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A kinase associated with chromatin that can be activated by ligand-p185c-Neu or epidermal growth factor-receptor
1Center for Receptor Biology, University of Pennsylvania, School of Medicine, Philadelphia 19104-6082, USA.
Abstract:
Some growth factors transduce positive growth signals, while others can act as growth inhibitors. Nuclear signaling events of previously quiescent cells stimulated with various growth factors have been studied by isolating the complexed chromatin-associated proteins and chromatin-associated proteins. Signals from the plasma membrane are integrated within the cells and quickly transduced to the nucleus. It is clear that several growth factors, such as epidermal growth factor, transforming growth factor alpha (but not transforming growth factor beta), and platelet-derived growth factor, utilize similar intracellular signaling biochemistries to modulate nucleosomal characteristics. The very rapid and consistent phosphorylation of nuclear p33, p54, and low molecular mass proteins in the range of 15-18 kDa after growth factor stimulation implies that there is a coordination and integration of the cellular signaling processes. Additionally, phosphorylation of p33 and some low molecular mass histones has been found to occur within 5 min of growth factor treatment and to reach a maximum by 30 min. In this study, we report that Neu receptor activating factor also utilizes the same signaling mechanism and causes p33 to become phosphorylated. In addition, both the tumor promoter okadaic acid (which inhibits protein phosphatases 1 and 2A) and phorbol ester (phorbol 12-tetradecanoate 13-acetate) stimulate phosphorylation of p33, p54, and low molecular mass histones. However, transforming growth factor beta, which is a growth inhibitor for fibroblasts, fails to increase p33 phosphorylation. In general, p33 phosphorylation patterns correspond to positive and negative mitogenic signal transduction. p33 isolated from the complexed chromatin-associated protein fraction appears to be a kinase, or tightly associated with a kinase, and shares antigenicity with the cell division cycle-dependent Cdk2 kinase as determined by antibody-dependent analysis. The rapid phosphorylation of nucleosomal proteins may influence sets of early genes needed for the induction and progression of the cell cycle.
Insights
Growth factors rapidly phosphorylate nuclear proteins like p33, influencing cell cycle progression. This phosphorylation pattern correlates with positive and negative growth signals, suggesting a key role in cell division regulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Growth factors transmit signals from the plasma membrane to the nucleus, regulating cell growth and division.
- Specific growth factors, including epidermal growth factor and platelet-derived growth factor, utilize shared signaling pathways to alter chromatin.
- Nuclear signaling integrates extracellular cues to modulate cellular responses, impacting gene expression and cell cycle progression.
Purpose of the Study:
- To investigate the role of nuclear protein phosphorylation in response to growth factor signaling.
- To identify specific nuclear proteins involved in transducing growth signals and their modification patterns.
- To determine if Neu receptor activating factor utilizes similar signaling mechanisms as other growth factors.
Main Methods:
- Isolation and analysis of complexed chromatin-associated proteins from growth factor-stimulated cells.
- Phosphorylation assays to detect modifications in nuclear proteins, including p33, p54, and low molecular mass proteins.
- Immunological analysis to assess antigenicity and potential kinase activity of isolated p33.
Main Results:
- Growth factor stimulation led to rapid and consistent phosphorylation of nuclear p33, p54, and low molecular mass proteins (15-18 kDa).
- Neu receptor activating factor induced p33 phosphorylation, indicating shared signaling pathways.
- Transforming growth factor beta, a growth inhibitor, did not increase p33 phosphorylation, while tumor promoters like okadaic acid and phorbol ester did.
- p33 showed characteristics of a kinase or kinase-associated protein and shared antigenicity with Cdk2 kinase.
Conclusions:
- The phosphorylation of nuclear proteins, particularly p33, is a rapid and integrated response to mitogenic growth factor signaling.
- p33 phosphorylation serves as an indicator of positive and negative growth signals, potentially regulating cell cycle initiation.
- These findings suggest that rapid nucleosomal protein phosphorylation influences the expression of early genes crucial for cell cycle progression.