Significance of the extracellular cleavage of BP180/type XVII collagen for skin biology and disease

半桥粒介导复杂复层上皮细胞与基底膜的粘附。大疱性类天疱疮抗原180（BP 180）/XVII型胶原是半桥粒跨膜蛋白，并且是锚定丝的主要组分。对BP 180的自身免疫反应和蛋白质的遗传缺陷都导致表皮下起泡，强调其对基底膜区完整性的重要性。BP 180的120 kDa细胞外部分可以作为蛋白水解切割的结果从细胞表面脱落。我们最近发现，裂解介导的膜相关的基质金属蛋白酶和定位在近膜NC 16 A结构域的BP 180。该位点与α 6 β 4整联蛋白的α 6亚基结合，代表BP 180最具免疫原性的部分。本建议的目的是检查卵裂过程的生理和病理意义。通过酶促消除培养的角质形成细胞中的细胞外胶原部分来再现切割，并且将使用针对BP 230、α 6 β 4整联蛋白和层粘连蛋白5的特异性单克隆抗体来研究其对半桥粒组分之间的相互作用的影响。通过定点突变，氨基酸的变化将被引入NC 16 A结构域内靠近切割位点。将来自缺乏BP 180的患者（GABEB）的角质形成细胞用这些突变形式的BP 180转染，以确定切割是否可以被消除。突变体BP 180也将用于研究切割与细胞迁移和分化的相关性。最后，将研究切割过程对患者自身抗体对BP 180的NC 16 A结构域的反应性的影响。这些研究将提高我们对基底膜区锚定机制的理解。

Hemidesmosomes mediate adhesion of complex and stratified epithelia to basement membranes. Bullous pemphigoid antigen 180 (BP180)/type XVII collagen is a hemidesmosomal transmembrane protein and a major component of anchoring filaments. Both an autoimmune response to BP180 and genetic defects of the protein result in subepidermal blistering emphasizing its importance for the integrity of the basement membrane zone. A 120 kDa extracellular portion of BP180 can be shed from the cell surface as a result of proteolytic cleavage. We recently found the cleavage to be mediated by a membrane-associated matrix metalloproteinase and to localize within the membraneproximal NC16A domain of BP180. This site associates with the a6 subunit of a6b4 integrin and represents the most immunogenic portion of BP180. The aim of the present proposal is to examine the physiological and pathological significance of the cleavage process. The cleavage will be reproduced by enzymatic elimination of the extracellular collagenous portion in cultured keratinocytes and its effect on the interaction between hemidesmosomal components will be studied using specific monoclonal antibodies to BP230, a6b4 integrin, and laminin 5. By sitedirectedmutagenesis, amino acid changes will be introduced within the NC16A domain near the cleavage site. Keratinocytes from patients lacking BP180 (GABEB) will be transfected with these mutant forms of BP180 to determine if the cleavage can be abolished. The mutant BP180 will also be used to study the relevance of the cleavage for cell migration and differentiation. Finally, the effect of the cleavage process on the reactivity of patients' autoantibodies to the NC16A domain of BP180 will be investigated. These studies should improve our understanding of anchoring mechanisms of basement membrane zones.