Functional Differences Of Actinin Isoforms In The Formation Of Invadopodia By Invasive Cancer Cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Invadopodia are ventral membrane protrusions that are formed by invasive cancer cells cultured on physiological substrates. They are actin-based structures and promote the degradation of the extracellular matrix by focally localizing matrix metalloproteinases. Accumulating evidence suggests that invadopodia play an important role in local invasion and distant metastasis of malignant tumors. Actinin is an actin-binding protein that forms dimers and crosslinks actin filaments. There are four isoforms of actinin in mammals and they are divided into the muscle type (actinin-2 and -3) and the non-muscle type (actinin-1 and -4). Actinin-1 is ubiquitously expressed and involved in the formation of focal adhesions, while actinin-4 is strongly expressed at the invading front of advanced cancers and its expression is correlated with poor prognosis. Although actinin-4 is thought to regulate cell motility and invasion, the detailed molecular mechanisms remain unclear. Moreover, functional differences between the two isoforms have yet to be fully defined. In this study, we studied the roles of and functional differences between actinin-1 and -4 in invadopodia formation to determine the impact of actinin-4 expression on cancer cells. Immunofluorescence analysis showed that both actinin-1 and -4 clearly localized at invadopodia in RPMI-7951 human melanoma cells and there was no obvious difference in their localization patterns. Likewise, invadopodia formation and degradation of fluorescent gelatin matrix were blocked by siRNA-mediated knockdown of either actinin-1 or -4. In contrast, only actinin-4, but not actinin-1, promoted invadopodia-mediated gelatin degradation activity when overexpressed in RPMI7951 cells. Similar results were obtained when MDA-MB-231 human breast cancer cells and SCC61 human head and neck squamous cell carcinoma cells were analyzed in the same manner. These results indicate that both actinin-1 and -4 are essential components of invadopodia, but only actinin-4 possesses an ability to promote invadopodia formation. Therefore, further analysis is conducted now to identify the unique functions actinin-4 in invadopodia formation. Citation Format: Yuumi Ito, Hideki Yamaguchi, Kiyoko Fukami, Kazufumi Honda, Nami Miura, Tesshi Yamada, Ryuichi Sakai. Functional differences of actinin isoforms in the formation of invadopodia by invasive cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4070. doi:10.1158/1538-7445.AM2014-4070