Hydrophobic coiled-coil domains regulate the subcellular localization of human heat shock factor 2

HSF2, one of the heat shock transcription factors in mammalian cells, is localized to the cytoplasm during normal growth and moves to the nucleus upon activation. Heat shock transcription factors in metazoans contain four hydrophobic heptad repeat sequences, three in the amino terminus and one in the carboxy terminus, which are predicted to form alpha-helical coiled-coil structures analogous to the leucine zipper. Here, we show that point mutations in either of two amino-terminal zippers or in the carboxy-terminal zipper disrupt normal localization of HSF2 and cause it to be constitutively nuclear. We demonstrate further that two sequences immediately surrounding the amino-terminal zipper domain are required for nuclear localization. These sequences fit the consensus for a bipartite nuclear localization signal (NLS). We suggest that interactions between the amino- and carboxy-terminal zippers normally mask the NLS sequences of HSF2 and that these interactions are disrupted upon activation to expose the NLS sequences and allow transport of HSF2 to the nucleus. We conclude that zipper domains can regulate subcellular localization.