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Interleukin-3-induced activation of the JAK/STAT pathway is prolonged by proteasome inhibitors
1Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.
Abstract:
One facet of cytokine receptor signaling involves the activation of signal transducers and activators of transcription (STATs). STATs are rapidly activated via tyrosine phosphorylation by Janus kinase (JAK) family members and subsequently inactivated within a short period. We investigated the effect of proteasome inhibition on interleukin-3 (IL-3) activation of the JAK/STAT pathway following stimulation of Ba/F3 cells. Treatment of Ba/F3 cells with the proteasome inhibitor, N-acetyl-L-leucinyl-L-leucinyl-norleucinal (LLnL), led to stable tyrosine phosphorylation of the IL-3 receptor, beta common (betac), and STAT5 following stimulation. The effects of LLnL were not restricted to the JAK/STAT pathway, as Shc and mitogen-activated protein kinase (MAPK) phosphorylation were also prolonged in LLnL-treated cells. Further investigation showed these stable phosphorylation events were the result of prolonged activation of JAK2 and JAK1. These observations were confirmed using pharmacologic inhibitors. In the presence of LLnL, stable phosphorylation of STAT5 and betac was abrogated if the tyrosine kinase inhibitor, staurosporine, was added. The effect of staurosporine on STAT5 phosphorylation could be overcome if the phosphatase inhibitor, vanadate, was also added, suggesting phosphorylated STAT5 could be stabilized by phosphatase, but not by proteasome inhibition per se. These observations are consistent with the hypothesis that proteasome-mediated protein degradation can modulate the activity of the JAK/STAT pathway by regulating the deactivation of JAK.
Insights
Proteasome inhibition stabilizes Janus kinase (JAK) and signal transducer and activator of transcription 5 (STAT5) phosphorylation in interleukin-3 (IL-3) signaling. This suggests proteasome-mediated degradation regulates JAK/STAT pathway deactivation.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Cytokine receptor signaling is crucial for cellular communication.
- Signal transducers and activators of transcription (STATs) are key mediators, rapidly activated and inactivated.
- The role of protein degradation in regulating JAK/STAT pathway dynamics was unclear.
Purpose of the Study:
- To investigate the impact of proteasome inhibition on the interleukin-3 (IL-3) induced JAK/STAT pathway.
- To determine if proteasome activity influences the duration of signaling events.
Main Methods:
- Ba/F3 cells were treated with the proteasome inhibitor N-acetyl-L-leucinyl-L-leucinyl-norleucinal (LLnL).
- Phosphorylation levels of IL-3 receptor, beta common (betac), STAT5, Shc, and mitogen-activated protein kinase (MAPK) were assessed.
- Pharmacologic inhibitors (staurosporine, vanadate) were used to probe signaling mechanisms.
Main Results:
- LLnL treatment led to sustained tyrosine phosphorylation of betac and STAT5.
- Prolonged activation of Janus kinase 2 (JAK2) and JAK1 was observed.
- Inhibition of tyrosine kinases abrogated STAT5 phosphorylation, while phosphatase inhibition stabilized it, indicating a role for phosphatases in deactivation.
Conclusions:
- Proteasome inhibition stabilizes key signaling components in the IL-3 JAK/STAT pathway.
- These findings support a model where proteasome-mediated degradation regulates the deactivation of Janus kinases (JAKs).
- The proteasome plays a significant role in modulating the duration and activity of cytokine receptor signaling pathways.