Activation of hematopoietic progenitor kinase-1 by erythropoietin.
Hematopoietic progenitor kinase-1 (HPK1), which is expressed predominantly in hematopoietic cells, was identified as a mammalian Ste20 homologue that, upon transfection, leads to activation of JNK/SAPK in nonhematopoietic cells. The JNK/SAPK pathway is activated by various environmental stresses and proinflammatory and hematopoietic cytokines. Upstream activators of HPK1 currently remain elusive, and its precise role in hematopoiesis has yet to be defined. We therefore examined the possible involvement of HPK1 in erythropoietin (Epo) and environmental stress-induced JNK/SAPK activation in the Epo-dependent FD-EPO cells and Epo-responsive SKT6 cells. We found that Epo, but not environmental stresses, induced rapid and transient activation of HPK1, whereas both induced activation of JNK/SAPK. A screen for HPK1 binding proteins identified the hematopoietic cell-specific protein 1 (HS1) as a potential HPK1 interaction partner. We found HPK1 constitutively associated with HS1 and that HS1 was tyrosine-phosphorylated in response to cellular stresses as well as Epo stimulation. Furthermore, antisense oligonucleotides to HPK1 suppressed Epo-dependent cell growth and Epo-induced erythroid differentiation. We therefore conclude that Epo induces activation of both HPK1 and HS1, whereas cellular stresses activate only HS1, and that the HPK1-JNK/SAPK pathway is involved in Epo-induced growth and differentiation signals.
Nagata
Y
Y
Tsukuba Life Science Center, The Institute of Physical and Chemical Research (RIKEN), Ibaraki, Japan.
Kiefer
F
F
Watanabe
T
T
Todokoro
K
K
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004789:Enzyme Activation; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D051379:Mice; D008969:Molecular Sequence Data; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D018909:src Homology Domains
D020319:Oligodeoxyribonucleotides, Antisense; D010446:Peptide Fragments; D011994:Recombinant Proteins; D004921:Erythropoietin; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases