Ilic Dusko, Mao-Qiang Man, Crumrine Debra, Dolganov Gregory, Larocque Nicholas, Xu Pu, Demerjian Marianne, Brown Barbara E, Lim Ssang-Taek, Ossovskaya Valeria, Schlaepfer David D, Fisher Susan J, Feingold Kenneth R, Elias Peter M, Mauro Theodora M
Dermatology Service, Veterans Affairs Medical Center, San Francisco, CA, USA.
Am J Pathol. 2007 Jun;170(6):2055-67. doi: 10.2353/ajpath.2007.061277.
Ubiquitously expressed focal adhesion kinase (FAK), linked to multiple intracellular signaling pathways, has previously been shown to control cell motility, invasion, proliferation, and survival. Using mice with a keratinocyte-restricted deletion of fak (FAK(K5 KO)), we report here a novel role for FAK: maintenance of adult epidermal permeability barrier homeostasis. Abundant lacunae of unprocessed lipids in stratum corneum (SC) of FAK(K5 KO) mice and delayed barrier recovery pointed to malfunction of pH-dependent enzymes active in extracellular space of SC. Measuring the SC pH gradient showed significantly more neutral pH values in FAK(K5 KO) mice, suggesting the importance of FAK for acidification. Moreover, normal functions were restored when FAK(K5 KO) mice were exposed to a surface pH typical of mouse SC (pH = 5.5). Baseline levels and response to barrier disruption of secretory phospholipase A2 isoforms, enzymes that mediate generation of free fatty acids in epidermis, appeared similar in both FAK(K5 KO) and control littermates. We found that the critical SC acidification regulator Na(+)/H(+) exchanger 1 failed to localize to the plasma membrane in FAK-deficient keratinocytes both in vivo and in vitro. Thus, for plasma membrane localization in terminally differentiated keratinocytes, Na(+)/H(+) exchanger 1 requires an intact actin cytoskeleton, which is impaired in FAK-deficient cells.
广泛表达的粘着斑激酶（FAK）与多种细胞内信号通路相关，此前已被证明可控制细胞运动、侵袭、增殖和存活。利用角质形成细胞特异性敲除fak的小鼠（FAK（K5 KO）），我们在此报告FAK的一个新作用：维持成年表皮通透性屏障的稳态。FAK（K5 KO）小鼠角质层（SC）中存在大量未加工脂质的空隙，且屏障恢复延迟，这表明在SC细胞外空间中起作用的pH依赖性酶存在功能障碍。测量SC的pH梯度显示，FAK（K5 KO）小鼠的中性pH值明显更多，这表明FAK对酸化的重要性。此外，当FAK（K5 KO）小鼠暴露于典型的小鼠SC表面pH值（pH = 5.5）时，其正常功能得以恢复。在FAK（K5 KO）小鼠和对照同窝小鼠中，分泌型磷脂酶A2同工型（介导表皮中游离脂肪酸生成的酶）的基线水平和对屏障破坏的反应似乎相似。我们发现，关键的SC酸化调节剂钠/氢交换体1在体内和体外的FAK缺陷角质形成细胞中均未能定位于质膜。因此，对于终末分化角质形成细胞中的质膜定位，钠/氢交换体1需要完整的肌动蛋白细胞骨架，而在FAK缺陷细胞中该骨架受损。
