Genetic ablation of cyclooxygenase-2 in keratinocytes produces a cell-autonomous defect in tumor formation.
Using a mouse skin tumor model, we reported previously that cyclooxygenase-2 (COX-2) deficiency reduced papilloma formation. However, this model did not differentiate between the effects of systemic COX-2-deficiency and keratinocyte-specific COX-2 deficiency on tumor formation. To determine whether keratinocyte-specific COX-2 deficiency reduced papilloma formation, v-H-ras-transformed COX-2+/+ and COX-2-/- keratinocytes were grafted onto nude mice and tumor development was compared. Transformed COX-2+/+ and COX-2-/- keratinocytes expressed similar levels of H-ras, epidermal growth factor receptor and phospho-extracellular signal-regulated kinase 1/2 in vitro; and COX-2-deficiency did not reduce uninfected or v-H-ras infected keratinocyte replication. In contrast, tumors arising from grafted transformed COX-2+/+ and COX-2-/- keratinocytes expressed similar levels of H-ras, but COX-2 deficiency reduced phospho-extracellular signal-regulated kinase 1/2 and epidermal growth factor receptor levels 50-60% and tumor volume by 80% at 3 weeks. Two factors appeared to account for the reduced papilloma size. First, papillomas derived from COX-2-/- keratinocytes showed about 70% decreased proliferation, as measured by bromodeoxyuridine incorporation, compared with papillomas derived from COX-2+/+ keratinocytes. Second, keratin 1 immunostaining of papillomas indicated that COX-2-/- keratinocytes prematurely initiated terminal differentiation. Differences in the levels of apoptosis and vascularization did not appear to be contributing factors as their levels were similar in tumors derived from COX-2-/- and COX-2+/+ keratinocytes. Overall, the data are in agreement with our previous observations that decreased papilloma number and size on COX-2-/- mice resulted from reduced keratinocyte proliferation and accelerated keratinocyte differentiation. Furthermore, the data indicate that deficiency/inhibition of COX-2 in the initiated keratinocyte is an important determinant of papilloma forming ability.
Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences,  Research Triangle Park,  NC 27709, USA.
Huei-Chen
HC
Lao
Jacqueline K
JK
Akunda
Kyung-Soo
KS
Chun
Gordon P
GP
Flake
Stuart H
SH
Yuspa
Robert
R
Langenbach
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000473:pathology*; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000502:physiology*; D007124:Immunoenzyme Techniques; D015603:Keratinocytes / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008819:Mice, Nude; D009389:Neovascularization, Pathologic; D010212:Papilloma / Q000201:enzymology / Q000209:etiology* / Q000473:pathology; D012878:Skin Neoplasms / Q000201:enzymology / Q000209:etiology* / Q000473:pathology
C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2