The nuclear localization signal (NLS) of PDX-1 is part of the homeodomain and represents a novel type of NLS

Authors: Hessabi, B.; Ziegler, P.; Schmidt, I.; Hessabi, C.; Walther, R.

Source: FEBS Journal, Volume 263, Number 1, 1 July 1999 , pp. 170-177(8)

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Abstract:

The β-cell homeodomain transcription factor PDX-1 has vital functions both in controlling the expression of pancreatic polypeptide hormones and in the development of the pancreas. The transactivating and DNA-binding properties of PDX-1 have been well characterized, but nuclear transport is still undefined. Here we show that PDX-1 bears a nuclear localization signal (NLS) that is part of helix 3 of the homeodomain. PDX-1 deletion mutants were tagged with enhanced green fluorescent protein (EGFP) and expressed in COS-7 cells. Subcellular localization of the respective PDX-1-EGFP fusion proteins was analyzed by direct fluorescence microscopy and Western immunoblotting using an anti-(GFP). As a result we were able to demonstrate that the homeodomain or helix 3 alone was sufficient and necessary for transport into the nucleus. Point mutations of basic amino acid residues within helix 3 led to identification of an NLS with six amino acids being crucial for nuclear transport of PDX-1. Because this NLS does not match known examples of NLSs, the PDX-1 NLS may represent a novel class of NLS.

Keywords: cell; homeodomain proteins; nuclear localization signal; nuclear transport; transcription factors

Document Type: Research article

Publication date: 1999-07-01