MitoNEET was discovered through interactions with a labeled and photoactive derivative of pioglitazone (pio), a drug used to increase peripheral insulin sensitivity. Its unique coordination of a [2Fe-2S] cluster by three cysteine residues (Cys-72, Cys-74, and Cys-83) and one histidine (His-87) gives this cluster both stability and the ability to be donated to acceptor proteins. These qualities allow mitoNEET to participate in a diversity of biological functions. Functions of mitoNEET and the consequences of pioglitazone (pio) treatment in human hepatocellular carcinoma (HepG2) cells cultured in glucose or galactose-based medium were examined by respiration and proliferation studies. Pio treatment decreased complex I stimulated respiration for cells grown in both glucose and galactose-based medium. Additionally, pio was found to significantly decrease cell proliferation. HepG2 cells cultured in galactose exhibited significantly higher oxygen flux than those cultured in glucose-based medium, but proliferation of these cells was notably reduced. Interestingly, mitoNEET levels were substantially lower in cells cultured in galactose. We hypothesize that some of the effects of pio may depend on the cellular levels of mitoNEET and the metabolic consequences of culturing cancerous cells in a galactose-based medium
