The Roles of PI3K/AKT/mTOR and MAPK/ERK Signaling Pathways in Human Pheochromocytomas

Area of Science:

• Endocrinology
• Oncology
• Molecular Biology

Background:

• The pathogenesis of pheochromocytoma and paraganglioma (PPGL) involves signaling pathways like PI3K/AKT/mTOR and MAPK/ERK.
• Previous studies on these pathways in PPGL were primarily *in vitro* using animal cells and focused on transcriptional levels.
• A gap exists in understanding the direct impact of these pathways on human PPGL cell proliferation and their activation status in human tumors.

Purpose of the Study:

• To investigate the role of PI3K/AKT/mTOR and MAPK/ERK signaling pathways in human PPGL pathogenesis.
• To determine the effect of pathway inhibitors on human PPGL cell proliferation.
• To assess the activation status of these key signaling pathways within human PPGL tissues.

Main Methods:

• Human PPGL cells were treated with specific inhibitors: LY294002 (PI3K), U0126 (MEK1/2), AZD8055 (mTORC1/2), and sunitinib.
• Cell proliferation was quantified using the MTT assay.
• Protein phosphorylation, indicative of pathway activation, was analyzed via Western blotting.

Main Results:

• AKT, ERK1/2, and mTOR signaling pathways were found to be activated in the majority of human PPGL samples.
• Inhibitors targeting PI3K, MEK1/2, mTOR, and sunitinib significantly inhibited proliferation in ten primary human PPGL cultures.
• Cross-talk between pathways was observed, with MEK1/2 inhibition reducing mTOR phosphorylation and mTOR inhibition affecting AKT and ERK1/2 phosphorylation. Sunitinib impacted ERK1/2 and mTOR activation.

Conclusions:

• The PI3K/AKT/mTOR and MAPK/ERK signaling pathways are critically involved and activated in human PPGL.
• Targeting these pathways demonstrates efficacy in reducing PPGL cell proliferation.
• Simultaneous inhibition of multiple signaling pathways presents a promising therapeutic strategy for PPGL treatment.