Lovastatin-induced apoptosis in thyroid cells: involvement of cytochrome cand lamin B

Objective: The 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, l ovastatin, induces apoptosis in the thyroid cell line TAD-2 and in prolifer ating normal human thyroid cells in culture, through a p53-independent mech anism involving caspase-3-like proteases. The combination of lovastatin wit h other anti-neoplastic drugs potentiates chemotherapy of tumors. This drug has been suggested for the chemotherapy of tumors and is potentially usefu l in the treatment of thyroid proliferative diseases. Based on this premise , we analyzed in more detail the role of some molecular effectors and the r ole of the caspase family proteases in the lovastatin-induced apoptotic pat hway in TAD-2 cells. Methods: TAD-2 cells were treated with lovastatin to induce apoptosis, and expression of p53, Bcl-2, Bcl-XL and Bax was analyzed by Western blot. Casp ase activation was evaluated by the assay of enzymatic activity with chromo genic peptides and Western blot. Nuclear, cytosolic and mitochondrial fract ions were prepared by differential centrifugation and the presence of cytoc hrome c and lamin B was evaluated by Western blot. Results: p53, Bcl-2, Bcl-XL and Bax protein expression were unchanged durin g apoptosis. Cytochrome c was released from mitochondria into the cytosol, a pivotal event in the activation of caspase-3. Caspase-3 and -6 but not ca spase-2 were activated, and proteolysis of PARP and lamin B, a caspase-6 su bstrate located in the inner nuclear membrane, was demonstrated by Western blot. The nuclear localization of lamin B was also inhibited by lovastatin. Conclusions: These data demonstrate that, in TAD-2 thyroid cells, lovastati n induces lamin B proteolysis and inhibits its nuclear localization and ind uces cytochrome c release from mitochondria into the cytosol.