Oncogenic potential of MEK1 in rat intestinal epithelial cells is mediated via cyclooxygenase-2.
OBJECTIVE
The mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase (MEK) pathway plays an important role in the regulation of cell growth and differentiation. Constitutively active components of the MEK signaling cascade can induce oncogenic transformation in many cell systems. Downstream MEK signaling also plays an important role in the regulation of cyclooxygenase-2 (COX-2), which is known to be involved in colorectal cancer. Therefore, we determined the role of COX-2 on the oncogenic potential of MEK1 in nontransformed rat intestinal epithelial cells.


METHODS
Constitutively active MEK1 (CA-MEK) mutant transfected rat intestinal epithelial cells were established and tested for their ability to grow in soft agar and form tumors in vivo. The effect of CA-MEK on sodium butyrate (NaB)-induced apoptosis was evaluated by the Annexin V assay. The transcriptional activity and posttranscriptional stability of the COX-2 gene was determined by transient transfection with COX-2 reporter variants and by Northern analysis. To address the role of COX-2 in tumor growth in vivo, xenografted mice were treated with celecoxib (100 mg/kg) or vehicle.


RESULTS
CA-MEK transfected RIE-1 and IEC-6 cells formed colonies in soft agar and tumors in nude mice. These cells showed resistance to NaB-induced apoptosis and cell cycle arrest. MEK activation led to increased expression of COX-2, Bcl-X(L), Mcl-1, and phosphorylated Bad and decreased expression of Bak. Along with elevated COX-2 levels, PGI(2) and PGE(2) levels were also increased. Pharmacologic inhibition of COX-2 inhibited MEK-induced tumor growth in vivo through enhanced apoptosis.


CONCLUSIONS
COX-2 and its bioactive lipid products may play an important role in MEK-induced transformation.
Komatsu
Koga
K
Department of Cell/Developmental Biology, Vanderbilt-Ingram Cancer Center, Nashville, Tennessee 37232, USA.
Buchanan
F Gregory
FG
Katkuri
Sharada
S
Morrow
Jason D
JD
Inoue
Hiroyasu
H
Otaka
Michiro
M
Watanabe
Sumio
S
DuBois
Raymond N
RN
D000818:Animals; D017209:Apoptosis / Q000235:genetics* / Q000502:physiology; D015152:Blotting, Northern; D002455:Cell Division / Q000502:physiology; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002478:Cells, Cultured; D051546:Cyclooxygenase 2; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000166:cytology* / Q000502:physiology; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D007413:Intestinal Mucosa / Q000166:cytology; D048369:MAP Kinase Kinase 1 / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D011336:Probability; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014183:Transplantation, Heterologous
D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D048369:MAP Kinase Kinase 1