Kawao Naoyuki, Okada Kiyotaka, Kawata Syuhei, Okamoto Chikako, Tsuritani Mitsuhiro, Ueshima Shigeru, Matsuo Osamu
Department of Physiology, School of Medicine, Kinki University, 377-2, Ohnohigashi, Osakasayama, 589-8511, Japan.
Biochim Biophys Acta. 2007 Jun;1773(6):718-27. doi: 10.1016/j.bbamcr.2007.03.019. Epub 2007 Apr 1.
Since the signal transduction mechanisms responsible for liver regeneration mediated by the plasminogen/plasmin system remain largely undetermined, we have investigated whether plasmin regulates the pro-apoptotic protein Bim(EL) in primary hepatocytes. Plasmin bound to hepatocytes in part via its lysine binding sites (LBS). Plasmin also triggered phosphorylation of ERK1/2 without cell detachment. The plasmin-induced phosphorylation of ERK1/2 was inhibited by the LBS inhibitor epsilon-aminocaproic acid (EACA), the serine protease inhibitor aprotinin, and the MEK inhibitor PD98059. DFP-inactivated plasmin failed to phosphorylate ERK1/2. Plasmin temporally decreased the starvation-induced expression of Bim(EL) and activation of caspase-3 via the ERK1/2 signaling pathway, resulting in an enhancement of cell survival. The amount of mRNA for Bim increased 1 day after the injection of CCl(4) in livers of plasminogen knockout (Plg-KO) and the wild-type (WT) mice. The increase in Bim(EL) protein persisted for at least 7 days post-injection in livers of Plg-KO mice, whereas WT mice showed an increase in Bim(EL) protein 1 day after the injection. Plg-KO and WT mice showed notable phosphorylation of ERK1/2 7 and 3 days after the injection of CCl(4), respectively. Our data suggest that the plasminogen/plasmin system could decrease Bim(EL) expression via the ERK1/2 signaling pathway during liver regeneration.
由于纤溶酶原/纤溶酶系统介导的肝脏再生信号转导机制在很大程度上仍未明确，我们研究了纤溶酶是否调节原代肝细胞中促凋亡蛋白Bim(EL)。纤溶酶部分通过其赖氨酸结合位点(LBS)与肝细胞结合。纤溶酶还能在不导致细胞脱离的情况下触发ERK1/2的磷酸化。纤溶酶诱导的ERK1/2磷酸化受到LBS抑制剂ε-氨基己酸(EACA)、丝氨酸蛋白酶抑制剂抑肽酶和MEK抑制剂PD98059的抑制。DFP失活的纤溶酶无法使ERK1/2磷酸化。纤溶酶通过ERK1/2信号通路暂时降低饥饿诱导的Bim(EL)表达和caspase-3的激活，从而提高细胞存活率。在纤溶酶原敲除(Plg-KO)小鼠和野生型(WT)小鼠肝脏中注射CCl4后1天，Bim的mRNA量增加。在Plg-KO小鼠肝脏中，注射后至少7天Bim(EL)蛋白持续增加，而WT小鼠在注射后1天Bim(EL)蛋白增加。Plg-KO和WT小鼠在注射CCl4后分别于第7天和第3天出现明显的ERK1/2磷酸化。我们的数据表明，在肝脏再生过程中，纤溶酶原/纤溶酶系统可通过ERK1/2信号通路降低Bim(EL)的表达。
