Cloning and characterization of the promoter of Hugl-2, the human homologue of Drosophila lethal giant larvae (lgl) polarity gene

The human lgl gene, Hugl-2 (llgl2, Lgl2), codes for a cytoskeletal protein involved in regulating cell polarity. Here, we report the identification and functional characterization of the promoter region (∼1.2 kb) of the Hugl-2 gene. Luciferase expression assays show a high basal Hugl-2 promoter activity in different cell lines and primary human hepatocytes. Truncations of the promoter identified a GC-rich region important for this activity. Alignment of human and mouse genomic sequences demonstrate that this is an evolutionary conserved region fcontaining putative binding sites for several transcription factors including Elk-1 and Sp-1. Mithramycin A reduces Hugl-2 expression indicating Sp-1 transcription factors activate Hugl-2. Treatment of primary hepatocytes with epidermal growth factor (EGF) suppresses Hugl-2, suggesting regulation by the EGF-signaling pathway. Downregulation of Hugl-2 by EGF may contribute to loss of cell polarity and tumour progression, therefore supporting a tumour suppressor role for Hugl-2.