Overlapping signal sequences control nuclear localization and endoplasmic reticulum retention of GRP58

Glucose-regulated GRP58 has shown clinical applications to endoplasmic reticulum (ER) stress and cancer. GRP58 is localized in the cytosol, endoplasmic reticulum (ER) and nucleus. Twenty-four amino acids at the N-terminal hydrophobic region are known to target GRP58 to ER for synthesis at the ER membrane and translocation into the ER lumen. In addition, GRP58 contains putative nuclear localization (494KPKKKKK500) and ER retention (502QEDL505) signals. However, the role of these signals in nuclear import and ER retention of GRP58 remains unknown. Present studies investigated the signals that control nuclear localization and ER retention of GRP58. Deletion/mutation of nuclear localization signal (NLS) abrogated nuclear import of GRP58. NLS attached to EGFP localized EGFP in the nucleus. However, deletion/mutation of putative ER retention signal alone did not alter ER retention of GRP58. Interestingly, a combined deletion/mutation of NLS and ER retention signals blocked the GRP58 retention in the ER. These results concluded that overlapping NLS and ER retention signal sequences regulate nuclear localization and ER retention of GRP58.