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Dominant negative effects of a carboxy-truncated Jak2 mutant on Epo-induced proliferation and Jak2 activation
1Department of Biochemistry & Molecular Biology and Veterinary Science, Pennsylvania State University, University Park 16802.
Abstract:
Members of the Janus family of protein tyrosine kinases are emerging as primary, receptor-associated transducing factors among numerous cytokine systems. However, little is understood regarding mechanisms of recruitment of these kinases to receptor complexes and their ligand-dependent activation. To initially address these questions, we have assessed effects of ectopically expressing a carboxy-truncated form of Jak2 (Jak2-829) in Epo-responsive DAER cells. Expression of this truncation mutant at low levels efficiently inhibited both Epo-dependent activation of endogenous Jak2 and Epo-induced mitogenesis (10% to 39% of parental DAER cells). These results suggest that amino-terminal domains of Jak2 may mediate the assembly of Jak2/Epo receptor complexes and that integration of Jak2-829 into receptor complexes may effectively inhibit the activity of oligomeric Jak2/receptor assemblages.
Insights
Janus kinase 2 (Jak2) N-terminal domains mediate receptor complex assembly. A truncated Jak2 mutant inhibited Epo-dependent Jak2 activation and cell growth, suggesting a mechanism for regulating kinase activity.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Janus kinases (JAKs) are critical for cytokine signaling.
- Mechanisms of JAK recruitment and activation by receptors are not fully understood.
Purpose of the Study:
- To investigate the role of JAK2 domains in receptor complex assembly.
- To explore mechanisms of JAK2 ligand-dependent activation.
Main Methods:
- Ectopic expression of a carboxy-truncated JAK2 mutant (JAK2-829) in Epo-responsive DAER cells.
- Assessment of Epo-dependent JAK2 activation and mitogenesis.
Main Results:
- Low-level expression of JAK2-829 inhibited Epo-dependent activation of endogenous JAK2.
- JAK2-829 expression reduced Epo-induced mitogenesis by 61-90%.
Conclusions:
- Amino-terminal domains of JAK2 likely mediate its assembly into receptor complexes.
- Integration of JAK2-829 into receptor complexes may inhibit the activity of JAK2/receptor assemblages.