PL(C)D4:3xCa2+ hydrolse PI(4,5)P2 to I(1,4,5)P3 and DAG at the ER membrane

At the endoplasmic reticulum (ER) membrane, 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase delta-4 (PLCD4) and phospholipase D4 (PLD4) hydrolyse phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) to inositol 1,4,5-trisphosphate (I(1,4,5)P3) and diacylglycerol (DAG). Both lipases are thought to require three Ca2+ ions per subunit for activity. PLD4 is attached to the ER membrane via its PH domain while its C2 domain binds to the PI(4,5)P2 in the membrane (Lee et al. 2004). Overexpression or dysregulated expression of PLCD4 may initiate oncogenesis in certain tissues through upregulation of ErbB expression and activation of ERK pathway. PLCD4 can therefore be a useful tumor marker for breast or testicular cancer tissues (Leung et al. 2004).

在内质网（ER）膜上，1-磷酸肌醇4,5-二磷酸磷酯酶δ-4（PLCD4）和磷脂酶D4（PLD4）将磷脂酰肌醇4,5-二磷酸（PI(4,5)P2）水解为肌醇1,4,5-三磷酸（I(1,4,5)P3）和二酰甘油（DAG）。据认为，这两种脂酶的每个亚基都需要三个钙离子（Ca2+）才能发挥活性。PLD4通过其PH结构域附着于ER膜，而其C2结构域则与膜中的PI(4,5)P2结合（Lee等，2004年）。PLCD4的过表达或表达失调可能通过上调ErbB表达和激活ERK通路，在某些组织中引发肿瘤发生。因此，PLCD4可以作为乳腺或睾丸癌组织的肿瘤标志物（Leung等，2004年）。