Many studies have confirmed the enzymatic activity of a mammalian phosphatidylcholine (PC) phospholipase C (PLC) (PC-PLC), which produces diacylglycerol (DAG) and phosphocholine through the hydrolysis of PC in the absence of ceramide. However, the protein(s) responsible for this activity have never yet been identified. Based on the fact that tricyclodecan-9-yl-potassium xanthate can inhibit both PC-PLC and sphingomyelin synthase (SMS) activities, and SMS1 and SMS2 have a conserved catalytic domain that could mediate a nucleophilic attack on the phosphodiester bond of PC, we hypothesized that both SMS1 and SMS2 might have PC-PLC activity. In the present study, we found that purified recombinant SMS1 and SMS2 but not SMS-related protein have PC-PLC activity. Moreover, we prepared liver-specific Sms1/global Sms2 double-KO mice. We found that liver PC-PLC activity was significantly reduced and steady-state levels of PC and DAG in the liver were regulated by the deficiency, in comparison with control mice. Using adenovirus, we expressed Sms1 and Sms2 genes in the liver of the double-KO mice, respectively, and found that expressed SMS1 and SMS2 can hydrolyze PC to produce DAG and phosphocholine. Thus, SMS1 and SMS2 exhibit PC-PLC activity in vitro and in vivo.

中文翻译：

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鞘磷脂合酶 1 和 2 表现出磷脂酰胆碱磷脂酶 C 活性。

许多研究证实了哺乳动物磷脂酰胆碱 (PC) 磷脂酶 C (PLC) (PC-PLC) 的酶活性，该酶在没有神经酰胺的情况下通过 PC 水解产生二酰基甘油 (DAG) 和磷酸胆碱。然而，尚未确定负责该活动的蛋白质。基于 tricyclodecan-9-yl-potassium xanthate 可以抑制 PC-PLC 和鞘磷脂合酶 (SMS) 活性，并且 SMS1 和 SMS2 具有可以介导对 PC 磷酸二酯键的亲核攻击的保守催化结构域，我们假设 SMS1 和 SMS2 都可能具有 PC-PLC 活动。在本研究中，我们发现纯化的重组 SMS1 和 SMS2 而不是 SMS 相关蛋白具有 PC-PLC 活性。此外，我们制备了肝脏特异性 Sms1/全局 Sms2 双敲除小鼠。我们发现，与对照小鼠相比，肝脏 PC-PLC 活性显着降低，肝脏中 PC 和 DAG 的稳态水平受到缺乏的调节。使用腺病毒，我们分别在双敲除小鼠的肝脏中表达了Sms1和Sms2基因，发现表达的SMS1和Sms2可以水解PC产生DAG和磷酸胆碱。因此，SMS1 和 SMS2 在体外和体内都表现出 PC-PLC 活性。