title: Growth/cell cycle regulation of Sp1 phosphorylation.
abstract: Sp1 sites can mediate growth/cell cycle induction of dihydrofolate reductase in late G1 (Jensen, D. E., Black, A. R. Swick, A. G., and Azizkhan, J. C. (1997) J. Cell. Biochem. 67, 24-31). To investigate mechanisms underlying this induction, effects of serum stimulation on regulation of Sp1 were examined. In Balb/c 3T3 cells, serum stimulation did not affect Sp1 synthesis or the relative binding of Sp1 family members to DNA; however, it did result in a rapid, approximately 2-fold increase in Sp1 levels and an approximately 3-fold increase in specific Sp1 phosphorylation in mid-G1. In normal human diploid fibroblasts, serum stimulation also increased Sp1 phosphorylation in mid-G1 but did not affect Sp1 levels. Therefore, Sp1 phosphorylation is regulated in a growth/cell cycle-dependent manner which correlates temporally with induction of dihydrofolate reductase transcription. Further studies revealed a kinase activity specifically associated with Sp1 in a growth-regulated manner. This activity is distinct from purified kinases previously shown to phosphorylate Sp1 in vitro and phosphorylates Sp1 between amino acids 612 and 678 in its C terminus, a region also phosphorylated in mid-G1 in vivo. Therefore, this study indicates that phosphorylation of the C terminus of Sp1 may play a role in the cell cycle regulation of its transcriptional activity.
authors.affiliation: Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Black
authors.forename: D
authors.initials: D
authors.lastname: Jensen
authors.forename: S Y
authors.initials: SY
authors.lastname: Lin
authors.forename: J C
authors.initials: JC
authors.lastname: Azizkhan
mesh_terms: D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D016329:Sp1 Transcription Factor / Q000378:metabolism*
chemical_list: D016329:Sp1 Transcription Factor; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C065999:Sp1 kinase