Identification of a Novel Function of PiT1 Critical for Cell Proliferation and Independent of Its Phosphate Transport Activity
Identification of a Novel Function of PiT1 Critical for Cell Proliferation and Independent of Its Phosphate Transport Activity
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DOI：
10.1074/jbc.m109.053132
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发表时间：
2009-11-06
影响因子：
4.8
通讯作者：
Friedlander, Gerard
中科院分区：
文献类型：
--
作者：
Beck, Laurent;Leroy, Christine;Friedlander, Gerard
PiT 1是位于质膜上的Na+-磷酸盐（P-i）共转运蛋白，其使P-i进入细胞。其广泛的组织表达模式导致了这样的想法，即与密切相关的家族成员PiT 2一起，PiT 1是细胞的P-i的普遍存在的供应者。此外，P-i在磷酸化反应、ATP产生、DNA结构和合成中的作用使得人们认为P-i的可用性可能是细胞生长的重要决定因素。然而，这些问题迄今尚未得到明确解决，并且P-i或PiT蛋白在细胞增殖中的作用是未知的。在HeLa和HepG 2细胞中使用RNA干扰，我们发现短暂或稳定的PiT 1耗尽显着降低细胞增殖，延迟细胞周期，并损害有丝分裂和胞质分裂。在体内，PiT 1耗尽大大降低了肿瘤生长时，工程HeLa细胞注射到裸鼠。我们提供的证据表明，这种对细胞增殖的影响是特定的PiT 1和不共享的PiT 2，是不是受损的膜Na+-Pi运输的后果。此外，我们表明，由PiT 1的细胞增殖的调制是独立于其运输功能，因为PiT 1耗尽的细胞的增殖可以通过非运输PiT 1突变体获救。PiT 1缺失导致p38丝裂原活化蛋白（MAP）激酶磷酸化，而其他MAP激酶和哺乳动物雷帕霉素靶蛋白（mTOR）的下游靶标不受影响。这项研究是第一个描述了β 1转运蛋白在细胞增殖、肿瘤生长和细胞信号传导中的作用。
PiT1 is a Na+-phosphate (P-i) cotransporter located at the plasma membrane that enables P-i entry into the cell. Its broad tissue expression pattern has led to the idea that together with the closely related family member PiT2, PiT1 is the ubiquitous supplier of P-i to the cell. Moreover, the role of P-i in phosphorylation reactions, ATP production, DNA structure, and synthesis has led to the view that P-i availability could be an important determinant of cell growth. However, these issues have not been clearly addressed to date, and the role of either P-i or PiT proteins in cell proliferation is unknown. Using RNA interference in HeLa and HepG2 cells, we show that transient or stable PiT1 depletion markedly reduces cell proliferation, delays cell cycle, and impairs mitosis and cytokinesis. In vivo, PiT1 depletion greatly reduced tumor growth when engineered HeLa cells were injected into nude mice. We provide evidence that this effect on cell proliferation is specific to PiT1 and not shared by PiT2 and is not the consequence of impaired membrane Na+-Pi transport. Moreover, we show that modulation of cell proliferation by PiT1 is independent from its transport function because the proliferation of PiT1-depleted cells can be rescued by nontransporting PiT1 mutants. PiT1 depletion leads to the phosphorylation of p38 mitogen-activated protein (MAP) kinase, whereas other MAP kinases and downstream targets of mammalian target of rapamycin (mTOR) remain unaffected. This study is the first to describe the effects of a P-i transporter in cell proliferation, tumor growth, and cell signaling.