Related Experiment Videos
Altered expression of mitogen-activated protein kinases in a rat model of experimental hepatocellular carcinoma
I H McKillop1, C M Schmidt, P A Cahill
1Georgetown University Medical Center, Department of Surgery, Washington, DC 20007, USA.
Abstract:
The mitogen-activated protein kinase (MAPK) cascade acts as a focal point for signal transduction following activation of both G-protein-linked and tyrosine kinase growth factor receptors. A common intermediate between both of these diverse receptor subtypes includes the small guanosine triphosphate (GTP)-binding protein, p21ras. Point mutations of p21ras have been identified in various tumor types and lead to constitutive activation of this protein and subsequent activation of downstream pathways including the MAPK cascade. Using an in vivo model of hepatocellular carcinoma (HCC), we investigated the abundance and function of individual components of the MAPK cascade and the presence of specific p21ras mutations in this model. Expression of components of the MAPK cascade were determined in tumor and adjacent, non-neoplastic liver specimens by Western blot analysis and functional activity confirmed by substrate phosphorylation assays. Mutations in p21ras were analyzed using an enzyme-linked immunosorbent assay. In tumor, extracellular regulated kinases (ERKs) ERK1, ERK2, and mitogen-activated ERK-regulated kinase-1 (MEK1) were elevated by three- to fourfold as compared with adjacent nontumorigenic normal liver. In contrast, MEK2 was elevated by only 28%. Substrate phosphorylation and detection of phosphorylated ERK1/2 proteins showed increased functional activity of these proteins of the same magnitude as that observed for protein expression. Mutations in p21ras were not detected in this experimental model of HCC. We conclude that HCC is associated with marked changes in expression and function of components of the MAPK cascade independent of common p21ras mutations.
Insights
Hepatocellular carcinoma (HCC) shows increased mitogen-activated protein kinase (MAPK) cascade activity, specifically ERK1, ERK2, and MEK1, independent of p21ras mutations. This suggests MAPK pathway alterations are key in HCC development.
Area of Science:
- Molecular Biology
- Oncology
- Signal Transduction
Background:
- The mitogen-activated protein kinase (MAPK) cascade is crucial for signal transduction, integrating signals from various receptors.
- The small guanosine triphosphate (GTP)-binding protein, p21ras, is a common intermediate in these pathways.
- p21ras mutations are implicated in cancer by causing constitutive pathway activation.
Purpose of the Study:
- To investigate the MAPK cascade components' abundance and function in hepatocellular carcinoma (HCC).
- To determine the presence of specific p21ras mutations in an in vivo HCC model.
Main Methods:
- Western blot analysis to assess MAPK cascade component expression in tumor and non-tumor liver tissues.
- Substrate phosphorylation assays to confirm functional activity of MAPK cascade components.
- Enzyme-linked immunosorbent assay (ELISA) for p21ras mutation analysis.
Main Results:
- Extracellular regulated kinases (ERKs) ERK1, ERK2, and mitogen-activated ERK-regulated kinase-1 (MEK1) showed a 3- to 4-fold increase in HCC tumors compared to normal liver.
- MEK2 elevation was less pronounced (28%).
- Increased phosphorylation of ERK1/2 confirmed heightened functional activity, correlating with elevated protein expression. No p21ras mutations were detected.
Conclusions:
- Hepatocellular carcinoma (HCC) is characterized by significant alterations in the expression and function of MAPK cascade components.
- These changes occur independently of common p21ras mutations in this experimental model.
- The findings highlight the MAPK pathway's critical role in HCC pathogenesis, irrespective of p21ras mutations.