Splice variants of SmgGDS control small GTPase prenylation and membrane localization.
Splice variants of SmgGDS control small GTPase prenylation and membrane localization.
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DOI：
10.1074/jbc.m110.129916
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发表时间：
2010-11-12
期刊：
影响因子：
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通讯作者：
Williams CL
中科院分区：
文献类型：
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作者：
Berg TJ;Gastonguay AJ;Lorimer EL;Kuhnmuench JR;Li R;Fields AP;Williams CL
Ras和Rho小GTP酶具有C末端多碱基区（PBR），是重要的信号蛋白，其失调可导致癌症。这些蛋白质的信号传导依赖于它们结合鸟嘌呤核苷酸的能力和它们与香叶基香叶基或法呢基类异戊二烯部分的异戊烯化以及随后向细胞膜的运输。以前很少有证据表明细胞信号可以抑制非异戊二烯化GTP酶进入异戊二烯化途径，导致人们普遍认为具有PB R的GTP酶在合成后立即被异戊二烯化。在这里，我们提出的证据挑战这一信念。我们证明，插入显性负突变，以抑制GDP/GTP交换减少异戊二烯化Rap 1A和RhoA，提高异戊二烯化的Rac 1，并没有可检测地改变异戊二烯化的K-Ras。我们的研究结果表明，这些小GTP酶通过异戊二烯化途径的入口和通道是由SmgGDS的两个剪接变体调节的，SmgGDS是一种蛋白质，据报道，它可以促进GDP/GTP交换，通过具有CBR的GTP酶，并在几种形式的癌症中上调。我们表明，以前的特点是558个残基SmgGDS剪接变异体（SmgGDS-558）选择性地与异戊二烯化的小GTP酶，促进Rap 1A的质膜运输，而较少的特点是607个残基SmgGDS剪接变异体（SmgGDS-607）与nonprenylated GTP酶和调节Rap 1A，RhoA，Rac 1进入异戊二烯化途径。这些结果表明，鸟嘌呤核苷酸交换和相互作用与SmgGDS剪接变异体可以调节的入口和通过的小GTP酶的PBR通过异戊二烯化途径。
Ras and Rho small GTPases possessing a C-terminal polybasic region (PBR) are vital signaling proteins whose misregulation can lead to cancer. Signaling by these proteins depends on their ability to bind guanine nucleotides and their prenylation with a geranylgeranyl or farnesyl isoprenoid moiety and subsequent trafficking to cellular membranes. There is little previous evidence that cellular signals can restrain nonprenylated GTPases from entering the prenylation pathway, leading to the general belief that PBR-possessing GTPases are prenylated as soon as they are synthesized. Here, we present evidence that challenges this belief. We demonstrate that insertion of the dominant negative mutation to inhibit GDP/GTP exchange diminishes prenylation of Rap1A and RhoA, enhances prenylation of Rac1, and does not detectably alter prenylation of K-Ras. Our results indicate that the entrance and passage of these small GTPases through the prenylation pathway is regulated by two splice variants of SmgGDS, a protein that has been reported to promote GDP/GTP exchange by PBR-possessing GTPases and to be up-regulated in several forms of cancer. We show that the previously characterized 558-residue SmgGDS splice variant (SmgGDS-558) selectively associates with prenylated small GTPases and facilitates trafficking of Rap1A to the plasma membrane, whereas the less well characterized 607-residue SmgGDS splice variant (SmgGDS-607) associates with nonprenylated GTPases and regulates the entry of Rap1A, RhoA, and Rac1 into the prenylation pathway. These results indicate that guanine nucleotide exchange and interactions with SmgGDS splice variants can regulate the entrance and passage of PBR-possessing small GTPases through the prenylation pathway.