Purvalanol A induces apoptosis and downregulation of antiapoptotic proteins through abrogation of phosphorylation of JAK2/STAT3 and RNA polymerase II.
To clarify the mechanisms of purvalanol A in the induction of apoptosis, we investigated whether purvalanol A influenced the RNA synthesis and expression of RNA polymerase II and signal transducer and activator of transcription 3 (STAT3). When MKN45 cells were treated with 30 micromol/l purvalanol A, mitochondrial dysfunction occurred before the induction of the apoptosis and the expression of antiapoptotic proteins survivin, Bcl-XL, and Bcl-2 was reduced. The treatment with parvalanol A was also shown to reduce not only mRNA for these proteins but also global RNA synthesis. The phosphorylation of the carboxy-terminal domain of RNA polymerase II, which was involved in transcriptional regulation, was strongly inhibited by purvalanol A, followed by the partial inhibition of the expression of RNA polymerase II. Furthermore, the phosphorylation at Tyr705 of STAT3, which is known to be a phosphorylation site for Janus kinase 2 (JAK2), was completely inhibited by purvalanol A early (3 h) after drug treatment, although the phosphorylation of STAT3 at Ser727, which is a phosphorylation site for Ras/Raf/MEK and extracellular signal-regulated protein kinase 1/2, was still detectable until late (12 h) after treatment. In addition, the tyrosine phosphorylation of JAK2 was efficiently inhibited by purvalanol A. These results suggest that the inhibition of JAK2/STAT3 and RNA polymerase II is crucial in the downregulation of antiapoptotic proteins leading to the apoptotic cell death induced by parvalanol A.
Department of Environmental Veterinary Sciences, Laboratory of Radiation Biology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Daisuke
D
Iizuka
Aki
A
Ogura
Mikinori
M
Kuwabara
Osamu
O
Inanami
D017209:Apoptosis / Q000187:drug effects*; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors*; D011687:Purines / Q000494:pharmacology*; D012313:RNA / Q000096:biosynthesis; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D051020:bcl-X Protein / Q000037:antagonists & inhibitors*
C471843:6-((3-chloro)anilino)-2-(isopropyl-2-hydroxyethylamino)-9-isopropylpurine; D047428:Protein Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011687:Purines; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D051020:bcl-X Protein; D012313:RNA; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D016203:CDC2 Protein Kinase; D012319:RNA Polymerase II