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Effects of increased Nuclear Localization of Tip60 in Cancer Cells

Tip60C is a 13-protein complex involved in transcription, DNA repair, and cell cycle regulation. In most cancers, the complex has been shown to be a tumor suppressor. Its catalytic subunit is the Tip60 protein, which is a lysine acetyltransferase responsible for acetylating targets including histones H3 and H4, transcription factor NF-κB, ATM kinase, and p53 tumor suppressor. We had previously shown that breast, lung, and pancreatic cancer cells treated with the chemotherapeutic drug paclitaxel and overexpressing Tip60 showed small but significant reductions in proliferation compared to paclitaxel treatment alone. We investigated whether the subcellular localization of Tip60 was necessary for its anti-proliferative activity. We added the prototypical nucleoplasmin bipartite nuclear localization signal to the amino-, carboxyl- and both termini of the Tip60 protein and analyzed the effects of overexpressing these proteins in breast and lung cancer cell lines. Using immunofluorescence we determined the localization of Tip60 and measured cell proliferation as compared to wildtype Tip60 (WT Tip60). While the addition of any NLS significantly increased nuclear localization, the C-terminal NLS had a larger effect than the N-terminal NLS. Although we increased nuclear localization, we did not observe any decreases in cancer cell proliferation with the NLS constructs compared to WT Tip60 in cells treated with paclitaxel. These results suggest that Tip60’s anti-proliferative activity in cancer cells does not necessarily take place in the nucleus. We are continuing to investigate the molecular effects of increasing the amount of Tip60 in the nucleus.