Abstract
Mst1 is a ubiquitously expressed serine-threonine kinase, homologous to the budding yeast Ste20, whose physiological regulation and cellular function are unknown. In this paper we show that Mst1 is specifically cleaved by a caspase 3-like activity during apoptosis induced by either cross-linking CD95/Fas or by staurosporine treatment. CD95/Fas-induced cleavage of Mst1 was blocked by the cysteine protease inhibitor ZVAD-fmk, the more selective caspase inhibitor DEVD-CHO and by the viral serpin CrmA. Caspase-mediated cleavage of Mst1 removes the C-terminal regulatory domain and correlates with an increase in Mst1 activity in vivo, consistent with caspase-mediated cleavage activating Mst1. Overexpression of either wild-type Mst1 or a truncated mutant induces morphological changes characteristic of apoptosis. Furthermore, exogenously expressed Mst1 is cleaved, indicating that Mst1 can activate caspases that result in its cleavage. Kinase-dead Mst1 did not induce morphological alterations and was not cleaved upon overexpression, indicating that Mst1 must be catalytically active in order to mediate these effects. Mst1 activates MKK6, p38 MAPK, MKK7 and SAPK in co-transfection assays, suggesting that Mst1 may activate these pathways. Our findings suggest the existence of a positive feedback loop involving Mst1, and possibly the SAPK and p38 MAPK pathways, which serves to amplify the apoptotic response.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Chloromethyl Ketones / pharmacology
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Amino Acid Sequence
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Animals
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Apoptosis*
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Binding Sites
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Calcium-Calmodulin-Dependent Protein Kinases / genetics
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism
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Caspase 3
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Caspases*
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Cell Line, Transformed
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Cysteine Endopeptidases / metabolism*
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Cysteine Proteinase Inhibitors / pharmacology
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Humans
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Intracellular Signaling Peptides and Proteins
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MAP Kinase Kinase Kinases
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Mammals
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Molecular Sequence Data
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Oligopeptides / pharmacology
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / metabolism*
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Saccharomyces cerevisiae Proteins*
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Serpins / genetics
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Serpins / metabolism
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Tumor Cells, Cultured
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Viral Proteins / genetics
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Viral Proteins / metabolism
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fas Receptor / metabolism
Substances
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Amino Acid Chloromethyl Ketones
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Cysteine Proteinase Inhibitors
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Intracellular Signaling Peptides and Proteins
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Oligopeptides
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Saccharomyces cerevisiae Proteins
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Serpins
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Viral Proteins
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aspartyl-glutamyl-valyl-aspartal
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benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone
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fas Receptor
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L 709049
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interleukin-1beta-converting enzyme inhibitor
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STK4 protein, human
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Protein Serine-Threonine Kinases
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Calcium-Calmodulin-Dependent Protein Kinases
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MAP Kinase Kinase Kinases
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STE20 protein, S cerevisiae
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CASP3 protein, human
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Caspase 3
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Caspases
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Cysteine Endopeptidases