Phosphorylation of DNA topoisomerase I is increased during the response of mammalian cells to mitogenic stimuli

D. Scott Samuels, Yoshiko Shimizu, Toshikatsu Nakabayashi, Nobuyoshi Shimizu

Research output: Contribution to journalArticlepeer-review

Abstract

DNA topoisomerase I is phosphorylated after mitogenic stimulation of 3T3-L1 mouse fibroblasts by 12-O-tetradecanoylphorbol 13-acetate (TPA), a phorbol ester tumor promoter. In vivo labeling with [32P]orthophosphate and immunoprecipitation with an anti-DNA topoisomerase I antibody has demonstrated an increase in the phosphorylation of DNA topoisomerase I in Swiss/3T3 mouse fibroblasts treated with epidermal growth factor (EGF) and H35 rat hepatoma cells treated with insulin. The only phosphorylated form of DNA topoisomerase I observed was the 100-kDa protein. Digestion of DNA topoisomerase I with trypsin revealed two phosphopeptides. In addition, VT-1, a non-responsive genetic variant of 3T3-L1, and the DNA topoisomerase I inhibitor camptothecin were used to further study TPA-induced DNA topoisomerase I phosphorylation. Our results indicate that the phosphorylation of DNA topoisomerase I may be an ubiquitous response of cultured mammalian cells to mitogenic agents, even in the absence of DNA replication.

Original languageEnglish
Pages (from-to)77-83
Number of pages7
JournalBBA - Molecular Cell Research
Volume1223
Issue number1
DOIs
StatePublished - Aug 11 1994

Keywords

  • (Fibroblast)
  • (Hepatoma cell)
  • (Mouse)
  • 12-O-Tetradecanoylphorbol 13-acetate
  • Camptothecin
  • DNA topoisomerase I
  • Epidermal growth factor
  • Insulin
  • Phosphorylation
  • TPA

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