title: Hematopoietic progenitor kinase 1 is a component of transforming growth factor beta-induced c-Jun N-terminal kinase signaling cascade.
abstract: The c-Jun N-terminal kinase (JNK) signaling pathway is involved in transforming growth factor beta (TGF-beta) signaling in a variety of cell systems. We report here that hematopoietic progenitor kinase 1 (HPK1), a novel Ste20-like protein serine/threonine kinase, serves as an upstream mediator for the TGF-beta-activated JNK1 cascade in 293T cells. TGF-beta treatment resulted in a time-dependent activation of HPK1, which was accompanied by similar kinetics of JNK1 activation. The activation of JNK1 by TGF-beta was abrogated by a kinase-defective HPK1 mutant but not by a kinase-defective mutant of kinase homologous to Ste20/Sps1. This result indicates that HPK1 is specifically required for TGF-beta-induced activation of JNK1. We also found that TGF-beta-induced JNK1 activation was blocked by a kinase-defective mutant of TGF-beta-activated kinase 1 (TAK1). In addition, interaction between HPK1 and TAK1 was observed in transient transfection assays, and this interaction was enhanced by TGF-beta treatment. Both stress-activated protein kinase/extracellular signal-regulated kinase kinase (SEK) and mitogen-activated protein kinase kinase 7 (MKK7) are immediate upstream activators of JNK1. Although SEK and MKK7 acted downstream of TAK1, only a kinase-defective SEK mutant blocked TGF-beta-induced activation of JNK1, indicating that the TGF-beta signal is relayed solely through SEK, but not MKK7, in vivo. Furthermore, TGF-beta-induced activating protein 1 activation was blocked by a HPK1 mutant, as well as by TAK1 and SEK mutants. Taken together, these studies establish a potential cascade of TGF-beta-activated interacting kinases beginning with HPK1, a Ste20 homolog, and ending in JNK1 activation: HPK1 --> TAK1 --> SEK --> JNK1.
authors.affiliation: Department of Microbiology and Immunology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: G
authors.initials: G
authors.lastname: Zhou
authors.forename: S C
authors.initials: SC
authors.lastname: Lee
authors.forename: Z
authors.initials: Z
authors.lastname: Yao
authors.forename: T H
authors.initials: TH
authors.lastname: Tan
mesh_terms: D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D015870:Gene Expression; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D007700:Kinetics; D020928:Mitogen-Activated Protein Kinases; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases