The Nucleo-cytoplasmic Actin-binding Protein CapG Lacks a Nuclear Export Sequence Present in Structurally Related Proteins

Impe, Katrien Van; Corte, Veerle De; Eichinger, Ludwig M.; Bruyneel, Erik; Mareel, Marc; Vandekerckhove, Joël; Gettemans, Jan

doi:10.1074/jbc.m209946200

Cited by 49 publications

(58 citation statements)

References 39 publications

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“…There is no typical nuclear localization signal (NLS), rather several regions of different subdomains are responsible for nuclear import (Gettemans et al 2005). In contrast to the other Gelsolin-related actin-binding proteins the CapG protein lacks a nuclear export sequence (van Impe et al 2003). Thus it is the only member of this family that accumulates in the nucleus.…”

Section: Known Capg Propertiesmentioning

confidence: 99%

Dynamics of the CapG actin-binding protein in the cell nucleus studied by FRAP and FCS

Renz

Langowski

2008

Chromosome Res

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FRAP (fluorescence recovery after photobleaching) and FCS (fluorescence correlation spectroscopy) are spectroscopic methods for monitoring the dynamic distribution of proteins inside the nucleus of living cells. As an example we report our studies on the intracellular mobility of the actin-binding protein CapG in live breast cancer cells. This Gelsolin-related protein is a putative oncogene. It appears to be overexpressed especially in metastasizing breast cancer. Furthermore, the CapG protein is known to be involved in the motility control of non-muscle benign cells. Its increased expression triggers an increase in cell motility of benign cells. Thus it can be expected that in cancer cells overexpressing the CapG protein, motility, invasiveness and metastasis might be particularly promoted. Since the nuclear CapG fraction seems to be pivotal to the increase in cell motility, we focused our studies on the CapG mobility in cell nuclei of live breast cancer cells. Using FCS and FRAP we showed that the eGFP-tagged CapG is monomeric and characterized its diffusional properties on the microsecond to minute timescale. This information about the mobility and compartmentalization of CapG might help to provide insight into its function within the cell nucleus and give clues about its altered cellular function in malignant dedifferentiation. Abbreviations ACF autocorrelation function CapGGelsolin-related actin binding capping protein CapG-eGFP CapG-eGFP fusion protein eGFP enhanced green fluorescent protein FCS fluorescence correlation spectroscopy FRAP fluorescence recovery after photobleaching NLS nuclear localization signal PI 3-kinase phosphatidylinositol 3-hydroxy kinase PIP 2 -binding phospatidylinositol 4,5-bisphosphate

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Section: Known Capg Propertiesmentioning

confidence: 99%

Dynamics of the CapG actin-binding protein in the cell nucleus studied by FRAP and FCS

Renz

Langowski

2008

Chromosome Res

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“…4,5 Both the transient overexpression of the CapG-eGFP fusion protein and the transient overexpression of the native CapG protein trigger an increase in cell motility. 3,20,25,30 On the other hand, the knockdown using siRNA in carcinoma cells constitutively overexpressing endogenous CapG impairs cell motility.…”

Section: Capg Knockdown Reduces Invasivenessmentioning

confidence: 99%

“…2 A couple of positively charged amino acids within the PIP 2 -binding region of the CapG protein or the amino acids 134-147, respectively, are proposed as potential equivalents of the canonical NLS. 3 , 4 In contrast to the other Gelsolin-related actin-binding proteins, the CapG protein lacks a nuclear export sequence, especially the decisive leucines 5 (L17, L21, L27). Thus, it is the only member of this family accumulating in the nucleus.…”

mentioning

confidence: 99%

Invasive breast cancer cells exhibit increased mobility of the actin‐binding protein CapG

Renz

Betz

Niederacher

et al. 2008

Intl Journal of Cancer

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The CapG protein, a Gelsolin-related actin-binding protein, is expressed at higher levels in breast cancer, especially in metastasizing breast cancer, than in normal breast epithelium. Furthermore, it is known that an increased expression of the CapG protein triggers an increase in cell motility. According to in vitro experiments, it was supposed that it is the nuclear fraction of the protein, which causes the increase in cell motility. Here, we examined the dynamical distribution of the CapG protein within the living cell, i.e. the import of the CapG protein into the nucleus. The nuclear import kinetics of invasive, metastasizing breast cancer cells were compared to the import kinetics of non-neoplastic cells similar to normal breast epithelium. FRAP kinetics showed a highly significant increase in the recovery of photobleached CapG-eGFP in the cancer cells, so that a differentiation of invasive, metastasizing cells and non-invasive, non-metastasizing cells on the basis of transport processes of the CapG protein between the nucleus and the cytoplasm seems to be possible. Comprehension of the mobility and compartmentalization of the CapG protein in normal and in cancer cells in vivo could constitute a new basis to characterize the invasiveness and metastasizing potential of breast cancer. ' 2007 Wiley-Liss, Inc.

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“…CapG was subcloned in the pEGFP-N1 vector (Clonetech) [9] and in the pcDNA3.1/V5-His vector (Invitrogen). Ran and RanQ69L were subcloned in the pEGFP-C1 vector (Clonetech).…”

Section: Methodsmentioning

confidence: 99%

“…Its capping activity is activated by calcium and inhibited by membrane polyphosphoinositides but unlike Gelsolin, CapG does not sever actin filaments [8]. CapG also localizes to the nucleus [9] and we recently showed that CapG is imported in the nucleus by the transport receptor NTF2 and Ran GTPase, a major regulator of nucleo-cytoplasmic transport [10]. The nuclear form of CapG has specifically been shown to promote cell invasion [11].…”

mentioning

confidence: 99%

The F-actin filament capping protein CapG is a bona fide nucleolar protein

Hubert

Impe

Vandekerckhove

et al. 2008

Biochemical and Biophysical Research Communications

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a b s t r a c tActin works in concert with myosin I to regulate the transcription of ribosomal genes in the nucleolus. Recently, nucleolar actin has been shown to be active in its polymeric form raising the question how actin dynamics is regulated in the nucleolus. Here, we show that the actin capping protein CapG localizes in the nucleolus of cultured cells. CapG transport to the nucleolus is an active and ATP-dependent process. Association of CapG with the nucleolus requires active RNA Polymerase I transcription. In addition, we show that activated Ran GTPase, an interaction partner of CapG, is also transported to the nucleolus. A constitutively active Ran mutant promotes CapG accumulation in the nucleolus indicating that CapG transport to the nucleolus can be supported by Ran. Our results suggest that filamentous actin in the nucleolus might be regulated by actin binding proteins such as CapG.

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The Nucleo-cytoplasmic Actin-binding Protein CapG Lacks a Nuclear Export Sequence Present in Structurally Related Proteins

Cited by 49 publications

References 39 publications

Dynamics of the CapG actin-binding protein in the cell nucleus studied by FRAP and FCS

Dynamics of the CapG actin-binding protein in the cell nucleus studied by FRAP and FCS

Invasive breast cancer cells exhibit increased mobility of the actin‐binding protein CapG

The F-actin filament capping protein CapG is a bona fide nucleolar protein

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