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MAP kinase stimulation by cAMP does not require RAP1 but SRC family kinases
Markus Klinger1, Oliver Kudlacek, Markus G Seidel
1Institute of Pharmacology, University of Vienna, Währinger Strasse 13a, A-1090 Vienna, Austria.
The Journal of Biological Chemistry
|June 26, 2002
Summary
Elevated cAMP activates MAP kinase through a SRC family kinase, not RAP1, downstream of protein kinase A. This pathway is crucial for cellular signaling and requires SRC kinases for cAMP-mediated responses.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Signal transduction
Background:
- The small G protein RAP1 and B-RAF kinase are implicated in linking cAMP elevations to ERK/MAP kinase activation.
- Understanding the precise signaling cascades from receptor-generated cAMP to MAP kinase activation is crucial.
Purpose of the Study:
- To delineate the specific signaling pathways involved in A(2A)-adenosine receptor-mediated MAP kinase activation.
- To investigate the roles of RAP1, protein kinase A, and SRC family kinases in this pathway.
Main Methods:
- Heterologous expression of human A(2A)-adenosine receptor in Chinese hamster ovary (CHO) cells.
- Utilized RAP1 GTPase-activating protein (RAP1GAP) to inhibit RAP1 activity.
- Employed inhibitors such as H89 (protein kinase A inhibitor) and PP1 (SRC family kinase inhibitor).
- Tested signaling in various cell lines including PC12 cells and SRC-deficient SYF fibroblasts.
Main Results:
- A(2A)-receptor stimulation activated RAP1 and formed RAP1-B-RAF complexes, but RAP1 inhibition did not affect MAP kinase stimulation.
- Inhibition of protein kinase A (PKA) suppressed A(2A)-agonist-mediated MAP kinase activation.
- SRC family kinase inhibition (PP1) blunted both A(2A)-receptor- and forskolin-induced MAP kinase stimulation.
- MAP kinase stimulation by cAMP was significantly reduced in SRC-deficient cells and restored upon c-SRC reintroduction.
Conclusions:
- SRC family kinases, acting downstream of PKA, are essential for cAMP-mediated MAP kinase activation.
- The involvement of RAP1 in this pathway is not essential and may depend on receptor internalization, unlike in other receptor systems.