Mutant α-actinin-4 promotes tumorigenicity and regulates cell motility of a human lung carcinoma

Abstract

The precise role of a-actinin-4 encoding gene (ACTN4) is not very well understood. It has been reported to elicit tumor suppressor activity and to regulate cellular motility. To further assess the function of human ACTN4, we studied a lung carcinoma cell line expressing a mutated aactinin-4, which is recognized as a tumor antigen by autologous CD8 þ cytotoxic T lymphocytes (CTL). Confocal immunofluorescence microscopy indicated that, while wild-type (WT) a-actinin-4 stains into actin cytoskeleton and cell surface ruffles, the mutated protein is only dispersed in the cytoplasm of the lung carcinoma cells. This loss of association with the cell surface did not appear to correlate with a decrease in in vitro a-actinin-4 crosslinking to filamentous (F)-actin. Interestingly, experiments using cell lines stably expressing ACTN4 demonstrated that as opposed to WT gene, mutant ACTN4 was unable to inhibit tumor cell growth in vitro and in vivo. Moreover, the expression of mutant a-actinin-4 resulted in the loss of tumor cell capacity to migrate. The identification of an inactivating mutation in ACTN4 emphasizes its role as a tumor suppressor gene and underlines the involvement of cytoskeleton alteration in tumor development and metastasis.

ACTN4 (actinin, alpha 4)

“…Furthermore, after extraction of the primary tumor the cytotoxic T lymphocyte clone targeting mutated α-actinin 4 persisted many years in the patient's blood (Echchakir et al, 2001). In the subsequent study, it has been shown that the above point mutation removes antiproliferative effect of ACTN4 protein in the cancer cell line and supports the notion that ACTN4 may be both tumor suppressor as well as tumor promoter gene (Menez et al, 2004).…”

α-Actinin 4 Potentiates Myocyte Enhancer Factor-2 Transcription Activity by Antagonizing Histone Deacetylase 7

“…Although the precise roles of ␣-actinin 4 in tumorigenesis are controversial, ␣-actinin 4 has been proposed to play a role in cell motility and cancer invasion (4,(22)(23)(24)(25). Our findings that ␣-actinin 4 has a role in transcriptional regulation provides a possible, additional mechanism by which mutant ␣-actinin 4 might contribute to the pathogenesis of these diseases.…”

Actin-bundling proteins in cancer progression at a glance

“…Loss of a-actinin-4 disrupts the integrity of tight junctions and has been associated with cancer invasion and metastasis (Nakatsuji et al, 2008). However, in most studies, high levels of a-actinin-4 correlate with poor outcome or advanced disease (Honda et al, 1998;Honda et al, 2005;Honda et al, 2004;Kikuchi et al, 2008;Menez et al, 2004;Patrie et al, 2002;Weins et al, 2007;Welsch et al, 2009;Yamada et al, 2010;Yamamoto et al, 2007;Yamamoto et al, 2009), and the relevance of its role in tight junction assembly for cancer thus remains unclear. Other functions of a-actinin-4, such as in leading edge protrusion (Honda et al, 1998) might contribute to metastasis and further study is warranted.…”

“…a-Actinin-4 is generally found at the leading edges of motile cells in lamellipodia. a-Actinin (especially a-actinin-4) is implicated in multiple tumours, including breast (Guvakova et al, 2002), ovarian (Yamamoto et al, 2009) (where it is a prognostic indicator of poor outcome), pancreas (Kikuchi et al, 2008) and lung cancers (Menez et al, 2004) (see Table 1). …”

“…A role for actin-bundling proteins in metastasis Metastatic cancer cells use actin bundles to underpin protrusions that allow them to break away from a primary tumour and (See poster insert) (Fu et al, 2007;Hirooka et al, 2011;Honda et al, 2005;Honda et al, 2004;Kikuchi et al, 2008;Menez et al, 2004;Welsch et al, 2009;Yamamoto et al, 2007;Yamamoto et al, 2009) Eplin Stress fibres of multiple cell types Actin filament bundling and side-binding Eplin downregulation correlates with progression and metastasis in prostate cancer and eplin might be antiangiogenic. Potential tumour suppressor in breast cancer Sanders et al, 2011;Sanders et al, 2010;Zhang et al, 2010) Fascin Neurons, dendritic cells, endothelial cells and cancer cells.…”