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Ciliary neurotrophic factor and phorbol ester each decrease selected STAT3 pools in neuroblastoma cells by
1Department of Biochemical Pharmacology, School of Pharmacy, State University of New York at Buffalo, Buffalo, NY 14260-1200, USA.
Abstract:
Many cytokines and growth factors activate common signal transduction pathways and yet are able to elicit distinct cell-specific responses. We are defining mechanisms regulating signalling molecules in order to understand how cytokines can produce unique responses. It was found that individual members of the signal transducer and activator of transcription (STAT) family are regulated by ciliary neurotrophic factor (CNTF) and by protein kinase C. Treatment of SH-SY5Y human neuroblastoma cells with the phorbol ester, 12- O -tetradecanoylphorbol 13-acetate (TPA), for 4-5 h caused a 60% decline in both STAT2 and STAT3 levels and no decline in levels of STATs 1, 5 or 6, or in Jaks 1 or 2. The decline in STAT3 was inhibited by treatment with MG132, an inhibitor of proteasome-dependent protein degradation. Treatment of cells with CNTF induced a rapid tyrosine phosphorylation of STAT3 followed by a time-dependent decay of this signal. Loss of tyrosine phosphorylated STAT3 was inhibited by MG132 but did not require protein kinase C activity. These results suggest that STAT3 availability can be controlled by proteasome-dependent pathways activated either by protein kinase C or by cytokines.
Insights
Cytokines and protein kinase C regulate signal transducer and activator of transcription (STAT) proteins. Proteasome-dependent pathways control STAT3 availability, influencing distinct cellular responses to signaling molecules.
Area of Science:
- Cellular signaling
- Molecular biology
- Neuroscience
Background:
- Cytokines and growth factors activate common signal transduction pathways, yet elicit distinct cell-specific responses.
- Understanding the regulation of signaling molecules is crucial for deciphering cytokine-induced unique cellular outcomes.
Purpose of the Study:
- To define mechanisms regulating signaling molecules, specifically signal transducer and activator of transcription (STAT) family members.
- To investigate how ciliary neurotrophic factor (CNTF) and protein kinase C (PKC) influence STAT protein levels and activity.
Main Methods:
- Treatment of SH-SY5Y human neuroblastoma cells with phorbol ester (TPA) and CNTF.
- Assessment of STAT protein levels (STAT1, STAT2, STAT3, STAT5, STAT6) and Jak kinases (Jak1, Jak2).
- Use of MG132, a proteasome inhibitor, to investigate protein degradation pathways.
Main Results:
- TPA treatment caused a significant decline in STAT2 and STAT3 levels, but not STAT1, STAT5, STAT6, or Jaks.
- MG132 inhibited the decline in STAT3 levels, indicating proteasome-dependent degradation.
- CNTF induced rapid tyrosine phosphorylation of STAT3, followed by a time-dependent decay inhibited by MG132, independent of PKC activity.
Conclusions:
- STAT3 availability is regulated by proteasome-dependent pathways.
- These pathways can be activated by either protein kinase C or cytokine signaling.
- This regulation contributes to the distinct cellular responses observed with different signaling molecules.