Concentration-Dependent Pleiotropic Effects of Thymosin beta4 and Cofilin On the Migratory Activity of Carcinoma Cells

Tumour cell migration depends on the actin cytoskeleton modified by particular actin binding proteins (ABPs). Overexpression of cofilin or thymosin beta4 (Tß4) has been correlated with an increase or decrease of their migratory activity, respectively. We modulated by transfection the intracellular concentrations of cofilin and Tß4 of two colon (3LNLN and EB3) and one breast carcinoma (MDA-MB-231) cell line and subsequently analysed their migratory activity. Increasing wildtype cofilin did not alter their migratory activity, whereas the constitutively active S3A-cofilin mutant elevated migration. Transfection leading to an up- or downregulation of Tß4 showed that MDA-MB-231 and 3LNLN cells responded with a decrease or increase of migration, respectively. Exposure of MDA-MB-231 and 3LNLN cells to increasing concentrations of extracellular Tβ4 (or His-tagged Tß4) induced a biphasic response of migration being highest around 0.24 µM and decreased at higher extracellular Tß4. Immunostaining of 3LNLN cells exposed to 0.24 µM extracellular His-tagged Tß4 with anti-His antibody indicated its uptake co-localising with integrin-linked kinase at cell attachment points. Furthermore, the exposure to 0.24 µM His-tagged Tß4 led to increased phosphorylation of AKT1/2 and secretion of matrix metalloproteases. These effects and tumour cell migration were abrogated after exposure of 3LNLN cells to 2.8 µM His-Tß4 that in a number of cells induced apoptosis.