Epidermal keratinocytes are primarily involved in the expression of semaphorin (Sema) 3A, which is involved in the regulation of cutaneous innervation. However, the mechanisms underlying the intracellular signaling of Sema3A expression in keratinocytes remain unknown. We herein investigated the signaling mechanisms for the induction of Sema3A expression in normal human epidermal keratinocytes (NHEKs). Sema3A expression is transiently increased in calcium-stimulated NHEKs, whereas it is markedly decreased in terminally differentiated NHEKs. Sema3A mRNA is mainly localized in the stratum basale and stratum suprabasale of the epidermis. We cloned the 5'-flanking region of the Sema3A gene and identified a critical region for Sema3A promoter activity within -134 base pairs of the start codon. We found transcription factor binding sites, including that for activator protein (AP)-1, in this region. Sema3A expression was increased by the co-overexpression of JunB and Fra-2 in the presence of 0.1 or 1.4 mM calcium. The calcium-mediated transient upregulation of Sema3A expression was significantly suppressed by mitogen-activated protein kinase (MAPK)/extracellular signal–regulated kinase (ERK) kinase (MEK) 1/2 or AP-1 inhibitors. These results demonstrate that the calcium-mediated transient upregulation of Sema3A in NHEKs is involved in the MEK/ERK and AP-1 signaling axis. Therefore, Sema3A mRNA may be expressed in the lower epidermis under controlled conditions by calcium via the MAPK–AP-1 axis.

表皮角质形成细胞主要参与信号量蛋白（Sema）3A的表达，而后者涉及皮肤神经支配的调节。然而，在角质形成细胞中Sema3A表达的细胞内信号转导的基础机制尚不清楚。我们在本文中研究了在正常人表皮角质形成细胞（NHEKs）中诱导Sema3A表达的信号传导机制。Sema3A表达在钙刺激的NHEKs中瞬时增加，而在终末分化的NHEKs中明显降低。Sema3A mRNA主要位于表皮的基底层和基底上层。我们克隆了Sema3A的5'侧翼区域基因并鉴定了起始密码子的-134个碱基对内Sema3A启动子活性的关键区域。我们在该区域中发现了转录因子结合位点，包括激活蛋白（AP）-1在内。在0.1或1.4 mM钙的存在下，JunB和Fra-2的共过量表达可提高Sema3A的表达。钙介导的Sema3A表达的瞬时上调被有丝分裂原激活的蛋白激酶（MAPK）/细胞外信号调节激酶（ERK）激酶（MEK）1/2或AP-1抑制剂显着抑制。这些结果表明，NHEKs中Sema3A的钙介导的瞬时上调与MEK / ERK和AP-1信号轴有关。因此，Sema3A 在受控条件下，钙可通过MAPK–AP-1轴在下表皮中表达mRNA。