Caspase-catalyzed cleavage and activation of Mst1 correlates with eosinophil but not neutrophil apoptosis.
We have examined the role of caspase-mediated cleavage of the Ste20-like kinases, mammalian sterile 20-like 1 and 2 (Mst1/Mst2), in the mechanism of human eosinophil and neutrophil apoptosis. Initial measurements of kinase activity, using myelin basic protein (MBP) as a substrate in "in-gel" renaturation assays, showed that constitutive eosinophil and neutrophil apoptosis were associated temporally with the activation of a 36-kd MBP kinase (p36 MBPK) and a 34-kd MBP kinase (p34 MBPK), respectively. A constitutively active 63-kd MBP kinase (p63 MBPK) was also detected in freshly prepared eosinophils but not neutrophils, whose activity was transiently augmented during spontaneous apoptosis. Immunoblotting studies demonstrated the expression of Mst1 and Mst2 in eosinophils but not neutrophils whereas immunoprecipitation studies identified the p63 MBPK activity as being Mst1 and Mst2 and showed that the p36 MBPK activity represented the N-terminal catalytic fragment of Mst1. A role for the p36 MBPK in eosinophil cell death was supported by studies showing increased activation upon exposure to the proapoptotic Fas/CD95-activating antibody, CH-11, and attenuation in the presence of the survival-promoting cytokine, interleukin-5. Furthermore, spontaneous and Fas-induced activation of p36 MBPK was inhibited by catalase and the general caspase inhibitor, z-Asp-CH(2)-DCB, at concentrations that suppressed eosinophil apoptosis. These studies therefore implicate a role for caspase- and H(2)O(2)-mediated cleavage of the Mst1 and the subsequent release of the 36-kd catalytic fragment in the mechanism of eosinophil apoptosis. In contrast, neutrophil apoptosis occurs independently of Mst1 and Mst2 but instead is correlated with the activation of an as-yet-unidentified 34-kd MBPK.
De Souza
Patricia M
PM
Department of Thoracic Medicine, Imperial College School of Medicine at the National Heart and Lung Institute, London, United Kingdom.
Kankaanranta
Hannu
H
Michael
Ashour
A
Barnes
Peter J
PJ
Giembycz
Mark A
MA
Lindsay
Mark A
MA
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D020169:Caspases / Q000378:metabolism* / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D004804:Eosinophils / Q000201:enzymology* / Q000502:physiology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008970:Molecular Weight; D009504:Neutrophils / Q000201:enzymology* / Q000502:physiology; D010446:Peptide Fragments / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology; D000090742:Serine-Threonine Kinase 3; D019014:fas Receptor / Q000494:pharmacology; D000099317:Hippo Kinases
D020169:Caspases; D006861:Hydrogen Peroxide; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D017346:Protein Serine-Threonine Kinases; D000090742:Serine-Threonine Kinase 3; D019014:fas Receptor; C095566:STK4 protein, human; D000099317:Hippo Kinases; C097835:STK3 protein, human