Chang Xiaotian, Han Jinxiang
Shandong Academy of Medical Sciences, Medicinal Biotechnology Centre, Jinan, Shandong, China.
Mol Carcinog. 2006 Mar;45(3):183-96. doi: 10.1002/mc.20169.
Peptidylarginine deiminase type 4 (PAD4/PADI4) posttranslationally converts peptidylarginine to citrulline, in a process known as citrullination. Evidence suggests that PAD4 plays an essential role in pathogenesis of rheumatoid arthritis (RA). RA synovium has many features in common with tumor tissues, including abnormal cell proliferation, extensive fibrin deposition, high coagulation activity, and extreme angiogenesis. The purpose of the present study was to investigate expression of PAD4 in various tumor tissues. Immunohistochemistry indicated that PAD4 had significant expression in many tumor tissues, especially various adenocarcinoma. Western blotting with anti PAD4 antibody and immunostaining with anti citrulline antibody confirmed the expression of the enzyme in these tumors. Furthermore, our immunohistochemistry also detected co-location of PAD4 with cytokeratin (CK), a well-known tumor marker for oncological study in many tumors. Western blot analysis also detected citrulline signals in CK extracted from the tumors. In addition, CK 8, 18, and 19 following in vitro citrullination resisted to the digestion of caspase. The results further confirm the expression of PAD4 in the tumors and support that PAD4 may contribute to the disrupted apoptosis of tumors by caspase-mediated cleavage of CK. Double immunofluorescent labeling detected co-location of PAD4 with CD34, a cell marker of heamatopoietic progenitor cells (HPC) in bone marrow and other normal tissues, as well as in some fibroblast-like cells at stroma region of tumors, but not in the tumor cells. The findings imply that PAD4 is initially expressed in CD34(+) cells of bone marrow and then distributed in derives of the multi-potent progenitor cells in diverse tissues. The development of tumor cells expressing PAD4 is possibly associated with abnormal proliferation of CD34(+) stem cells.
4型肽基精氨酸脱亚氨酶（PAD4/PADI4）在翻译后将肽基精氨酸转化为瓜氨酸，这一过程称为瓜氨酸化。有证据表明，PAD4在类风湿性关节炎（RA）的发病机制中起重要作用。RA滑膜具有许多与肿瘤组织相同的特征，包括异常细胞增殖、广泛的纤维蛋白沉积、高凝血活性和极度血管生成。本研究的目的是调查PAD4在各种肿瘤组织中的表达情况。免疫组织化学表明，PAD4在许多肿瘤组织中都有显著表达，尤其是各种腺癌。用抗PAD4抗体进行蛋白质印迹分析以及用抗瓜氨酸抗体进行免疫染色证实了该酶在这些肿瘤中的表达。此外，我们的免疫组织化学还检测到PAD4与细胞角蛋白（CK）共定位，CK是许多肿瘤肿瘤学研究中一种著名的肿瘤标志物。蛋白质印迹分析也在从肿瘤中提取的CK中检测到瓜氨酸信号。此外，体外瓜氨酸化后的CK 8、18和19对半胱天冬酶的消化具有抗性。这些结果进一步证实了PAD4在肿瘤中的表达，并支持PAD4可能通过半胱天冬酶介导的CK裂解导致肿瘤细胞凋亡紊乱。双重免疫荧光标记检测到PAD4与CD34共定位，CD34是骨髓和其他正常组织中造血祖细胞（HPC）的细胞标志物，在肿瘤基质区域的一些成纤维细胞样细胞中也有共定位，但在肿瘤细胞中没有。这些发现表明，PAD4最初在骨髓的CD34(+)细胞中表达，然后分布在不同组织中多能祖细胞的衍生物中。表达PAD4的肿瘤细胞的发生可能与CD34(+)干细胞的异常增殖有关。
