Digital Commons @ LIU

Where is the NLS in Tip60?

Tip60 is a lysine acetyltransferase (KAT), coded by the KAT5 gene, which is involved in transcription, DNA repair, and apoptosis. It acetylates histones, the ATM protein kinase, and the p53 tumor suppressor, among other targets, making it a key regulator of cell homeostasis. Tip60 has been shown to be a tumor suppressor in most cancers but an oncogene in prostate cancer. Some of Tip60’s functions take place in the nucleus while others occur in the cytoplasm. We were interested in investigating whether the nuclear localization of Tip60 is important for its tumor suppressor function. We hypothesized that decreasing Tip60 nuclear localization would reduce its anti-proliferative effect in breast and lung cancer cells. To test this hypothesis, we mutated a putative Tip60 nuclear localization signal (NLS) and measured nuclear localization by immunofluorescence, as well as proliferation of two different transiently transfected breast and lung cancer cells lines. Tip60 lacking the putative NLS (Tip60ΔNLS) had a significantly different localization pattern compared to the wild type Tip60 in all of the cell lines we tested, suggesting that we mutated the correct NLS. Although Tip60ΔNLS showed significantly less nuclear localization than WT Tip60, neither construct reduced proliferation of breast and lung cancer cell lines in combination with paclitaxel, a chemotherapeutic drug used in the treatment of various cancers including breast and lung. These results suggest that we have identified the Tip60 NLS, but that the effects of changing Tip60 localization are more subtle than large changes in cell growth.