alternating stripes of affected and unaffected skin that follow the lines of Blaschko. These nonrandom patterns may be caused by a postzygotic mutation during embryogenesis. We studied the genetic basis of one such disorder, epidermal nevus of the epidermolytic hyperkeratotic type. Epidermolytic hyperkeratosis is an autosomal dominant blistering skin disease arising from mutations in the genes for keratin (K) 1 and 10. The offspring of patients with epidermal nevi may have generalized epidermolytic hyperkeratosis. METHODS: We studied the K1 and K10 genes in blood and in the keratinocytes and fibroblasts of lesional and nonlesional skin from three patients with epidermal nevi and four of their offspring with epidermolytic hyperkeratosis. RESULTS: In the patients with epidermal nevi, point mutations in 50 percent of the K10 alleles of epidermal cells were found in keratinocytes from lesional skin; no mutations were detected in normal skin. This mutation was absent or underrepresented in blood and skin fibroblasts. In the offspring with epidermolytic hyperkeratosis, the same mutations as those in the parents were found in 50 percent of the K10 alleles from all cell types examined. CONCLUSIONS: Epidermal nevus of the epidermolytic hyperkeratotic type is a mosaic genetic disorder of suprabasal keratin. The correlation of mutations in the K10 gene with lesional skin and the correlation of the normal gene with normal skin provide evidence that genetic mosaicism can cause clinical mosaicism.

Alleles↗