Mehis Põld

COX-2-dependent stabilization of survivin in non-small cell lung cancer

Elevated tumor cyclooxygenase 2 (COX‐2) expression is associated with increased angiogenesis, tumor invasion and promotion of tumor cell resistance to apoptosis. The mechanism(s) by which COX‐2 exerts its cytoprotective effects are not completely understood but may be due to an imbalance of pro‐ and anti‐apoptotic gene expression. To analyze COX‐2‐dependent gene expression and apoptosis, we created cell lines constitutively expressing COX‐2 cDNA in sense and antisense orientations. Whereas COX‐2 sense cells have significantly heightened resistance to radiation and drug‐induced apoptosis, COX‐2 antisense cells are highly sensitive to apoptosis induction. We found that the expression of the anti‐apoptotic protein survivin correlated positively with COX‐2 expression. A COX‐2‐dependent modulation of survivin ubiquitination led to its stabilization in COX‐2 overexpressing cells, and this effect was replicated by exogenous PGE2 treatment of parental tumor cells. In contrast to previous studies in other cell types, in nonsmall cell lung cancer cells survivin was expressed in a cell cycle‐independent manner. When established in SCID mice in vivo, COX‐2 antisense‐derived tumors had significantly decreased survivin levels while COX‐2 sense‐derived tumors demonstrated elevated levels compared with controls. In accord with these findings, survivin and COX‐2 were frequently upregulated and co‐expressed in human lung cancers in situ.

Cyclooxygenase-2-Dependent Expression of Angiogenic CXC Chemokines ENA-78/CXC Ligand (CXCL) 5 and Interleukin-8/CXCL8 in Human Non-Small Cell Lung Cancer

Elevated tumor cyclooxygenase (COX)-2 activity plays a multifaceted role in non-small cell lung cancer (NSCLC). To elucidate the role of COX-2 in the in vitro and in vivo expression of two known NSCLC angiogenic peptides, CXC ligand (CXCL) 8 and CXCL5, we studied two COX-2 gene-modified NSCLC cell lines, A549 and H157. COX-2 overexpression enhanced the in vitro expression of both CXCL8 and CXCL5. In contrast, specific COX-2 inhibition decreased the production of both peptides as well as nuclear translocation of nuclear factor κB. In a severe combined immunodeficient mouse model of human NSCLC, the enhanced tumor growth of COX-2-overexpressing tumors was inhibited by neutralizing anti-CXCL5 and anti-CXCL8 antisera. We conclude that COX-2 contributes to the progression of NSCLC tumorigenesis by enhancing the expression of angiogenic chemokines CXCL8 and CXCL5.

Cyclooxygenase 2-Dependent Expression of Survivin Is Critical for Apoptosis Resistance in Non-Small Cell Lung Cancer

Elevated tumor cyclooxygenase 2 (COX-2) expression is associated with increased angiogenesis, tumor invasion, and promotion of tumor cell resistance to apoptosis. In our previous studies using non-small cell lung cancer (NSCLC) cell lines constitutively expressing COX-2 cDNA in sense and antisense orientations, we demonstrated that constitutive overexpression of COX-2 leads to stabilization of the inhibitor of apoptosis protein survivin resulting in the elevated apoptosis resistance of COX-2–overexpressing cells. Genetic or pharmacologic suppression of COX-2 activity increased proteasomal degradation of survivin and cellular response to apoptosis induction. Our data show that expression of survivin in non-small cell lung cancer cells can be significantly down-regulated by RNA interference. Whereas COX-2–overexpressing NSCLC cells have significantly higher apoptosis resistance than the parental cells, inhibition of survivin expression by small interfering RNA decreases apoptosis resistance to the level of the parental non-small cell lung cancer. We conclude that COX-2-dependent expression of survivin is critical for apoptosis resistance in non-small cell lung cancer.

Cyclooxygenase-2 Modulates the Insulin-Like Growth Factor Axis in Non–Small-Cell Lung Cancer

Constitutive overexpression of cyclooxygenase-2 (COX-2) occurs frequently in several different malignancies, including lung, colon, breast, and prostate cancer. Clinical studies have established elevated serum insulin-like growth factor (IGF-I) content and IGF-I:IGF-binding protein 3 (IGFBP-3) ratio as risk factors for these same malignancies. Therefore, we sought to determine the link between COX-2 expression and the IGF axis in COX-2 gene-modified human non–small-cell lung cancer (NSCLC) cells. Overexpression of COX-2 in NSCLC cells enhanced the antiapoptotic and mitogenic effects of IGF-I and IGF-II, facilitated the autophosphorylation of the type 1 IGF receptor, increased class IA phosphatidylinositol 3′-kinase activity, and decreased expression of IGFBP-3. Thus, these findings show that COX-2 augments the stimulatory arm of the IGF axis.