Unphosphorylated STAT6 contributes to constitutive cyclooxygenase-2 expression in human non-small cell lung cancer.
Cyclooxygenase-2 (COX-2) is frequently overexpressed in human cancers and contributes to the malignant phenotype. Our data indicate unphosphorylated signal transducers and activators of transcription 6 (STAT6) may transcriptionally upregulate COX-2 expression and protect against apoptosis in NSCLC cells. In A427 and H2122, NSCLC cell lines that constitutively express COX-2, only unphosphorylated STAT6 was detectable by western blot, thus, all of the following STAT6-dependent effects are attributed to the unphosphorylated protein. In both cell lines, small-interfering RNA-mediated knockdown of STAT6 or stable expression of dominant-negative STAT6 decreased COX-2 expression. In contrast, transfection with a phosphorylation-deficient mutant STAT6 increased COX-2 levels. Immunofluorescent staining revealed the presence of STAT6 in H2122 nuclei, suggesting a direct role in gene regulation for the unphosphorylated protein. Consistent with this hypothesis, unphosphorylated STAT6 increased luciferase expression from a COX-2 promoter reporter construct. STAT6 co-immunoprecipitated with the transcriptional co-activator, p300, and chromatin immunoprecipitation assays demonstrated that these proteins bind a consensus STAT6 binding site located within the COX-2 promoter. STAT6 DNA-binding specificity was confirmed by electrophoretic mobility shift assay. As COX-2 over-expression has been clearly linked to apoptosis resistance and other hallmarks of malignancy, these findings suggest a novel role of unphosphorylated STAT6 in the pathogenesis of non-small cell lung cancer.
Cui
X
X
Division of Pulmonary and Critical Care Medicine, Department of Medicine, Lung Cancer Research Program of the Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA 90095, USA.
Zhang
L
L
Luo
J
J
Rajasekaran
A
A
Hazra
S
S
Cacalano
N
N
Dubinett
S M
SM
D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D006801:Humans; D008175:Lung Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D050800:STAT6 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015854:Up-Regulation / Q000235:genetics / Q000502:physiology*
D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human; D051546:Cyclooxygenase 2