Regulation of cell proliferation and cell density by the inorganic phosphate transporter PiT1
Regulation of cell proliferation and cell density by the inorganic phosphate transporter PiT1
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DOI：
10.1186/1747-1028-7-7
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发表时间：
2012-03-06
期刊：
影响因子：
2.3
通讯作者：
Pedersen, Lene
中科院分区：
文献类型：
--
作者：
Byskov, Kristina;Jensen, Nina;Pedersen, Lene
背景：无机磷酸盐 (Pi) 转运蛋白 PiT1 (SLC20A1) 在哺乳动物细胞中普遍表达。此前已有研究表明，PiT1的下调严重损害了两种转化的人类细胞系HepG2和HeLa的增殖，以及HeLa细胞在裸鼠中的致瘤性。此外，PiT1 敲除小鼠在 E12.5 之后无法存活，从 E10.5 开始，胚胎被发现生长迟缓，肝细胞增殖减少。 PiT1 表达水平被敲除和降低的分离小鼠胚胎成纤维细胞也表现出增殖受损。这些结果共同表明一定水平的 PiT1 对于增殖很重要。我们在这里使用两种严格密度抑制的细胞系（小鼠 MC3T3-E1 和 NIH3T3 细胞）研究了 PiT1 在细胞增殖调节中的作用。 结果：我们发现 MC3T3-E1 细胞中 PiT1 的敲低会导致增殖受损，这支持了至少一定水平的 PiT1 对于野生型水平的增殖很重要。然而，我们还观察到 MC3T3-E1 和 NIH3T3 细胞本身以较低水平调节其内源性 PiT1 mRNA 水平，通常与增殖减少/细胞密度增加相关。此外，人PiT1的过度表达导致MC3T3-E1和NIH3T3培养物的增殖增加，并导致这两种严格密度抑制的细胞系的培养物中的细胞密度更高。此外，当我们在胎牛血清中培养转化NIH3T3细胞时，过表达人PiT1的细胞在软琼脂中形成的集落比对照细胞更多。结论：我们得出的结论是，不仅如先前发表的研究表明的那样，一定水平的PiT1对于正常细胞分裂是必需的，而且细胞PiT1水平参与调节细胞增殖和细胞密度，并且PiT1表达增加确实可以使NIH3T3细胞对转化更加敏感。因此，我们提供了第一个证据，证明 III 型 P-i 转运蛋白 PiT1 的表达高于内源水平可以驱动细胞增殖并推翻细胞密度限制，并且结果弥补了之前的观察结果，表明一定的 PiT1 水平对于调节正常胚胎生长/发育和 HeLa 细胞的致瘤性非常重要。
Background: The inorganic phosphate (Pi) transporter, PiT1 (SLC20A1), is ubiquitously expressed in mammalian cells. It has previously been shown that down-regulation of PiT1 severely impaired the proliferation of two transformed human cells lines, HepG2 and HeLa, and the tumorigenicity of HeLa cells in nude mice. Moreover, PiT1 knock-out mice do not survive past E12.5 and from E10.5, the embryos were found to be growth-retarded and showed reduced proliferation of liver cells. Isolated mouse embryonic fibroblasts with knocked out as well as reduced PiT1 expression levels also exhibited impaired proliferation. Together these results suggest that a certain level of PiT1 is important for proliferation. We have here investigated the role of PiT1 in regulation of cell proliferation using two strictly density-inhibited cells lines, the murine MC3T3-E1 and NIH3T3 cells.Results: We found that knock-down of PiT1 in MC3T3-E1 cells led to impaired proliferation supporting that at least a certain level of PiT1 is important for wildtype level of proliferation. We, however, also observed that MC3T3-E1 and NIH3T3 cells themselves regulate their endogenous PiT1 mRNA levels with lower levels in general correlating with decreased proliferation/increased cell density. Moreover, over-expression of human PiT1 led to increased proliferation of both MC3T3-E1 and NIH3T3 cultures and resulted in higher cell densities in cultures of these two strictly density-inhibited cell lines. In addition, when we transformed NIH3T3 cells by cultivation in fetal bovine serum, cells over-expressing human PiT1 formed more colonies in soft agar than control cells.Conclusions: We conclude that not only is a certain level of PiT1 necessary for normal cell division as suggested by previously published studies, rather the cellular PiT1 level is involved in regulating cell proliferation and cell density and an increased PiT1 expression can indeed make NIH3T3 cells more sensitive to transformation. We have thus provided the first evidence for that expression of the type III P-i transporter, PiT1, above the endogenous level can drive cell proliferation and overrule cell density constraints, and the results bridge previous observations showing that a certain PiT1 level is important for regulating normal embryonic growth/development and for tumorigenicity of HeLa cells.