Lack of phosphorylation of lipocortin I in A431 epidermoid carcinoma cells treated with phorbol esters

• Published in: Biochemical and biophysical research communications Vol. 160; no. 2; pp. 474 - 479
• Main Authors: William, Felicia, Haigler, Harry T., Kraft, Andrew S.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 28.04.1989; Elsevier
• Subjects: Annexins; Antibody Specificity; Biological and medical sciences; carcinoma; Carcinoma, Squamous Cell - enzymology; Carcinoma, Squamous Cell - metabolism; Cell Line; Cell physiology; Cross Reactions; Fundamental and applied biological sciences. Psychology; Glycoproteins - immunology; Glycoproteins - metabolism; Humans; Immune Sera; Molecular and cellular biology; phorbol 12-myristate 13-acetate diester; Phosphorylation; Precipitin Tests; Protein Kinase C - metabolism; Responses to growth factors, tumor promotors, other factors; Substrate Specificity; Tetradecanoylphorbol Acetate - pharmacology; Cell culture; Phosphorylation; Protein kinase C; Carcinoma; Purification; Radiolabelling; Peptides; Antibody; Enzyme; Metabolism; In vitro; Proteins; Binding protein; Immunoprecipitation reaction; Cell line; Lipocortin; Immunoblotting assay; Tumor
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/0006-291X(89)92457-1

To examine in vivo phosphorylation of lipocortin I we made use of a polyclonal antibody to an amino terminal peptide of lipocortin I. This antibody does not recognize any other member of the annexin protein family, and can both immunoprecipitate lipocortin I and recognize this protein on western blots. Using cleaved forms of lipocortin I, we have been able to demonstrate that protein kinase C phosphorylates this protein in vitro within the first 29 amino terminal amino acids. However, the addition of phorbol esters to A431 cells over a wide range of concentrations and for varying periods of time did not stimulate the phosphorylation of this protein. Since in vitro lipocortin I is an excellent substrate for all three isoforms, alpha, beta, gamma, of protein kinase C, the discrepancy in these finding is not secondary to the presence of varying forms of this protein kinase within different cell types.