Nuclear translocation of 3'-phosphoinositide-dependent protein kinase 1 (PDK-1): a potential regulatory mechanism for PDK-1 function.
3'-Phosphoinositide-dependent protein kinase 1 (PDK-1) phosphorylates and activates members of the AGC protein kinase family and plays an important role in the regulation of cell survival, differentiation, and proliferation. However, how PDK-1 is regulated in cells remains elusive. In this study, we demonstrated that PDK-1 can shuttle between the cytoplasm and nucleus. Treatment of cells with leptomycin B, a nuclear export inhibitor, results in a nuclear accumulation of PDK-1. PDK-1 nuclear localization is increased by insulin, and this process is inhibited by pretreatment of cells with phosphatidylinositol 3-kinase (PI3-kinase) inhibitors. Consistent with the idea that PDK-1 nuclear translocation is regulated by the PI3-kinase signaling pathway, PDK-1 nuclear localization is increased in cells deficient of PTEN (phosphatase and tensin homologue deleted on chromosome 10). Deletion mapping and mutagenesis studies unveiled that presence of a functional nuclear export signal (NES) in mouse PDK-1 located at amino acid residues 382 to 391. Overexpression of constitutively nuclear PDK-1, which retained autophosphorylation at Ser-244 in the activation loop in cells and its kinase activity in vitro, led to increased phosphorylation of the predominantly nuclear PDK-1 substrate p70 S6KbetaI. However, the ability of constitutively nuclear PDK-1 to induce anchorage-independent growth and to protect against UV-induced apoptosis is greatly diminished compared with the wild-type enzyme. Taken together, these findings suggest that nuclear translocation may be a mechanism to sequestrate PDK-1 from activation of the cytosolic signaling pathways and that this process may play an important role in regulating PDK-1-mediated cell signaling and function.
Lim
Mei A
MA
Department of Pharmacology, University of Texas Health Science Center, San Antonio, TX 78229, USA.
Kikani
Chintan K
CK
Wick
Michael J
MJ
Dong
Lily Q
LQ
D064413:3-Phosphoinositide-Dependent Protein Kinases; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D019913:Nuclear Localization Signals; D051059:PTEN Phosphohydrolase; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
D004791:Enzyme Inhibitors; D005231:Fatty Acids, Unsaturated; D007328:Insulin; D019913:Nuclear Localization Signals; D000081082:Phosphoinositide-3 Kinase Inhibitors; D025521:Tumor Suppressor Proteins; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D017346:Protein Serine-Threonine Kinases; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; C038753:leptomycin B