Nuclear import of aristaless-related homeobox protein via its NLS1 regulates its transcriptional function
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Nucleocytoplasmic transport of transcription factors is essential in eukaryotes. We previously reported the presence of two functional NLSs in the homeodomain protein, aristaless-related homeobox (Arx) protein, which is a key transcriptional repressor of LMO1, SHOX2, and PAX4 during development. NLS2, that overlaps the homeodomain, is recognized directly by multiple importin βs, but not by importin αs. In this study, we found that the N-terminal NLS1 of Arx is targeted by multiple importin α proteins, including importin α3 and α5. Both in vivo and in vitro assays demonstrated that nuclear import of Arx via NLS1 is mediated by the importin α/β pathway. Mutagenesis analysis indicated that two basic amino acids, 84K and 87R, are essential to the function of NLS1, and that their mutation prevents interactions of Arx with importin αs. Interestingly, inhibition of nuclear import of Arx via NLS1 clearly attenuates its ability of transcriptional repression, suggesting that nuclear import of Arx via NLS1 contributes to its transcriptional function.
KeywordsArx Importin α/β Nuclear localization signal Transcriptional repression
This study was supported by Grants from National Science Foundation of China (#30971669 to Dr. Tao Tao; #31100599 to Dr. Wenbo Lin), and a Grant from Xiamen Center for Brain Research (#NK5888 to Dr. Qilin Ma). Dr. Alan Tartakoff is supported by NIH Grant R01-GM089872. Plasmids expressing importin αs were kindly provided by Dr. Nancy C. Reich of Stony Brook University. The (TAATTA)4 luciferase reporter plasmid was a gift from Dr. Jeffrey A Golden of Harvard University.
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