title: Down-regulation of the mixed-lineage dual leucine zipper-bearing kinase by heat shock protein 70 and its co-chaperone CHIP.
abstract: Dual leucine zipper-bearing kinase (DLK) is a mixed-lineage kinase family member that acts as an upstream activator of the c-Jun N-terminal kinases. As opposed to other components of this pathway, very little is currently known regarding the mechanisms by which DLK is regulated in mammalian cells. Here we identify the stress-inducible heat shock protein 70 (Hsp70) as a negative regulator of DLK expression and activity. Support for this notion derives from data showing that Hsp70 induces the proteasomal degradation of DLK when both proteins are co-expressed in COS-7 cells. Hsp70-mediated degradation occurs with expression of wild-type DLK, which functions as a constitutively activated protein in these cells but not kinase-defective DLK. Interestingly, the Hsp70 co-chaperone CHIP, an E3 ubiquitin ligase, seems to be indispensable for this process since Hsp70 failed to induce DLK degradation in COS-7 cells expressing a CHIP mutant unable to catalyze ubiquitination or in immortalized fibroblasts derived from CHIP knock-out mice. Consistent with these data, we have found that endogenous DLK becomes sensitive to CHIP-dependent proteasomal degradation when it is activated by okadaic acid and that down-regulation of Hsp70 levels with an Hsp70 antisense attenuates this sensitivity. Therefore, our studies suggest that Hsp70 contributes to the regulation of activated DLK by promoting its CHIP-dependent proteasomal degradation.
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada.
authors.forename: Alex
authors.initials: A
authors.lastname: Daviau
authors.forename: Roxanne
authors.initials: R
authors.lastname: Proulx
authors.forename: Karine
authors.initials: K
authors.lastname: Robitaille
authors.forename: Marco
authors.initials: M
authors.lastname: Di Fruscio
authors.forename: Robert M
authors.initials: RM
authors.lastname: Tanguay
authors.forename: Jacques
authors.initials: J
authors.lastname: Landry
authors.forename: Cam
authors.initials: C
authors.lastname: Patterson
authors.forename: Yves
authors.initials: Y
authors.lastname: Durocher
authors.forename: Richard
authors.initials: R
authors.lastname: Blouin
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D019319:Okadaic Acid / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D019319:Okadaic Acid; C492951:Stub1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D020930:MAP Kinase Kinase Kinases; C090757:mitogen-activated protein kinase kinase kinase 12; D046988:Proteasome Endopeptidase Complex