Lagrost L, Athias A, Gambert P, Lallemant C
Laboratoire de Biochimie des Lipoprotéines, INSERM CJF 93-10, Faculté de Médecine, Dijon, France.
J Lipid Res. 1994 May;35(5):825-35.
In the present study, a sequential procedure was set up to separate simultaneously cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PTP), and lecithin:cholesterol acyltransferase (LCAT) from human plasma. Subsequently, phospholipid transfer activities of purified lipid transfer proteins, deprived of LCAT activity, were compared and potential interactions between the two proteins were studied. Phospholipid transfer (PT) activity was determined by using three independent assays that measured the transfer of radiolabeled phosphatidylcholine ([14C]PC) either from phospholipid liposomes to high density lipoproteins-3 (PTliposome-->HDL3), from high density lipoproteins-3 to phospholipid liposomes (PTHDL3-->liposome), or from HDL3 to low density lipoproteins (PTHDL3-->LDL). Comparative study of CETP and PTP pointed out several differences in the ability of the two proteins to transfer phospholipids. i) Whereas both CETP and PTP were able to mediate phospholipid transfers from [14C]PC-HDL3 to LDL, only PTP facilitated phospholipid transfers from [14C]PC-liposomes to HDL3. ii) As PTP did not promote the transfer of phospholipids from [14C]PC-HDL3 to liposomes, it was concluded that it functions as a phospholipid transfer protein rather than a phospholipid exchange protein. This latter point was confirmed by the ability of purified PTP to induce the net mass transfer of phospholipids from PC-liposomes to HDL3. iii) While PTP presented no intrinsic cholesteryl ester transfer activity, it was able to significantly increase CETP-mediated cholesteryl ester transfers from HDL3 to LDL. iv) CETP did not influence the PTliposome-->HDL3 activity induced by PTP. v) Oleic acid was able to significantly increase the cholesteryl ester transfer activity of CETP, but not the PTliposome-->HDL3 activity of PTP. vi) PTHDL3-->LDL activity of purified CETP was explained, for a large part, by the copurification of nonesterified fatty acids. Taken together, data of the present report suggest that phospholipid transfer activity of CETP and PTP could occur through distinct processes. Since, in human plasma, PTP is not only responsible for the major part of phospholipid net mass transfer but is also able in vitro to modulate the CETP-mediated transfer of cholesteryl esters between various plasma lipoprotein fractions, it could play a determinant role in lipoprotein remodeling in vivo.
在本研究中，建立了一种连续程序，用于同时从人血浆中分离胆固醇酯转移蛋白（CETP）、磷脂转移蛋白（PTP）和卵磷脂胆固醇酰基转移酶（LCAT）。随后，比较了去除LCAT活性的纯化脂质转移蛋白的磷脂转移活性，并研究了这两种蛋白之间的潜在相互作用。磷脂转移（PT）活性通过三种独立的测定方法来确定，这些方法测量放射性标记的磷脂酰胆碱（[14C]PC）从磷脂脂质体向高密度脂蛋白3（PT脂质体→HDL3）、从高密度脂蛋白3向磷脂脂质体（PTHDL3→脂质体）或从HDL3向低密度脂蛋白（PTHDL3→LDL）的转移。CETP和PTP的比较研究指出了这两种蛋白在转移磷脂能力方面的几个差异。i）虽然CETP和PTP都能够介导磷脂从[14C]PC-HDL3向LDL的转移，但只有PTP促进了磷脂从[14C]PC-脂质体向HDL3的转移。ii）由于PTP不促进磷脂从[14C]PC-HDL3向脂质体的转移，因此得出结论，它作为一种磷脂转移蛋白而不是磷脂交换蛋白发挥作用。纯化的PTP能够诱导磷脂从PC-脂质体向HDL3的净质量转移，这证实了后一点。iii）虽然PTP没有内在的胆固醇酯转移活性，但它能够显著增加CETP介导的胆固醇酯从HDL3向LDL的转移。iv）CETP不影响PTP诱导的PT脂质体→HDL3活性。v）油酸能够显著增加CETP的胆固醇酯转移活性，但不能增加PTP的PT脂质体→HDL3活性。vi）纯化的CETP的PTHDL3→LDL活性在很大程度上是由未酯化脂肪酸的共纯化所解释的。综上所述，本报告的数据表明，CETP和PTP的磷脂转移活性可能通过不同的过程发生。由于在人血浆中，PTP不仅负责磷脂净质量转移的主要部分，而且在体外还能够调节CETP介导的各种血浆脂蛋白组分之间胆固醇酯的转移，因此它可能在体内脂蛋白重塑中起决定性作用。
