Sergei A. Grando

Novel Human α9 Acetylcholine Receptor Regulating Keratinocyte Adhesion is Targeted by Pemphigus Vulgaris Autoimmunity

Pemphigus vulgaris (PV) is a potentially fatal autoimmune mucocutaneous blistering disease. It was assumed that PV is caused by anti-desmoglein (Dsg) 3 autoimmunity because absorption of PV sera with a chimeric baculoprotein containing the Dsg 3 and IgG1 portions, rDsg3-Ig-His, eliminated disease-causing antibodies. In this study we demonstrate that rDsg3-Ig-His adsorbs out autoantibodies to different keratinocyte antigens, including a non-Dsg 3 130-kd polypeptide. Because the pool of disease-causing PV IgGs contains antibodies against the keratinocyte acetylcholine receptor (AChR), we sought to identify the targeted receptor(s). Preincubation of monkey esophagus with PV antibodies blocked specific staining of the keratinocyte cell membrane with rabbit monoepitopic antibody to alpha9 AChR, indicating that this first of its kind AChR with dual, muscarinic and nicotinic pharmacology is targeted by PV autoimmunity. Anti-alpha9 antibody stained keratinocytes in a fishnet-like intercellular pattern, and visualized a single band at approximately 50 kd in Western blots of keratinocyte membrane proteins. Using step-by-step reverse transcription polymerase chain reactions with primers based on known alpha9 sequence regions, we identified the complete reading frame of human alpha9. Its amino acid sequence showed 85% similarity with rat alpha9. Treatment of keratinocyte monolayers with anti-alpha9 antibody induced pemphigus-like acantholysis, which could be reversed either spontaneously or by using the cholinergic agonist carbachol. We conclude that alpha9 is coupled to physiological regulation of keratinocyte adhesion, and its interaction with PV IgG may lead to blister development.

Receptor-mediated tobacco toxicity: cooperation of the Ras/Raf-1/MEK1/ERK and JAK-2/STAT-3 pathways downstream of α7 nicotinic receptor in oral keratinocytes

The use of tobacco products is associated with an increased incidence of periodontal disease, poor response to periodontal therapy, and a high risk for developing head and neck cancer. Nicotine and tobacco‐derived nitrosamines have been shown to exhibit their pathobiologic effects due in part to activation of the nicotinic acetylcholine (ACh) receptors (nAChRs), mainly α7 nAChR, expressed by oral keratinocytes (KCs). This study was designed to gain mechanistic insight into α7‐mediated morbidity of tobacco products in the oral cavity. We investigated the signaling pathways downstream of α7 nAChR in monolayers of oral KCs exposed for 24 h to aged and diluted sidestream cigarette smoke (ADSS) or an equivalent concentration of pure nicotine. By both real‐time polymerase chain reaction (PCR) and In‐cell Western, the KCs stimulated with ADSS or nicotine showed multifold increases of STAT‐3. These effects could be completely blocked or significantly P < <0.05) diminished if the cells were pretreated with the α7 antagonist ‐bungarotoxin (BTX) or transfected with anti‐α7 small interfering RNA (siRNA‐α7). The use of pathway inhibitors revealed that signaling through the Ras/Raf‐1/MEK1/ ERK steps mediated 7‐dependent up‐regulation of STAT‐3. Targeted mutation of the α7 gene prevented ERK1/2 activation by nicotine. Using the gel mobility shift assay, we demonstrated that an increased protein binding activity of STAT‐3 caused by ADSS or pure nicotine was mediated by janus‐activated kinase (JAK)‐2. Activation of JAK‐2/STAT‐3 pathway could be prevented by BTX or siRNA‐α7. Thus, nuclear transactivation of STAT‐3 in KCs exposed to tobacco products is mediated via intracellular signaling downstream from α7, which proceeds via two complementary pathways. The Ras/Raf‐1/MEK1/ERK cascade culminates in up‐regulated expression of the gene encoding STAT‐3, whereas recruitment and activation of tyrosine kinase JAK‐2 phosphorylates it. Elucidation of this novel mechanism of nicotine‐dependent nuclear transactivation of STAT‐3 identifies oral α7 nAChR as a promising molecular target to prevent, reverse, or retard tobacco‐related periodontal disease and progression of head and neck cancer by receptor inhibitors.—Arredondo, J., Chernyavsky, A. I., Jolkovsky, D. L., Pinkerton, K. E., Grando, S. A. Receptor‐mediated tobacco toxicity: cooperation of the Ras/Raf‐1/MEK1/ ERK and JAK‐2/STAT‐3 pathways downstream of α7 nicotinic receptor in oral keratinocytes. FASEB J. 20, 2093–2101 (2006)

The Nicotinic Acetylcholine Receptor: Structure and Autoimmune Pathology

The nicotinic acetylcholine receptors (AChR) are presently the best-characterized neurotransmitter receptors. They are pentamers of homologous or identical subunits, symmetrically arranged to form a transmembrane cation channel. The AChR subunits form a family of homologous proteins, derived from a common ancestor. An autoimmune response to muscle AChR causes the disease myasthenia gravis. This review summarizes recent developments in the understanding of the AChR structure and its molecular recognition by the immune system in myasthenia.

Definitions and outcome measures for bullous pemphigoid: recommendations by an international panel of experts

Our scientific knowledge of bullous pemphigoid (BP) has dramatically progressed in recent years. However, despite the availability of various therapeutic options for the treatment of inflammatory diseases, only a few multicenter controlled trials have helped to define effective therapies in BP. A major obstacle in sharing multicenter-based evidences for therapeutic efforts is the lack of generally accepted definitions for the clinical evaluation of patients with BP. Common terms and end points of BP are needed so that experts in the field can accurately measure and assess disease extent, activity, severity, and therapeutic response, and thus facilitate and advance clinical trials. These recommendations from the International Pemphigoid Committee represent 2 years of collaborative efforts to attain mutually acceptable common definitions for BP and proposes a disease extent score, the BP Disease Area Index. These items should assist in the development of consistent reporting of outcomes in future BP reports and studies.

Central role of α7 nicotinic receptor in differentiation of the stratified squamous epithelium

Several ganglionic nicotinic acetylcholine receptor (nAChR) types are abundantly expressed in nonneuronal locations, but their functions remain unknown. We found that keratinocyte α7 nAChR controls homeostasis and terminal differentiation of epidermal keratinocytes required for formation of the skin barrier. The effects of functional inactivation of α7 nAChR on keratinocyte cell cycle progression, differentiation, and apoptosis were studied in cell monolayers treated with α-bungarotoxin or antisense oligonucleotides and in the skin of Acra7 homozygous mice lacking α7 nAChR channels. Elimination of the α7 signaling pathway blocked nicotine-induced influx of 45Ca2+ and also inhibited terminal differentiation of these cells at the transcriptional and/or translational level. On the other hand, inhibition of the α7 nAChR pathway favored cell cycle progression. In the epidermis of α7−/− mice, the abnormalities in keratinocyte gene expression were associated with phenotypic changes characteristic of delayed epidermal turnover. The lack of α7 was associated with up-regulated expression of the α3 containing nAChR channels that lack α5 subunit, and both homomeric α9- and heteromeric α9α10-made nAChRs. Thus, this study demonstrates that ACh signaling through α7 nAChR channels controls late stages of keratinocyte development in the epidermis by regulating expression of the cell cycle progression, apoptosis, and terminal differentiation genes and that these effects are mediated, at least in part, by alterations in transmembrane Ca2+ influx.

Desmoglein Versus Non-desmoglein Signaling in Pemphigus Acantholysis CHARACTERIZATION OF NOVEL SIGNALING PATHWAYS DOWNSTREAM OF PEMPHIGUS VULGARIS ANTIGENS

Although it is accepted that pemphigus antibody binding to keratinocytes (KCs) evokes an array of intracellular biochemical events resulting in cell detachment and death, the triggering events remain obscure. It has been postulated that the binding of pemphigus vulgaris IgG (PVIgG) to KCs induces “desmosomal” signaling. Because in contrast to integrins and classical cadherins, desmoglein (Dsg) molecules are not known to elicit intracellular signaling, and because PV patients also produce non-Dsg autoantibodies, we investigated the roles of both Dsg and non-desmoglein PV antigens. The time course studies of KCs treated with PVIgG demonstrated that the activity of Src peaked at 30 min, EGF receptor kinase (EGFRK) at 60 min, and p38 MAPK at 240 min. The Src inhibitor PP2 decreased EGFRK and p38 activities by ∼45 and 30%, respectively, indicating that in addition to Src, PVIgG evokes other triggering events. The shrinkage of KCs (cell volume reduction) became significant at 120 min, keratin aggregation at 240 min, and an increase of TUNEL positivity at 360 min. Pretreatment of KCs with PP2 blocked PVIgG-dependent cell shrinkage and keratin aggregation by ∼50% and TUNEL positivity by ∼25%. The p38 MAPK inhibitor PD169316 inhibited these effects by ∼15, 20, and 70%, respectively. Transfection of KCs with small interfering RNAs that silenced expression of Dsg1 and/or Dsg3 proteins, blocked ∼50% of p38 MAPK activity but did not significantly alter the PVIgG-dependent rise in Src and EGFRK activities. These results indicate that activation of p38 MAPK is a late signaling step associated with collapse of the cytoskeleton and disassembly of desmosomes caused by upstream events involving Src and EGFRK. Therefore, the early acantholytic events are triggered by non-Dsg antibodies.

Autoimmunity to Keratinocyte Acetylcholine Receptors in Pemphigus

Pemphigus autoimmunity is not limited to antides- moglein antibodies. Nondesmoglein antibodies induce pemphigus-like lesions in neonatal mice. Acantholytic activity of pemphigus IgG harbors pharmacologic effects on keratinocyte shape and adhesion. Acantholytic antireceptor autoantibodies target: (1) a novel human α9 acetylcholine receptor regulating keratinocyte adhesion, and (2) pemphaxin, a novel keratinocyte annexin-like molecule binding acetylcholine. A ‘multiple-hit’ hypothesis reconciles recent findings of anti-acetylcholine-receptor autoimmunity in pemphigus and the fact that pemphigus patients also develop autoantibodies to adhesion molecules. The antiacantholytic activity of cholinergic agonists suggests a novel avenue for the development of a nonhormonal treatment of pemphigus.

Pemphigus Vulgaris Antibody Identifies Pemphaxin A NOVEL KERATINOCYTE ANNEXIN-LIKE MOLECULE BINDING ACETYLCHOLINE

Because pemphigus vulgaris (PV) IgGs adsorbed on the rDsg3-Ig-His baculoprotein induced blisters in neonatal mice, it was proposed that anti-desmoglein 3 (Dsg 3) autoantibody causes PV. However, we found that rDsg3-Ig-His absorbs autoantibodies to different antigens, including a non-Dsg 3 keratinocyte protein of 130 kDa. This prompted our search for novel targets of PV autoimmunity. The PV IgG eluted from a 75-kDa keratinocyte protein band both stained epidermis in a pemphigus-like pattern and induced acantholysis in keratinocyte monolayers. Screening of a keratinocyte λgt11 cDNA library with this antibody identified clones carrying cDNA inserts encoding a novel molecule exhibiting ∼40% similarity with annexin-2, named pemphaxin (PX). Recombinant PX (rPX-His) was produced inEscherichia coli M15 cells, and, because annexins can act as cholinergic receptors, its conformation was tested in a cholinergic radioligand binding assay. rPX-His specifically bound [3H]acetylcholine, suggesting that PX is one of the keratinocyte cholinergic receptors known to be targeted by disease-causing PV antibodies. Preabsorption of PV sera with rPX-His eliminated acantholytic activity, and eluted antibody immunoprecipitated native PX. This antibody alone did not cause skin blisters in vivo, but its addition to the preabsorbed PV IgG fraction restored acantholytic activity, indicating that acantholysis in PV results from synergistic action of antibodies to different keratinocyte self-antigens, including both acetylcholine receptors and desmosomal cadherins.

Connections of nicotine to cancer

This Opinion article discusses emerging evidence of direct contributions of nicotine to cancer onset and growth. The list of cancers reportedly connected to nicotine is expanding and presently includes small-cell and non-small-cell lung carcinomas, as well as head and neck, gastric, pancreatic, gallbladder, liver, colon, breast, cervical, urinary bladder and kidney cancers. The mutagenic and tumour-promoting activities of nicotine may result from its ability to damage the genome, disrupt cellular metabolic processes, and facilitate growth and spreading of transformed cells. The nicotinic acetylcholine receptors (nAChRs), which are activated by nicotine, can activate several signalling pathways that can have tumorigenic effects, and these receptors might be able to be targeted for cancer therapy or prevention. There is also growing evidence that the unique genetic makeup of an individual, such as polymorphisms in genes encoding nAChR subunits, might influence the susceptibility of that individual to the pathobiological effects of nicotine. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the evaluation of regulations on nicotine product manufacturing, distribution and marketing.

Cholinergic control of epidermal cohesion

Abstract:  The non‐neuronal cholinergic system of human epidermis includes the keratinocyte (KC) acetylcholine (ACh) axis composed of the enzymes mediating ACh synthesis and degradation, and two classes of ACh receptors, the nicotinic and muscarinic ACh receptors, mediating biological effects of the cutaneous cytotransmitter ACh. Regulation of KC cell–cell and cell–matrix adhesion is one of the important biological functions of cutaneous ACh. The downstream targets of ACh effects mediated by distinct ACh receptor subtypes include both the intercellular adhesion molecules, such as classical and desmosomal cadherins, and integrins mediating KC adhesion to a substrate. The signaling pathways include activation or inhibition of kinase cascades resulting in either up‐ or down‐regulation of the expression of cell adhesion molecules or changes in their phosphorylation status, or both. The components of the KC ACh axis are involved in cutaneous blistering in patients with autoimmune pemphigus, junctional and dystrophic forms of epidermolysis bullosa, thermal burns, and mustard‐induced vesication. Recent progress with the development of antiacantholytic therapies of patients with pemphigus using cholinomimetics indicates that cholinergic drugs may be a promising approach for other cutaneous blistering disorders.