Acquired radioresistance accompanied with increased metastatic potential is a major hurdle in effective radiotherapy of breast cancers. However, the nature of their inter-dependence and the underlying mechanism remains largely intangible. By employing radioresistant (RR) cell lines, we herein demonstrate that MCF-7 RR cells display phenotypic and molecular alterations evocative of epithelial to mesenchymal transition (EMT) with increased traction forces and membrane ruffling culminating in boosted invasiveness. We then show that these changes can be attributed to overexpression of alpha-actinin-4 (ACTN4), with ACTN4 knockdown near-completely abrogating both radioresistance and EMT-associated changes. We further found that in MCF-7 RR cells, ACTN4 mediates the observed effects by activating AKT, and downstream AKT/GSK3β signalling. Though ACTN4 plays a similar role in mediating radioresistance and invasiveness in MDA-MB-231 RR cells, co-immunoprecipitation studies reveal that these changes are effected through increased association with AKT and not by overexpression of AKT. Taken together, our study identifies ACTN4/AKT/GSK3β as a novel pathway regulating radioresistance coupled invasion which can be further explored to improve the radiotherapeutic gain.
Keywords: AKT; Actinin-4; Breast cancer; Epithelial-mesenchymal transition; Invasion; Radioresistance.
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