Zhu W, Chan E K, Li J, Hemmerich P, Tan E M
W. M. Keck Autoimmune Disease Center, Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Exp Cell Res. 2001 Oct 1;269(2):312-21. doi: 10.1006/excr.2001.5320.
Autoantibodies to intracellular proteins have been detected in sera of patients with various forms of cancer. Nuclear autoantigen SG2NA (S, G2 phase nuclear antigen) was isolated using autoantibodies from a patient with bladder and lung cancers and its expression is enhanced in the S and G2 phases of the cell cycle. Molecular cloning revealed that the C-terminal region of SG2NA contains six WD-40 repeats, motifs that are present in a large family of proteins with diverse functions. We show that the N-terminal region of SG2NA (aa 1-391) acted as a strong transcriptional activator in both yeast and mammalian cells. In contrast, the C-terminal WD-40 repeats had an inhibitory effect on transcription activation. We performed molecular swapping experiments by substituting the WD-40 repeats of SG2NA with those of yeast Met30 and Cdc4 and showed that the WD-40 regions from either Met30 or Cdc4 were capable of reproducing transcription repression function. The SG2NA WD-40 repeats were also able to repress basal level transcription and transactivation function of a GAL4-VP16 chimera. These observations suggest that some WD-40 repeats may have, as one of their functions, a negative regulatory role in the biological activities of their own and perhaps other proteins.
在患有各种癌症的患者血清中已检测到针对细胞内蛋白质的自身抗体。核自身抗原SG2NA（S、G2期核抗原）是从一名患有膀胱癌和肺癌的患者的自身抗体中分离出来的，其表达在细胞周期的S期和G2期增强。分子克隆显示，SG2NA的C末端区域包含六个WD-40重复序列，这些基序存在于一大类具有不同功能的蛋白质中。我们发现，SG2NA的N末端区域（氨基酸1-391）在酵母和哺乳动物细胞中均作为强转录激活因子发挥作用。相反，C末端的WD-40重复序列对转录激活具有抑制作用。我们通过将SG2NA的WD-40重复序列替换为酵母Met30和Cdc4的WD-40重复序列进行了分子交换实验，结果表明，来自Met30或Cdc4的WD-40区域能够重现转录抑制功能。SG2NA的WD-40重复序列也能够抑制GAL4-VP16嵌合体的基础水平转录和反式激活功能。这些观察结果表明，一些WD-40重复序列可能具有作为其自身以及可能其他蛋白质生物活性的负调控作用这一功能。
