Centrin 2 Localizes to the Vertebrate Nuclear Pore and Plays a Role in mRNA and Protein Export

Abstract

Centrins in vertebrates have traditionally been associated with microtubule-nucleating centers such as the centrosome. Unexpectedly, we found centrin 2 to associate biochemically with nucleoporins, including the Xenopus laevis Nup107-160 complex, a critical subunit of the vertebrate nuclear pore in interphase and of the kinetochores and spindle poles in mitosis. Immunofluorescence of Xenopus cells and in vitro reconstituted nuclei indeed revealed centrin 2 localized at the nuclear pores. Use of the mild detergent digitonin in immunofluorescence also allowed centrin 2 to be clearly visualized at the nuclear pores of human cells. Disruption of nuclear pores using RNA interference of the pore assembly protein ELYS/MEL-28 resulted in a specific decrease of centrin 2 at the nuclear rim of HeLa cells. Functionally, excess expression of either the Nor C-terminal calcium-binding domains of human centrin 2 caused a dominant-negative effect on both mRNA and protein export, leaving protein import intact. The mRNA effect mirrors that found for the Saccharomyes cerevisiae centrin Cdc31p at the yeast nuclear pore, a role until now thought to be unique to yeast. We conclude that in vertebrates, centrin 2 interacts with major subunits of the nuclear pore, exhibits nuclear pore localization, and plays a functional role in multiple nuclear export pathways.

The human TREX-2 complex is stably associated with the nuclear pore basket

“…In addition, our IF experiments in parental HeLa cells using antibodies specific for different TREX-2 subunits showed that GANP is localized predominantly at the nuclear envelope while PCID2 is found at the nuclear periphery along with a cytoplasmic and nuclear staining. Finally, both CETN2 and CETN3 localized at the centriole as reported earlier (Middendorp et al, 1997;Trojan et al, 2008;Resendes et al, 2008) and also displayed a perinuclear staining ( Fig. 1D; supplementary material Fig.…”

SUMO-dependent regulation of centrin-2

“…Although little is presently known about a possible role of SUMO at the centrosome, recent studies have identified several proteins that undergo SUMOylation and are known to localize to both centrosomal structures and the nuclear compartment (Cheng et al, 2006;Haindl et al, 2008;Yun et al, 2008). Our present data suggest that the SUMOylation machinery does not influence centrin-2 localization to the centrosome but is required for the efficient accumulation of the protein in the nucleus, where it functions in NER and mRNA export (Fischer et al, 2004;Resendes et al, 2008). A priori, the nuclear accumulation of centrin-2 could be regulated at the level of transport or retention (or both).…”

“…Remarkably, ~90% of the centrin-2 protein is not associated with centrosomal structures (Paoletti et al, 1996) and instead much of it is present within the nucleus. In line with this localization, centrin-2 has been implicated in mRNA export from the nucleus (Resendes et al, 2008) and this function seems to be conserved (Fischer et al, 2004). Furthermore, within the nucleus, centrin-2 associates with the xeroderma pigmentosum group C (XPC) protein and the human homolog of Rad23 B (HR23B) to form the trimeric XPC complex (Araki et al, 2001).…”

Sfr13 is a member of a large family of asymmetrically 1 localized Sfi1-repeat proteins and is important for basal body separation and stability inTetrahymena thermophila

“…Centrins are small calcium binding proteins that function at centrioles and basal bodies but also in a diverse array of additional activities including nuclear export and DNA damage repair (Chen and Madura, 2008;Fischer et al, 2004;Nishi et al, 2005;Paoletti et al, 1996;Resendes et al, 2008;Yang et al, 2010). Presumably, specificity of localization and function is accomplished through centrin-binding partners.…”