title: TRAIL-induced cleavage and inactivation of SPAK sensitizes cells to apoptosis.
abstract: Ste20-related proline-alanine-rich kinase (SPAK) has been linked to various cellular processes, including proliferation, differentiation, and ion transport regulation. Recently, we showed that SPAK mediates signaling by the TNF receptor, RELT. The presence of a caspase cleavage site in SPAK prompted us to study its involvement in apoptotic signaling induced by another TNF member, TRAIL. We show that TRAIL stimulated caspase 3-like proteases that cleaved SPAK at two distinct sites. Cleavage had little effect on the activity of SPAK but removed its substrate-binding domain. In addition, TRAIL reduced the activity of SPAK in HeLa cells in a caspase-independent manner. Thus, TRAIL inhibited SPAK by two mechanisms: activation of caspases, which removed its substrate-binding domain, and caspase-independent down-regulation of SPAK activity. Furthermore, reducing the amount of SPAK by siRNA increased the sensitivity of HeLa cells to TRAIL-induced apoptosis. Thus, TRAIL down-regulation of SPAK is an important event that enhances its apoptotic effects.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Tara C
authors.initials: TC
authors.lastname: Polek
authors.forename: Moshe
authors.initials: M
authors.lastname: Talpaz
authors.forename: Taly R
authors.initials: TR
authors.lastname: Spivak-Kroizman
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000494:pharmacology*; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D020169:Caspases / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D013379:Substrate Specificity; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D051017:Apoptosis Regulatory Proteins; D008562:Membrane Glycoproteins; D034741:RNA, Small Interfering; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D001224:Aspartic Acid; D017346:Protein Serine-Threonine Kinases; C486409:STK39 protein, human; D020169:Caspases