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Decrease in K-ras p21 and increase in Raf1 and activated Erk 1 and 2 in murine lung tumors initiated by
Gayatri Ramakrishna1, Christine Perella, Lisa Birely
1Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, Frederick, Maryland 21702, USA.
Abstract:
Recent evidence suggests that K-ras protooncogene protein p21 may have a tumor-suppressive role in the context of development of lung adenocarcinoma. Levels of K-ras p21, raf-1, mitogen-activated protein kinases Erk 1 and 2, the phosphorylated-activated forms of Erk 1 and 2 (Erk 1P and 2P), and proliferating cell nuclear antigen (PCNA) were measured by immunoblotting in mouse lung tumors (5 to 9 mm in size) caused by N-nitrosodimethylamine (NDMA) and in control lungs. In tumors compared with normal lung, cell membrane-associated K-ras p21 was significantly decreased and cytosolic K-ras p21 increased. Total, membrane, and cytosolic raf-1 and Erk 1P and 2P were increased in tumors compared with normal lung. A single dose of 5 nmol/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) given after NDMA resulted in a significant 2.4-fold increase in tumor multiplicity. A significantly greater decrease in membrane-associated K-ras p21 and increase in total and membrane associated raf-1 occurred in the NDMA/TCDD tumors compared with the NDMA-only tumors. PCNA levels increased in tumors, a finding confirmed by immunohistochemistry, and correlated with tumor size after NDMA/TCDD treatment but not after NDMA only. The increase in raf-1 in the tumors was confirmed by immunohistochemistry, which also revealed an increase in raf-1-positive alveolar macrophages specifically associating with tumors from the earliest stages. These results suggest a possible tumor-suppressive function for K-ras p21 in lung and a positive role for raf-1 and Erk 1/2 in lung tumorigenesis. TCDD may promote tumors by contributing to downregulation of K-ras and stimulation of raf-1.
Insights
K-ras p21 may suppress lung tumors, while raf-1 and Erk 1/2 promote them. Dioxin (TCDD) may enhance lung adenocarcinoma by reducing K-ras and increasing raf-1.
Area of Science:
- Oncology
- Molecular Biology
- Toxicology
Background:
- K-ras protooncogene protein p21's role in lung adenocarcinoma is debated.
- Evidence suggests K-ras p21 might suppress tumor development.
Purpose of the Study:
- Investigate K-ras p21, raf-1, Erk 1/2, and PCNA levels in lung tumors.
- Determine the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lung tumorigenesis.
Main Methods:
- Immunoblotting to quantify protein levels in mouse lung tumors induced by N-nitrosodimethylamine (NDMA).
- Immunohistochemistry to confirm protein expression and localization.
- Assessing tumor multiplicity after NDMA and TCDD exposure.
Main Results:
- Tumors showed decreased membrane K-ras p21 and increased cytosolic K-ras p21, raf-1, and Erk 1P/2P compared to normal lung.
- TCDD significantly increased tumor multiplicity and exacerbated K-ras p21 decrease and raf-1 increase.
- PCNA levels correlated with tumor size in NDMA/TCDD treated mice.
Conclusions:
- K-ras p21 may have a tumor-suppressive role in lung adenocarcinoma.
- Raf-1 and Erk 1/2 appear to promote lung tumorigenesis.
- TCDD may promote lung tumors by downregulating K-ras and upregulating raf-1.