Abstract：
Formation and maintenance of skin barrier function require tightly controlled membrane-associated proteolysis, in which the integral membrane Kunitz-type serine protease inhibitor, HAI-1, functions as the primary inhibitor of the membrane-associated serine proteases, matriptase and prostasin. Previously, HAI-1 loss in HaCaT human keratinocytes resulted in an expected increase in prostasin proteolysis but a paradoxical decrease in matriptase proteolysis. The paradoxical decrease in shed active matriptase is further investigated in this study with an unexpected discovery of novel functions of fibroblast growth factor-binding protein 1 (FGFBP1), which acts as an extracellular ligand that can rapidly elicit F-actin rearrangement and subsequently affect the morphology of human keratinocytes. This novel growth factor-like function is in stark contrast to the canonical activity of this protein through interactions with FGFs for its pathophysiological functions. This discovery began with the observation that HAI-1 KO HaCaT cells lose the characteristic cobblestone morphology of the parental cells and exhibit aberrant F-actin formation along with altered subcellular targeting of matriptase and HAI-2. The alterations in cell morphology and F-actin status caused by targeted HAI-1 deletion can be restored by treatment with conditioned medium from parental HaCaT cells, in which FGFBP1 was identified by tandem mass spectrometry. Recombinant FGFBP1 down to 1 ng/ml was able to revert the changes caused by HAI-1 loss. Our study reveals a novel function of FGFBP1 in the maintenance of keratinocyte morphology, which depends on HAI-1.
摘要：
皮肤屏障功能的形成和维持需要严格控制膜相关蛋白水解，其中整合膜Kunitz型丝氨酸蛋白酶抑制剂，HAI-1，作为膜相关丝氨酸蛋白酶的主要抑制剂，间质蛋白酶和前列腺素。以前,HaCaT人角质形成细胞中的HAI-1损失导致前列腺蛋白水解的预期增加，但间质蛋白酶蛋白水解的矛盾减少。在这项研究中，进一步研究了脱落活性间质蛋白酶的矛盾减少，并意外发现了成纤维细胞生长因子结合蛋白1（FGFBP1）的新功能，它作为细胞外配体，可以快速引发F-肌动蛋白重排，并随后影响人角质形成细胞的形态。这种新的生长因子样功能与该蛋白通过与FGFs的病理生理功能相互作用而具有的典型活性形成鲜明对比。这一发现始于观察到HAI-1KOHaCaT细胞失去了亲本细胞的特征性鹅卵石形态，并表现出异常的F-肌动蛋白形成以及间质蛋白酶和HAI-2的亚细胞靶向改变。由靶向HAI-1缺失引起的细胞形态和F-肌动蛋白状态的改变可以通过用来自亲本HaCaT细胞的条件培养基处理来恢复,其中FGFBP1通过串联质谱鉴定。低至1ng/ml的重组FGFBP1能够恢复由HAI-1损失引起的变化。我们的研究揭示了FGFBP1在维持角质形成细胞形态方面的新功能，这取决于HAI-1。
