TRANSCRIPTIONAL REGULATION OF THE SIS PDGF-B GENE IN HUMAN OSTEOSARCOMA CELLS BY THE SP FAMILY OF TRANSCRIPTION FACTORS/

Expression of PDGF-B, the gene encoding the platelet-derived growth fa ctor B chain, has been implicated as a participant in an autocrine gro wth loop in the human osteosarcoma cell line U2-OS. In previous work, we identified a primary site in the PDGF-B promoter, the SIS proximal element (SPE), which is critical for transcription of the PDGF-B gene in U2-OS cells. We also identified Spl as one of the SPE-binding prote ins in U2-OS nuclear extracts. In the present work, we have identified another SPE-binding protein to be Sp3. Gel mobility shift assays show ed that both Spl and Sp3 require the CACCC motif within the SPE for bi nding. In vitro transcription assays showed that Sp1 or/and Sp3 is nec essary for transcription of the PDGF-B gene. Cotransfection experiment s functionally demonstrated that Sp1 and Sp3 can independently or addi tively activate the PDGF-B promoter through the SPE as well as a synth etic promoter. However, the CACCC motif within the SPE is not the only site within the minimal PDGF-B promoter through which Sp1/Sp3 acts; a dditional nested deletion analyses showed that multiple cis-acting ele ments within the minimal promoter are required for full level transcri ption of the PDGF-B gene in U2-OS cells.