Zhang F, White R L, Neufeld K L
Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope, Building 555, Room 5263, Salt Lake City, UT 84112, USA.
Proc Natl Acad Sci U S A. 2000 Nov 7;97(23):12577-82. doi: 10.1073/pnas.230435597.
Mutation of the adenomatous polyposis coli (APC) gene is an early step in the development of colorectal carcinomas. APC protein is located in both the cytoplasm and the nucleus. The objective of this study was to define the nuclear localization signals (NLSs) in APC protein. APC contains two potential NLSs comprising amino acids 1767-1772 (NLS1(APC)) and 2048-2053 (NLS2(APC)). Both APC NLSs are well conserved among human, mouse, rat, and fly. NLS1(APC) and NLS2(APC) each were sufficient to target the cytoplasmic protein beta-galactosidase to the nucleus. Mutational analysis of APC demonstrated that both NLSs were necessary for optimal nuclear import of full-length APC protein. Alignment of NLS2(APC) with the simian virus 40 large T antigen NLS (NLS(SV40 T-ag)) revealed sequence similarity extending to adjacent phosphorylation sites. Changing a serine residue (Ser(2054)) to aspartic acid mutated the potential protein kinase A site adjacent to NLS2(APC), resulting in both inhibition of the NLS2(APC)-mediated nuclear import of a chimeric beta-galactosidase fusion protein and a reduction of full-length APC nuclear localization. Our data provide evidence that control of APC's nuclear import through phosphorylation is a potential mechanism for regulating APC's nuclear activity.
腺瘤性息肉病大肠杆菌（APC）基因的突变是结直肠癌发生过程中的早期步骤。APC蛋白位于细胞质和细胞核中。本研究的目的是确定APC蛋白中的核定位信号（NLSs）。APC包含两个潜在的NLSs，由氨基酸1767 - 1772（NLS1(APC)）和2048 - 2053（NLS2(APC)）组成。APC的两个NLSs在人、小鼠、大鼠和果蝇中都高度保守。NLS1(APC)和NLS2(APC)各自都足以将细胞质蛋白β-半乳糖苷酶靶向细胞核。对APC的突变分析分析分析表明，两个NLSs对于全长APC蛋白的最佳核输入都是必需的。将NLS2(APC)与猿猴病毒40大T抗原NLS（NLS(SV40 T-ag)）进行比对，发现序列相似性延伸至相邻的磷酸化位点。将一个丝氨酸残基（Ser(2054)）突变为天冬氨酸，使与NLS2(APC)相邻的潜在蛋白激酶A位点发生突变，导致NLS2(APC)介导的嵌合β-半乳糖苷酶融合蛋白的核输入受到抑制，同时全长APC的核定位减少。我们的数据提供了证据，表明通过磷酸化控制APC的核输入是调节APC核活性的一种潜在机制。
