Novel human alpha9 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.