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Gene regulation by tyrosine kinases: src protein activates various promoters, including c-fos
M Fujii1, D Shalloway, I M Verma
1Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92138.
Abstract:
A promoter of the nuclear proto-oncogene fos was activated by cotransfection with the viral src gene. Ability to transactivate the c-fos promoter was dependent on tyrosine kinase activity, because (i) src mutants which have reduced tyrosine kinase activity due to mutation of Tyr-416 to Phe showed lower promoter activation, (ii) pp60c-src mutants which have increased tyrosine kinase activity due to mutation of Tyr-527 to Phe also augmented c-fos promoter induction, and (iii) mutation in the ATP-binding site of pp60v-src strongly suppressed c-fos promoter activation. Tyrosine kinase activity alone, however, was not sufficient for promoter activation, because of pp60v-src mutant which lacked its myristylation site and consequently membrane association showed no increased c-fos promoter activation. Both the tyrosine kinase- and membrane-association-defective mutants were also unable to induce transformation. Therefore, phosphorylation of membrane-associated substrates appears to be required for both gene expression and cellular transformation by the src protein. Two regions of the c-fos promoter located between positions -362 and -324 and positions -323 and -294 were responsive to src stimulation. We believe that protein tyrosine phosphorylation represents an important step of signal transduction from the membrane to the nucleus.
Insights
The viral src gene activates the c-fos gene promoter through tyrosine kinase activity and membrane association. This process is crucial for both gene expression and cellular transformation, highlighting signal transduction
Area of Science:
- Molecular Biology
- Oncology
- Cellular Signaling
Background:
- The nuclear proto-oncogene fos plays a role in cellular processes.
- Viral src gene is known to influence cellular functions.
Purpose of the Study:
- To investigate the mechanism by which the viral src gene activates the c-fos gene promoter.
- To determine the role of tyrosine kinase activity and membrane association in src-mediated c-fos promoter activation.
Main Methods:
- Cotransfection of cells with viral src gene and c-fos promoter constructs.
- Utilizing src mutants with altered tyrosine kinase activity or membrane association.
- Analyzing c-fos promoter activation and cellular transformation.
Main Results:
- Src-mediated c-fos promoter activation is dependent on tyrosine kinase activity.
- Src mutants with reduced kinase activity or impaired membrane association failed to activate the c-fos promoter.
- Specific regions of the c-fos promoter (-362 to -324 and -323 to -294) were responsive to src stimulation.
- Both tyrosine kinase activity and membrane association are required for src-induced cellular transformation.
Conclusions:
- Phosphorylation of membrane-associated substrates by src is essential for c-fos gene expression.
- Protein tyrosine phosphorylation is a key step in signal transduction from the membrane to the nucleus.
- This pathway is critical for both gene regulation and cellular transformation mediated by src.