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Tumor promoter-dependent phosphorylation of a Triton X-100 extractable form of lipocortin I in T51B rat liver cells.

Abstract
The phosphorylation of lipocortin (a substrate of EGF-receptor kinase, and a putative phospholipase A2 inhibitor) was examined in T51B cells. By using Western blot procedures and antisera specific to lipocortin I, we found that most immunoreactive lipocortin I was located in the cytosol (lipocortin(cvt] of cells extracted in Ca2+-free buffers These cells however had another pool of immunoreactive lipocortin I located in the particulate fraction that was Triton X-100 extractable (lipocortin(mem]. Increasing Ca2+ concentrations in the extraction buffer resulted in more lipocortin(mem) recovered. In vitro phosphorylation of endogenous proteins demonstrated that lipocortin I became phosphorylated in a Ca2+ and phosphatidylserine-dependent manner, suggesting an involvement of protein kinase C. Treatment of cells with 100 ng/ml 12-0-tetradecanoylphorbol-13-acetate (TPA) but not with 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD) resulted in the in vitro phosphorylation of lipocortin(mem) by protein kinase C. TPA also increased the phosphorylation of lipocortin(mem) in [32P]phosphate-labeled cells.
AuthorsR Campos-Gonzalez, M Kanemitsu, A L Boynton
JournalExperimental cell research (Exp Cell Res) Vol. 184 Issue 2 Pg. 287-96 (Oct 1989) ISSN: 0014-4827 [Print] United States
PMID2530098 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)
Chemical References
  • Annexins
  • Calcium-Binding Proteins
  • Carcinogens
  • Polyethylene Glycols
  • Octoxynol
  • Protein Kinase C
  • Phospholipases
Topics
  • Animals
  • Annexins
  • Calcium-Binding Proteins (metabolism)
  • Carcinogens (pharmacology)
  • Cells, Cultured
  • Cytosol (metabolism)
  • Epithelial Cells
  • Epithelium (drug effects, metabolism)
  • Liver (cytology, drug effects, metabolism)
  • Octoxynol
  • Phospholipases (antagonists & inhibitors)
  • Phosphorylation
  • Polyethylene Glycols
  • Protein Kinase C (analysis, metabolism, pharmacology)
  • Rats

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