Tye C E, Pham C T, Simmer J P, Bartlett J D
Department of Cytokine Biology, Forsyth Institute, Harvard School of Dental Medicine, 140 The Fenway, Boston, MA 02115, USA.
J Dent Res. 2009 Apr;88(4):323-7. doi: 10.1177/0022034509334240.
Kallikrein-4 (KLK4) is a serine protease expressed during enamel maturation, and proteolytic processing of the enamel matrix by KLK4 is critical for proper enamel formation. KLK4 is secreted as an inactive zymogen (pro-KLK4), and identification of its activator remains elusive. Dipeptidyl peptidase I (DPPI) is a cysteine aminopeptidase that can activate several serine proteases. In this study, we sought to examine DPPI expression in mouse enamel organ and determine if DPPI could activate KLK4. Real-time PCR showed DPPI expression throughout amelogenesis, with highest expression at maturation, and immunohistochemical staining of mouse incisors confirmed DPPI expression by ameloblasts. We demonstrate in vitro that DPPI activates pro-KLK4 to cleave a fluorogenic peptide containing a KLK4 cleavage site. Examination of mature enamel from DPPI null mice by FTIR showed no significant accumulation of protein; however, microhardness testing revealed that loss of DPPI expression significantly reduced enamel hardness.
激肽释放酶-4（KLK4）是一种在釉质成熟过程中表达的丝氨酸蛋白酶，KLK4对釉质基质的蛋白水解加工对于正常的釉质形成至关重要。KLK4以无活性的酶原形式（前激肽释放酶-4）分泌，其激活剂的身份仍然不明。二肽基肽酶I（DPPI）是一种可以激活多种丝氨酸蛋白酶的半胱氨酸氨基肽酶。在本研究中，我们试图检测DPPI在小鼠釉质器官中的表达，并确定DPPI是否能够激活KLK4。实时PCR显示DPPI在整个釉质形成过程中均有表达，在成熟阶段表达量最高，对小鼠切牙的免疫组织化学染色证实成釉细胞表达DPPI。我们在体外证明DPPI激活前激肽释放酶-4以切割含有KLK4切割位点的荧光肽。通过傅里叶变换红外光谱对DPPI基因敲除小鼠的成熟釉质进行检测，结果显示没有明显的蛋白质积累；然而，微硬度测试表明，DPPI表达缺失显著降低了釉质硬度。
