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Exp Cell Res. 1993 May;206(1):157-61.

Microinjected catalytic subunit of cAMP-dependent protein kinase induces apoptosis in myeloid leukemia (IPC-81) cells.

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Department of Anatomy and Cell Biology, University of Bergen, Norway.


Rat IPC-81 promyelocytic leukemia cells responded to cAMP analog by undergoing apoptotic cell death both when anchored to fibronectin and when free in the medium. The protein kinase C stimulator 12-O-tetradecanoylphorbol 13-acetate enhanced the anchoring to substratum without impeding cAMP-induced cell death. The immobilized cells could be microinjected. This made it possible to study the effect on apoptosis of microinjected catalytic (C alpha) and regulatory (RI alpha D199) subunits of cAMP-dependent protein kinase as well as of phosphatase inhibitors. Microinjection of C alpha reproduced the morphological effects of cAMP, including nuclear fragmentation. RI alpha D199 blocked the effect of C alpha. Injection of microcystin-LR, which inhibits protein phosphatases 1 and 2A, led to pronounced apoptoid changes of the leukemia cells, but failed to produce nuclear fragmentation. Microinjection of peptide inhibitors ("inhibitor 1" and "inhibitor 2") specific for phosphatase 1 had no effect on cell morphology. The failure of the phosphatase inhibitors to reproduce completely the effect of the C subunit underscores the specificity of action of the latter.

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