Neufeld K L, Nix D A, Bogerd H, Kang Y, Beckerle M C, Cullen B R, White R L
Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112, USA.
Proc Natl Acad Sci U S A. 2000 Oct 24;97(22):12085-90. doi: 10.1073/pnas.220401797.
Mutational inactivation of the adenomatous polyposis coli (APC) tumor suppressor initiates most hereditary and sporadic colon carcinomas. Although APC protein is located in both the cytoplasm and the nucleus, the protein domains required to maintain a predominantly cytoplasmic localization are unknown. Here, we demonstrate that nuclear export of APC is mediated by two intrinsic, leucine-rich, nuclear export signals (NESs) located near the amino terminus. Each NES was able to induce the nuclear export of a fused carrier protein. Both APC NESs were independently able to interact with the Crm1 nuclear export factor and substitute for the HIV-1 Rev NES to mediate nuclear mRNA export. Both APC NESs functioned within the context of APC sequence: an amino-terminal APC peptide containing both NESs interacted with Crm1 and showed nuclear export in a heterokaryon nucleocytoplasmic shuttling assay. Also, mutation of both APC NESs resulted in the nuclear accumulation of the full-length, approximately 320-kDa APC protein, further establishing that the two intrinsic APC NESs are necessary for APC protein nuclear export. Moreover, endogenous APC accumulated in the nucleus of cells treated with the Crm1-specific nuclear export inhibitor leptomycin B. Together, these data indicate that APC is a nucleocytoplasmic shuttle protein whose predominantly cytoplasmic localization requires NES function and suggests that APC may be important for signaling between the nuclear and cytoplasmic compartments of epithelial cells.
腺瘤性息肉病 coli（APC）肿瘤抑制因子的突变失活引发了大多数遗传性和散发性结肠癌。尽管 APC 蛋白位于细胞质和细胞核中，但维持其主要定位于细胞质所需的蛋白结构域尚不清楚。在这里，我们证明 APC 的核输出由位于氨基末端附近的两个内在的、富含亮氨酸的核输出信号（NESs）介导。每个 NES 都能够诱导融合载体蛋白的核输出。APC 的两个 NES 都能够独立地与 Crm1 核输出因子相互作用，并替代 HIV-1 Rev NES 来介导核 mRNA 输出。APC 的两个 NES 在 APC 序列的背景下起作用：包含两个 NES 的氨基末端 APC 肽与 Crm1 相互作用，并在异核体核质穿梭试验中显示出核输出。此外，APC 的两个 NES 的突变导致全长约 320 kDa 的 APC 蛋白在细胞核中积累，进一步证实了两个内在的 APC NES 对于 APC 蛋白的核输出是必需的。此外，内源性 APC 在使用 Crm1 特异性核输出抑制剂雷帕霉素 B 处理的细胞的细胞核中积累。总之，这些数据表明 APC 是一种核质穿梭蛋白，其主要定位于细胞质需要 NES 功能，并表明 APC 可能在上皮细胞的核和细胞质区室之间的信号传导中起重要作用。
