Transcription factor Sp3 activates the liver/bone/kidney-type alkaline phosphatase promoter in hematopoietic cells

The promoter region of the liver/bone/ kidney-type alkaline phosphatase gene was examined to define the cis-acting regulatory sequences and transcription factors responsible for its expression in hematopoietic cells. Transient transfection experiments revealed that regions deleted up to -154 base pairs upstream from the transcription initiation site had significant activities to induce bacterial chloramphenicol acetyltransferase gene. The shortest DNA fragment was found to contain three GC boxes in addition to a TATA box. Electrophoretic mobility shift assay and Southwestern analysis showed that Sp3 could bind to the fragment. Western blot analysis also detected Sp3 protein in eluate from the DNA probe mixed with the nuclear extracts. Through the use of Drosophila Schneider cells that lack the Sp1 family of transcription factors, Sp3 was shown to activate the basal promoter in a dose-dependent manner. When the amount of Sp3 was limited, the most proximal GC box was found to be critical for the basal promoter activity.