Ecto-protein kinase release differs from cleavage by phospholipases of a glycosyl-phosphatidylinositol membrane anchor.
Ecto-protein kinases have been detected as physiological constituents of cells. One feature of ecto-phosvitin/casein kinase (ecto-PK) is its release from the surface in a soluble form when cells are incubated with exogenous substrate protein. This is interesting in view of the fact that some ecto-enzymes are anchored to the plasma membrane via glycosylphosphatidylinositol (GPI). Such enzymes are known to be released from the surface through cleavage by a phospholipase activity. We therefore investigated whether bacterial phospholipase C (PI-PLC) was able to release ecto-PK from intact HeLa cells. The data show that whereas alkaline phosphatase, known to be GPI-anchored, was solubilized, the ecto-PK was neither released nor affected in its activity. Another effect of treatment of cells with phospholipases was the formation of diacylglycerol or phosphatidic acid which, however, did not occur when cells were incubated with phosvitin, the condition which induces ecto-PK release. These results coherently indicate that cellular phospholipases are not involved in the release mechanism of ecto-PK. Also, the presence of various protease inhibitors did not affect ecto-PK release. Cross-linking of cell-surface proteins by bifunctional agents of the succinimidyl-type suggest a protein-protein interaction responsible for membrane anchoring of the ecto-PK.
Jordan
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Department of Pathochemistry, German Cancer Research Center, Heidelberg.
Kübler
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D000469:Alkaline Phosphatase / Q000378:metabolism; D047390:Casein Kinase II; D002462:Cell Membrane / Q000201:enzymology*; D003432:Cross-Linking Reagents; D004075:Diglycerides / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006017:Glycolipids / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D003432:Cross-Linking Reagents; D004075:Diglycerides; D006017:Glycolipids; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D011480:Protease Inhibitors; D011494:Protein Kinases; C034454:ectoprotein kinase; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D010740:Phospholipases; D000469:Alkaline Phosphatase; D010738:Type C Phospholipases