HSP27 protects AML cells against VP-16-induced apoptosis through modulation of p38 and c-Jun.
OBJECTIVE
To investigate 1) the signal transduction pathways affected by heat shock protein 27 (HSP27) expression; and 2) the expression and regulation of HSP27 in acute myeloid leukemia (AML).


METHODS
RNA interference studies for HSP27 in leukemic TF-1 cells were used to investigate the effects on downstream signal transduction and apoptosis after VP-16 and CD95/Fas treatment. HSP27 expression and activation was investigated in AML blasts through Western blot analysis.


RESULTS
RNA interference for HSP27 resulted in a twofold increase in VP-16-induced apoptosis, which was preceded by enhanced p38 and c-Jun phosphorylation and a twofold increased cytochrome c release into the cytoplasm. DAXX co-immunoprecipitated with HSP27, suggesting an inhibitory role of HSP27 in VP-16-mediated activation of the ASK1/p38/JNK pathway. CD95/Fas-induced apoptosis, however, was unaffected by HSP27 siRNA, due to upregulation of HSP27. Although HSP27 was highly expressed and phosphorylated in primitive monocytic AML blasts (M4-M5, 91%, n=11) and undetectable in myeloid blasts (M1-M2, n=5), VP-16-mediated apoptosis correlated moderately with HSP27 expression. This is likely due to the co-expression of p21Waf1/Cip1, which is in the majority of the monocytic AML M4-M5 blasts constitutively localized in the cytoplasm. Overexpression of cytoplasmic p21 inhibited the enhanced p38 phosphorylation after HSP27 RNAi, suggesting a predominant anti-apoptotic role of p21 over HSP27.


CONCLUSIONS
1) HSP27 inhibits VP-16-mediated phosphorylation of p38 and c-Jun, cytochrome c release, and subsequent apoptosis; 2) HSP27 is expressed and activated in monocytic AML blasts; 3) cytoplasmic expression of p21 compensates for the lack of HSP27.
Schepers
Hein
H
Division of Hematology, Department of Medicine, University Medical Center Groningen, Groningen, The Netherlands.
Geugien
Marjan
M
van der Toorn
Marco
M
Bryantsev
Anton L
AL
Kampinga
Harm H
HH
Eggen
Bart J L
BJ
Vellenga
Edo
E
D000208:Acute Disease; D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000187:drug effects*; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D056970:Co-Repressor Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004797:Enzyme-Linked Immunosorbent Assay; D005047:Etoposide / Q000494:pharmacology*; D006360:Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007951:Leukemia, Myeloid / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism; D018832:Molecular Chaperones; D009687:Nuclear Proteins / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D034622:RNA Interference; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C493956:CDKN1A protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D056970:Co-Repressor Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C106985:DAXX protein, human; D006360:Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D016755:Proto-Oncogene Proteins c-jun; D005047:Etoposide; D048051:p38 Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human