Targeted activation of PKA and Epac promotes glioblastoma regression in vitro.
Naotoshi Sugimoto1, Shinji Miwa2, Hiroyuki Tsuchiya2
1Departments of Physiology, Kanazawa University, Kanazawa, Ishikawa 920-8640, Japan.
Abstract:
Ras-p44/42 mitogen-activated protein kinase (MAPK) and Akt signaling are the key pathways involved in the promotion of glioblastoma formation. Notably, phosphodiesterase 4 (PDE4) is widely expressed in brain tumors and promotes their growth. PDE4 inhibitors have been reported to suppress glioblastoma growth in vitro and in vivo. The mechanisms underlying these actions, however, have yet to be elucidated. The aim of this study was to investigate whether intracellular cyclic adenosine monophosphate (cAMP) was able to suppress the Ras-p44/42 MAPK signaling pathway via protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) in U87MG human malignant glioma cells. Forskolin, an activator of adenylate cyclase, inhibited cell growth and the phosphorylation of p44/42 MAPK in U87MG cells, whereas the non-hydrolyzable cAMP analog 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP) considerably suppressed cell growth and phosphorylation of p44/42 MAPK. The inhibitory effects of forskolin were partially prevented by the PKA inhibitor H89. The Epac-selective agonist 8-(4-chlorophenylthio)-2'-O-methyladenosine cAMP (8-CPT-cAMP) inhibited phosphorylation of p44/42 MAPK. These findings suggest that PKA and Epac are involved in the effect of intracellular cAMP on the Ras-p44/42 MAPK signaling pathway.
Insights
Intracellular cyclic adenosine monophosphate (cAMP) suppresses glioblastoma growth by inhibiting the Ras-p44/42 mitogen-activated protein kinase (MAPK) pathway. Protein kinase A (PKA) and Epac mediate these effects in glioma cells.
Area of Science:
- Neuro-oncology
- Molecular Biology
- Cell Signaling
Background:
- Glioblastoma growth is promoted by Ras-p44/42 MAPK and Akt signaling pathways.
- Phosphodiesterase 4 (PDE4) is expressed in brain tumors and enhances their growth, with PDE4 inhibitors showing suppressive effects.
- The precise mechanisms by which PDE4 inhibitors affect glioblastoma remain unclear.
Purpose of the Study:
- To investigate if intracellular cyclic adenosine monophosphate (cAMP) suppresses the Ras-p44/42 MAPK pathway in U87MG human malignant glioma cells.
- To determine the involvement of protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) in mediating cAMP's effects on this pathway.
Main Methods:
- Utilized forskolin (adenylate cyclase activator) and 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP, a cAMP analog) to modulate intracellular cAMP levels.
- Administered H89 (PKA inhibitor) and 8-(4-chlorophenylthio)-2'-O-methyladenosine cAMP (8-CPT-cAMP, an Epac agonist) to assess pathway involvement.
- Monitored cell growth and phosphorylation of p44/42 MAPK in U87MG cells.
Main Results:
- Forskolin and 8-Br-cAMP inhibited U87MG cell growth and p44/42 MAPK phosphorylation.
- The inhibitory effects of forskolin were partially blocked by the PKA inhibitor H89.
- The Epac agonist 8-CPT-cAMP also inhibited p44/42 MAPK phosphorylation.
Conclusions:
- Intracellular cAMP plays a role in suppressing glioblastoma cell growth.
- Both PKA and Epac are involved in mediating the inhibitory effects of cAMP on the Ras-p44/42 MAPK signaling pathway in glioma cells.
- These findings elucidate potential mechanisms for PDE4 inhibitor efficacy in glioblastoma treatment.
