Decrease in K-ras p21 and increase in Raf1 and activated Erk 1 and 2 in murine lung tumors initiated by N-nitrosodimethylamine and promoted by 2,3,7,8-tetrachlorodibenzo-p-dioxin.
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.
Ramakrishna
Gayatri
G
Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, Frederick, Maryland 21702, USA.
Perella
Christine
C
Birely
Lisa
L
Diwan
Bhalchandra A
BA
Fornwald
Laura W
LW
Anderson
Lucy M
LM
D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D004252:DNA Mutational Analysis; D004128:Dimethylnitrosamine / Q000633:toxicity*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D015151:Immunoblotting; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000139:chemically induced* / Q000235:genetics* / Q000473:pathology; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000096:biosynthesis* / Q000235:genetics; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D015689:Oncogene Protein p21(ras) / Q000096:biosynthesis* / Q000235:genetics; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000096:biosynthesis* / Q000235:genetics
D002273:Carcinogens; D000072317:Polychlorinated Dibenzodioxins; D018809:Proliferating Cell Nuclear Antigen; D019908:Proto-Oncogene Proteins c-raf; C107753:proto-oncogene protein v-RAF1, pig; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D015689:Oncogene Protein p21(ras); D004128:Dimethylnitrosamine