Identification of a nuclear localization signal, RRMKWKK, in the homeodomain transcription factor PDX-1

Pancreatic duodenal homeobox-containing transcription factor 1 (PDX-1) play s a crucial role in pancreas development and beta-cell gene regulation. Abs ence of PDX-1 leads to pancreas agenesis and its malfunction causes MODY4 d iabetes mellitus. PDX-1 has been suggested to be involved in the glucose-de pendent regulation of insulin gene transcription. Whereas DNA-binding and t ransactivation domains of PDX-1 are in the process of being characterized, protein sequences responsible for its nuclear translocation remain unknown, By combining site-directed mutagenesis of putative phosphorylation sites a nd nuclear localization signal (NLS) motifs with on-line monitoring of GFP- tagged PDX-1 translocation, we demonstrate that the NLS motif RRMKWKK is ne cessary and in conjunction with the integrity of the 'helix 3' domain of th e PDX-1 homeodomain is sufficient for the nuclear import of PDX-1, Furtherm ore, we show that there is no glucose-dependent cytoplasmic-nuclear cycling of PDX-1. (C) 1999 Federation of European Biochemical Societies.