Mitogen-activated protein kinase expression and activation does not differentiate benign from malignant mesothelial...

Area of Science:

• Oncology
• Molecular Biology
• Cell Signaling

Background:

• In vitro studies suggest mitogen-activated protein kinase (MAPK) activation in malignant mesothelioma (MM) cells upon asbestos exposure.
• Investigating MAPK protein expression and activity in vivo is crucial for understanding MM pathogenesis.
• This study focuses on extracellular-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK), and high-osmolarity glycerol response kinase (p38).

Purpose of the Study:

• To analyze the in vivo protein expression and phosphorylation status of ERK, JNK, and p38 in malignant mesothelioma (MM) and reactive mesothelium (RM) specimens.
• To compare MAPK levels and activation between MM and RM tissues.
• To evaluate the potential of MAPKs as therapeutic targets in MM.

Main Methods:

• Analysis of 36 fresh-frozen MM and 14 RM specimens using immunoblotting for total (pan-) and activated (phospho-) MAPK.
• Comparison of pan-MAPK and phospho-MAPK (p-MAPK) expression and p-MAPK/pan-MAPK ratios.
• Immunocytochemistry was used to confirm MAPK localization in selected specimens.

Main Results:

• Frequent expression of pan-ERK, pan-JNK, and pan-p38 was observed in both MM and RM specimens.
• Activated p-p38 was common, while p-ERK and p-JNK activation was less frequent.
• MM specimens from female patients showed higher levels of pan-ERK, pan-JNK, pan-p38, and p-ERK. Peritoneal MM also showed higher pan-p38.
• Crucially, MM and RM exhibited similar MAPK expression, activation, and activation ratios.

Conclusions:

• This study provides the first in vivo evidence of MAPK activation in clinical MM and RM.
• The comparable MAPK profiles in MM and RM suggest that these pathways may not be critical drivers in the transformation from benign to malignant mesothelium.
• The findings raise doubts about the efficacy of targeting MAPKs as a therapeutic strategy for patients with MM.