Modification of survival pathway gene expression in human breast cancer cells by tetraiodothyroacetic acid (tetrac).

Tetraiodothyroacetic acid (tetrac) inhibits the cellular actions of thyroid hormone initiated at the hormone receptor on plasma membrane integrin alphavbeta3. Via interaction with the integrin, tetrac is also capable of inhibiting the angiogenic effects of vascular endothelial growth factor and basic fibroblast growth factor. MDA-MB-231 cells are estrogen receptor-negative human breast cancer cells shown to be responsive to tetrac in terms of decreased cell proliferation. Here we describe actions initiated at the cell surface receptor by unmodified tetrac and nanoparticulate tetrac on a panel of survival pathway genes in estrogen receptor-negative human breast cancer (MDA-MB-231) cells. Nanoparticulate tetrac is excluded from the cell interior. Expression of apoptosis inhibitors XIAP (X-linked inhibitor of apoptosis) and MCL1 (myeloid cell leukemia sequence 1) was downregulated by nanoparticulate tetrac in these breast cancer cells whereas apoptosis-promoting CASP2 and BCL2L14 were upregulated by the nanoparticulate formulation. Unmodified tetrac affected only XIAP expression. Expression of the angiogenesis inhibitor thrombospondin 1 (THBS1) gene was increased by both formulations of tetrac, as was the expression of CBY1, a nuclear inhibitor of catenin activity. The majority of differentially regulated Ras-oncogene family members were downregulated by nanoparticulate tetrac. The latter downregulated expression of epidermal growth factor receptor gene and unmodified tetrac did not. Nanoparticulate tetrac has coherent anti-cancer actions on expression of differentially-regulated genes important to survival of MDA-MB-231 cells.