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Deactivation of regulatory proteins hnRNP A1 and A2 during SC-1 induced apoptosis
R Hermann1, F Hensel, E C Müller
1Institute of Pathology, Josef-Schneider-Str. 2, D-97080 Würzburg, Germany.
Abstract:
Phosphorylation and activation of caspases play an important role in the induction of apoptosis. During tumor specific apoptosis, induced by the human monoclonal antibody SC-1, tyrosine phosphorylation and serine dephosphorylation of several proteins is observed. In this paper we describe the identification of two dephosphorylated proteins as heterogeneous nuclear ribonucleoproteins A1 and A2 (hnRNP A1, hnRNP A2). The dephosphorylation of these proteins is important for apoptosis since the amount of apoptotic cell death can be decreased by the specific serine/threonine phosphatase inhibitor okadaic acid. We also investigated the effect of serine kinase inhibitor H7 on SC-1 induced apoptosis, which leads to a dose dependent increase in apoptosis. We could also show that 24 hours after the induction of apoptosis the hnRNP A1 protein is cleaved into different cleavage products. Further, we found a decreased expression of caspase-2 in early apoptosis signalling and an overexpression 24 hours after induction of apoptosis. Our results show that the phosphorylation status of the hnRNP A1 and A2 plays a significant role in early SC-1 induced apoptosis signalling and further indicate the role of caspase activation during the apoptotic process.
Insights
The human monoclonal antibody SC-1 triggers tumor cell death by altering protein phosphorylation. Key proteins, heterogeneous nuclear ribonucleoproteins A1 and A2 (hnRNP A1, hnRNP A2), are dephosphorylated, impacting apoptosis.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Apoptosis, or programmed cell death, is crucial for development and disease.
- Caspase activation and protein phosphorylation are key regulators of apoptosis.
- Tumor-specific apoptosis can be induced by agents like the human monoclonal antibody SC-1.
Purpose of the Study:
- To identify proteins involved in SC-1-induced apoptosis.
- To elucidate the role of protein phosphorylation in this process.
- To investigate the involvement of caspases in SC-1-induced apoptosis.
Main Methods:
- Treatment of cells with SC-1 antibody.
- Analysis of protein phosphorylation and dephosphorylation.
- Use of phosphatase and kinase inhibitors (okadaic acid, H7).
- Western blotting to detect protein cleavage and expression levels (caspase-2).
Main Results:
- SC-1 antibody induces tyrosine phosphorylation and serine dephosphorylation of hnRNP A1 and hnRNP A2.
- Dephosphorylation of hnRNP A1/A2 is critical for apoptosis, as inhibited by okadaic acid.
- H7 enhances SC-1-induced apoptosis in a dose-dependent manner.
- hnRNP A1 undergoes cleavage 24 hours post-apoptosis induction.
- Caspase-2 expression is decreased in early apoptosis and overexpressed later.
Conclusions:
- The phosphorylation status of hnRNP A1 and A2 is significant in early SC-1-induced apoptosis signaling.
- Caspase activation plays a role in the apoptotic process initiated by SC-1.
- These findings highlight novel regulatory mechanisms in antibody-mediated tumor apoptosis.