Abstract 482: Comparison of the actin-binding proteins actinin-1 and actinin-4: Their role in cancer

Abstract

Actinins are cytoskeleton proteins that crosslink actin filaments. Evolution of the actinin family resulted in the formation of calcium-insensitive muscle isoforms (actinin-2 and- 3) and calcium-sensitive non-muscle isoforms (actinin-1 and -4) with regard to their actin-binding function. Although the non-muscle actinin isoforms show 87% amino acid identity, they are currently viewed as distinct entities. Each isoform is reported to exert distinct effects on cell migration, adhesion and proliferation depending on the cell type studied. Actinin-4 is the predominant isoform reported to be associated with the cancer phenotype. Actinin-4 protein levels are elevated in a number of cancers including breast, ovarian, colorectal, bladder, pancreatic, ovarian and glioblastomas. Actinin-4 enhances the motility and metastatic potential of various carcinoma cell lines. This suggests that actinin-4 may have some unique characteristic that facilitates its role in cancer. We aimed to compare the actin-binding affinities, actin-bundling capacities and calcium sensitivities of the non-muscle actinins. We found that the non-muscle actinins have similar actin-binding affinities and calcium sensitivities with regard to their actin-binding and actin-bundling functions. Actinin structure consists of two anti-parallel monomers that form a homodimer. Heterodimer formation is reported to occur between the muscle actinin isoforms however this has not been systematically examined for the non-muscle isoforms. Through yeast two-hybrid analysis and in vitro binding assays we have shown that non-muscle actinin homodimers and heterodimers form with equal affinity. Using native gel electrophoresis we have shown that non-muscle actinin heterodimer formation occurs in a number of cancer cell lines studied. Comparison of non-muscle actinin protein levels indicates that the heterodimer represents the most abundant form of actinin present in the majority of cell lines studied. siRNA- mediated knockdown of actinin-4 resulted in a decrease in heterodimer levels and an increase in actinin-1 homodimer levels. Taken together this data suggests that actinin-1 and actinin-4 cannot be viewed as distinct entities from each other but rather as proteins that can exist in both homodimeric and heterodimeric forms. The ability to behave in this manner may have functional implications. This may be of importance considering that these proteins are central to such processes as cell migration and adhesion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 482. doi:1538-7445.AM2012-482