Ottawa Hospital Research Institute and Department of Biochemistry Microbiology and Immunology, University of Ottawa, Ottawa, ON K1H 8L6, Canada.
J Lipid Res. 2010 May;51(5):1144-56. doi: 10.1194/jlr.M003145. Epub 2009 Dec 1.
ATP-binding cassette transporter A1 (ABCA1) is required for the lipidation of apolipoprotein A-I (apoA-I), although molecular mechanisms supporting this process remain poorly defined. In this study, we focused on the role of cytosolic Ca(2+) and its signaling and found that cytosolic Ca(2+) was required for cholesterol efflux to apoA-I. Removing extracellular Ca(2+) or chelating cytosolic Ca(2+) were equally inhibitory for apoA-I lipidation. We provide evidence that apoA-I induced Ca(2+) influx from the medium. We further demonstrate that calcineurin activity, the downstream target of Ca(2+) influx, was essential; inhibition of calcineurin activity by cyclosporine A or FK506 completely abolished apoA-I lipidation. Furthermore, calcineurin inhibition abolished apoA-I binding and diminished JAK2 phosphorylation, an established signaling event for cholesterol efflux to apoA-I. Finally, we demonstrate that neither Ca(2+) manipulation nor calcineurin inhibition influenced ABCA1's capacity to release microparticles or to remodel the plasma membrane. We conclude that this Ca(2+)-dependent calcineurin/JAK2 pathway is specifically responsible for apoA-I lipidation without directly modifying ABCA1 activity.
三磷酸腺苷结合盒转运蛋白 A1（ABCA1）是载脂蛋白 A-I（apoA-I）脂质化所必需的，尽管支持这一过程的分子机制仍未得到明确界定。在这项研究中，我们专注于细胞质 Ca（2+）及其信号的作用，并发现细胞质 Ca（2+）是胆固醇流出到 apoA-I 所必需的。去除细胞外 Ca（2+）或螯合细胞质 Ca（2+）对 apoA-I 的脂质化同样具有抑制作用。我们提供了 apoA-I 诱导从中性粒细胞外液中摄取 Ca（2+）的证据。我们进一步证明，钙调神经磷酸酶活性是 Ca（2+）内流的下游靶点，钙调神经磷酸酶活性的抑制通过环孢菌素 A 或 FK506 完全抑制了 apoA-I 的脂质化。此外，钙调神经磷酸酶抑制作用削弱了 apoA-I 的结合，并减少了 JAK2 的磷酸化，这是胆固醇流出到 apoA-I 的一种已建立的信号事件。最后，我们证明 Ca（2+）操纵或钙调神经磷酸酶抑制均不影响 ABCA1 释放微颗粒或重塑质膜的能力。我们的结论是，这种依赖 Ca（2+）的钙调神经磷酸酶/JAK2 途径专门负责 apoA-I 的脂质化，而不会直接修饰 ABCA1 的活性。
