Mitotic and stress-induced phosphorylation of HsPI3K-C2alpha targets the protein for degradation.
Activation of the phosphoinositide 3-kinases (PI 3-kinases) has been implicated in multiple cellular responses such as proliferation and survival, membrane and cytoskeletal reorganization, and intracellular vesicular trafficking. The activities and subcellular localization of PI 3-kinases were shown to be regulated by phosphorylation. Previously we demonstrated that class II HsPIK3-C2alpha becomes phosphorylated upon inhibition of RNA pol II-dependent transcription (Didichenko, S. A., and Thelen, M. (2001) J. Biol. Chem. 276, 48135-48142). In this study we investigated cell cycle-dependent and genotoxic stress-induced phosphorylation of HsPIK3-C2alpha. We find that the kinase becomes phosphorylated upon exposure of cells to UV irradiation and in proliferating cells at the G2/M transition of the cell cycle. Stress-dependent and mitotic phosphorylation of HsPIK3-C2alpha occurs on the same serine residue (Ser259) within a recognition motif for proline-directed kinases. Mitotic phosphorylation of HsPIK3-C2alpha can be attributed to Cdc2 activity, and stress-induced phosphorylation of HsPIK3-C2alpha is mediated by JNK/SAPK. The protein level of HsPIK3-C2alpha is regulated by proteolysis in a cell cycle-dependent manner and in response of cells to stress. Phosphorylation appears to be a prerequisite for proteasome-dependent degradation of HsPIK3-C2alpha and may therefore contribute indirectly to the regulation of the activity of the kinase.
Institute for Research in Biomedicine, Via Vincenzo Vela 6, Bellinzona CH 6500, Switzerland.
Svetlana A
SA
Didichenko
Cristina M
CM
Fragoso
Marcus
M
Thelen
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002453:Cell Cycle; D002455:Cell Division; D058541:Class II Phosphatidylinositol 3-Kinases; D003546:Cysteine Endopeptidases / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016195:G2 Phase; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008938:Mitosis; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011687:Purines / Q000494:pharmacology; D000077546:Roscovitine; D012694:Serine / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases
D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; D011687:Purines; D000077546:Roscovitine; D049452:Green Fluorescent Proteins; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D058541:Class II Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex