Nuclear Import of the Yeast AP-1-like Transcription Factor Yap1p Is Mediated by Transport Receptor Pse1p, and This Import Step Is Not Affected by Oxidative Stress

Abstract

The yeast AP-1-like transcription factor, Yap1p, is essential for the oxidative stress response in budding yeast. Yap1p is located predominantly in the cytoplasm; however, upon imposition of oxidative stress, Yap1p concentrates in the nucleus and activates target genes. Yap1p is constitutively transported in and out of the nucleus. Oxidative stress inhibits the Crm1p/Xpo1p-dependent nuclear export step, resulting in nuclear accumulation of Yap1p. In this study, we examined the mechanism for Yap1p nuclear import, and determined whether the import step is affected by oxidative stress. The nuclear accumulation of Yap1p required the activity of the small GTPase, Ran/Gsp1p. Under conditions in pse1-1 cells carrying a temperature-sensitive mutation of the importin ␤ family member PSE1/KAP121, nuclear translocation of Yap1p was inhibited dramatically. In an in vitro assay, we showed that Yap1p could directly bind to Pse1p and that this interaction was dissociated by Ran-GTP. These results indicate that Pse1p is the nuclear import receptor for Yap1p. In addition to Pse1p, we suggest that Kap123p, which is homologous to Pse1p, has a minor effect on the nuclear import of Yap1p. Furthermore, we identified the nuclear localization signal of Yap1p and demonstrated that the nuclear import of Yap1p was not affected by oxidative stress.

KapI, a non-essential member of the Pse1p/Imp5 karyopherin family, controls colonial and asexual development in Aspergillus nidulans

“…In diverse transport processes, Kap121p/Pse1p requires coordination with Kap123p (Isoyama et al, 2001;Rout et al, 1997;Schaper et al, 2005;Seedorf & Silver, 1997). In A. nidulans, a redundancy between KapI and KapJ (Kap123p putative homologue) could be also proposed.…”

“…In humans, Imp5 regulates, for example, neuronal differentiation and degeneration by the import of p35 protein (Fu et al, 2006), chromosome structure by the import of core histones (Baake et al, 2001), and specific DNA recombination processes through RAG-2 binding (Ross et al, 2003). In yeast, Kap121p/Pse1p is an essential protein that regulates multiple pathways such as the phosphate stress response via Pho4p import (Kaffman et al, 1998), the oxidative stress response via Yap1 (Isoyama et al, 2001), membrane biogenesis by Pdr1 (Delahodde et al, 2001), and both mating response and pseudohyphal transition mediated by Ste12 (Leslie et al, 2002). From our study in A. nidulans, evidence of different levels of control has emerged.…”

“…Most karyopherins belong to the superfamily defined by importin-b, and 22 and 15 such proteins have been identified in mammals and Saccharomyces cerevisiae, respectively (Mosammaparast & Pemberton, 2004;Strom & Weis, 2001). The genome of Aspergillus nidulans is predicted to contain 14 importin-b-type coding genes (Espeso & Osmani, 2008 from Schizosaccharomyces pombe and Saccharomyces cerevisiae Glover & Harrison, 1995;Isoyama et al, 2001). Moreover, FlbB was capable of binding the same target sequences as those recognized by Pap1 at the p25 gene promoter from Schiz.…”

Nuclear localization signals and human disease

“…Chook et al defined the PY-NLS as a consensus sequence containing a hydrophobic or basic region followed by an arginine (R)/lysine (K)/histidine (H) then a proline and tyrosine (R/K/H-X (2-5) -PY) (35,62). Using these guidelines, the human proteome was searched and 81 potential cargoes for Kapb2 were identified, (49,50) some of which they demonstrated interact directly with Kapb2 in vitro (35). A follow-up study provided evidence that the PY-NLS motif is conserved in budding yeast in the RNA binding protein, Hrp1 (Table 1), and also that the PY-NLS functions as a nuclear targeting signal in vivo (36).…”

Yap4 PKA‐ and GSK3‐dependent phosphorylation affects its stability but not its nuclear localization

“…It is known that the nuclear import of Yap1, the well-studied member of the Yap family, is mediated by the importin Pse1 (Isoyama et al, 2001). To verify whether Yap4 localization would also be mediated by this importin, we have used the conditional pse1-1 mutant.…”