Inhibition of Protein Dephosphorylation Results in the Accumulation of Splicing snRNPs and Coiled Bodies within the Nucleolus

CAROL E. LYON, KERSTIN BOHMANN,* JUDITH SLEEMAN, AND ANGUS I. LAMOND
Department of Biochemistry, University of Dundee, Dundee DD1 4HN, Scotland, United Kingdom

---

Abstract
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.

EXPERIMENTAL CELL RESEARCH 230
84-93 (1997)
ARTICLE NO. EX963380
Copyright © 1996 Academic Press, Inc.

*Address (1996): Max-Planck-Institut für Entwicklungsbiologie, Abteilung 111 (Genetik), Spemannstr. 35/111, D72076 Tübingen, Germany .