A novel Sp1-related cis element involved in intestinal alkaline phosphatase gene transcription

We have used sodium butyrate-treated HT-29 cells as an in vitro model syste m to study the molecular mechanisms underlying intestinal alkaline phosphat ase (IAP) gene activation. Transient transfection assays using human IAP-CA T reporter genes along with DNase I footprinting were used to localize a cr itical cis element (IF-III) corresponding to the sequence 5'-GACTGGGCGGGGTC AAGATGGA-3 '. Deletion of the IF-III element resulted in a dramatic reducti on in reporter gene activity, and IF-III was shown to function in the conte xt of a heterologous (SV40) promoter in a cell type-specific manner, furthe r supporting its functional role in IAP transactivation. Electrophoretic mo bility shift assays revealed that IF-III binds Spl and Sp3, but these facto rs comprise only a portion of the total nuclear binding and appear to media te only a small portion of its transcriptional activity. IF-III does not co rrespond to any previously characterized regulatory region from other intes tine-specific genes. We have thus identified a novel, Spl-related cis-regul atory;element in the human IAP gene that appears to play a role in its tran scriptional activation during differentiation in vitro.