RRR‐α‐tocopheryl succinate enhances TGF‐β₁, ‐β₂, and ‐β₃ and TGF‐βR‐II expression by human MDA‐MB‐435 breast cancer cells

Abstract

The proliferation of MDA‐MB‐435 human breast cancer cells was inhibited by RRR‐α‐tocopheryl succinate (vitamin E succinate, VES). Conditioned media (CM) from VES growth‐inhibited cells contained potent antiproliferative activity, part of which is contributed by transforming growth factor‐β: (TGF‐β) isoforms. Antibody neutralization analyses, employing TGF‐β isoform‐specific antibody reagents, showed that TGF‐β₁, ‐β₂, and ‐β₃ were present in the CM from VES‐treated cells. Culturing MDA‐MB‐435 cells with VES did not alter the levels of constitutively expressed 2.4‐kb TGF‐β₁, 3.0‐ and 4.0‐kb TGF‐β₂, or 1.2‐ and 3.5‐kb TGF‐β₃ mRNA transcripts. Inhibition of DNA synthesis by MDA‐MB‐435 cells was increased by combinations of suboptimal levels of VES and purified TGF‐β₁. VES‐treated MDA‐MB‐435 cells exhibited enhanced binding of radiolabeled TGF‐β₁, and Western immunoblotting analyses showed that VES treatment enhanced TGF‐β type II receptor protein expression. TGF‐β type I receptor protein levels were not modified by VES treatments. Although the mRNA transcript for the 5.5‐kb TGF‐β type II receptor was upregulated after four hours of treatment with VES, this treatment did not modify the 6.5‐kb TGF‐β type I or the 6.5‐kb TGF‐β type II receptor mRNAs. Results demonstrate that biologically active TGF‐β₁ ‐β₂, ‐β₃ and levels of TGF‐β type II receptor expressed by human breast cancer cells are enhanced by VES treatments.