Lyon C E, Bohmann K, Sleeman J, Lamond A I
Department of Biochemistry, University of Dundee, Scotland, United Kingdom.
Exp Cell Res. 1997 Jan 10;230(1):84-93. doi: 10.1006/excr.1996.3380.
Coiled bodies are conserved subnuclear organelles that contain splicing snRNPs, a subset of nucleolar antigens, and the autoantigen p80 coilin. Most nuclei contain one to five nucleoplasmic coiled bodies, often with one or more located at the nucleolar periphery. Here we show that exposure of mammalian cells to low levels of the specific Ser/Thr protein phosphatase inhibitor, okadaic acid, results in the accumulation of p80 coilin and splicing snRNPs within nucleoli. Mutation of a single serine residue in p80 coilin to aspartate (S202D) also causes coiled bodies and splicing snRNPs to localize within nucleoli when the mutant is transiently transfected and expressed in HeLa cells. Neither okadaic acid nor the S202D coilin mutant causes nucleolar accumulation of serine-arginine-domain proteins. These data indicate that protein dephosphorylation is required to allow normal formation of nucleoplasmic coiled bodies and point to p80 coilin as a substrate whose phosphorylation state may regulate snRNP-nucleolar interactions. The data are consistent with a trafficking mechanism whereby splicing snRNPs cycle through the nucleolus.
卷曲小体是保守的亚核细胞器，包含剪接小核核糖核蛋白（snRNP）、核仁抗原的一个子集以及自身抗原p80卷曲素。大多数细胞核含有一到五个核质卷曲小体，通常有一个或多个位于核仁周边。我们在此表明，将哺乳动物细胞暴露于低水平的特异性丝氨酸/苏氨酸蛋白磷酸酶抑制剂冈田酸，会导致p80卷曲素和剪接snRNP在核仁内积累。当p80卷曲素中的单个丝氨酸残基突变为天冬氨酸（S202D）时，将该突变体瞬时转染并在HeLa细胞中表达，也会导致卷曲小体和剪接snRNP定位于核仁内。冈田酸和S202D卷曲素突变体均不会导致丝氨酸-精氨酸结构域蛋白在核仁中积累。这些数据表明，蛋白质去磷酸化是核质卷曲小体正常形成所必需的，并指出p80卷曲素是一种底物，其磷酸化状态可能调节snRNP与核仁的相互作用。这些数据与一种转运机制一致，即剪接snRNP通过核仁循环。
