Barber Latorya A, Palascak Mary B, Qi Xiaoyang, Joiner Clinton H, Franco Robert S
Division of Internal Medicine-Hematology/Oncology, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
Department of Pediatrics, Division of Hematology Oncology, Children's Healthcare of Atlanta, Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA, USA.
Eur J Haematol. 2015 Nov;95(5):405-10. doi: 10.1111/ejh.12506. Epub 2015 Apr 24.
Externalization of phosphatidylserine (PS) is thought to contribute to sickle cell disease (SCD) pathophysiology. The red blood cell (RBC) aminophospholipid translocase (APLT) mediates the transport of PS from the outer to the inner RBC membrane leaflet to maintain an asymmetric distribution of PL, while phospholipid scramblase (PLSCR) equilibrates PL across the RBC membrane, promoting PS externalization. We previously identified an association between PS externalization level and PLSCR activity in sickle RBC under basal conditions. Other studies showed that activation of protein kinase C (PKC) by PMA (phorbol-12-myristate-13-acetate) causes increased external PS on RBC. Therefore, we hypothesized that PMA-activated PKC stimulates PLSCR activity in RBC and thereby contributes to increased PS externalization. In the current studies, we show that PMA treatment causes immediate and variable PLSCR activation and subsequent PS externalization in control and sickle RBC. While TfR+ sickle reticulocytes display some endogenous PLSCR activity, we observed a robust activation of PLSCR in sickle reticulocytes treated with PMA. The PKC inhibitor, chelerythrine (Chel), significantly inhibited PMA-dependent PLSCR activation and PS externalization. Chel also inhibited endogenous PLSCR activity in sickle reticulocytes. These data provide evidence that PKC mediates PS externalization in RBC through activation of PLSCR.
磷脂酰丝氨酸（PS）外化被认为与镰状细胞病（SCD）的病理生理过程有关。红细胞（RBC）氨基磷脂转位酶（APLT）介导PS从红细胞膜外侧小叶向内测小叶的转运，以维持磷脂（PL）的不对称分布，而磷脂翻转酶（PLSCR）使PL在红细胞膜上达到平衡，促进PS外化。我们之前在基础条件下确定了镰状红细胞中PS外化水平与PLSCR活性之间的关联。其他研究表明，佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）激活蛋白激酶C（PKC）会导致红细胞上PS外化增加。因此，我们推测PMA激活的PKC刺激红细胞中的PLSCR活性，从而导致PS外化增加。在当前研究中，我们发现PMA处理会立即且可变地激活PLSCR，并随后导致对照红细胞和镰状红细胞发生PS外化。虽然转铁蛋白受体阳性（TfR+）的镰状网织红细胞显示出一些内源性PLSCR活性，但我们观察到用PMA处理的镰状网织红细胞中PLSCR有强烈激活。PKC抑制剂白屈菜红碱（Chel）显著抑制了PMA依赖的PLSCR激活和PS外化。Chel还抑制了镰状网织红细胞中的内源性PLSCR活性。这些数据证明PKC通过激活PLSCR介导红细胞中的PS外化。
