We had previously reported that trivalent arsenic (As(3+)), a well-known environmental carcinogen, induces phosphorylation of several putative Akt substrates. In the present report, we characterized one of these substrates by immunoprecipitation and proteomics analysis. The results indicate that a cytoskeleton remodeling protein, filamin A, with a molecular weight around 280 kDa, is phosphorylated by Akt in HEK-293 cells treated with As(3+), which was also confirmed in human bronchial epithelial cell line, BEAS-2B cells. Additional biochemical and biological studies revealed that serine 2152 (S2152) of filamin A is phosphorylated by activated Akt in the cells treated with As(3+). To further confirm the importance of Akt-dependent filamin A S2152 phosphorylation in As(3+)-induced cell migration, we over-expressed either wild type filamin A or the mutated filamin A in which the S2152 was substituted with alanine (S2152A). The capability of cell migration was reduced significantly in the cells expressing the mutated filamin A (S2152A). Clinically, we found that increased expression of filamin A predicts poorer overall survival of the lung cancer patients with adenocarcinoma. Thus, these data suggest that Akt dependent filamin A phosphorylation is one of the key events in mediating As(3+)-induced carcinogenesis. Antagonizing Akt signaling can ameliorate As(3+)-induced filamin A phosphorylation and cell migration, which may serve as a molecular targeting strategy for malignancies associated with environmental As(3+) exposure.
Keywords: Akt; arsenic; filamin A; migration; patient survival.