Violaceols function as actin inhibitors inducing cell shape elongation in fibroblast cells

Violaceol-I and -II were isolated from a fractionated library of marine-derived fungal metabolites. These compounds increased the calcium ion concentration inside the cell and caused F-actin aggregation in rat fibroblast 3Y1 cells within 3 h resulting in cell shape elongation. Calcium chelator BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester) inhibited violaceol-I and -II induced F-actin aggregation in 3Y1 cells, and hence violaceol-I and -II act in a calcium dependent manner. Violaceol-I and -II inhibited G-actin polymerization in vitro in a dose-dependent manner and strongly associated with G-actin, at dissociation equilibrium constants of 1.44 × 10(-8) M and 2.52 × 10(-9) M respectively. Here we report the identification of a novel function of violaceol-I and -II as actin inhibitors. Violaceol-I and -II induced cell shape elongation through F-actin aggregation in 3Y1 fibroblasts. These compounds may give researchers new insights into the role of actin in tumorigenesis and lead to the development of additional anti-tumor drugs.