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

Abstract

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.

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

“…Studying protein dynamics inside the living cell provides an analytical tool to elucidate the spatiotemporal organization of cell nuclei, which may provide insights beyond mere description. In this context, the comparative FRAP analysis of CapG distribution in normal and neoplastic breast epithelial cells from our recent work (Renz et al 2007) may serve as an example: The CapG protein appears to be transported much faster into the nucleus of breast cancer cells and is far less immobilized in the nucleus of cancer cells than in normal breast epithelial cells on the timescale of minutes. Both the immobilized fraction of CapG within the nucleus and its import kinetics distinguish normal and cancer …”

“…Normal breast epithelium cells exhibit a much higher fraction of immobilized component (Renz et al 2007). Given the fit uncertainty, the immobile fraction in the neoplastic cells is negligible for both the slow and the fast subgroup.…”

“…In what follows, the FRAP and FCS measurements of a CapG-eGFP construct in breast cancer cells are described. These methods provide complementary information about intranuclear CapG distribution, forming the basis for comparative kinetic analyses of normal and neoplastic cells, an example of which we recently published (Renz et al 2007). In that work we concentrated on FRAP studies of the transport of CapG into the nucleus and could show that in neoplastic cells the recovery rate of CapG was greatly enhanced and the immobilized fraction reduced relative to normal cells.…”

“…For kinetic analysis in living breast cancer cells, the human CapG protein was C-terminally labelled with eGFP which alters neither the localization of the protein nor its function in the context of cell motility, as reported in our earlier work (Renz et al 2007). Live cell measurements, FRAP and FCS, were performed at 37-C in Hepes-buffered medium or 5% CO 2 atmosphere, respectively.…”

Overexpression of Gelsolin-Like Actin-Capping Protein Is Associated with Progression of Lung Adenocarcinoma

“…De Corte et al (2004) showed that CapG may modulate the invasive properties of MDCK-AZ, HeLa, and HEK293T cells. Renz et al (2008) also found that the import of CapG into the nucleus is increased in invasive breast cancer cells. Our results showed that reduction of CapG expression in A549 and H358 cells was accompanied by significantly impaired motility, especially under hypoxia.…”