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Complementation of growth factor receptor-dependent mitogenic signaling by a truncated type I phosphatidylinositol
1Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Abstract:
Substitution of phenylalanine for tyrosine at codon 809 (Y809F) of the human colony-stimulating factor 1 (CSF-1) receptor (CSF-1R) impairs ligand-stimulated tyrosine kinase activity, prevents induction of c-MYC and cyclin D1 genes, and blocks CSF-1-dependent progression through the G1 phase of the cell cycle. We devised an unbiased genetic screen to isolate genes that restore the ability of CSF-1 to stimulate growth in cells that express mutant CSF-1R (Y809F). This screen led us to identify a truncated form of the murine type Ibeta phosphatidylinositol 4-phosphate 5-kinase (mPIP5K-Ibeta). This truncated protein lacks residues 1 to 238 of mPIP5K-Ibeta and is catalytically inactive. When we transfected cells expressing CSF-1R (Y809F) with mPIP5K-Ibeta (delta1-238), CSF-1-dependent induction of c-MYC and cyclin D1 was restored and ligand-dependent cell proliferation was sustained. CSF-1 normally triggers the rapid disappearance of CSF-1R (Y809F) from the cell surface; however, transfection of cells with mPIP5K-Ibeta (delta1-238) stabilized CSF-1R (Y809F) expression on the cell surface, resulting in elevated levels of ligand-activated CSF-1R (Y809F). These results suggest a role for PIP5K-Ibeta in receptor endocytosis and that the truncated enzyme compensated for a mitogenically defective CSF-1R by interfering with this process.
Insights
A specific mutation in the colony-stimulating factor 1 receptor (CSF-1R) blocks cell growth. Introducing a truncated phosphatidylinositol 4-phosphate 5-kinase (PIP5K-Ibeta) enzyme restored cell proliferation by stabilizing the mutant CSF-1R.
Area of Science:
- Cell Biology
- Molecular Biology
- Signal Transduction
Background:
- The colony-stimulating factor 1 receptor (CSF-1R) is crucial for cell proliferation.
- A specific mutation (Y809F) in CSF-1R impairs its tyrosine kinase activity, hindering cell growth and gene induction.
- Understanding compensatory mechanisms for defective CSF-1R is vital for cell growth regulation.
Purpose of the Study:
- To identify genes that restore CSF-1-dependent growth in cells with mutant CSF-1R (Y809F).
- To investigate the role of identified genes in CSF-1R signaling and cell cycle progression.
Main Methods:
- Utilized an unbiased genetic screen to isolate genes that rescue growth in Y809F CSF-1R mutant cells.
- Transfected cells expressing mutant CSF-1R with a truncated murine type Ibeta phosphatidylinositol 4-phosphate 5-kinase (mPIP5K-Ibeta).
- Assessed restoration of c-MYC and cyclin D1 gene induction, cell proliferation, and CSF-1R cell surface stability.
Main Results:
- Identified a catalytically inactive, truncated mPIP5K-Ibeta (delta1-238) as a suppressor of the Y809F CSF-1R mutation.
- Transfection with mPIP5K-Ibeta (delta1-238) restored CSF-1-dependent c-MYC and cyclin D1 induction and sustained cell proliferation.
- The truncated mPIP5K-Ibeta stabilized cell surface expression of mutant CSF-1R, preventing its normal endocytosis.
Conclusions:
- The truncated mPIP5K-Ibeta (delta1-238) compensates for a mitogenically defective CSF-1R.
- PIP5K-Ibeta plays a role in regulating CSF-1R endocytosis.
- Interference with receptor endocytosis can restore signaling and proliferation in cells with impaired CSF-1R.