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Increased Kit/SCF receptor induced mitogenicity but abolished cell motility after inhibition of protein kinase C
P Blume-Jensen1, A Siegbahn, S Stabel
1Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
Abstract:
The product of the c-kit proto-oncogene, denoted Kit/SCF-R, encodes a tyrosine kinase receptor for stem cell factor (SCF). Kit/SCF-R induces proliferation, differentiation or migration of cells within the hematopoietic, gametogenic and melanogenic lineages at different developmental stages. We report here that protein kinase C (PKC) mediates phosphorylation of Kit/SCF-R on serine residues in response to SCF or PMA in intact cells. The phosphorylation inhibits SCF-induced tyrosine autophosphorylation of Kit/SCF-R. In vitro studies showed that PKC phosphorylated the Kit/SCF-R directly on serine residues and inhibited autophosphorylation of Kit/SCF-R, as well as its kinase activity towards an exogenous substrate. The PKC-induced phosphorylation did not affect Kit/SCF-R ligand binding affinity. Inhibition of PKC led to increased SCF-induced tyrosine autophosphorylation, as well as increased SCF-induced mitogenicity. In contrast, PKC was necessary for SCF-induced motility responses, including actin reorganization and chemotaxis. Our data suggest that PKC is involved in a negative feedback loop which regulates the Kit/SCF-R and that the activity of PKC determines whether the effect of SCF will be preferentially mitogenic or motogenic.
Insights
Protein kinase C (PKC) regulates the Kit/stem cell factor receptor (Kit/SCF-R) through phosphorylation. This feedback mechanism determines whether stem cell factor (SCF) promotes cell proliferation or migration.
Area of Science:
- Cellular signaling
- Molecular biology
- Developmental biology
Background:
- The c-kit proto-oncogene product, Kit/SCF-R, is a tyrosine kinase receptor crucial for stem cell factor (SCF) signaling.
- Kit/SCF-R mediates critical cellular processes including proliferation, differentiation, and migration in various cell lineages.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) in regulating Kit/SCF-R activity.
- To elucidate the mechanism by which PKC modulates SCF-induced cellular responses.
Main Methods:
- In vitro kinase assays to assess direct phosphorylation of Kit/SCF-R by PKC.
- Cell-based assays using intact cells stimulated with SCF or PMA to study phosphorylation and downstream effects.
- Analysis of SCF-induced tyrosine autophosphorylation, mitogenicity, and motility (actin reorganization, chemotaxis).
Main Results:
- PKC mediates serine phosphorylation of Kit/SCF-R in response to SCF or PMA, inhibiting tyrosine autophosphorylation.
- PKC directly phosphorylates Kit/SCF-R on serine residues, reducing its kinase activity without affecting ligand binding.
- Inhibition of PKC enhances SCF-induced tyrosine autophosphorylation and mitogenicity but impairs SCF-induced motility.
Conclusions:
- PKC acts as a negative regulator in a feedback loop controlling Kit/SCF-R signaling.
- The activity of PKC dictates the cellular outcome of SCF stimulation, balancing mitogenic and motogenic pathways.